State-of-the-Art Electric Vehicle Modeling: Architectures, Control, and Regulations

Abstract

The global reliance on electric vehicles (EVs) has been rapidly increasing due to the excessive use of fossil fuels and the resultant CO₂ emissions. Moreover, EVs facilitate using alternative energy sources, such as energy storage systems (ESSs) and renewable energy sources (RESs), promoting mobility while reducing dependence on fossil fuels. However, this trend is accompanied by multiple challenges related to EVs’ traction systems, storage capacity, chemistry, charging infrastructure, and techniques. Additionally, the requisite energy management technologies and the standards and regulations needed to facilitate the expansion of the EV market present further complexities. This paper provides a comprehensive and up-to-date review of the state of the art concerning EV-related components, including energy storage systems, electric motors, charging topologies, and control techniques. Furthermore, the paper explores each sector’s commonly used standards and codes. Through this extensive review, the paper aims to advance knowledge in the field and support the ongoing development and implementation of EV technologies.

1. Introduction

Climate change is a worldwide problem that has an enormous influence on people’s lives, upsetting economies in every country. Rising sea levels, more intense weather events, and changing weather patterns are some of the ways that its consequences are still felt today. Since greenhouse gas (GHG) emissions are higher than the desired limits according to the UN’s regular emission gas reports, these emissions are the main cause of climate change. In the absence of any action, it is predicted that the average global surface temperature will climb by more than 3 degrees Celsius this century. Sectors relying on fossil fuel combustion, such as energy and transportation, are considered the main source of the higher rates of GHG levels globally [1,2,3,4]. According to the United States Environmental Protection Agency (EPA), the contribution of the transportation and energy sectors to CO₂ emissions, as shown in Figure 1, is 24% and 42%, respectively [5]. To align with the goals of the Paris Agreement held in 2015, the widespread utilization of renewable energy resources became essential. In the same context, replacing the existing internal combustion engine-based (ICE) vehicles with another sustainable and clean energy source is considered a crucial step in the transportation sector.

The shift to electric mobility provides significant advantages, including reduced oil dependence and enhanced environmental health. Electric vehicles (EVs), which exemplify this transition, are known for their lower energy consumption and zero GHG emissions [6]. As a result, many developed nations are promoting the adoption of EVs to reduce air pollution, CO₂ emissions, and other greenhouse gases. They support sustainable and efficient transportation through various initiatives, including tax incentives, purchase subsidies, free public parking, and toll-free motorway access [7]. As a result, the global share of electric vehicles is expected to rise from 2% in 2016 to 22% by 2030 [8]. Moreover, EVs present several benefits compared to conventional vehicles regarding cost, reliability, efficiency, and simplicity. The running cost is way lower in terms of maintenance and electricity costs. With fewer and simpler components, EVs experience fewer breakdowns. They also avoid the wear and tear caused by engine explosions, vibrations, and fuel corrosion inherent in traditional vehicles. Moreover, their simple structure eliminates the need for conventional engines’ cooling systems, gearshift, clutch, or noise reduction elements [7,9], Additionally, the EVs, as ancillary services, can support the power grid stability in vehicle-to-grid (V2G) and vehicle-to-home (V2H) operating modes or even minimize the disturbance caused by the dynamic charging profiles while operating in vehicle-to-vehicle (V2V) charging situations.

These benefits, driven by the noticeable progress in EV technologies and models, have motivated public users and countries to rely on EVs as a promising option. Since the mid-2010s, EVs have seen rapid growth, consistently breaking sales records, particularly in light-duty vehicles (LDVs), buses, and smaller vehicles. Global automakers have invested over USD 140 billion in transportation electrification, with 50 LDV EV models currently available in the U.S. and around 130 models anticipated by 2023. Projections for EV market share in LDVs vary significantly, from 10% of sales by 2050 to complete market dominance before 2050. Numerous studies indicate that EVs are becoming, or have already become, economically competitive with internal combustion engine vehicles (ICEVs) in certain applications [10].

Globally, China is leading the EV market. In 2016, six countries had E4W market shares above 1% of passenger light-duty vehicle sales. Norway led with 29% due to effective incentives and tax reductions [11]. The Netherlands and Sweden followed with 6.4% and 3.4%, respectively. The U.K., Netherlands, and Sweden prefer plug-in hybrids (PHEVs), while France and China favor battery electric vehicles (BEVs). Norway, Japan, and other regions have a balanced mix of BEVs and PHEVs [12]. According to [13], EV sales are projected to reach 17 million in 2024, making up over 20% of global car sales. Based on the statistics of the past three years shown in Figure 2, the market share in 2024 could reach 45% in China, 25% in Europe, and over 11% in the U.S., driven by manufacturer competition, decreasing battery and car prices, and continued policy support.

Electric vehicles (EVs) are soon poised to dominate the transportation market. Integrating diverse technologies across multiple engineering fields, including mechanical, electrical, electronics, automotive, and chemical engineering, drives this transformation. By amalgamating these technologies, the overall efficiency of EVs can be significantly enhanced, leading to reduced fuel consumption and lower emissions. As shown in Figure 3, EVs comprise several significant systems: the electric motor, power converter, and energy source, with each contributing to the vehicle’s performance and sustainability. As the adoption of EVs accelerates, the market will witness a substantial shift toward greener and more efficient transportation solutions underpinned by continuous advancements in these integrated technologies.

Several papers have reviewed the technological evolution of EVs from various aspects regarding the charging topologies, the types of motors used, converter configurations, battery management, and standards. In [14], the authors have introduced a review of lithium-ion batteries for EV systems and energy management. They have also discussed challenges, issues, and future research recommendations and highlighted EV energy management system problems and recommendations. However, the research lacks focus on battery safety and recycling processes and the discussion on environmental impacts and memory effects of batteries is limited.

A review of EVs aiming to replace ICE cars and reduce CO₂ emissions is carried out by the authors in [15]. They discussed EV drive circuits, battery technology, and future challenges. The EV efficiency, battery types, and motor drives are also addressed. However, the research focus on autonomous driving technology advancements is insufficient and the discussion on the impact of EV adoption on energy infrastructure is limited as the paper gives brief discussion on most of the sections.

Insights into EVs and HEV advancements in current challenges are proposed in [16] Optimization strategies for traction motors, converters, and energy management systems are thoroughly compared. Improved traction motor drives for HEV applications with reliability and control are presented. Moreover, the analysis of power electronic converters for HEVs is unidirectional and bidirectional, but the discussion lacks focus on emerging battery technologies for EVs.

The author’s research work in [17] analyzes EV types, technology, sales evolution, charging modes, and future technologies. It is further extended to reviewing battery technologies, charging standards, power control, and energy management. The research is mainly focused on battery technologies from lead-acid to lithium-ion for EVs. However, the authors have not addressed the converter configurations, the motors employed in EVs, or the standards and regulations needed for operation.

Moreover, the research carried out in [18] presents a comprehensive review of HEV components, architectures, and MPPT techniques. The authors also introduced a comparison of existing hybrid vehicles. Furthermore, the paper focuses on traction motors, battery performance enhancement, and inverter selection. But the whole work is only limited to HEVs while other types of EVs are not addressed.

A comprehensive review is presented in [19] covering EV charging technologies, standards, architectures, and converter configurations broadly. The paper also analyzed charging systems, onboard and offboard chargers, and AC-DC and DC-DC converters and discussed future trends, challenges in EV charging, and grid integration. The limitation of the paper is the lack of focus on EV battery technology advancements and the limited discussion on grid integration challenges with EV charging systems.

The authors in [20] focused on the environmental impact associated with the employment of EVs regarding the reduction in Greenhouse Gases (GHG). They addressed the impact of EVs on reducing carbon footprint in the transport sector through sustainable mobility solutions. Challenges for EVs are proposed in the paper including driving range and charging station availability. However, the paper’s focus was on vehicle emissions and their environmental impact without addressing the vehicle’s key components and their configurations.

In [21], the authors introduced a review of Battery Management Systems (BMSs), charging stations, and traction motors employed in EVs. They concluded that lithium-ion batteries are ideal for EVs based on analysis. Furthermore, for the motor aspect, PMSM is suitable for low power while an induction motor is more convenient for high power. They also addressed that EVs have drawbacks like excessive costs, limited range, and charging time. However, the research work presented lacks the control techniques employed in EVs and the comparison between EVs and HEVs.

This paper comprehensively examines the latest developments in electric vehicle technologies and their regulatory frameworks. It begins by addressing the urgent issue of climate change and the pivotal role EVs play in mitigating its impact. In Section 2, the paper then offers a detailed background and market status on various types of EVs, including battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell electric vehicles (FCEVs). In Section 3, it further explores in Section 3 the spectrum of energy storage options, from lithium-ion batteries to advanced technologies like solid-state batteries and supercapacitors as well as the critical role of battery management systems. The discussion extends in Section 4 on charging technologies, covering both wired and wireless topologies and on-board and off-board chargers, emphasizing the control approaches for each type. Additionally, the paper delves into the state-of-the-art electric motors used in EVs in Section 5, highlighting their advancements and efficiencies. Finally, in Section 6, it examines the standards and regulations that harmonize the EV market, ensuring compatibility and safety across all sectors are discussed. Through this extensive review, the paper aims to provide valuable insights for advancing EV technology and supporting sustainable transportation solutions.

2. Background

There are diversified types of EVs on the market, and they use different technologies and ways of operation. The most common type is battery electric vehicles (BEV) or all-electric vehicles (all-EV). The key concept of this type is to replace conventional combustion engines with electric motors driven by high-capacity rechargeable batteries or more than one energy storage system (ESS). The BEVs are purely electric, with no fuel tank or tailpipe, highlighting them as an emission-free vehicle [22]. However, the Environmental Protection Agency’s (EPA) range is typically between 100 and 250 miles before the next recharging cycle. Several models are available on the market in this category, such as the Nissan LEAF, Hyundai Kona Electric, Tesla Model 3, and Rivian R1T. However, battery-electric vehicles (BEVs) face notable drawbacks, such as shorter driving ranges and longer charging times, compared to other EV types. Over time, these vehicles may experience battery degradation, leading to reduced range and costly replacements. Furthermore, the infrastructure needed for the charging stations and their availability are considered a big challenge for the heavy utilization of BEVs. Additionally, BEVs have a lower energy density than gasoline, affecting their overall efficiency [23,24,25,26]. The BEV is yet to be available in the market, with advancements in research toward overcoming the obstacles to their future dominance.

Hybrid electric vehicles (HEVs) enhance engine flexibility by incorporating an additional propulsion system. Besides the internal combustion engine (ICE), a typical HEV powertrain includes an energy storage system (ESS) and one or more electric motors (EMs). HEVs combine the power of ICE with the emission-free benefits of electric vehicles, offering superior fuel efficiency compared to traditional ICE vehicles [27,28]. They generally operate in charge-sustaining (CS) mode, maintaining the battery’s charge throughout the trip via regenerative braking or the combustion engine. A key limitation of HEVs is that they cannot be charged from the grid. However, the multiple energy sources in HEVs allow various power flow patterns to meet vehicle load requirements through different powertrain topologies and energy management strategies [29,30]. The Honda Civic Hybrid, Kia Sportage Hybrid, and Toyota Crown Signia are examples of the HEV models available on the market. Hybrid cars offer improved fuel economy by using low-speed electric power and assisting the internal combustion engine, leading to fuel savings and reduced emissions. They also have cheaper running costs due to regenerative braking and less brake wear. Additionally, hybrids provide better performance in urban settings and eliminate range anxiety. However, they are more expensive up front, require charging, have battery longevity concerns, and still produce emissions [31].

Unlike HEVs, plug-in hybrid electric vehicles (PHEVs) can be externally charged through power outlets. In PHEVs, most power comes from an electric motor (EM), with the internal combustion engine (ICE) as a backup. When the battery’s state of charge (SOC) drops to a certain level, the PHEV operates like a regular HEV, with the ICE taking over as the primary power source. PHEVs mainly function in charge depletion (CD) mode, depleting the SOC to a threshold level. They extend the all-electric range, enhance local air quality, and can be connected to the grid. Unlike regular HEVs, which must travel 1–2 miles on electric power alone, PHEVs can go 10–40 miles before requesting gas engine assistance [32,33] Additionally, PHEVs support grid tasks by using their onboard batteries as storage in smart homes. Through bidirectional chargers, they enhance energy management by aiding renewable generators, contributing to more efficient energy use in residential settings [34]. The PHEVs are available on the market in different models, such as the BMW i-8, Audi A3 E-Tron, Jeep Wrangler 4xe, and Toyota RAV4.

