Search Results (790)

This study aims to minimize component requirements by presenting a novel topology for a single-phase 15-level asymmetrical multilevel inverter. Utilizing an H-bridge configuration, the proposed design achieves a maximum 15-level output voltage using asymmetrical DC sources. The initial 15-level inverter structure is further enhanced to support a 25-level variant suitable for renewable energy applications, effectively reducing system costs and size. However, the increased component count in multilevel inverters poses reliability challenges, particularly concerning total harmonic distortion reduction, which remains a focal point for researchers. Various parameters, including total standing voltage, multilevel inverter cost function, and power loss, are analyzed for both the proposed 15-level and the expanded 25-level multilevel inverters. This study contributes a new topology for a single-phase 15-level asymmetrical multilevel inverter, optimizing component usage and paving the way for renewable energy integration. Despite the advantages of multilevel inverters, addressing reliability concerns related to total harmonic distortion reduction remains crucial for future advancements in this domain. Full article

Transformerless inverters (TIs) are becoming increasingly popular in solar photovoltaic (PV) applications due to their enhanced efficiency and cost-effectiveness. Unlike transformer-based inverters, TIs, which lack transformers and additional components, offer significant advantages in terms of reduced weight, compactness, and lower costs. Research studies have demonstrated that multilevel TIs can achieve lower total harmonic distortion (THD), reduced switching stresses, and higher AC output voltage levels suitable for high voltage applications. However, achieving these outcomes simultaneously with maximum power ratings and the lowest switching frequencies poses a challenge for TI topologies. In light of these challenges, this research proposes the implementation of a 13-level single-source switched-capacitor boost multilevel inverter (SSCBMLI) designed for solar PV systems. The SSCBMLI consists of a single DC power source, switched-capacitor (SC) units, and a full H-bridge. Compared to other existing 13-level multilevel inverter (MLI) configurations, the proposed SSCBMLI utilizes the fewest components to minimize development costs. Moreover, the SSCBMLI offers voltage boosting and can drive high inductive loads, self-voltage-balanced capacitors, an adaptable topology structure, and reliable system performance. Simulations and experimental tests are conducted using PLECS 4.5 and SIMULINK to assess the performance of the proposed SSCBMLI under varying modulation indices, source powers, and loads. A comparative analysis is then conducted to evaluate the SSCBMLI against existing inverter topologies. Full article

Photovoltaic energy is increasingly used in irrigation processes, particularly in arid regions, to pump water from rivers to fields. Rising oil prices, global warming, and the limited availability of fossil fuels have increased the need for alternative energy sources. This study focuses on the design and implementation of a transformerless single-phase photovoltaic system that powers a single-phase induction motor to drive a centrifugal water pump. The methodology aims to achieve the best system performance. A DC–DC boost converter maximizes the output voltage by utilizing maximum power point tracking (MPPT) and extracting the maximum power from the photovoltaic (PV) array. A bidirectional buck-boost converter charges the battery from the DC bus and discharges the battery voltage to the DC bus for loads. The DC voltage is then converted to AC output voltage using a single-phase inverter, which supplies power to the single-phase induction motor driver (IMD). The voltage/frequency (V/f) scaler control is used for a single-phase induction motor. The system employs scalar motor control to achieve the maximum motor speed required to operate the centrifugal water pump efficiently. All results and simulations are carried out in MATLAB/Simulink R2019a version and are compared for different motor and PV parameters numerically. Full article

There is a paradigm shift to hybrid (AC/DC) networks that integrate both AC and DC to meet growing energy demands, mitigate global warming, and interconnect distributed energy sources (DERs). However, the unique characteristics of AC/DC faults, the mutual interaction of hybrid lines, the harmonic components of converters/inverters, multiple directions of energy flow, and varying current levels have challenged the existing protection algorithms. Therefore, this paper presents a data-driven coordination AC/DC fault protection algorithm. The algorithm utilizes faulty voltage and current signals to retrieve the precise time-domain characteristics of AC, DC, and intersystem (IS) faults to develop the algorithm. The proposed algorithm consists of four stages: stage 1 includes the detection of faults, stage 2 identifies the fault as either AC or DC, stage 3 classifies the respective AC and DC faults, and stage 4 locates the AC/DC fault precisely. The hybrid test system is developed in a MATLAB/Simulink environment, and the data-driven algorithm is trained and tested in Python. The extensive simulation results for multiple fault cases, either AC or DC, and the comparisons of various performance indicators confirm the effectiveness of the developed algorithm, which performs efficiently under a noisy and extended hybrid AC/DC network. Compared to other schemes, the proposed coordination protection approach can enhance the speed and accuracy of hybrid AC/DC networks. Full article

