The traditional coupling mechanism of multi-directional wireless power transfer (WPT) often adopts an xyz orthogonal circular coil structure, which requires three power supplies and has a charging area limited by the coil structure. To solve this problem, a novel multi-directional WPT coupling mechanism composed of two groups of 8-shaped coils and one group of circular coils is proposed. It presents five circular rings in different directions as a whole and only needs one single power supply. Based on the S-S type transmitter topology, the magnetic field distribution in the coil is changed by controlling the circuit, thus realizing power transfer inside and outside the coil and broadening the charging area. Based on the coil structure, a mathematical model of the proposed coupling mechanism is established, and the calculation formulas for mutual inductance and efficiency at any spatial position are derived. The best working area of the coupling mechanism is determined according to simulation and experimental results.

The common-mode(CM) inductor is composed of windings and a magnetic core. Mn-Zn ferrite can be used as the magnetic core of CM inductor, and the frequency-dependent characteristics of its high-frequency parameters make the CM inductor exhibit non-linearity within a range of 150 kHz-30 MHz. It is difficult to accurately predict the impedance characteristics of the CM inductor in a high-frequency band due to the large deviation between the traditional lumped circuit model of CM inductor and the measured impedance characteristics. The effects of material parameters of the magnetic core and the winding scheme on the high-frequency impedance characteristics of CM inductor are analyzed, and the mechanism of magnetic material parameters and the winding structure affecting the distributed capacitance is described from the perspective of the distributed capacitance characteristics of CM inductor. A wide-band impedance simulation modeling method for CM inductor with the consideration of related frequency-dependent parameters of magnetic core was proposed, and its validity was verified by combining with the impedance test result.

Based on the passive damping method of capacitor in parallel with resistor, the active damping method of virtual resistor in parallel with capacitor can complete the virtualization of shunt resistor using the control algorithm and realize the active damping of the resonant peak from the output filter through the capacitor current feedback. However, the existing method of virtual resistor in parallel with capacitor cannot achieve a strict equivalence of shunt resistance, which leads to the problem of poor dynamic performance. To solve this problem, through the transformation of the control block diagram, an active damping control method of fully equivalent shunt resistor based on capacitor voltage and capacitor current feedback is proposed, thus realizing the strict equivalence of passive damping method of capacitor in parallel with resistor. At the same time, the active damping control method of fully equivalent shunt resistor is obtained through the analysis of dominant poles of the system. Compared with the method of virtual resistor in parallel with capacitor based on the current loop, this method can effectively improve the damping ratio and response speed of the system while reducing the overshoot. Finally, simulation and experimental results verified the effectiveness of the proposed method.

With the development of industrial demand, higher requirements are put forward for the reliability of power transistors. The real-time measurement of device junction temperature can ensure the normal operation of the device, so it is very important. Through the research on the on-line measurement method for turn-on delay time, a measurement circuit is designed. By measuring the turn-on delay time at different junction temperatures, the relationship between them is established, the on-line measurement of device junction temperature is realized by measuring the turn-on delay time under actual working conditions, and the device junction temperature is deduced. The results measured using the proposed method are similar to those obtained by an infrared temperature gun. In this way, an on-line measurement method for MOSFET junction temperature based on turn-on delay time is proposed, providing a new idea for the on-line measurement of junction temperature in the future.

Virtual DC motor(VDCM) control has been widely applied in suppressing the power fluctuations of DC microgrid and improving the voltage stability of DC bus. Due to the randomness and uncertainty of distributed generations in microgrid, as well as the load switching in microgrid, the DC bus voltage will fluctuate greatly. To improve the regulation capability of bus voltage, a virtual energy storage control strategy based on the coordination of VDCM control and controllable load is proposed by using the regulation capability of controllable load and the virtual motor control of load converter. By adjusting the angular speed of the virtual motor, the power consumption of the controllable load can be adjusted to compensate the fluctuation of bus power and improve the stability of bus voltage. In addition, the relationship between the rotational kinetic energy of VDCM and the charging and discharging energy of the DC capacitor is established. Finally, a simulation model is built on the MATLAB/Simulink platform to verify the effectiveness of the proposed control strategy.