Fuel Cell Electric Vehicles (FCEVs) are considered a zero-emission type of electric vehicle fueled by hydrogen fuel cells. Toyota Mirai and Hyundai Nexo are available models in this category on the market nowadays. The key concept is to utilize hydrogen to generate electricity through a chemical reaction with oxygen from the air instead of drawing electricity from a battery. Furthermore, FCEVs can recapture the regenerative energy during braking driving situations. Contrary to BEVs, which use batteries to store their energies, FCEVs generate electricity on demand based on the volume of the hydrogen storage tank available onboard [35]. This allows FCEVs to reach longer driving ranges, typically exceeding 300 miles on a single tank of hydrogen, with a refueling time almost like that of conventional gasoline vehicles [36]. Nonetheless, the widespread adoption of FCEVs is impacted by multiple challenges related to the infrastructure needed to install several charging stations, besides the relatively high cost of hydrogen production and storage compared with conventional fuels. Despite these challenges, FCEVs are gaining attention for their potential to provide long driving ranges, typically more than 300 miles. In addition, they have environmentally friendly transportation solutions. These benefits motivated governments and manufacturers to invest more in hydrogen infrastructure and technology development to realize the full potential of FCEVs in achieving sustainable mobility objectives worldwide [37,38]. Other classes, such as Mild Hybrid Electric Vehicles (MHEV), like the Chevrolet Silverado Hybrid, and Range Extended Electric Vehicles (REEV), like the BMW i3, are available on the market. More details regarding the comparison among the commonly available EVs on the market are highlighted in

Table 1. Comparison between the common available EV types in the market.

Parameters	BEV	HEV	PHEV	FCEV
Source of Energy	ESS	Fossil Fuel/ESS	Fossil Fuel/ESS	Hydrogen/ESS
Powertrain	Electric Motor	IC engine/Electric Motor	IC engine/Electric Motor	Electric Motor
Emission	No	Yes	Yes	No
Noise	Low	Median	Median	Low
All-electric range	100–250 miles	short	5–50 miles	100–300+ miles
Grid connected	Yes	No	Yes
Price	High	Median	Median	Highest
Average top speed	94	120	120	100
Charging Time (min)	60–450	5–120	5–120	5
Major Issues	Battery sizing and management Charging Facilities Battery life cycle Cost	Battery sizing and management Control and optimization management of multiple energy resources		Fuel cell cost, life cycle, and reliability Hydrogen production Cost

[39,40,41,42,43].

The development of control strategies for EVs is a crucial area of research aimed at optimizing energy management, ensuring system stability, improving fuel economy, and reducing emissions. Control strategies in these vehicles typically involve the coordination of energy management systems, power electronic converters, and electric machines. These strategies can be broadly categorized into rule-based methods, optimization-based methods, and learning-based methods. Rule-based strategies, including deterministic and fuzzy logic rules, are known for their simplicity and real-time applicability but often fall short in terms of optimization and adaptability. Optimization-based methods, such as Dynamic Programming (DP), Model Predictive Control (MPC), and Pontryagin’s Minimum Principle (PMP), offer more precise energy management by forecasting future states and optimizing control actions accordingly, though they can be computationally intensive. Recently, learning-based approaches like Artificial Neural Networks (ANN) and Reinforcement Learning (RL) have emerged as promising alternatives due to their ability to learn and adapt to complex nonlinear system behaviors. These strategies are particularly beneficial for handling the dynamic and unpredictable nature of driving environments, contributing to improved fuel economy and reduced emissions. For instance, an adaptive energy management strategy combining ANN and PMP has been shown to improve fuel economy significantly by adjusting to varying vehicle mass, demonstrating the potential of integrating machine learning with traditional optimization techniques [44,45].

3. Energy Storage System (ESS)

Energy storage systems are considered key elements in real-world applications. The high technologies, power, and energy capacities offered by the ESS make it crucial in several applications, such as power utilities, renewable energy systems, and transportation electrification. For instance, the ESS is used for grid support from the generation levels downstream to the end users in voltage and frequency regulations, stability and resiliency enhancement, and load balancing [44,45]. Regarding the EV industry, ESS plays a pivotal role as the main source of energy for types like the BEV and the backup source for others, such as the HEV and PHEV. Furthermore, it is expected that the short-term grid storage demand can be fulfilled by EVs only by 2030 [46]. ESSs come in various forms: chemical, electrical, electrochemical, thermal, and mechanical. With their distinct features of cyclability, efficiency, power, and energy densities, electrochemical ESSs are highly valued in industrial, commercial, and utility applications. Furthermore, its integration with other ESSs is applicable, forming hybrid energy storage systems (HESS). This category encompasses a wide array of devices, as shown in Figure 4, including batteries, supercapacitors (SCs), and fuel cells (FC), making them a preferred choice for EVs [47,48]. Nonetheless, several obstacles must be considered when integrating the ESS, including its life cycle, dependability, cost, and environmental and safety concerns. Therefore, advanced management systems are needed to address these challenges. This section is organized to delve into details on the different ESS in the EV market, the main objectives of the BMS systems, and the common management strategies for the HESS.

3.1. Battery Energy Storage System (BESS)

The driving range of EVs, which is heavily dependent on battery capacity, is crucial to their success. The driving range of EVs, which is heavily dependent on battery capacity, is crucial to their success. EV batteries must be compact, flexible, and capable of rapid and frequent recharging. A high energy density, low maintenance profile, long lifespan, and cost-effectiveness are also imperative [49]. Broadly, different commercial batteries are used in the EV market. Besides the traditional lead-acid batteries, a broader array of battery types is now extensively used, such as ZEBRA batteries, nickel-metal hydride (NiMH) batteries, and lithium-ion batteries (LIBs). It is worth mentioning that battery utilization, defined as C-rate, is measured by the ratio between the charging and discharging currents of the battery concerning its capacity. This rate provides a detailed indication regarding the charging and discharging process of the battery and how heavily it is being used [50]. More details regarding each model and a summary are provided at the end of this section.

3.1.1. Lithium-Ion Batteries (LIBs)

LIBs are leading EVs in the meantime due to their remarkable features in terms of sustainability, high efficiency, extended life cycle, excellent high-temperature performance, and noticeable high energy densities [51,52]. Although some concerns about their safety and environmental impacts during their production and recycling processes are debated, LIBs are still the winning horse in the EV market [53,54]. Moreover, advanced research is going to minimize these challenges and improve their overall performance [55,56,57].

The operation concept of LIBs is performed by shuttling the lithium ions through an electrolyte between the anode, typically made of graphite, and the lithium metal cathode. A separator prevents physical contact between the anode and the cathode, facilitating efficient energy storage and release [58]. Different lithium-ion chemistries are used in commercial EVs; each has advantages and disadvantages. To date, Li-iron-phosphate (LFP), Li-ion manganese oxide (LMO), Li-titanate-oxide (LTO), Li-nickel-cobalt-aluminum-oxide (NCA), and Li-nickel-manganese-cobalt-oxide (NMC) batteries are employed by carmakers such as Toyota, Nissan, Tesla, BMW, etc. In 2016, 83% of the EV market relied on LFP and NMC batteries. Reaching 2025, NMC batteries are expected to reach 41% of the market share compared to LFP [59].

Table 2. Comparison between the commercial chemistries of LIBs.

Parameters	LFP	LMO	NMC	NCA	LTO
Year	1993	1996	2008	1999	2008
Anode	Graphite carbon	Graphite carbon	Graphite carbon	Graphite carbon	Lithium titanate
Cathode	Lithium iron phosphate	Lithium manganese oxide	Lithium nickel manganese cobalt oxide	Lithium nickel cobalt aluminum oxide	Lithium manganese oxide
Separator	Polyolefin	Polyolefin	Polyolefin	Polyolefin	Polyolefin
Specific energy (Wh/kg)	90–150	100–150	150–220	200–260	50–80
Thermal Runaway (°C)	270	250	210	150	Highest
Charge (C-rate)	1	0.7–1	0.7–1	0.7	1
Discharge (C-rate)	1	1	1–2	1	10
Nominal Voltage (V)	3.2–3.3	3.7–4.0	3.8–4.0	3.6–3.65	2.3–2.5
Weight	Light	Heavy	Light	Light	Light
Self-discharge (monthly %)	5	1	10	-	5
Application	Industrial Medical EVs	Medical Powertrains Power tools	Industrial Medical EVs E-bikes	Industrial Medical EVs	UPS EVs Solar lights

summarizes the key differences among all these types [60,61,62,63].

Long life spans, enhanced safety, and remarkable thermal stability are all offered by LFP batteries. Compared to the other LIBs, they offer improved cycle performance and structural stability. Furthermore, their cost and durability make them perfect for heavy-duty purposes like buses and vehicles [59,64]. However, they have a low nominal voltage and less electronic conductivity, reducing energy density [65]. The LMO batteries are renowned for being non-toxic, having a solid construction, and being less expensive. In addition, they are providing three-dimensional diffusion channels for lithium, which enhances their rate capabilities. Despite their benefits, their low performance in high-temperature conditions and their low capacities are the main drawbacks of this type. However, merging the LMO with NMC has achieved noticeable enhancements in specific energy and longevity [59].

Known for their outstanding overall performance, low self-heating levels, and high energy density, NMC batteries are considered the perfect option for the automotive industry. In addition, NMC chemistry can be tailored to achieve specific performance for several applications that require frequent cycling. However, relying on expensive materials such as cobalt and nickel and the complex manufacturing process are challenging the widespread use of NMC batteries [66,67]. Replacing manganese with aluminum introduced NCA batteries with improved performance and a longer life span. Additionally, NCA batteries are highly valued for their exceptional power and energy densities, making them an optimal option for long-range and high-performance applications. However, the primary challenges for NCA batteries are their low thermal stability and the high cost of cobalt [68,69,70]. Regarding the LTO, they are distinguished by their fast charging and discharging patterns, robust spinel structure, and unique safety performance. Furthermore, their high operating potential prevents the formation of lithium dendrites and allows the use of cost-effective aluminum foil. Additionally, LTO batteries excel in extreme temperature conditions and boast an exceptionally long cycle life. However, their low energy density and low electrical conductivity present challenges that necessitate advancements in stable electrolytes and high-voltage cathode materials [68,71,72,73]

Because they are reliable and reasonably priced, LFP batteries are ideal for heavy-duty applications; nevertheless, their energy density is low. When combined with NMC for EVs, LMO batteries offer good rate capability at a reasonable cost. High specific capacities and energy densities are provided by NMC and NCA batteries, making them appropriate for various automotive applications. Although LTO batteries offer exceptional lifespan and safety, further research and development are required to surpass their energy density constraints. Because each type of battery has distinct advantages, it may be used in various ways in the developing EV industry. Figure 5 highlights the main differences among the selected common LIBs in the EV market [60,61,62,63].

3.1.2. Nickel-Metal Hydride (NiMH) Batteries

NiMH battery stands among the most promising ESSs. The commercial use of NiMH batteries started in the early 1990s. The early chemistry of NiMH batteries employed a metal alloy for the cathode of a mixture of lanthanum, nickel, cobalt, and silicon. Later, advancements occurred to the battery featuring it with more energy densities than lead-acid batteries [74]. In addition, Nickel Metal Hydride (NiMH) batteries offer a three times higher specific energy compared with the standard Nickel Cadmium (NiCd) batteries [75]. These rechargeable batteries are widely used for various electric loads, including mobile applications, stationary ESSs, and especially transportation systems. Over one billion cylindrical NiMH cells are produced annually to replace toxic NiCd batteries and primary alkaline batteries, providing the same rated voltage and higher energy capacity [76,77].

