In the background of environment protection and power-saving awareness, the requests for new energy electric vehicles and their on-board charger(OBC) keep growing. As one of the important components in the OBC module, magnetics is getting more and more attention accordingly. The magnetics integration of differential mode (DM) and com-mon mode(CM) chokes for a 3-phase 4-wire (3P4W) electromagnetic interference(EMI) filter used in OBC is theoretically analyzed and studied. Based on the analysis and comparison of the background of power supply applications, the inte-gration principle for DM and CM chokes, and the available integration schemes in industry and academia, an integration of DM and CM chokes for 3P4W with quasi-cross DM magnetic branches is proposed. Through the magnetic flux simula-tion analysis, electrical characteristics under DC-bias and the on-board tested data, the effect of the magnetics integra-tion scheme was proved, i.e., it can obviously decrease the DC-bias on DM magnetic branches in the case of unbalanced 3-phase current and effectively improve the anti-EMI performance of power supply.

Silicon carbide metal-oxide-semiconductor field effect transistor (SiC MOSFET) has attracted attention from the industry owing to its excellent characteristics such as high voltage, high frequency and low conduction loss. However, compared with the silicon-based IGBT, the problem of gate oxide reliability caused by the high defect density at the SiC/SiO2 gate oxide interface has become a key bottleneck restricting the large-scale applications of SiC MOSFET devices. By sorting out and analyzing the research results of the gate oxide reliability of SiC MOSFET at home and abroad in recent years, the causes of the gate oxide reliability problems at present were elaborated upon, and various commonly-used gate oxide reliability evaluation methods were summarized and compared. Finally, the gate oxide reliability of SiC MOSFET under extreme operating conditions and the development status of technologies for improving its performance were discussed.

The traditional linear control method for a Boost converter has a poor dynamic performance and weak robustness to load disturbance. To solve this problem, a fixed-frequency sliding mode current control method based on power balance is proposed. First, the observed value of load current is used to calculate the input power, which is required to maintain the stability of output voltage. Then, the input power of the converter is adjusted by controlling the inductor current, so that the system's state trajectory is restrained on the sliding mode surface that possesses invariance to load disturbance, thus ensuring the system's large signal stability and improving its dynamic performance. Finally, based on the equivalent control principle, the equivalent sliding mode control is achieved through the PWM technique to avoid problems of chattering and unstable switch frequency. Simulations of the Boost converter under the condition of step load change are carried out in Simulink, and the proposed method is compared with the traditional linear control method. Results show that when using the proposed method, the system's dynamic performance is better and its large signal stability under large load disturbances is guaranteed.

The design of DC-DC converters which are applied to vehicle auxiliary power modules (APMs) is taken as a research object, the topology of a two-stage DC-DC converter consisting of a three-level Boost (TL-Boost) topology and a half-bridge LLC resonant topology is proposed, and its working principle is analyzed. The front-stage TL-Boost topology converts a wide range of input voltage into a stable voltage, ensuring the high-efficiency operation of the back-stage half-bridge LLC resonant topology. The feasibility and correctness of the proposed DC-DC converter were verified by establishing an experimental platform and carrying out relevant experiments.

Under the background of energy crisis and environmental issues, the high-gain DC-DC converter is indispensable in renewable energy applications. A dual-switch quadratic structure is proposed to enhance the voltage gain of the traditional quadratic boost converter while reducing the current stress of switches. On this basis, by combining the switched capacitors and a coupled inductor, a dual-switch quadratic high-gain DC-DC converter with a couple inductor is put forward. This converter has advantages such as a very high voltage gain, a pair of switches with the same phase, low voltage stress of switches and output diode, and zero-current switching off in many diodes. The operating principle and steady-state performance of the converter are analyzed in detail, including the voltage gain derivation and the voltage and current stresses of components. Finally, a 120 W prototype was fabricated to verify the theoretical analysis and the feasibility of the converter.

