EREV Topological Configurations

The EREV configuration combines the ICEV and EV configurations. It attempts to integrate the best parts of each one, and it is relatively flexible. This flexibility is due to several factors unique to the EV. An EREV works like an EV. First, the energy flow is mainly via flexible electrical wires rather than rigid and mechanical links, achieving distributed subsystems. Second, different EREV propulsion arrangements produce significant differences in system configuration. Third, different energy sources (such as auxiliary power units) have different characteristics and refueling systems. In general, the EREV consists of three major subsystems. Electric propulsion, which comprises an electronic controller, a power converter, an electric motor, mechanical transmission, a final drive, and driving wheels. An energy source, which involves the energy source, energy managemen<sup>t</sup> unit, and charger. An auxiliary power unit, which consists of the generator, and depending on the technology, an ICE, a fuel cell, regenerative braking, regenerative shock absorbers, a flywheel, a thermoacoustic engine, photovoltaic cells, a gas turbine, a rotary engine, and a wind turbine/refueling unit. The energy managemen<sup>t</sup> unit cooperates with the electronic controller to control regenerative energy and its energy recovery. It also works with the energy charger and monitors the usability of the energy source.

At present, there are many possible EREV configurations due to the variations in electric propulsion and energy sources. Thirteen alternatives focus on electric propulsion variations; some are in typical vehicles, and others are in high-performance vehicles.

(1) All-wheel drive (AWD; Figure 12a) is the first alternative, a direct extension of the existing ICEV adopting a longitudinal front engine. It consists of an electric motor, a gearbox, differential, an APU, battery, and a BMS connected to the electric motor; this configuration has two differentials to transmit the power to both axles.

Figure 12b shows a typical configuration for pick-ups and high-performance sedan vehicles. The electric motor changes its orientation from longitudinal to cross-wise, maintaining a gearbox, two differentials, an APU, a battery, and a BMS. Figure 12c shows one electric motor in each axle; this configuration keeps a gearbox coupled with the motor. The gearbox can be single-gear or two-gear to multiply and divide torque and revolutions. Figure 12d shows an electric motor for each wheel. The mechanical differential is replaced by an electronic differential that controls the speed differentiation of one wheel concerning the other. This type of configuration uses small, high-efficiency electric motors. Figure 12e shows a configuration with in-wheel motors. Again, one variant can have no gearbox. In this configuration, the electric motor has high efficiency and high velocity. The electric motor is connected directly to the wheel, and the other components are like those in the previous configurations. Figure 12f similarly uses in-wheel motors but simultaneously incorporates an electric differential, maintaining an APU, a battery, and a BMS; each wheel efficiently transmits power and reduces weight compared to other configurations.

(2) Front-wheel drive (FWD; Figure 12g). In this configuration, the electric motor changes from longitudinal to cross while maintaining the same components as the allwheel-drive configuration. The difference is that the mechanical power transmission is only to the front wheels, and it can have an electric motor for each wheel with or without a gearbox. Figure 12h shows a configuration in which an electronic differential replaces the mechanical one. Figure 12i shows a similar configuration using electric motor in-wheel technology while keeping the battery, the BMS, and the APU.

**Figure 12.** All possible EREV configurations.

(3) Rear-wheel drive (RWD) maintains a longitudinal electric motor in Figure 12j, but the rear wheels receive the mechanical power. In Figure 12k, the significant from

with the previous one is the position of the electric motor; it changes from longitudinal to cross; the rest of the components are the same. A configuration that improves the performance is having an electric motor in each wheel, with or without a gearbox, as shown in Figure 12l. Figure 12m shows the last configuration, which uses the electric motor inwheel with electric differential. The selection of the configuration will depend on the size and application of the EREV. The primary criteria for selection are compactness, performance, weight, and cost.

Using driving cycles lets us know the emissions released and the energy consumption. However, due to the complexity and diversity of the vehicles, it is not easy to simulate a whole vehicle fleet using a physical approach [119], so we can use some software to estimate the emissions and energy consumption. Software such as MATLAB-Simulink, AVL Cruise, ADAMS, ANSYS, ADVISOR, ANSOFT, and MAPLESim can simulate driver/vehicle systems.

#### *3.2. Key Components of an EREV*

First, vehicle weight directly affects performance, especially the range and gradeability. Lightweight materials such as aluminum and composite materials for the body and chassis help with weight reduction. Second, achieving a low drag coefficient with the body design effectively reduces aerodynamic resistance, significantly extending the range of the EREV on highways or when cruising. The aerodynamic resistance can be reduced by tapering front and rear ends, and adopting a flat, covered, low-floor design. One can also optimize the airflow around the front and rear windows while using this flow to cool the batteries to minimize battery losses efficiently. Third, low rolling resistance tires effectively reduce running resistance at low and medium driving speeds and play an essential role in extending the range of EREVs in city driving. The design of an EREV requires considering the interactions of all the components that it may have. Figure 13 shows all the main components and the interactions that they may have with each other.

**Figure 13.** Key components and interactions.

## **4. Control and Management**

The control issue of power electronic interface converters plays a vital role in the efficient and safe operation of EREVs. There are many studies on the control of power flow and energy management. Table 2 shows studies about energy managemen<sup>t</sup> methods. The control and managemen<sup>t</sup> strategies are focused on (1) minimization of fuel consumption and loss of energy, (2) simplifying the structure, (3) increasing the maximum efficiency, and (4) ensuring robustness and satisfactory driving performance. Energy management: Adopting an intelligent energy managemen<sup>t</sup> system (EMS) helps maximize onboard stored energy. Using sensor inputs, such as air temperature and currents and voltages for the motors and batteries, among other data, the EMS can perform the following functions:



**Table 2.** A summary of control methods and strategies for EREVs.


**Table 2.** *Cont.*