Several benefits make nickel-metal hydride (NiMH) batteries a desirable option for a range of applications. They are perfect for devices that need continuous power because of their longer runtimes due to their higher energy density as compared to nickel-cadmium (NiCd) batteries. NiMH batteries pose fewer threats to the environment and human health since they do not contain harmful cadmium. Compared to lithium-ion batteries, they are also considered safer because of their decreased danger of thermal runaway and high cycle life, which allows them to withstand several charge-discharge cycles [78,79,80]. However, NiMH batteries do have certain drawbacks. Their increased self-discharge rate causes them to lose charge more quickly while not in use [81]. Even though it is not as bad as with NiCd batteries, the memory effect might nonetheless happen and eventually reduce capacity if the battery is not periodically fully drained. Furthermore, although still superior to NiCd, their energy density is still lower than that of lithium-ion batteries, which means they are less appropriate for small lightweight applications. Lastly, extreme weather conditions might cause NiMH batteries to function less well [78,79,82].

The NiMH industry has experienced rapid growth since mass production started in Japan in 1990, with well-known battery makers accelerating their development. This growth occurred in the volumetric and gravimetric energy densities, which are aimed at enhancing the overall power density. By 2000, Japan had produced 1 billion small Ni-MH batteries annually. Moreover, China, which participated early in Ni-MH battery development by building numerous production lines, such as the Shenzhen BYD and Shenyang Sanpu Companies, now leads global production and export, surpassing Japan. However, the market has declined due to the global economic crisis and the rise of lithium-ion battery utilization. Despite this, 85% of HEVs still rely on Ni-MH batteries. With increasing demands for energy density, high power, and long cycle life, ongoing efforts focus on enhancing Ni-MH battery properties [83,84]. Nowadays, different car makers use NiMH batteries in their HEV models, including the Toyota Prius, Honda Insight, Ford Escape Hybrid, and Lexus Hybrid.

3.1.3. ZEBRA Batteries

Developed since the 1980s, sodium-nickel chloride (Na-NiCl2) batteries are high-temperature rechargeable batteries called ZEBRA (Zero Emission Battery Research Activity). Featured by better safety, reliability, and life span profiles, it is considered one of the most valuable electrochemical devices for stationary energy storage and EV applications [85]. Melted sodium and nickel chloride undergo electrochemical processes that underpin the ZEBRA battery’s operation. The solid ceramic electrolyte, composed of beta-alumina, separates the positive electrode of nickel chloride from the negative electrode of molten sodium in the cell. As a result of the reaction between sodium ions and nickel chloride during discharge, nickel and sodium chloride (table salt) are produced. Electrical energy is produced by releasing electrons in this process [86]. Since all the sodium is added as salt, ZEBRA cells are created in a discharged condition, contrary to LIBs, assembled in a charging state, preventing the processing of metallic sodium. Generally, battery packs, including up to 500 ZEBRA cells, with cooling plates and vacuum insulation for thermal control, can be configured in parallel or series [87]

There are multiple noteworthy benefits to ZEBRA batteries. For instance, their high energy density makes them perfect for applications needing small energy storage solutions. In addition, these batteries are intrinsically safe. Since it employs a solid-state ceramic electrolyte, the possibility of short circuits and inhibiting dendrite development has decreased. Furthermore, the lack of harmful chemicals highlighted it as safe for the environment compared to the other available batteries. ZEBRA batteries’ high working temperature guarantees superior thermal stability and reliable performance. However, more insulation and heating components are needed to achieve that. This will add to the complexity of the battery design and increase energy consumption. Another negative aspect is the starting time, which delays instant utilization as the battery warms from a cold condition to its operational temperature. Moreover, ZEBRA batteries are more expensive than alternative technologies due to the high cost of the materials and production techniques. The battery system becomes more complicated and has more potential sites of failure because of the demand for thermal control devices [88,89,90,91,92]. It is worth mentioning that ZEBRA batteries can achieve robust performance for EV operations when aligned with additional storage devices, such as supercapacitors [93,94].

3.1.4. Solid-State Batteries (SSB)

Since LIBs were commercialized in the 1990s, significant research has been dedicated to improving this technology. Although high-voltage cathode materials can modestly boost LIB energy density, this method is impractical due to the decomposition of the liquid electrolyte at the negative electrode under high-voltage conditions. Moreover, the flammability and volatility of liquid electrolytes and additives raise safety concerns [95]. In this context, solid-state batteries (SSBs) represent a major advancement in battery technology, offering several advantages over traditional LIBs. Unlike LIBs, which use a liquid electrolyte for ion transport between the cathode and anode, SSBs employ a solid-state electrolyte (SSE). This advancement promises significant enhancements in safety, energy density, and lifespan compared to conventional lithium-ion batteries [96]. For instance, SSBs have better energy densities than lithium-ion batteries. This is largely because they can employ lithium metal as an anode, which has a larger theoretical capacity than graphite anodes in typical lithium-ion cells [97]. In addition, SSEs are more chemically stable and resistant to deterioration over time than liquid electrolytes. This contributes to a longer cycle life. Furthermore, the possibility of dendrite development is minimized, which is a typical problem in LIBs, resulting in short circuits and possible failures [98]. Moreover, SSBs can function safely at elevated temperatures without the threat of thermal runaway, a significant safety issue for lithium-ion batteries.

Generally, SSBs can be categorized into three types based on their chemical composition. Firstly, the inorganic solid ceramic electrolytes, usually made from lithium ceramics, provide high ion conductivity and thermal stability. However, they are fragile and challenging to make [99]. Secondly, organic solid polymer electrolytes, made from polymers like polyethylene oxide (PEO) or polyvinylidene fluoride (PVDF), offer good mechanical flexibility and processability but have lower ion conductivity. Lastly, composite solid electrolytes (CSEs) combine inorganic ceramics with organic polymers to achieve high ion conductivity and good mechanical properties, allowing for tailored properties through varied compositions and structures [100].

3.1.5. Lead Acid Batteries (LABs)

Lead-acid batteries, invented by Gaston Planté in 1859, are the earliest rechargeable batteries still used today due to their durability, dependability, and low cost [101]. They are structurally made up of lead dioxide and sponge lead electrodes bathed in a sulfuric acid electrolyte, separated by a porous substance to prevent short circuits. While discharging, chemical reactions produce lead sulfate, water, and electrical energy, whereas charging reverses these processes. In general, they are classified as either flooded or sealed batteries. Regarding the flooded LAB, the plates are fully submerged by a liquid electrolyte [102]. This type is commonly used in vehicle starters, industrial forklifts, and backup power systems. However, regular maintenance is required to restore the water lost through electrolysis and evaporation. In contrast, sealed LABs have immobilized electrolytes in gel form or absorbed in a glass mat. This type, featuring a maintenance-free profile, can be found in motorized scooters, uninterruptible power supplies (UPSs), and backup lighting systems [103].

Although LABs have a relatively small energy density (30–40)% of the theoretical limit compared to 90% for lithium-ion batteries (LIBs), their production methods and recyclability significantly reduce their ecological footprint due to the use of readily available, inexpensive materials, and an inflammable water-based electrolyte [104]. Nonetheless, they are heavier and bulkier than other advanced batteries. Additionally, their low energy density, the need for frequent maintenance, and their short cycle life stand against their wide utilization in the transportation sector [105]. Even though LABs are among the earliest battery technologies, they are still widely used in many applications. Sustained progress endeavors to mitigate their constraints and enhance their efficacy, guaranteeing their pertinence within the dynamic terrain of energy storage. In this context, improved performance and more excellent durability are provided by enhanced flooded batteries (EFBs), especially for applications involving start-stop vehicles. Moreover, advanced lead-acid batteries use innovative chemicals and production processes to boost longevity and efficiency. Research is also focused on developing lead-acid battery recycling procedures to improve sustainability. It is worth mentioning that LAB’s low cost and great recyclability make them more attractive for use in grid storage. In the future, these developments might be combined to produce more competitive LABs that satisfy the needs of contemporary applications such as energy storage without sacrificing their dependability and affordability [106,107,108].

To conclude, the market for electric vehicles (EVs) has witnessed the use of multiple battery technologies, each with distinct features. The first kind of batteries were LABs. Despite their lower energy density and heavy weight, they are dependable and cost-effective. Since its introduction in the 1980s, nickel-metal hydride (NiMH) batteries have been extensively utilized in hybrid automobiles due to their increased energy density. ZEBRA batteries, developed in the 1990s, are noted for their high working temperatures and were early candidates in electric vehicles. However, the complexity regarding their production besides their costs stands against their broad use. In the meantime, LIBs are dominating the EV industry because of their high energy density and efficiency while the SSBs are expecting to revolutionize the electric vehicle industry. It is worth mentioning that there are three types of cell housing for these batteries: cylindrical, prismatic, and pouch batteries. Today’s EVs include all three, and each has advantages and disadvantages. For instance, Tesla utilizes cylindrical cases for their reliability and high energy density, despite their bulkiness. Volkswagen favors prismatic housings, which are lighter and fit well in compact spaces, although they have a shorter life cycle. Regarding the type of pouch used by GM and Hyundai, it offers flexibility to fit small irregular spaces but is prone to swelling and potential fire risks.

Table 3. Summary of the commonly available batteries in the EV market.

Parameters	Lead-Acid	NiMH	Li-Ion
Safety	Thermally stable	Thermally stable with a protective fuse	Protection circuit and management are mandated
Specific energy (Wh/kg)	30–50	60–120	90–250
Specific power (w/kg)	180	Up to 1300	2500
Cell voltage (V)	2.0	1.2	3.2–3.7
Life cycle (y)	200–300	300–500	500–2000
Efficiency (%)	90	90.3	99
Cost	Low	Moderate	high
Charge time (h)	8–16	2–4	1–4

provides a comparison of the most common types of batteries in the EV market [109,110]

3.1.6. Other Energy Storage Types

Supercapacitors (SCs)

Recently, there has been a noticeable growth in the power needs in specific applications beyond the capacity of typical design batteries. Hence, supercapacitors (SCs), or ultracapacitors, are becoming a more popular alternative storage medium due to the increasing need for instantaneous energy storage solutions, especially in the renewable and electric car industries. Unlike batteries, which rely on chemical reactions, capacitors, in general, store energy physically, allowing for rapid charge and discharge cycles. However, SCs, compared to traditional capacitors, have a different structure and working mechanism. In addition, SCs have significantly higher capacitance and energy density due to their larger surface area and very small separation distance [111].

Three categories may be used to categorize SCs based on the various charge storage techniques they use [112]. The standard type is the electric double layer (Helmholtz layer) SC. Typically, they are structured as two porous electrodes immersed in an electrolyte with a separator. Due to porous materials like activated carbon frequently used to make electrodes, the surface area used for charge storage has dramatically increased. Electrostatic and electrochemical reactions are critical to the SC concept. Supercapacitors retain energy in the electric dual layers that develop at the interface between the electrode material and the electrolyte, in contrast, conventional capacitors store energy by electrostatic charge separation on metal plates. Because of the double-layer process and the permeable electrodes’ large surface area, SC can attain more significant capacitance values than conventional capacitors. Second, there are pseudo capacitors that store energy using Faradaic redox reactions, which are rapid reversible chemical adsorption and desorption processes. Through this method, the energy storage capacity is increased beyond what can be achieved using electrostatic means. Hybrid SCs combine the Faradaic redox reactions with the Helmholtz layer [112,113,114].

Table 4. Comparison among the different supercapacitors’ chemistries.

Parameters	Electric Double-Layer	Pseudo-Capacitor	Hybrid Capacitor
Electrode material	Activated carbon	Metal oxides	Carbon/metal oxide
Charge storage mechanisms	Charge separation	Redox charge transfer	Double layer/charge transfer
Specific energy (Wh/kg)	5–7	10–15	10–15
Specific power (w/kg)	1000–3000	1000–2000	1000–2000
Cell voltage (V)	2.5–3	2–3.5	2–3.3
Life cycle (y)	40	40	40
Efficiency (%)	>95	>95	>95

summarizes more details regarding these three types [115].