In the application of wide output voltage range, some problems exist in an LLC resonant converter under the traditional frequency control, such as a wide switching frequency regulation range, a large circulation current and difficulty in high-efficiency operation. To solve these problems, a dual-full-bridge LLC resonant converter under a fixed-frequency phase-shift and fixed-frequency PWM hybrid control strategy is proposed, which is suitable for the wide range of output voltage. This converter is composed of two full-bridge LLC resonant converters sharing one bridge arm, and the output voltage is modulated by the hybrid control, so that a quadruple voltage gain and a wider output voltage range of the resonant converter can be realized. Meanwhile, the problems that the large circulation current exists under the traditional frequency control and the soft switching cannot be realized at a small phase shift angle are solved, thus improving the system efficiency. The switching frequency of the converter is always equal to the resonance frequency, and the voltage gain is independent of load, which is helpful for the design of the magnetic element. At the same time, the soft switching can be realized in the full load range. Finally, a detailed analysis of the circuit principle was given, which was further verified by simulations. An experimental platform was also established to validate the feasibility and effectiveness of the proposed converter.

The dual-active-bridge (DAB) converter is a key device in a bidirectional power transmission system. In this paper, its fundamental operation principle and topologies are reviewed at first. Then, four basic modulation strategies for the DAB converter are introduced, including single-phase-shifted, dual-phase-shifted, extended-phase-shifted and triple-phase-shifted strategies. Moreover, the modeling and optimization methods based on these four modulation strategies are compared and analyzed. Finally, some problems faced by practical applications and the corresponding solutions are discussed. Along with the development of DC power distribution, energy storage and distributed energy resources, DAB converters will have broad application prospects.

Aimed at the problems of a traditional dual-active-bridge (DAB) converter such as large switching loss, large circulating current, narrow range of load variation and low operating efficiency, a novel power control method for DAB converter based on variable inductance and phase shift (PS) angle is proposed, in which the variable inductance and PS angle are taken as the main control parameters to improve the operating efficiency of the DAB converter in a wider range of load variations. In addition, the transfer function of the DAB converter is linearized to improve the practicality and convenience of the controller. Because the device saturation is controllable in the proposed method, the core size can be reduced to optimize the converter size. Finally, the effectiveness and superiority of the proposed method were verified by experiments. Results show that under the condition of maximum PS angle, the inductance variation significantly affected the power transmission of the DAB converter, and its overall operating efficiency was about 5% higher than that of the traditional DAB converter under both the light and heavy load conditions.

Based on the two-stage (AC/DC and DC/DC) structure of a DC charging pile for electric vehicles(EVs) and through the analysis of the functional requirements of the two-stage circuit structure, a MATLAB/Simulink simulation model is built with a main circuit which consists of a Vienna circuit as the front-stage AC/DC rectifier and a Buck-Boost circuit as the rear-stage DC/DC voltage conversion circuit. Simulations are performed with load set as a pure resistive load and the PNGV model of a battery, respectively. Simulation results meet the requirement of parameters such as output voltage stability accuracy, output voltage ripple and input current harmonics, which proves that the model can be used to analyze the power grid loaded by EVs and promote the study on the impact of EVs on power grid.

Aimed at the problems in the existing nine-level inverter such as many devices and a complex modulation strategy, a novel switched capacitor nine-level inverter is proposed. The topology of this inverter is composed of only one single DC power supply, nine switches, two capacitors and two diodes, and it can output nine levels and double the boost at the same time. The voltages of capacitors are self-balancing, and the complex control algorithm and external voltage sharing circuit are not required. The phase disposition PWM strategy is adopted to modulate the inverter. The working states of four pairs of switches in the inverter are complementary, and the NOT gate logic circuit can be used to reduce the complexity of the modulation strategy. First, the topology and working principle of the inverter are analysed theoretically. Second, the modulation strategy is introduced in detail, and the advantages of this topology are introduced by comparing it with other nine-level inverters. Finally, the feasibility and effectiveness of the proposed topology and modulation strategy were verified based on the established simulation circuit and experimental platform.