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This paper proposes a space vector modulation (SVM)-based common-mode (CM) currents reduction method of an H8 inverter for permanent magnet synchronous motor (PMSM) drives. There are power quality issues in the PMSM drive systems, such as current distortions and CM electromagnetic interference (EMI) due to the fast-switching operation of the inverter. These issues are related to CM voltage (CMV) and CM current (CMC). Although several studies have been conducted to reduce the CMV and CMC, some CMV variations and CMCs are still generated in the real implementation. Unlike conventional methods, the proposed method selects the voltage vectors with similar CMV levels and arranges them considering the series-connected switch operation of the H8 inverter in a voltage vector modulation sequence. At a low modulation index (MI), the proposed method completely restricts the CMV variations into six times. At high MI, the proposed method synthesizes the reference voltage vector differently, depending on the position of the reference vector, to reduce both current distortions and CMCs. The validity of the proposed method is verified through simulations and experimental results.

In this paper, a switched-capacitor multilevel inverter with voltage boosting and common-mode-voltage reduction capabilities is put forth. The proposed inverter is synthesized with one-half bridge and several switched-capacitor cells. Due to the voltage boosting and common-mode current reduction features, the proposed multilevel inverter is suitable for grid-connected PV applications. In addition, an analytical lifetime evaluation based on mission profile of the proposed inverter has been presented to derive lifetime distribution of semiconductors. Whereas in the proposed inverter, any components failure can bring the whole system to a shutdown. The series reliability model is used to estimate the lifetime of the overall system. The performance of the suggested multilevel inverter in grid-connected applications is verified through the simulation results using the grid-tied model in Matlab/Simulink. Moreover, the viability and feasibility of the presented inverter are proven by using a one kW lab-scaled prototype.

The use of the common mode current for stator winding insulation condition assessment has been extensively studied. Two main approaches have been followed. The first models the electric behavior of ground-wall insulation as an equivalent RC circuit; these methods have been successfully applied to high-voltage high-power machines. The second uses the high frequency of the common mode current which results from the voltage pulses applied by the inverter. This approach has mainly been studied for the case of low-voltage, inverter-fed machines, and has not yet reached the level of maturity of the first. One fact noticed after a literature review is that in most cases, the faults being detected were induced by connecting external elements between winding and stator magnetic core. This paper presents a case study on the use of the high-frequency common mode current to monitor the stator insulation condition. Insulation degradation occurred progressively with the machine operating normally; no exogenous elements were added. Signal processing able to detect the degradation at early stages will be discussed.

Power conversion equipment based on high-voltage SiC devices offers significant advantages in efficiency and power density. However, during high-voltage, high-power switching operations, severe electromagnetic interference (EMI) can easily occur. It could cause the false triggering of devices and result in converter failure in severe conditions. This paper firstly establishes a mathematical model and conducts simulation analysis of the conducted common-mode interference path in high-voltage SiC device gate driver circuits. Based on the driver circuit architecture, a modeling method for the common-mode interference conduction network in half-bridge submodules is proposed, clarifying the key factors contributing to high common-mode currents. A low common-mode current design methodology for high-voltage SiC submodules is presented, including driver loop structure optimization, capacitor design, and submodule integration. A highly integrated 3.3 kV SiC-based submodule prototype has been successfully developed, serving as a building block for constructing multilevel modular converters (MMCs). Simulation and experimental results indicate that the amplitude of the common-mode current is primarily influenced by the coupling capacitance of the auxiliary power supply, exhibiting a proportional relationship. The developed SiC submodule achieves high-speed switching at 50 kV/μs under a 2 kV DC bus voltage, with excellent thermal stability and low common-mode current characteristics, validating the effectiveness of the proposed model and design approach.

Presence of a transformer in a grid connected photovoltaic system provides galvanic isolation between the photovoltaic panels and the grid. However, it increases the overall cost, makes the circuit bulky and reduces the efficiency of the system. Hence, transformerless inverters have gained significant importance owing to its low cost, light weight and increased efficiency. However, due to the absence of the transformer, there is no galvanic isolation between photovoltaic panels and the grid and there is always a threat of flow of leakage current. In this research paper, an elaborate analysis of H4, H5 and H6 transformerless inverter is carried out. DC side decoupled circuits are studied to eliminate the leakage current. Their performances are compared based on the simulations carried out in MATLAB/SIMULINK software. A novel H6 inverter is proposed by introducing an additional switch in H5 topology. A direct current path is provided in H5 topology during one of the active modes, so that current flows through few switches thereby reducing the conduction losses. Common mode voltage remains constant in the proposed H6 inverter and hence the leakage current is eliminated. The proposed H6 inverter can thus be a promising topology to eliminate leakage current and reduce conduction loss in the transformerless grid connected photovoltaic system.