Known for their unique features, such as their high-power density, long life span, and sustainability, SCs have found significant uses in many sectors. For instance, specific power fluctuations in renewable energy systems and regenerative braking modes may be mitigated, improving their systems’ stability and dependability [116]. Moreover, SCs are heavily utilized in hybrid and electric buses. In Shanghai, by August 2006, supercapacitor electric city buses had begun offering their commercial services in Shanghaist to LIB electric buses, and SC buses do not require specialized charging facilities. Additionally, when the supercapacitor electric city buses remain at the departure station, they are fully charged in a few minutes [112]. Regarding passenger cars, SCs are utilized for various purposes, including high-voltage energy storage systems and engine start-stop, energy regeneration, voltage stabilization, and backup power supply [116,117]. Moreover, using hybrid energy storage systems, incorporating SCs, for EV applications has witnessed promising progress through the years. This hybridization enhances vehicle performance and extends the life cycle of the storage system [118,119,120].

Fuel Cells (FCs)

As we stated earlier, FCs are using hydrogen as a fuel to generate electricity through reactions. They are typically structured with the electrolyte layer in contact between the anode and cathode electrodes. FCs can be divided into categories based on operating temperatures and chemistries. Solid oxide fuel cells (SOFC), alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), direct methanol fuel cells (DMFC), and proton exchange membrane fuel cells (PEMFCs) are among the several fuel cell types in the industry. Because different fuel cells produce varied operating temperatures and power levels, choosing the suitable fuel cell is crucial. Efficiency and cost are crucial when choosing the finest fuel cell [121].

A fuel cell’s (FC) efficiency is influenced by the power demand placed upon it; typically, higher power draws result in lower efficiency. This decrease in efficiency is primarily due to voltage drops caused by internal resistances. Moreover, fuel cells have a relatively longer response time compared to batteries and SC. FCs are also costly, priced at five times more than internal combustion engines (ICEs). The main cost drivers are the membrane, electrocatalyst, and bipolar plates. Ongoing research aims to develop hydrocarbon membranes to replace perfluorinated membranes [122]. In automotive applications, low-temperature and low-pressure PEMFCs are the most frequent FCs owing to their exceptionally high-power density, lower working temperature (60–80 °C), and reduced corrosion compared to other FCs [78]. More details regarding the key differences among the commercial FCs are summarized in

Table 5. Key differences between the different fuel cells.

Parameters	PEMFC	PAFC	AFC	SOFC	MCFC	DMFC
Temp (°C)	<100	150–200	90–100	500–1000	600–700	60–200
Cell Voltage (V)	1.1	1.1	1	0.8–1	0.7–1	0.2–0.4
Stack power (kW)	<1–250	50–100	1–100	<1–3000	300–3000	0.001–100
Efficiency (%)	40–60	40	60	60	50	40
Advantages	Low operating temperature Fast starting Less corrosion and electrolyte management problem	Higher efficiency with CHP Increased tolerance in fuel impurities	Higher performance Faster cathode reaction and start Lower material cost Low operating temperature	Suitable for CHP Higher efficiency Fuel flexibility Hybrid/gas turbine cycle	Suitable for CHP Higher efficiency Fuel flexibility	Low cost due to lack of fuel reformer
Disadvantages	Expensive catalyst cost Sensitive to hydrogen impurity	Expensive catalyst cost Long start time	Sensitive to CO2 levels in oxygen and hydrogen	High operation temperature, corrosion, and breakdown Long start time	High operation temperature Long start Power density	Intermediates adhesion to the catalyst surface

[122,123,124].

3.2. Battery Management Systems

Battery management systems (BMSs) are crucial for the secure operation of EVs. While the BESS incorporates different chemicals with their various characteristics in terms of voltage, current, and temperature levels, regardless of the driving patterns and weather conditions, maintaining these values within safe operating levels is mandatory. The main objectives of the BMS shown in Figure 6 include but are not limited to the following aspects [125,126,127,128].

• Measuring the status of each component of the EV, such as the battery state of charge (SoC), state of health (SoH), and voltage and current levels.
• Conducting the necessary investigation on this data to assess the battery capacity and ensure cells and battery balance.
• Predict any degradation possibilities for the BESS.
• Running the thermal checkup and regulating the BESS temperature.
• Observing any fault conditions with detection, diagnosis, and mitigation.
• Regulating the charging and discharging signals through the proper power and control management approaches.
• Supporting data exchange with other IoT devices toward enhancing data acquisition, storage, and performance optimization.

The decision-making processes involved in battery management systems (BMS) depend on several critical factors, including the estimation of battery state of charge (SOC) and state of health (SOH). These core tools enable the BMS to implement precise control, protection, and management actions. The initial step in achieving this involves estimating these values through various methods, such as direct estimation techniques, battery equivalent models, and data-driven approaches. Each method presents distinct advantages and disadvantages regarding complexity, computational demands, accuracy, and other relevant aspects [128].

Subsequently, these estimated signals are transmitted using specific communication technologies for visualization and management purposes. Based on these measurements, appropriate control signals are generated, utilizing suitable management strategies to regulate the power and operation of the electric vehicle (EV). Technologies such as cloud computing, artificial intelligence, blockchain, and digital twinning can facilitate these processes [125,128]

Given the BMS’s essential role in executing and managing these tasks efficiently, it must be equipped with advanced technologies to ensure smooth, secure, enhanced, and optimized vehicle operation. With ongoing research and development, the future of battery management systems appears promising, heralding a more sustainable and efficient transportation ecosystem.

3.2.1. SOC/SOH Estimation Approaches

While the concept of SoC appears straightforward, achieving accurate estimation is remarkably complex. This complexity arises from the battery’s inherently non-linear electrochemical properties, combined with variations in cell performance and differing operating conditions within each battery pack. Furthermore, these characteristics are not fixed; they evolve over time due to battery aging, fluctuations in temperature, and the complexities of charge and discharge cycles. This dynamic behavior demands a sophisticated and continuous assessment of the battery’s performance parameters, significantly complicating the accurate determination of its available capacity under a wide range of internal and external conditions.

There are only a few methods for directly measuring the SoC and SoH of a battery through its physical and chemical characteristics, such as electrolyte pH, density measurements, and cathodic galvanostatic pulses. However, these techniques require highly precise instruments, which can be costly and often impractical due to the difficulty of accessing the internal components of the battery [58]. As a result, SoC estimation typically relies on parameters that can be easily measured, including voltage, current, impedance, and temperature. Despite the low computational demands of these traditional approaches, they frequently lack accuracy. This inaccuracy is further exacerbated by the flat OCV-SoC curve characteristic of LIBs, making the SoC-voltage relationship less reliable. To overcome these limitations, indirect SoC estimation methods have been introduced. These approaches leverage directly measurable variables from the battery to achieve a more precise SoC estimation [129,130].

Indirect methods for estimating the SoC can be broadly categorized into two main types. The first category includes model-based methods, which rely on battery models to establish a relationship between measurable parameters and SoC. The accuracy of these methods is highly dependent on the specific battery model employed. The second category comprises data-driven approaches, which necessitate a large and diverse dataset to train models that can effectively approximate the relationship between the input data and SoC. It is worth noting that some of these methodologies require the battery to be charged and discharged according to predefined profiles during the feature extraction phase to generate accurate estimates. This process, known as “offline estimation”, is often impractical for many BMS applications. Consequently, there is increasing interest in developing online SoC estimation techniques that can function under the normal operating conditions of batteries. Figure 7 highlights the main SoC/SoH estimation techniques [131,132,133].

Despite the reduced accuracy of Ampere-Hour (AH) models due to their open-loop nature and the extended relaxation time in OCV methods, model-based techniques remain robust and effectively represent the dynamics of batteries. However, integrating these techniques with adaptive algorithms, such as Kalman filters and observers, is crucial to mitigate errors in model parameter calculations. This integration, though complex, presents an opportunity for Data-Driven (DD) models to serve as valuable tools for SoC/SoH estimation, either independently or by simplifying the complexity of model-based methods through predictive analysis of battery dynamics. The adoption of DT technology further enhances this approach, improving the efficiency of BESS and preventing unexpected degradation. Consequently, this review suggests that combining model-based estimation techniques with data-driven approaches, which are rapidly advancing in their ability to identify dynamic patterns within batteries, can yield precise SoC estimations while reducing model complexity.

Table 6. Comparison between common estimation techniques [128].

Technique		Advantages	Disadvantages
Ampere Hour		Simple Low computational burden Independent of battery models Aging state is considered	An accurate initial value of SOC is needed Error accumulation Battery lifespan is affected by the maximum capacity-determining process
Look-up table-based	OCV	Low computational burden Cost-effective Independent of battery models Aging state is considered	Suitable only at the high and low SOC levels. Needs a long relaxation time The estimated SOC value is largely affected by the battery hysteresis
	EIS	Low cost High estimation accuracy Reflects the dynamic characteristics	Affected by aging and temperature Influenced by battery hysteresis Varies with battery type and test conditions
Model-Based		Insensitive to initial SOC Simulate the capacity fading	High correlation between model parameter and estimated accuracy Rely on modeling accuracy
Data Driven		Ability to work in battery nonlinear conditions Independent of battery model or characteristics Real-time detection of SOC status High precision	Required massive data for model training Large computational efforts Model cannot be generalized Adaption to aging state is not possible

provides a summary of the key features and limitations of the frequently used SoC/SoH estimation approaches discussed [128,132,134].

3.2.2. Battery Thermal Management

A battery’s thermal environment has a direct impact on its lifetime, efficiency, and safety. Excessive heat within the battery can cause catastrophic occurrences, such as explosions. As a result, adopting a battery thermal management system (BTMS) is critical to keeping the battery temperature within a safe range, often between 20 °C and 40 °C, therefore avoiding possible risks. The heat dissipation process within the battery is driven by electrochemical reactions, which can pose risks, especially when multiple cells are packed together. High temperatures can compromise battery safety, reduce cycle life, and diminish capacity, particularly in LiFePO4 batteries. BTMS relies on thermal models to accurately simulate the detailed temperature profiles within a battery or cell during operation, accounting for factors like ohmic losses, chemical reactions, and polarization. However, these models require a thorough understanding of the thermodynamic properties of the battery’s materials and components. The complexity of these approaches ranges from simple one-dimensional models, which assume constant heat generation rates, to advanced three-dimensional models that provide a comprehensive description of the battery’s thermophysical properties under varying conditions. These models are crucial for ensuring that the BTMS can effectively control the charging temperature and maintain optimal conditions under various operational scenarios [135,136].

The thermal management system, which can use air, liquid, or Phase-Change Material (PCM), is critical for regulating heat dispersion within the battery pack [137]. The air-cooling system uses ventilation fans or air extractors to provide a flow of cold air across the surface of the battery pack, dispersing heat produced by chemical processes within the battery [138,139]. Despite its use in automobiles such as the Toyota Prius and Honda Insight, this approach frequently results in severe irregular distribution of temperature, especially during extreme temperatures of operation and rates of discharge [140]. In the PCM system, the battery pack is submerged in the phase-change material, which dissipates heat from the outside throughout the phase-change process [141]. However, PCM’s low heat conductivity limits its usefulness, particularly when quick reaction to thermal swelling is required [142]. The liquid cooling system consists of flow channels designed around the battery surfaces, as well as heat exchangers such as a water jacket. This design allows you to modify the liquid temperature, which aids in the absorption of heat created by the battery pack [143,144]. Cooling mediums can be refrigerants, water, or mineral oil, with heat transmitted from the battery to the cooling fluid by direct or indirect contact. This technology provides more consistent temperature distribution and better thermal management than air and PCM systems.

3.3. Technical Challenges and Future Tre Systems

There are several concerns in the field of the BESS for any applications, particularly for the EV market. In the case of EVs, an extended cycle life means that the battery can withstand more years of everyday usage, which is critical for both cost-effectiveness and consumer confidence. A battery’s capacity to retain performance over several cycles is also critical for decreasing the need for premature battery replacements and lowering total ownership costs. The deterioration mechanisms built into batteries’ electrochemical processes have a substantial impact on their lifetime and efficiency. High charge and discharge rates repeated deep drain cycles and exposure to severe temperatures can all cause deterioration, resulting in reduced battery capacity and overall performance. Furthermore, cycle life is heavily influenced by the type of battery chemistry used. For example, LiFePO4 batteries have a longer cycle life than NCA batteries, while having a lower energy density on average. Using a solid electrolyte rather than a liquid electrolyte is at the forefront of research due to its potential to significantly increase cycle life. This breakthrough is due to a decrease in breakdown processes commonly associated with liquid electrolytes. Concurrently, developments in BMS improve the oversight and management of each cell inside a battery pack. These technologies contribute significantly to improving battery cycle life by enhancing charging cycles and regulating temperatures [145,146,147].