To improve the efficiency of a dual-active-bridge (DAB) converter, a control strategy of minimum current stress with varying switching frequency control is proposed. First, the minimum-current-stress-optimized control method when the voltage changes in a wide range is analyzed, the expressions for the conduction loss and switching loss of the DAB converter under light load conditions are established, and the conduction loss and switching loss at different switching frequencies are further compared. Then, the implementation method for closed-loop control and the power transmission range in each mode are introduced in detail. Under light load conditions, the proposed method can significantly reduce the current stress while improving the efficiency of the DAB converter. Finally, simulation and experimental results verified the advantage of the proposed control method.

With the rapid development of power generation by renewable energy and the grid-connection technology, the microgrid dominated by power electronic converters has attracted more and more attention in recent years. Owing to the low inertia and high nonlinearity of power electronic converters, an islanded microgrid under large disturbances is more likely to lose its transient stability. Considering the interactions between grid-forming and grid-following converters in the microgrid, a transient stability criterion based on the equal area criterion(EAC) and an improved control strategy for transient stability are proposed. First, the simplified second-order dynamic model of the islanded microgrid is established, which contains a nonlinear damping term relying on the power angle. Then, the impact of the nonlinear damping term on the acceleration and deceleration areas is revealed from the energy perspective. Considering the distribution characteristics of nonlinear damping, a transient stability criterion is formulated for the positive damping region. In addition, according to the stable boundary conditions, an improved control strategy for transient stability based on voltage feedforward is also put forward. Finally, simulations are carried out with MATLAB/Simulink to verify the effectiveness of the proposed stability criteria and the improved control strategy. The results show that the microgrid transient stability criterion and the improved control strategy proposed can provide a theoretical basis for the parameter optimization design of power electronic converters and the improvement of the stable operation capability of microgrid.

An evaluation platform for the CM noise suppression characteristics of high-frequency transformer was established, which was suitable for batch applications in engineering. The conduction mechanism of common-mode (CM) noise in a transformer was analyzed, and the conduction characteristics of CM noise along the coupling path in the transformer was investigated for evaluating the transformer's capability of suppressing the CM noise. First, a function generator was used to generate a high-frequency voltage pulsation signal, which was assigned on the primary winding of the transformer to simulate the transmission characteristics of CM noise. Then, an oscilloscope was used to capture the voltage drop generated by the CM signal on the sampling resistor to judge the suppression effect of the transformer on the CM noise, so as to analyze the influence of the sampling resistor selection on the evaluation results. The effectiveness of the proposed evaluation method for the CM noise suppression characteristics of transformer was verified by comparing the evaluation results with the test results of conducted electromagnetic interference spectrum.

Since there is only one working mode of continuous wave or pulse after the design of a traditional spaceborne travelling wave tube(TWT) amplifier is finished and the output power at the saturated working point is fixed, a novel design scheme for space TWT power supply is proposed, which is compatible with multiple working modes including continuous wave and pulse. The TWT power supply and multi-mode TWT designed through this scheme are integrated into a multi-mode TWT amplifier, which have functions of continuous wave mode, low repetition rate pulse mode, high repetition rate pulse mode and adjustable on-orbit power. As a result, it can be applied to communication, navigation, data transmission and remote sensing observation satellites, thus making the on-orbit reconfigurable load possible. Through a simulation test, it is found that the power efficiency of the multi-mode space TWT reaches 94%, the repetition frequency range covers the continuous wave up to 10 kHz, and the adjustable output power ranges between 47 and 53 dBm.

The triple active bridge(TAB) DC-DC converter based on the phase-shifting plus duty cycle control strategy has advantages such as a high efficiency and an expandable soft switching range. However, its small signal modeling process is complex, and the parameter setting of closed-loop control loop is difficult. To solve these problems, a full-orer continuous generalized state space average modeling and PI controller design method for TAB converter under phase-shifting plus duty cycle control is proposed. First, the operation principle and Y-type equivalent structure of the TAB converter are analyzed. Second, combined with the characteristics of phase-shifting plus duty cycle control and the equivalent method of AC square wave source, the generalized state space average model of the TAB converter is derived. Third, based on the derived model, the transfer function from input to output is obtained, and the parameters of PI controller are designed. Finally, the correctness and effectiveness of the proposed method were verified by digital simulations and prototype tests.