Bearing current problems frequently appear in wind turbine systems, which cause wind turbines the break down and result in very large losses. This paper investigates and compares bearing current problems in three kinds of wind turbine generators, namely doubly-fed induction generator (DFIG), direct-drive permanent magnet synchronous generator (PMSG), and semi-direct-drive PMSG turbines. Common mode voltage (CMV) of converters is introduced firstly. Then stray capacitances of three kinds of generators are calculated and compared through the finite element method. The bearing current equivalent circuits are proposed and simulations of the bearing current are carried out. It is verified that the bearing currents of DFIGs are more serious than the two kinds of PMSG, while common mode current (CMC) of the direct-drive PMSG is much greater than the other two types of wind turbine generators.

Multi-input power supply systems are mostly used in the field of combined power supply of multiple new energy sources. Multi-input inverters play an important role in these systems; however, they often face the issue of common-mode currents. This paper proposes an improved modulation mod for a non-isolated series simultaneous power supply type dual-input inverter with low common-mode current for new energy generation applications. In this paper, a circuit simulation is designed and a dual-input inverter circuit model is fabricated for experiments, after which it is verified that the improved modulation method can suppress the common-mode current to below 30 mA, providing an effective modulation scheme for mitigating common-mode currents in the joint power supply of multiple new energy sources.

High carrier-frequency Pulse Width Modulation (PWM) is a popular and widely used method for driving the induction motors in Electric Vehicles (EVs) using voltage source inverters. However, it often generates high-frequency Common Mode (CM) voltages, resulting in shaft voltages. This, in turn, leads to a flow of leakage current to the earth, known as CM current, which can cause serious problems, including premature failure of the ball bearings in the motor. This paper introduces an Active Cancellation Circuit (ACC) method aimed at extensively reducing the CM current and, consequently, the CM voltage in three-phase induction motor drives. In this technique, Y-configured capacitors are employed for detecting CM voltage. After amplification, this voltage is applied to the motor frame to eliminate both the CM current and the CM voltage. Unlike conventional voltage compensating techniques, the proposed approach eliminates the need for a CM transformer between the inverter and the motor. As a result, there is no need for a high-power-rated CM transformer or any of its associated losses. To assess the effectiveness of the proposed method, experiments were conducted using an induction motor (3-phase, 1.1 kW, 415 V/60 Hz) connected to a two-level three-phase voltage source inverter.

The commercial mature gallium nitride high electron mobility transistors (GaN HEMT) technology has drawn much attention for its great potential in industrial power electronic applications. GaN HEMT is known for low on-state resistance, high withstand voltage, and high switching frequency. This paper presents comparative experimental evaluations of GaN HEMT and conventional Si insulated gate bipolar transistors (Si IGBTs) of similar power rating. The comparative study is carried out on both the element and converter level. Firstly, on the discrete element level, the steady and dynamic characteristics of GaN HEMT are compared with Si-IGBT, including forward and reverse conducting character, and switching time. Then, the elemental switching losses are analyzed based on measured data. Finally, on a complementary buck converter level, the overall efficiency and EMI-related common-mode currents are compared. For the tested conditions, it is found that the GaN HEMT switching loss is much less than for the same power class IGBT. However, it is worth noting that special attention should be paid to reverse conduction losses in the PWM dead time (or dead band) of complementary-modulated converter legs. When migrating from IGBT to GaN, choosing a dead-time and negative gate drive voltage in conventional IGBT manner can make GaN reverse conducting losses high. It is suggested to use 0 V turn-off gate voltage and minimize the GaN dead time in order to make full use of the GaN advantages.

Nowadays, high-speed permanent magnet synchronous machines (HSPMSMs) are widely used in high-speed direct-drive applications. Moreover, modular multilevel converters (MMCs) have attracted a lot of attention. In this paper, the mathematical model of the MMC for the HSPMSM was built on high- and low-speed regions, respectively, and the control of each model is completely decoupled. Moreover, energy balance control schemes based on the common mode current injection of the MMC with HSPMSM drive applications have been proposed for high- and low-speed cases, respectively. Based on this model, the controller is proposed for high- and low-speed cases, respectively. Simulation and experiment results indicate that the proposed energy balance control method for an MMC in the high-speed PMSM drive application exhibits significant performance, which can ensure the energy balance of the MMC and eliminate the circulating current of the MMC directly.