Another critical aspect is the growing demand for effective battery recycling and disposal methods due to the environmental risks posed by improper disposal. Batteries include hazardous elements including lead, cobalt, and organic solvents, which, if not properly handled, can cause substantial environmental damage. Recycling is essential for recovering precious minerals such as lithium, cobalt, and nickel, which may be utilized in the manufacturing of new batteries. This not only decreases the need for ecologically harmful mining, but it also helps to cut carbon emissions. However, recycling EV batteries poses various obstacles. For instance, the technological difficulty of recycling LIBs, as opposed to typical LABs, necessitates the use of unique procedures for each battery chemistry. Furthermore, the dismantling procedure is dangerous and labor-intensive. Furthermore, the economic viability of recycling is currently restricted since the expenses of recycling lithium-ion batteries sometimes outweigh the value of the recovered elements. This has led to insufficient investment in large-scale recycling facilities. To address these difficulties, governments and regulatory agencies are enforcing stronger battery recycling standards, such as extended producer responsibility (EPR) rules that make manufacturers liable for their products’ end-of-life management. Recycling technologies are also being improved technologically, such as hydrometallurgical and direct recycling processes, with the goal of increasing efficiency, lowering costs, and recovering a greater percentage of resources while reducing environmental effects [148,149,150,151]

In the same framework, the surge in electric vehicle (EV) manufacturing has resulted in a considerable increase in demand for critical battery materials such as lithium, cobalt, nickel, and graphite. These minerals are critical to the functioning of lithium-ion batteries, yet they are scarce and concentrated in certain geographical locations. However, the mining and processing of these commodities create significant environmental issues. These operations are energy-intensive and can lead to habitat damage, water pollution, and higher carbon emissions. Furthermore, the geographical concentration of these resources leads to supply chain vulnerabilities and geopolitical conflicts, which can affect material stability and price. Therefore, researchers are focusing on a variety of sustainable alternatives and technologies such as batteries with little or no reliance on limited or problematic materials, like cobalt-free batteries. In addition, the notion of a circular economy, in which old batteries are recycled into new ones, is critical for lowering reliance on newly mined resources while mitigating environmental concerns. Battery technology advancements, like solid-state batteries and alternative chemistries like lithium-sulfur or sodium-ion, also offer promise in terms of lowering the demand for crucial raw materials [152,153,154,155].

Another technical issue is the battery memory effect. This phenomenon is most linked with NiCd batteries and causes a loss of battery capacity when the battery is repeatedly recharged before being fully exhausted. This phenomenon happens because of electrochemical reactions within NiCd batteries, which cause crystalline formations to develop on the cadmium electrodes after repeated partial discharges. These crystals impede the battery’s ability to reach full charge, lowering its effective capacity over time. Symptoms include a considerable decrease in runtime and overall performance, particularly for devices that require a high-power output. To reduce this impact, it is advised to complete full drain and recharge cycles on a regular basis, to use contemporary smart chargers with deep discharge capabilities, and to optimize charging cycles using sophisticated BMS. Recent improvements in battery technology, such as NiMH and LIBs, have virtually removed the memory effect due to their differing electrochemical characteristics and superior design, hence improving both performance and longevity [156,157,158].

4. Charging Technologies and Control

Battery technology has mostly been responsible for the market’s expansion. Commercialization of EVs is dependent on the EV battery’s weight, price, charging time, and lifetime [159,160] The parameters of the battery charger significantly impact battery lifetime and charging time, and battery module performance is influenced by how modules are charged and discharged [161]. The charging time must coincide with refueling a conventional ICE vehicle to achieve ultra-fast charging. The EV supply equipment must also be expanded to accommodate higher power levels. Using high-power converters and smart control strategies can shorten the charging period. As a result, numerous studies have developed converter topologies, designs, and control algorithms for EV charging systems. Therefore, this cutting-edge technology relies heavily on battery chargers.

4.1. EV Charging Levels

The charger’s power level provides data concerning the equipment, cost, location, charging time, rate, and impact on the grid. The power levels of EV chargers are categorized into three main levels, as shown in

Table 7. EV charging levels.

Power Level Types	Charger Location	Typical Use	Power Level	Charging Time
Level 1 (Opportunity/Slow) 120 V (US) or 230V (EU)	On-board 1-phase	Charging at home or office	1.4 kW (12 A) 1.9 kW (20 A)	4–11 h 11–36 h
Level 2 (Primary) 240 V (US) 300V (EU)	On/off-board 1- or 3-phase	Charging at private or public outlets	4 kW (17 A) 8 kW (32 A) 19.2 kW (80 A)	1–4 h 2–6 h 2–3 h
Level 3 (Fast) (208–600 Vac or Vdc)	Off/on-board 3-phase	Commercial, analogous to a filling station	50 kW 100 kW	0.4–1 h 0.2–0.5 h
Extreme Fast Charging (XFC) 1000 Vdc and above	Off-board	Commercial	>350 kW	~5 min

. Since Level 1 EV chargers draw their power from a standard power plug, they do not need any special installation. The most common EV chargers installed in homes are level 2 chargers, albeit they need certain installation. Level 3 EV chargers, with their high-power delivery capabilities, are called DC fast-charging chargers for commercial use [162]. Extrema fast charging (XFC) can provide an ICE-like refilling experience. Power electronic components for the XFC stations are designed to emphasize front-end AC-DC converter stages and controllers, isolated DC-DC converters, and solid-state transformers (SST). The XFC requires a separate EVSE to deliver high power, and the installation costs are extremely costly. Furthermore, SST offers benefits over traditional line-frequency transformers in terms of galvanic isolation in XFC stations and converting medium voltage into low voltage levels [163].

4.2. EV Charging Methods

EV chargers can be divided into conductive and inductive categories according to how they physically interact, as shown in Figure 8. While the inductive charging method (also known as the wireless charging method, or WLC) uses an electromagnetic field to transfer power to the vehicles, the conductive charging method transfers electrical power by directly contacting the vehicles. However, compared to the WLC, the conductive charging approach is more effective [164]. Thanks to the Wireless Power Transfer (WPT) technology, power transfer is incredibly simple throughout the charging process. The fundamental principle of WPT technology is to create magnetic fields by first converting AC energy to DC energy and then, at a high frequency, converting it back to AC energy [165].

4.2.1. Conductive Chargers

The EV chargers’ place of installation and power rating can be utilized to classify them. Off-board, on-board, and integrated on-board battery chargers (IOBC) with unidirectional and bi-directional power flow capability are the three basic categories into which EV battery chargers can be divided. Bi-directional charging supports Vehicle-to-Grid mode (V2G), thus assisting in injecting power back into the smart grid, preferably during peak-load hours, while unidirectional charging reduces the amount of hardware needed and enhances battery degradation [166].

Off-Board Chargers

Off-board chargers are DC fast chargers that support (level 3) charging and are installed at designated charging stations, which require substantial infrastructure development. However, they offer increased power transfer capabilities by providing the vehicle with a high DC charging current fed directly to the battery. As a result, the charging time of off-board battery chargers can be limited to a few minutes. Consequently, DC charging is considered fast charging. Moreover, this type of charger does not affect the vehicle’s weight since the charger is placed at already-built stations [164].

On-Board Chargers

On-board chargers ease the charging process as they offer mobility since the EV can be directly connected to the grid terminals, yet they can add extra weight and cost to the vehicle. Additionally, the power transfer capability is significantly reduced since the size of the charger is constrained by the vehicle’s space and weight. Therefore, the charging time is increased compared to off-board chargers. Since battery chargers are usually categorized according to their power transfer capability and charging time, onboard chargers support three-phase charging (fast charging) as well as single-phase charging (slow charging) [167].

Integrated On-Board Battery Chargers (IOBC)

IOBC utilizes the already-existing propulsion components in the charging process through a bi-directional DC/AC converter, which works as a rectifier during charging. At the same time, the motor windings are used as a coupling inductor to smooth the grid line currents [138]. This topology can reduce the weight, cost, and space per vehicle by directly charging the battery without needing a bulky separate charging unit upon the vehicle or an already existing infrastructure [168]. The effectiveness of this technique depends on the type of used motor, the number of phases, and the employed converter to ensure that the produced average torque is nullified and achieves minimum hardware reconfiguration to switch between different modes of operation [169].

Figure 9 shows the key differences between the types of conductive chargers. First, the charging unit is in the charging station outside the vehicle for the off-board battery charger, which requires an already-built infrastructure. Therefore, there are no constraints on the charger’s weight, cost, or space. This results in high power transfer capability due to high-rating components. Consequently, the charging time of this charger is the fastest. However, a separate unit is installed on the vehicle for the on-board battery charger type. This topology offers more mobility as the charging can be carried out from power outlets and does not require an infrastructure. However, it adds extra cost, space, and weight per vehicle. As a result, the power transfer capability is restricted, and the charging time is increased. Finally, the integrated onboard charger utilizes the EV propulsion components in the charging by using a bidirectional converter while the motor windings act as filtering inductances. This concept can support the vehicle-to-grid (V2G) mode. However, the machine design and control can be a bit challenging [170].

4.2.2. Wireless Chargers

The Wireless Power Transfer System (WPTS), which has crucial power transmission capabilities, has been developed for charging EVs. The transmitter and the receiver are the electrically isolated power parts that comprise the WPTS for EV charging. The receiver is positioned in the electric vehicle (EV) and supplies power to the battery system, while the transmitter is in the roadway and powered by the grid. This eliminates the need for physical cables and plugs. A power converter and a coupling system are the two components of every wireless power transfer (WPT) section. The transmitter coupling unit produces an alternating field that can be electromagnetic, electric, or magnetic [171]. Various techniques transmit energy, with force and field form variations. The most common techniques are known as inductive, capacitive, resonant inductive, and magnetic gear power transfer [172].

Inductive Coupling Chargers

The two coils that make up the inductive WPTS coupling units are coupled to one another mutually, as shown in the schematic diagram in Figure 10. The transmitting coil is driven by high alternating current frequencies, typically between 10 kHz and 150 kHz or higher. Inductive WPTSs can operate at a higher power rating and can handle more power than capacitive WPTSs due to the increased energy density of the free space magnetic field. However, they produce a lot of electromagnetic noise, have high electric losses in coil resistance, and cannot operate if a metal object is positioned between the coils [173,174].

Inductive Resonant Chargers

Capacitors are added to the coupling coils in resonant WPTS to reduce the voltage and/or current required to power the WPTS. When the coupling coils are in the resonance state, their decreasing magnetic fields cause an electrical current to flow through the resonant circuit, charging the capacitor. As a result, the discharging capacitor also generates an electrical current, which in turn generates a magnetic field in the coupling units, allowing equivalent power to be transmitted between the inductor and the capacitor, as illustrated in Figure 11. The theory of resonance between the coils is the foundation of resonant coupling [175,176].

Capacitive Wireless Chargers

Capacitive wireless charging operates on the principle of creating an electric field between two plates: one in the ground (charging pad) and one on the vehicle. When the vehicle is positioned over the charging pad, capacitive coupling occurs between these plates, allowing for the transfer of electrical energy without direct physical contact [177] as shown in Figure 12. This method typically involves high-frequency alternating current (AC) to create the electric field. The main advantages of capacitive WPTSs are their low losses, low electromagnetic radiation, and the ability to transfer power via metal shields without eddy currents [178]. However, because of the extremely low energy density that can be held between plates in free space, capacitive WPTSs can only be used in low-power applications.

Magnetic Gear Wireless Chargers

The mechanical forces transfer power in the magnetic gear charger system. Certain applications, such as wind power generators and EV motors, use magnetic gear in place of traditional contacting gear. Unlike other frequent applications in EV and wind generators, this technique uses two synchronized permanent magnets as the principal coupling mechanism, and they are positioned side by side instead of coaxially. A current source that feeds into the transmitter winding causes an electro-mechanical torque to be generated on the primary side. At the same speed as the transmitter’s permanent magnet, the primary side permanent magnet rotates, causing the secondary side permanent magnet to rotate as well [179], as shown in Figure 13. Finally, a detailed comparison is presented in

Table 8. Comparison between charger types [19,180,181,182].

