The electric-field coupled wireless power transfer (ECPT) system possesses several advantages, including lightweight coupling pole plates, cross-metal power transmission and negligible eddy current losses. Specifically, the par-ity-time symmetric ECPT(PT-ECPT) system characterized by its capability to maintain a constant output under variations in the coupling pole plate spacing exhibits promising application prospects. Consequently, the electric-field radiation distribution of the PT-ECPT system was studied. The theoretical analysis, simulations and experimental results indicate that compared with those of the conventional resonant ECPT systems, the electric-field distribution of the PT-ECPT sys-tem is more concentrated in the regions of strong coupling while maintaining identical output power. This concentration is particularly pronounced when the coupling coefficient is small, which makes the PT-ECPT system more secure under conditions of reduced coupling coefficients.

Nowadays, wide band gap(WBG) semiconductor power electronic devices have caused increasingly serious electromagnetic interference(EMI) problems as noise sources due to their high switching frequency, fast switching speed and large parasitic parameters. However, the conventional study on noise sources mainly focused on the conduction emission frequency range within 30 MHz, and how to evaluate the impact of noise sources within the radiated emission frequency range(30-300 MHz) still remains uncertain. Therefore, an enhanced analytical EMI model for WBG devices is proposed. Compared with the conventional asymmetric trapezoidal wave EMI model, the proposed model takes into account the nonlinear characteristics of junction capacitor and transconductor in WBG devices in detail for the first time. The impact of nonlinear parameters on noises within the radiated emission frequency range is evaluated, and the application of the proposed model to the suppression of noise sources in this frequency range is further put forward. Simulation results demonstrated the accuracy of the proposed calculation method, and the results of hardware tests based on SiC devices were consistent with the theoretical analysis.

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.

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.

In view of the serious current harmonics in a doubly-fed induction generator (DFIG)-DC connection system and the large loss of a dual-voltage source inverter (VSI) connection system, a novel dual-converter connection system which connects a three-phase DFIG to DC microgrid is designed. First, the topology, pulse-width modulation (PWM) measurement and DFIG model of the dual-converter connection system are described in detail. Different from the traditional connection systems, the proposed connection system adopts an open-end winding structure and uses a three-bridge arm rectifier on each side of the stator winding. Considering that these arms are usually composed of insulated gate bipolar transistors (IGBTs), a diode is used instead of the IGBT in the rectifier to decrease the number of control switches and reduce the cost. Second, the control strategies for a stator-side converter (SSC) and a rotor-side converter(RSC) under the new topology are given. Third, a comparison with the DFIG-DC connection system and the dual-VSI connection system is performed through simulations, and results show the advantages of the proposed method in terms of current harmonic distortion, torque ripple and semiconductor loss. Finally, experimental verification was carried out on a 0.56 kW DFIG, and results also verified the advantages of this method in terms of loss, harmonics and torque ripple.

To improve the reliability and efficiency of a T-type three-level inverter, a discontinuous pulse width modulation (DPWM) strategy is proposed to reduce the common-mode voltage while reducing the switching loss, which is also named as the RCVDPWM strategy. According to the mechanism of switching sequence in the T-type three-level topology which acts on the common-mode voltage, five DPWM clamping methods for common-mode voltage reduction are summarized. It can be found that there is at least one clamping method for common-mode voltage reduction at any modulation ratio or phase angle. For those phase angle regions where multiple clamping methods exist, the switch tube of the phase with the largest absolute value of current is preferentially selected for clamping to reduce the switching loss. Meanwhile, the proposed strategy can ensure that the DC component of neutral-point voltage is zero, and thus the neutral point shows a self-balancing capability. Experimental results verify the feasibility and effectiveness of the proposed RCVDPWM strategy.

To improve the dynamic response performance of a dual active bridge (DAB) converter with dual phase shift(DPS) control during load switching and reduce the current stress, a novel dual phase shift (NDPS) control method is studied. By changing the shifting direction of the internal phase shift angle in traditional dual phase shift (TDPS), the relationship between the transmission power and phase shift ratio is reconstructed, and the adjusting range of phase shift ratio is extended. The solving method for the optimal phase shift ratio of DPS control under the condition of current stress minimization is studied, and the dynamic response characteristics of NDPS and TDPS control under load switching conditions are compared and analyzed. Finally, an experimental platform of DAB converter was built to verify the theoretical analysis, and experimental results show that the optimal phase shift ratio combination based on current stress minimization can effectively reduce the current stress under light load conditions. At the same time, NDPS control has better dynamic response characteristics than TDPS control.

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.

Since lithium-ion batteries have been widely applied in energy storage systems and electric vehicles, the accurate estimation of their state-of-health(SOH) is a necessary condition for ensuring the reliable and safe operation of the system. SOH is analyzed from the perspective of capacity, with seven health indicators which are extracted from the constant current-constant voltage charging voltage and temperature curves as input. Based on the data-driven method, a sparrow search algorithm-back propagation neural network(SSA-BPNN) SOH estimation method for lithium-ion batteries is proposed, and data enhancement is applied to further improve the model's robustness. Finally, this method is verified on the NASA Randomized Battery Usage Dataset. Compared with the traditional BP neural network without data enhancement, the SOH estimation accuracy of the proposed method is significantly improved. The maximum absolute error and root mean square error of SOH estimation on the test set are less than 3% and 1.32%, respectively. Experimental results show that this method has advantages of small error, fast convergence, global search capability and adaptation to different characteristics of battery aging.

The cables of switching power supply which are connected in parallel is an important radiated electromag-netic interference(EMI) source for the switching power supply. Aimed at the problem of inaccurate prediction of radiated EMI of cables connected in parallel due to an unclear mutual-coupling effect, a radiated EMI model of cables of switch-ing power supply is proposed by taking into account the mutual-coupling effect between cables. Through the modeling of mutual-impedance which describes the mutual-coupling effect between cables, the radiated EMI input impedance model de-scribing the radiation characteristics of cables of switching power supply is obtained. Then, the radiated EMI model of cables of switching power supply is obtained considering the mutual-coupling effect. Finally, an experimental platform for measuring the radiated EMI was built, and experimental results show that the proposed radiated EMI model which takes the mutual-cou-pling effect into account can predict the radiated EMI of cables of switching power supply more accurately.