Energy storage systems (ESSs) and active power filters (APFs) are key power electronic technologies for FACTS (Flexible AC Transmission Lines). Battery energy storage has a structure similar to a shunt active power filter, i.e., a storage element and a voltage source inverter (VSI) connected to the grid using a PWM filter and/or transformer. This similarity allows for the design of an ESS with the ability to operate as a shunt APF. One of the key milestones in ESS or APF development is the DC-link design. The proper choice of the capacitance of the DC-link capacitors and their equivalent resistance ensures the proper operation of the whole power electronic system. In this article, it is proposed to estimate the required minimum DC-link capacitance using a spectral analysis of the DC-link current for different operating modes, battery charge mode and harmonic compensation mode, for a nonlinear load. It was found that the AC component of the DC-link current is shared between the DC-link capacitors and the rest of the DC stage, including the battery. This relation is described analytically. The main advantage of the proposed approach is its universality, as it only requires calculating the harmonic spectrum using the switching functions. This approach is demonstrated for DC-link capacitor estimation in two-level and three-level NPC inverter topologies. Moreover, an analysis of the AC current component distribution between the DC-link capacitors and the other elements of the DC-link stage was carried out. This part of the analysis is especially important for battery energy storage systems. The obtained results were verified using a simulation model. Full article

With power demands continuously growing, the penetration of renewable energy resources, particularly solar photovoltaic (PV) systems, across the residential sector has been extensive. A voltage source inverter (VSI) is the key element for efficiently processing energy conversion and connecting PV systems to home loads or utility grids. The operation of this inverter relies heavily on power-switching devices, which suffer from larger power losses due to the conventional semiconductors used based on silicon (Si) material. The new materials of wide bandgap (WBG) semiconductors, for example, gallium nitride (GaN) and silicon carbide (SiC), provide remarkably distinct characteristics of semiconductor devices to minimize power loss and boost the inverter’s operational capabilities. This research paper assesses the effects of integrating SiC-MOSFET devices into VSIs in order to improve the switching behavior and efficiency level. An experimental double-pulse testing (DPT) circuit was configured and set up for investigating the switching characterization of SiC-MOSFETs compared to the widely used Si-IGBTs. Under various operating circumstances, the switching behavior of two different types of power transistors was tested while their turning-on and turning-off losses were measured. The VSI based on SiC and Si transistors was simulated to examine the performance of the inverter. The results reveal that incorporating SiC-MOSFETs into the VSI substantially enhances the switching operation and reduces total power losses while increasing the efficiency compared to the inverter based on Si-IGBTs. Full article

As renewable energy sources (RES) continue to expand and the use of power inverters has surged, inverters have become crucial for converting direct current (DC) from RES into alternating current (AC) for the grid, and their security is vital for maintaining stable grid operations. This paper investigates the security vulnerabilities of photovoltaic (PV) inverters, specifically focusing on their internal sensors, which are critical for reliable power conversion. It is found that both current and voltage sensors are susceptible to intentional electromagnetic interference (IEMI) at frequencies of 1 GHz or higher, even with electromagnetic compatibility (EMC) protections in place. These vulnerabilities can lead to incorrect sensor readings, disrupting control algorithms. We propose an IEMI attack that results in three potential outcomes: Denial of Service (DoS), physical damage to the inverter, and power output reduction. These effects were demonstrated on six commercial single-phase and three-phase PV inverters, as well as in a real-world microgrid, by emitting IEMI signals from 100 to 150 cm away with up to 20 W of power. This study highlights the growing security risks of power electronics in RES, which represent an emerging target for cyber-physical attacks in future RES-dominated grids. Finally, to cope with such threats, three detection methods that are adaptable to diverse threat scenarios are proposed and their advantages and disadvantages are discussed. Full article