Feature	Onboard Chargers	Offboard Chargers	Wireless Chargers
Control Topologies	Constant Voltage (CV) Constant Curent (CC) Combination of CV and CC	Fast Charging Techniques High Power DC Charging (CHAdeMO, CCS)	Resonant Inductive Coupling Magnetic Resonance Coupling Frequency Control Phase Control Dynamic Load Matching
Power Conversion Stages	AC-DC: Rectification Techniques DC-DC: Buck, Boost, Buck-Boost Converters	AC-DC: Advanced Rectification Techniques DC-DC: High Power Converters, Inverter Technologies	Power Electronics: Rectifiers and Inverters
Communication Protocols	CAN (Controller Area Network) LIN (Local Interconnect Network)	PLC (Power Line Communication) OCPP (Open Charge Point Protocol)	Nearfield Communication (NFC) Standard Communication Protocols
Efficiency	Moderate Efficiency Dependent on control strategy and power electronics	High Efficiency Advanced control strategies optimize performance	Lower Efficiency compared to wired methods Efficiency decreases with misalignment and air gap size
Performance	Good for regular overnight charging Limited by onboard power conversion capabilities	Excellent for rapid, high-power charging High power delivery, up to hundreds of kW	Suitable for convenience and ease of use Challenges in maintaining
Cost	Integrated into the vehicle, increasing vehicle cost Lower infrastructure cost	High infrastructure cost Requires substantial installation and maintenance	High implementation cost Cost of coils and alignment systems
Practical Applications	Home Charging Work Charging	Public Fast Charging Stations Fleet Operations	Home and Public Wireless Charging Dynamic Charging (In Motion Charging)
Advantages	Convenient for daily use Integrated into the vehicle	Rapidly reduces charging time Supports long-distance travel	Ultimate convenience with no physical connection Reduced wear on connectors and ports
Challenges	Limited by the vehicle’s onboard systems Complex control algorithms Requires precise monitoring and switching	High infrastructure and installation costs Potential thermal management issues Impact on battery longevity	Lower efficiency, alignment, and air gap challenges More complex control strategies Higher implementation costs
Charger Manufacturer	Conventional On-board Chevy Volt [183] Nissan Leaf [184] Delta Q [185] Integrated on-board Valeo Dual inverter [186] Renault Chameleon [187]	Tesla Supercharger V2 [188] ABB Tera HP 150-kW [189] Enercon E-charger [190] Porsche Modular Fast Charging Park A [191] Static HEVO [192] WiTricity [193] KAIST [194] Dynamic ORNL [195] Bombardier [196] WAVE [197]

, discussing different charging types concerning performance, efficiency, employed control topologies, and many other aspects.

4.3. Control of Chargers

4.3.1. Control of Conductive Chargers

Control strategies for conductive chargers of electric vehicles (EVs) are crucial for ensuring efficient and effective charging processes. While EVs primarily operate in Grid-to-Vehicle (G2V) mode, future advancements in EV infrastructure are expected to enable Vehicle-to-Grid (V2G), Vehicle-to-Building (V2B), and Vehicle-to-Vehicle (V2V) modes. V2G technology allows EVs to support the grid by discharging power, with incentives for EV owners managed by aggregators [168]. V2B applications can integrate EVs into building energy management systems, leveraging excess energy from renewable sources [198]. V2V technology, using short-range communication, enables cars to exchange information on their status, enhancing traffic safety and efficiency.

Researchers have identified potential negative impacts of EV integration on smart grids, which can be mitigated through optimal management. Two primary control models are used to manage EV charging: centralized and decentralized [199]. In the centralized model, a central controller, such as an aggregator, collects data on EV states and system information to manage charging centrally. This model optimizes resource use but requires a highly reliable communication infrastructure [200]. In contrast, the decentralized model encourages EVs to manage their charging and discharging based on signals from the system operator, preserving private information and allowing EVs to act according to their preferences [201].

Battery chargers for EVs typically include single-phase or three-phase power factor correction (PFC) converters and DC-DC battery interface stages. PFC converters use dual-loop controllers with a fast inner current loop and a slower outer voltage loop to draw a sinusoidal input current and regulate the DC link voltage. DC-DC converters maintain the desired voltage or current at the battery terminals [202]. These control loops are generally managed with linear proportional-integral (PI) controllers in the synchronous DQ-reference frame, although tuning these controllers can be complex. To address this, model predictive control (MPC) methods are increasingly adopted for their fast dynamic response and ability to handle multiple objectives [203].

Implementing MPC-based control architectures for two-stage battery chargers involves using a converter predictive model and cost function minimization to generate switching pulses in the inner loops. In contrast, the outer loops remain the same. This approach offers advantages in dynamic response and objective handling but poses challenges such as variable switching frequency, high computational burden, and dependence on weighting factor selection. Despite these challenges, advanced control strategies are essential for maintaining efficient and reliable EV charging processes, particularly as EV integration into smart grids and broader energy systems continues to evolve [204,205].

4.3.2. Control of Wireless Chargers

Wireless Power Transfer (WPT) systems can be controlled by primary-side, secondary-side, or dual-side controls since both sides have power electronics converters for transmitting and receiving techniques [206,207,208]. Primary-side control involves regulation at the main winding, using a full primary bridge controlled by a regulated transmitter current. In some cases, power factor correction (PFC) is also utilized for regulation [209]. Secondary-side control employs an active rectifier and converter to charge the battery. While this method increases the vehicle’s weight and cost due to additional electronics on the secondary side, it ensures precise control over the charging process [210]. Dual-side control requires control on both the primary and secondary sides, necessitating a communication link between them. This method can involve either independent or coordinated control of both sides, addressing dynamic charging challenges. Dual-side control is ideal for dynamic wireless charging applications, though it requires careful consideration of stability issues when utilizing independent controllers on both sides [211]. The following are the fundamental control methods, as shown in Figure 14.

Primary Side Control

The primary-side control in wireless charging systems involves using a DC/AC converter to regulate the transmitter current, sometimes with power factor correction. It relies on minimal communication with the receiving side, utilizing information such as the state of charge, battery voltage, and state of health to adjust to the load, thereby reducing onboard electronics and lowering vehicle weight and cost [209]. The primary side also controls the working frequency, which must match the receiving side, and regulates the output by adjusting the switching cycles per second [212]. To achieve zero voltage switching, the operating frequency must exceed the resonance frequency of the inductive impedance, although frequency splitting and multiple peaks can occur [213].

Secondary Side Control

This control uses an active AC/DC converter and a DC/DC regulator to manage battery charging, enhancing infrastructure while adding weight and cost due to increased electrical components. Researchers in [214] proposed a model that maximizes efficiency by directly controlling the battery charging current and stabilizing the DC terminal voltage. Advances include simultaneous wireless data and power transmission, which monitors and adjusts charging based on battery health, though it is less suitable for high-frequency communications in limited-power systems [210]. A 3 kW WPT device for supercapacitor recharging uses a Buck converter with a PI controller to handle varying loads, despite performance impacts from resistance fluctuations [215]. Electronically tuning mismatched coils using saturable reactors and decoupled control systems for impedance matching further improved efficiency. Comparative studies highlight that Fuzzy control strategies stabilize parameters more quickly than PI controllers despite the latter’s smooth outputs [216].

Dual Side Control

The Rx-side control regulates the output to track the reference, while the Tx-side control minimizes inverter output power, often using phase shift adjustments. This approach reduces reactive power and operates similarly to a dual-active bridge system [208,217]. In dynamic wireless charging, individual control of both sides is preferable, although stability must be managed using separate controllers. Various voltage control techniques, such as DC voltage regulation, phase shift control, and pulse density modulation, can be applied on either side of the WPT system [207]. Adjustments in the primary side inverter input or secondary side rectifier output voltage help maintain efficiency despite misalignments [218].

Frequency control can mitigate issues by tuning out of resonance coils, allowing for stable operation across a wide coupling range. Advanced control schemes, including constant-current (CC) and constant-voltage (CV) modes, help manage variable loads, although they may face stability challenges due to frequency bifurcation [214,216]. Effective control in WPT systems requires both open-loop and closed-loop strategies to handle power flow, segmentation, and compensation. Closed-loop controls, while complex, offer improved reliability and response consistency [219]. Communication between the Tx and Rx sides is crucial, with stringent requirements for stability and bandwidth. Phase shift control, employed on both sides, adjusts the phase angles to regulate power transfer, supporting bidirectional power flow [220]. Recent advancements and high-power wireless chargers demonstrate the practical applications of these control techniques, as shown in

Table 9. Comparison of control methods for WPT [207].

Control Strategy	Advantages	Disadvantages
Primary Side Control	Maintains constant current for the transmitter. Load-independent control Eliminates the need for communication links between primary and secondary	Lower system efficiency due to load independence
Secondary Side Control	Provides constant current control Enables implementation of maximum efficiency control	Necessitates controlled power electronics on the secondary side
Dual Side Control with Communication	Achieves desired power control and maximum efficiency Supports bidirectional power flow	Requires secure and minimal delay wireless communication between primary and secondary
Dual Side Control without Communication	Allows independent control of primary and secondary Facilitates desired power with maximum efficiency	Potential stability issues due to conflicts between primary and secondary control

.

5. Electric Motors

Electric motors are the heart of modern electric vehicles (EVs), being crucial in their performance, efficiency, and overall success. This chapter explores the diverse landscape of electric motor technologies shaping the future of transportation electrification. We delve into five key motor types that have emerged as significant players in the EV industry: Induction Motors (IMs), Permanent Magnet Synchronous Motors (PMSMs), Synchronous Reluctance Motors (SynRMs), Switched Reluctance Motors (SRMs), Axial Flux Motors, and Sub-Harmonic Synchronous Machines (SHSMs).

These motor technologies bring unique advantages and challenges to EV propulsion systems. Induction motors, known for their robustness and cost-effectiveness, have been a mainstay in industrial applications and continue to be used in EVs. Due to their high efficiency and power density, PMSMs have become the dominant choice for many EV manufacturers. SynRMs and SRMs offer simpler construction and the potential for high-speed operation without relying on permanent magnets. Axial flux motors are innovative with their compact design and high torque density. Finally, the emerging SHSM technology aims to combine the benefits of wound rotor machines with brushless operation, potentially overcoming some limitations of traditional PMSMs.

This chapter will examine the working principles, advantages, challenges, and recent developments in these motor technologies. By understanding the strengths and weaknesses of each motor type, we can better appreciate the complexities involved in selecting and optimizing electric motors for the diverse requirements of modern electric vehicles. As the EV market continues to evolve, these motor technologies will play a pivotal role in shaping the future of sustainable transportation.

5.1. Induction Motor (IM)

Due to their robustness, reliability, and cost-effectiveness, induction motors (IMs) have been a significant player in electric vehicle (EV) propulsion systems. These motors, also known as asynchronous motors, operate on the principle of electromagnetic induction and have been successfully implemented in various EV models [221]. The induction motor consists of a stator with poly-phase windings and a rotor with short-circuited conductors. When AC current flows through the stator windings, it creates a rotating magnetic field. This field induces currents in the rotor, producing a magnetic field that interacts with the stator field, resulting in torque production [222].

Induction motors offer several advantages for EV propulsion. They are robust, reliable, and require minimal maintenance due to the absence of brushes or permanent magnets. IMs can operate efficiently over a wide speed range, which is crucial for vehicular applications [223]. The technology is mature, well-understood, and does not rely on rare-earth materials, making it an attractive option for mass production [224]. Another significant advantage is the inherent field-weakening capability of IMs, which allows for extended constant-power operation at high speeds. This characteristic is particularly beneficial for highway driving conditions [225]. Despite their advantages, induction motors face some challenges in EV applications. They generally have lower efficiency at low speeds and partial loads than permanent magnet motors. The rotor losses in IMs can be significant, especially at high speeds, leading to thermal management issues [226]. The power factor of induction motors is typically lower than that of permanent magnet motors, which can result in higher current requirements and potentially larger inverter ratings [227].

Advanced control techniques have been developed to improve the performance of induction motors in EVs. Field-oriented control (FOC) and direct torque control (DTC) are widely used strategies that enable precise torque and flux control, improving dynamic performance and efficiency [228]. Recent developments in sensor-less control techniques have further enhanced the attractiveness of IMs for EV applications by eliminating the need for speed or position sensors, thereby increasing reliability and reducing costs [229]. Research efforts have focused on addressing the limitations of induction motors. Advanced rotor designs, such as copper and optimized slot geometries, have improved efficiency and power density [230]. An example of an induction motor used in an Audi Q8 e-tron is shown in Figure 15 [231]. Integrating wide-bandgap semiconductor devices in motor drives has enabled higher switching frequencies, improved motor performance, and reduced losses [232]. Hybrid designs combining the characteristics of induction and synchronous reluctance motors have also been explored, aiming to leverage the advantages of both motor types [233].

5.2. Permanent Magnet Synchronous Motor (PMSM)

Due to their superior performance characteristics, Permanent Magnet Synchronous Motors (PMSMs), shown in Figure 16 [234], have become the dominant choice for electric vehicle (EV) propulsion systems. These motors combine high efficiency, excellent power density, and a wide constant power speed range, making them ideal for the demanding requirements of modern EVs [235]. PMSMs operate on the principle of electromagnetic interaction between a rotating magnetic field in the stator and permanent magnets in the rotor. The stator typically consists of a three-phase winding arrangement. At the same time, the rotor contains high-strength permanent magnets, usually made from rare-earth materials such as neodymium-iron-boron (NdFeB) or samarium-cobalt (SmCo) [236]. Two main types of PMSMs are used in EVs: surface-mounted PMSMs (SPMSMs) and interior PMSMs (IPMSMs). In SPMSMs, the magnets are attached to the surface of the rotor, while in IPMSMs, the magnets are embedded within the rotor structure. IPMSMs are more common in EV applications due to their ability to achieve higher power density and better field-weakening capabilities [237,238].

PMSMs offer several advantages that make them attractive for EV applications. They can achieve efficiencies over 95% across a wide operating range, contributing to increased vehicle range [239]. Using strong permanent magnets allows for compact designs with high torque-to-weight ratios. PMSMs can operate efficiently at low and high speeds, which is crucial for EV performance. The absence of brushes and slip rings in PMSMs reduces maintenance requirements and improves reliability. Additionally, PMSMs allow for accurate torque and speed control, enhancing vehicle dynamics and drivability [240]. Despite their advantages, PMSMs face some challenges in EV applications. Relying on rare-earth materials for permanent magnets can lead to high and volatile costs. The limited global supply of rare-earth elements has raised geopolitical and sustainability concerns [241]. At high temperatures or under fault conditions, permanent magnets can lose their magnetic properties, potentially leading to motor failure. Compared to induction motors, PMSMs have a more limited constant power speed range, which may require additional gearing for high-speed operation.

To address these challenges, researchers and manufacturers are exploring several avenues. PMSMs are currently being developed using ferrite magnets or other alternative materials to reduce dependence on rare-earth elements [242]. Some researchers are investigating hybrid excitation, combining permanent magnets with electromagnetic excitation to improve field-weakening capabilities and efficiency [243]. Advanced thermal management techniques are implemented to prevent demagnetization and improve power density [244]. Additionally, novel rotor and stator designs are explored to enhance performance and reduce material usage [245]. PMSMs remain at the forefront of electric vehicle propulsion technology due to their excellent performance characteristics. As research continues to address current limitations and improve designs, PMSMs will likely maintain their dominant position in the EV market. The ongoing developments in materials, design optimization, and control strategies promise to enhance the capabilities of PMSMs further, contributing to the advancement of electric vehicle technology.

5.3. Synchronous Reluctance Motor (SynRM) and Switched Reluctance Motor (SRM)

SynRM and SRM have gained increasing attention in the electric vehicle (EV) industry due to their simple and robust construction, absence of permanent magnets, and potential for high-speed operation. These characteristics make SRMs an attractive alternative to permanent magnet and induction motors in certain EV applications [246]. SRMs operate on the principle of magnetic reluctance. The motor consists of a stator with concentrated windings and a rotor made of soft magnetic material with a salient pole structure. When the stator windings are energized, the rotor moves to align itself with the stator’s magnetic field, minimizing the magnetic reluctance path. Continuous rotational motion is achieved by sequentially energizing the stator poles [247].

SynRM and SRM offer several advantages for EV propulsion systems. They have a simple and robust construction, with no windings or permanent magnets on the rotor. This simplicity leads to lower manufacturing costs and improved reliability [248]. SynRM and SRM can operate efficiently at high speeds, which benefits EV applications requiring a wide speed range [249]. The absence of permanent magnets eliminates concerns about rare-earth material supply and demagnetization at high temperatures. This characteristic makes SynRM and SRM particularly suitable for harsh operating environments [250]. Additionally, SynRM and SRM have inherent fault tolerance due to their independent phase structure, enhancing system reliability [251]. However, some hybrid PM-assisted SRMs are used in EV applications to incorporate the advantages of both PM and SRM technologies. One example is the Internal Permanent Magnet Synchronous Reluctance Motor (IPM-SynRM) used in the Tesla Model 3, shown in Figure 17 [252].

Despite their advantages, SynRM and SRM face challenges in widespread EV adoption. One of the primary issues is acoustic noise and vibration, which result from the pulsed nature of torque production and radial forces acting on the stator [253]. Torque ripple is another significant challenge, as it can affect vehicle drivability and passenger comfort [254]. The nonlinear magnetic characteristics of SynRM and SRM make precise torque control more complex than other motor types. This complexity often necessitates sophisticated control strategies and power electronics [255]. Advanced control techniques have been developed to address the challenges associated with SynRM and SRM. Current profiling methods aim to minimize torque ripple by shaping the phase current waveforms [256]. Direct Instantaneous Torque Control (DITC) has shown promise in reducing torque ripple and improving dynamic performance [257]. Model Predictive Control (MPC) has also been applied to SynRM and SRM, demonstrating improvements in efficiency and torque ripple reduction [258]. These advanced control strategies, combined with high-performance power electronics, have significantly enhanced the viability of SynRM and SRM for EV applications.

Recent research has focused on addressing the acoustic noise and torque ripple issues of SynRM and SRM. Novel rotor and stator designs, such as segmented rotor structures and asymmetric stator poles, have shown the potential to reduce acoustic noise and improve torque characteristics [259]. The integration of wide-bandgap semiconductors, such as Silicon Carbide (SiC) devices, in SynRM and SRM drives has enabled higher switching frequencies and more precise current control, improving overall system performance [260]. Multiphase SynRM and SRM configurations, with more than three phases, have been explored to increase power density and reduce torque ripple [261]. These designs offer potential fault tolerance and power segmentation advantages for EV powertrains.

5.4. Axial Flux Motors

Axial flux motors, or axial gap, as shown in Figure 18, have gained increasing attention in the electric vehicle (EV) industry due to their unique geometry and performance characteristics. Unlike traditional radial flux motors, axial flux motors have a disc-shaped structure where the magnetic flux flows parallel to the motor’s rotational axis [262]. The stator and rotor are arranged face-to-face in an axial flux motor. The stator typically contains windings or permanent magnets, while the rotor consists of permanent magnets or a ferromagnetic core, depending on the specific design. The interaction between the magnetic fields of the stator and rotor produces torque, causing rotation [263]. There are several configurations of axial flux motors, including single-sided, double-sided, and multi-stack designs. The single-sided configuration has one stator and one rotor, while the double-sided design features a rotor sandwiched between two stators or vice versa. Multi-stack designs involve multiple rotor-stator pairs arranged in series to increase power output [264].

Axial flux motors offer several advantages that make them attractive for EV applications. They provide high torque density, as the disc-shaped design allows for a larger air gap diameter, resulting in higher torque production per unit volume compared to radial flux motors [266]. The compact axial length of these motors can be advantageous in vehicles where space is at a premium, allowing for more flexible powertrain layouts [267]. Efficient cooling is another benefit, as the disc-shaped structure provides a large surface area for heat dissipation, which can lead to improved thermal management and potentially higher power density [268]. Additionally, axial flux motors can be easily scaled by adding more stator-rotor pairs, allowing for modular designs adapted to different power requirements [269]. Despite their advantages, axial flux motors face some challenges in widespread adoption. The unique geometry of axial flux motors can make mass production more challenging and potentially more expensive than traditional radial flux motors [270]. Strong axial magnetic forces between the stator and rotor can increase mechanical stress on the motor structure, requiring careful design and robust bearings [271]. Some axial flux motor designs can exhibit significant cogging torque, affecting smooth operation at low speeds [272].

Recent research has focused on addressing the challenges associated with axial flux motors. Technological advancements, such as 3D printing of soft magnetic composites, have shown promise in simplifying production and reducing costs [273]. Novel winding configurations and magnet arrangements are being explored to minimize cogging torque and improve efficiency [274]. Recent studies have also focused on integrating axial flux motors with advanced power electronics and control systems. These developments aim to optimize motor performance across a wide operating range, making axial flux motors more competitive with traditional radial flux designs [275].

5.5. Sub-Harmonic Synchronous Machine (SHSM)

The transportation electrification sector has witnessed the rise of Permanent Magnet Synchronous Motors (PMSMs) due to their impressive torque density and efficiency despite the continued prevalence of induction machines in industrial settings [276]. Notwithstanding these merits, the high production costs and fixed flux characteristics of PMSMs have deterred manufacturers from widespread adoption [277]. This challenge has spurred research into PM-less and PM-assisted alternatives, such as wound rotor synchronous and switching reluctance machines, which offer a blend of design simplicity, robustness, efficiency, and power density [278]. Conventional wound rotor synchronous machines, hampered by the drawbacks of brushes and slip rings for DC excitation, have historically been unsuitable for traction applications. The brushless wound rotor synchronous machine (BL-WRSM) topology has been established, which is a promising solution that enables rotor excitation adjustment while maintaining high performance in traction scenarios. Among the various brushless excitation methods, harmonic excitation is elegant, utilizing the synchronous machine’s inherent properties without requiring additional bulky components [279].

Harmonic excitation techniques encompass higher- and lower-order (sub-harmonic) magnetomotive forces (MMF). Studies have revealed the superiority of the sub-harmonic MMF (SH-MMF) approach, which boasts enhanced performance and reduced losses compared to its higher-order counterpart [280]. Consequently, BL-WRSMs employing SH-MMF excitation have emerged as strong contenders for traction applications, offering a trifecta of tunable excitation, high power density, and efficient operation. The evolution of sub-harmonic synchronous machines (SHSMs) began with their initial introduction [281], followed by the development of a single inverter SHSM [282] and its subsequent design optimization [283]. Innovation continued with the creation of novel stator winding configurations, including a 2-layer design for a new SHSM topology [284] and a 3-layer configuration for another SHSM variant [285], as shown in Figure 19. Further advancements saw 2L-SHSM and 3L-SHSM designs adapted for dual inverter configurations [286], enhancing their controllability.

In the quest for even greater torque generation and power density, researchers introduced PM-assisted hybrid SHSM topologies [287,288]. The success of these hybrid designs, particularly the 2L-SHSM, paved the way for exploration into hybrid 3L-SHSM configurations. Recent studies have proposed promising PM-assisted 3L-SHSM designs [289,290], further expanding the horizons of electric machine performance. This ongoing research in SHSM technology exemplifies the relentless pursuit of overcoming PMSM limitations while preserving their advantages, potentially revolutionizing electric motor applications across various industries.

This section has examined various electric motor technologies used in electric vehicles, including Induction Motors, Permanent Magnet Synchronous Motors, Synchronous and Switched Reluctance Motors, Axial Flux Motors, and Sub-Harmonic Synchronous Machines. The comparison

Table 10. Comparison between electric motors used in EV applications.