The recent trend in analog design to replace typical analog circuits with digital implementations has led to the use of resistive feedback to pull a CMOS inverter into the switching threshold region to achieve gain, which is ideal for analog operations. Here, we report a three-transistor (3T) CMOS resistive-feedback inverter-based amplifier capable of achieving high gain paralleled with reduced noise, low power consumption, and enhanced stability. Unlike conventional resistive-feedback inverter-based amplifiers, the transistors are operated in the subthreshold region, which allows for a lower supply voltage and current, leading to lower power consumption. Subthreshold conduction also reduces typical amplifier noise sources. This design provides a novel approach to resistive feedback in the inverter amplifier, allowing for a large gain while occupying minimal layout area. The reported amplifier design facilitates unique capabilities, e.g., detection of ultra-low (fC) charges or sub-pA currents for newly emerging PHz electronic and optoelectronic devices driven by few-cycle laser pulses. As proof of concept, the specifications of the proposed amplifier are successfully measured and verified by multiple test chips designed and fabricated in TSMC’s 180 nm CMOS process. The fabricated amplifier operates at a 1.35 V power supply with a measured voltage gain of 53.61 dB (or 480 V/V), a bandwidth of 94 kHz, and an equivalent input voltage noise of 6.4 nV/$\sqrt{\mathrm{Hz}}$, consuming only 13.5 µW. Full article

In non-synchronous machine sources (N-SMSs), power sources are connected to the grid through power electronic devices, which typically exhibit a voltage-controlled current source characteristic during faults. Due to the current-limiting feature of inverters, the voltage and current demonstrate a strong nonlinearity. As a result, the short-circuit current (SCC) of N-SMSs is commonly calculated using iterative methods. For renewable energy plants, which contain a large number of N-SMSs, the calculation is often based on the single-machine multiplication method, ignoring internal discrepancies among machines. To address these issues, this paper proposes a calculation method for the SCC contributed by a renewable energy plant based on single-machine multiplication. This method is simple, does not require iteration, and ensures engineering practicability. This paper first analyzes the SCC calculation model under a low-voltage ride-through (LVRT) control strategy. Inspired by the single-machine multiplication approach, a fast initial voltage calculation method at the machine terminal is proposed, along with an active current correction method. With this approach, a more accurate SCC can be obtained, avoiding convergence issues and ensuring practical applicability in engineering. The validity of this method is verified through PSCAD/EMTDC simulations. The error in calculating SCC does not exceed 3.02%. Compared with the single-machine multiplication method, the accuracy is significantly improved, while the accuracy is roughly equivalent to that of the iterative method. Full article

This study outlines the creation and lab verification of a low-voltage direct current (LVDC) back-to-back (B2B) converter intended as a versatile connection point for low-voltage users. The converter configuration features dual inverters that regulate the power distribution to AC loads and grid connections through a shared DC circuit. This arrangement enables the integration of various DC generation sources, such as photovoltaic systems, as well as DC consumers, like electric vehicle chargers, supported by DC/DC converters. Significant advancements include sensorless current estimation for grid-forming inverters, which removes the necessity for conventional current sensors by employing mathematical models and established system parameters. The experimental findings validate the system’s effectiveness in grid-connected and isolated microgrid modes, demonstrating its ability to sustain energy quality and system stability under different conditions. Our results highlight the considerable potential of integrating grid-forming functionalities in inverters to improve microgrid operations. Full article

The development of the elastic balance area within the distribution network places greater demands on the interaction between sources and loads, which impacts the stability of the power system. While achieving symmetry in active power is essential for stable operation, it is challenging to attain perfection due to various disruptions that can exacerbate frequency and voltage instability. Additionally, due to the inherent resonance characteristics of LCL filters and the time-varying nature of weak grid line impedance, grid-connected inverters may interact with the grid, potentially leading to oscillation issues. A grid-forming inverter control method that incorporates resonance suppression is proposed to address these challenges. First, a control model for the grid-forming inverter based on the Virtual Synchronous Generator (VSG) is established, enabling the system to exhibit inertia and damping characteristics. Considering the interaction between the VSG grid-connected system and the weak grid, sequence impedance models of the VSG system, which feature voltage and current double loops within the αβ coordinate system, are developed using harmonic linearization techniques. By combining the impedance analysis method, the stability of the system under weak grid conditions is evaluated using the Nyquist criterion. The validity of the analysis is confirmed through simulations. Finally, in order to ensure the effectiveness and correctness of the simulation, an experimental prototype of an NPC three-level LCL grid-forming inverter is built, and the experimental results have verified that the system has good elastic support capability and resonance suppression capability in the elastic region. Full article