Motor Type	Key Characteristics	Advantages	Challenges
IM	Asynchronous operation Rotor with short-circuited conductors	Robust and reliable Cost-effective Wide speed range No rare-earth materials Good field-weakening capability	Lower efficiency at low speeds Significant rotor losses at high speeds Lower power factor
PMSM	Permanent magnets in the rotor Synchronous operation	High efficiency (>95%) Excellent power density Wide speed range Accurate torque and speed control	Reliance on rare-earth materials Risk of demagnetization Limited constant power speed range
SynRM and SRM	No permanent magnets Salient pole rotor structure	Simple and robust construction Lower manufacturing costs High-speed operation capability Fault tolerance	Acoustic noise and vibration Torque ripple Complex control requirements
Axial Flux	Disc-shaped structure Axial magnetic flux path	High torque density Compact axial length Efficient cooling Scalable design	Manufacturing challenges Strong axial forces Potential for high cogging torque
SHSM	Brushless wound rotor design Sub-harmonic MMF excitation	Tunable excitation High power density Efficient operation No need for rare-earth materials	Relatively new technology Complex winding configurations

provided summarizes each motor type’s key characteristics, advantages, and challenges.

This overview demonstrates that no single motor technology is universally superior for all EV applications. Each type offers unique benefits and trade-offs regarding performance, cost, manufacturability, and operational characteristics. The choice of motor depends on specific vehicle requirements, manufacturing considerations, and technological advancements. As the EV industry evolves, we expect continued innovation in these motor technologies, addressing current limitations and potentially leading to hybrid design types. The ongoing development of electric motors will play a crucial role in enhancing future electric vehicles’ performance, efficiency, and affordability.

5.6. Requirements of Motor Performance for Electric Vehicles

Manufacturers must consider various performance requirements when designing or selecting electric motors for EVs to ensure optimal vehicle operation. These requirements are influenced by factors such as vehicle type, intended use, and market segment [291,292].

Table 11. Key performance requirements for electric motors in EV applications.

Performance Metric	Typical Requirement	Importance
Power Density	>5 kW/kg	High
Torque Density	>20 Nm/kg	High
Peak Efficiency	>95%	High
Wide Speed Range	0–15,000 RPM	Medium to High
Constant Power Speed Range	>3:1	Medium
Torque Ripple	<5%	Medium
Overload Capability	150–200% for short durations	Medium
Noise and Vibration	<80 dBA	Medium
Thermal Management	Operating temp < 150 °C	High
Reliability	>150,000 miles/15 years	High
Cost	< USD 10/kW	High

summarizes key performance requirements for electric motors in EV applications.

Power and torque density are crucial for minimizing the motor’s weight and size, directly impacting vehicle performance and range [227,235]. High efficiency across a wide operating range is essential for maximizing the vehicle’s energy utilization and range [236]. A wide and constant power speed range is important for vehicle drivability and performance in various driving conditions [227,235]. Low torque ripple and noise levels improve passenger comfort and overall vehicle refinement [293]. Overload capability is necessary for handling short-term high-power demands, such as during acceleration or hill climbing. Effective thermal management is critical for maintaining performance and ensuring longevity [294].

Reliability is paramount in automotive applications, with motors expected to last the vehicle’s lifetime. Finally, cost considerations are vital for mass-market adoption of EVs [291,293]. These requirements can vary based on the specific vehicle application (e.g., passenger car, commercial vehicle, and high-performance sports car) and may evolve as EV technology advances [291]. Motor designers and vehicle manufacturers must balance these often-competing requirements to create optimal solutions for their target markets [292,294]. Ongoing research and development in electric motor technology continue to push the boundaries of performance, aiming to meet and exceed these requirements [292]. As the EV market matures, we can expect further refinement and potential shifts in these performance criteria to meet evolving consumer expectations and regulatory standards.

6. Standards and Regulations

The standards and regulations for EV charging infrastructure, batteries, and motors are crucial in ensuring safety, compatibility, and efficiency in the electric vehicle ecosystem. Standard organizations like IEC, IEEE, ISO, SAE, ANSI, BIS, and BSI provide comprehensive guidelines covering design, construction, communication, and safety requirements for EV charging stations [295]. These standards are essential for both conductive and inductive charging methods, emphasizing safety and reliability, especially with the increasing use of high-voltage lithium-ion batteries in electric vehicles vehicles [296]. Additionally, the development of international standards for electric vehicles focuses on the importance of efficient energy storage devices like traction batteries and the necessity of universal access to charging infrastructures to promote the widespread adoption of electric vehicles [297]. Furthermore, wireless power transfer (WPT) regulations for EV charging are being established to enhance charging speed and safety, particularly in adverse weather conditions, highlighting the significance of electromagnetic compatibility and human exposure limits [298].

Table 12. Battery standards.

Standard	Description
IEC 62133	Developed by the International Electrotechnical Commission (IEC), this standard specifies safety requirements for portable sealed secondary lithium cells and batteries, covering electrical, mechanical, thermal criteria, and testing procedures.
UL 1642	Underwriters Laboratories (UL) created this safety standard for lithium batteries. It includes various tests to evaluate battery safety, often required for lithium-ion batteries in consumer electronics.
UN 38.3	Established by the United Nations, these safety standards are crucial for transporting lithium-ion batteries. They involve multiple tests assessing resistance to environmental factors such as mechanical stress, vibration, and temperature changes, and compliance is essential for international shipping.
ISO 12405	This standard pertains to the testing and characterizing lithium-ion cells and modules used in electric vehicles, addressing electrical properties, mechanical integrity, thermal behavior, and abuse testing, along with performance, safety, and environmental considerations.
IEEE 1625	Issued by the Institute of Electrical and Electronics Engineers (IEEE), this standard covers rechargeable lithium-ion battery packs in portable computing devices, focusing on safety issues like overcharging, over-discharging, and short-circuit prevention to minimize the risk of battery-related incidents.
NFPA 70	Published by the National Fire Protection Association (NFPA) as part of the National Electrical Code (NEC), this standard governs the installation of energy storage systems, including lithium-ion batteries, specifying fire safety, ventilation, electrical, and other safety measures.

,

Table 13. Communication and safety standards.

Standard	Description
SAE J2293	Details the communication and network requirements necessary for efficient EV charging infrastructure. This standard ensures interoperability and seamless data exchange within the charging network.
SAE J2344	Establishes comprehensive safety guidelines for electric vehicles, focusing on minimizing risks during operation and charging. It covers aspects such as electrical safety, crashworthiness, and thermal management.
SAE J2847	Defines the specific communication protocols required between various components of the EV charging system. This includes interactions between the EV, charging station, and the grid to ensure effective and safe power transfer.
IEC 63110	Sets the management protocol for EV charging and discharging infrastructure, ensuring standardized communication for energy management, billing, and user authentication across different systems and platforms.
IEC 62752	Outlines standards for cable control and protection devices used in EV charging, including requirements for detecting faults, disconnecting power, and ensuring user safety.
IEC 61851	Specifies comprehensive safety regulations for EV charging stations, covering electrical safety, operational requirements, and compatibility with different EV models to ensure safe and efficient charging.
ISO 15118	Defines the communication protocols between an EV and a charging station, facilitating features like Plug and Charge. This standard also includes protocols for vehicle-to-grid (V2G) interactions, enabling bi-directional energy flow.
ISO 17409	Specifies safety requirements for conductive charging systems in electric vehicles, focusing on ensuring safe operation during connection, charging, and disconnection.
ISO 18246	Sets safety standards for charging electric motorcycles and mopeds, addressing risks associated with electrical faults, overheating, and improper connections.
GB/T 27930-2015	Establishing the communication protocol between off-board conductive chargers and the EV battery management system ensures coordinated and efficient charging.
NEC 625, NEC 626	Specifies safety measures for off-board EV charging, including requirements for electrical installation, fire safety, and grounding.
UL2231, UL2251, UL2202	Defines protection device requirements for EV charging equipment, covering aspects such as overcurrent protection, isolation, and durability to enhance safety.
CHAdeMO	Specifies the communication requirements for DC fast charging, ensuring that EVs and charging stations can effectively exchange data to manage high-power charging sessions safely.

,

Table 14. Connectors standards.

Standard	Description
SAE J1772	Defines the general physical requirements for conductive charging connectors used in electric vehicles. This includes specifications for plug design, durability, and safety features to ensure reliable and secure connections.
IEC 62196	Specifies the requirements and testing procedures for plugs, socket outlets, vehicle connectors, and inlets for conductive charging. This standard ensures compatibility and safety across different EV models and charging stations.
GB/T 20234.1-2015	Details the physical requirements for connectors and interfaces used in EV charging, aligning with international standards such as IEC 62196 and SAE J1772 to promote global interoperability.
CHAdeMO	Sets the physical requirements for DC fast charging connectors, ensuring they can handle high currents and voltages while maintaining safety and reliability during fast charging sessions.

and

Table 15. System requirements standards.

Standard	Description
SAE J1772	Specifies the general electrical and performance requirements for conductive charging systems in electric vehicles. It covers aspects such as voltage levels, current capacity, and system architecture to ensure efficient and safe charging.
SAE J1773	Provides standards for inductively coupled charging systems, detailing the requirements for wireless power transfer between the charging pad and the EV, including alignment, efficiency, and safety measures.
SAE J2293	Establishes standards for both on-board and off-board charging equipment, covering conductive AC and DC charging and inductive charging. It also defines power requirements and system architecture for these charging methods.
SAE L2894/2	Specifies requirements for power quality in EV charging systems, ensuring that the power supplied meets specific standards for voltage stability, harmonics, and overall quality to protect both the vehicle and the grid.
SAE J2953	Sets standards for the interoperability of electric vehicles with the grid, ensuring that EVs can effectively communicate and interact with different types of charging infrastructure for seamless charging experiences.
SAE J2954	Provides guidelines for wireless power transfer (WPT) for light-duty plug-in/electric vehicles, including alignment methodology and system requirements to ensure efficient and safe wireless charging.
SAE J3068	Specifies the requirements for three-phase AC charging of electric vehicles, detailing the necessary electrical parameters and system configurations to support high-power AC charging.
IEC 60038	Specifies voltage standards for EV charging applications, ensuring that the voltage levels used in charging systems are compatible with both the EVs and the grid infrastructure.
IEC 60664-1	Provides standards for installation coordination of EV charging equipment in low voltage supply systems, covering insulation requirements and protection against electrical surges.
IEC 61851	Specifies the general requirements for conductive charging systems for electric vehicles, including safety, compatibility, and performance standards to ensure reliable and efficient charging.
IEC 61980	Defines wireless power transfer (WPT) systems standards, specifying requirements for systems operating up to 1000 V AC and 1500 V DC to ensure safe and effective wireless charging.
GB/T 18487.1-2015	Sets general requirements for conductive charging systems, aligning with IEC 61851 to ensure compatibility and safety across different EV charging infrastructures.
GB/T 20234.2-2015	Specifies the parameters for AC charging interfaces, including rated voltage, current, and maximum power to ensure reliable and efficient AC charging.
GB/T 20234.3-2015	Defines the parameters for DC charging interfaces, specifying rated voltage and current to support high-power DC fast charging.
UL2594, UL1741	Specifies requirements for EV supply equipment concerning converters and controllers, ensuring that these components meet safety and performance standards.
CHAdeMO	Details the electrical requirements for DC fast charging, ensuring EVs can safely handle high-power charging sessions.

show the related standards included in electric vehicle charging [19,299,300,301].

7. Conclusions

The increasing global reliance on electric vehicles (EVs) is a response to the excessive use of fossil fuels and rising CO₂ emissions. EVs enable the integration of alternative energy sources, such as energy storage systems (ESSs) and renewable energy sources (RESs), fostering sustainable mobility and reducing fossil fuel dependency. Despite their benefits, EVs face numerous challenges related to traction systems, storage capacity, charging infrastructure, and energy management technologies. Moreover, the expansion of the EV market requires comprehensive standards and regulations. This review paper, titled “State-of-the-art of Electric Vehicles: Architectures, Control, and Regulations”, provides an in-depth analysis of current advancements in EV components, including energy storage systems, electric motors, and charging technologies. It also explores various control techniques and the prevailing standards and regulations that ensure market harmonization. By synthesizing the latest developments and regulatory frameworks, the paper aims to advance knowledge in the field and support EV technologies’ continued evolution and implementation, ultimately contributing to a more sustainable and efficient transportation future.