This article presents the experimental validation of a model-based predictive control (MPC) strategy for the safe interconnection of voltage source inverters (VSI) with output LC filters for the grid connection of DC energy resources. The MPC is formulated as a quadratic programming (QP) problem and solved using the operator splitting quadratic programs (OSQP). The proposed approach incorporates integral action to achieve precise voltage magnitude reference tracking while accounting for modulated voltage limits and nominal current constraints within the control design. The effectiveness of the proposed strategy is validated through simulations conducted in MATLAB, demonstrating superior dynamic performance compared to the traditional hierarchical PI control. The implementation of the proposed MPC is experimentally verified on a VSI setup using the dSPACE MicroLabBox. The results confirm that the computational requirements are satisfied, establishing this approach as a practical alternative for modern power electronic systems. The proposed MPC for VSIs offers an effective approach to enforcing operational constraints, improving dynamic performance, and facilitating the robust integration of renewable energy sources in microgrids. Full article

The limits of direct current (DC) injection and output current distortion of grid-connected photovoltaic (PV) inverters are specified in the IEEE 1547-2018 standard. The standard prescribes limits of output current harmonics, but the input voltage and power at which output current distortion is measured are not specified. This manuscript presents the results of DC injection and output current distortion measurements for three commercial single-phase PV inverters, with 3 kVA, 3.3 kVA, and 6 kVA rated power. During the measurements, the inverters are powered by a programmable DC source that emulates the power voltage characteristic of a PV array, providing different input conditions. In addition to steady-state measurements at constant input voltage and power, the change in the output current spectrum over time during the maximum power point tracking (MPPT) is also measured. The results show that the output current distortion depends on the input voltage and power. Moreover, the current distortion of some of the tested inverters exceeds the limits specified by the standard in some cases. The presented results suggest that further research on the dependence of the output current distortion from PV inverters on their input power and voltage is needed. Full article

With the growth of energy demand and the aggravation of environmental problems, solar photovoltaic (PV) power generation has become a research hotspot. As the key interface between new energy generation and power grids, a PV grid-connected inverter ensures that the power generated by new energy can be injected into the power grid in a stable and safe way, and its power grid adaptability has also received more and more close attention in the field of new energy research. This research focuses on the discussion of PV grid-connected inverters under the complex distribution network environment, introduces in detail the domestic and international standards and requirements on grid-connected inverter grid adaptability, and then analyzes in depth the impacts of the access point voltage changes, access point frequency changes, and access point harmonic changes on the inverters. In order to enhance the adaptability of grid-connected inverters under these abnormal conditions, this research systematically summarizes and concludes a series of inverter adaptive control strategies, which provide literature guidance to effectively reduce the probability of power system faults and improve the reliability of the power system. Finally, the future development direction of PV inverter technology is outlooked, pointing out that, with the increase in the proportion of PV power generation in the power system, PV inverters need to evolve gradually from adapting to the grid to supporting the grid and promote the transformation of PV power generation from the auxiliary power source to the main power source through the integration of PV and energy storage. Full article

This paper describes a mathematical model of the AC/DC converter. The analytic expressions define fundamental physical variables of the converter and their relations: phase current and voltage, shift angle between these quantities, power factor, and supply voltage U_D. The mains voltage is defined as a digitalized sine wave while the current’s wave takes the form of a line segment defined in an appropriate time interval. The model permits the description of two modes of operation: inverter and rectifier. The assumed control method of the converter depends on the successive switching of selected vectors. They are qualified according to the principle of the lowest error between the reference and measured phase current value. The control method is realized by using hysteresis algorithms. Five different algorithm solutions and comparative results are implemented. Several examples of current, voltage, and vectors taken during the simulation and experimental works are executed. Full article