Aimed at the problem that the failure of electronic components or power off in the current control unit of a short-circuit current protection device will lead to a protection failure, a passive electromagnetic current transformer is proposed. The working principle for the trigger device is analyzed, and the maximum magnetic flux of iron core within the effective working range of the transformer is determined according to the magnetization curve of the core material. Considering that the magnetic flux in the iron core is easily saturated at a large current, simulations are performed to analyze the influence of air gap distribution on magnetic flux intensity in the transformer. An electromagnetic current transformer core structure is designed, which can still effectively work at the 15 kA short-circuit current peak. The 3D transient electromagnetic simulations show that when the short-current rising rate is 20 A/µs and the number of turns in the secondary winding is 30, the output voltage from the secondary winding is not less than 14 V. Finally, an engineering prototype of hybrid current-limiting fuse with a passive electromagnetic current transformer as its trigger device was made, and a short-circuit current detection test was carried out. The experimental results basically agreed with simulations, indicating the accuracy and validity of the design of iron core.

As the number of charge and discharge cycles of a lithium-ion battery increases, its state-of-health (SOH) will degrade to some degree accordingly. Aimed at this problem, a method for estimating the SOH of lithium-ion battery based on an improved multi-objective Cuckoo search (IMOCS)-BP neural network is designed, which adaptively changes the update probability and search step size of the Cuckoo search (CS) algorithm while avoiding the algorithm from falling into the local optimum, thereby solving the problems of slow convergence speed and low solution accuracy in the CS algorithm. The IMOCS algorithm is combined with BP neural network to conduct a global search in the node space, reduce the influence of initial values of weight and threshold on BP neural network, and realize the parameter optimization. Through Matlab simulations, it is verified that the SOH estimation algorithm based on IMOCS-BP neural network has a low error and a strong performance, thus realizing an accurate SOH prediction of lithium-ion battery.

To improve the performance of modern unipolar power diodes and further break through the "Silicon limit", by increasing the junction depth of P+ region in traditional JBS diodes and introducing a super junction structure to reduce the chip thickness, the contradiction between on-state voltage drop and reverse blocking voltage of traditional unipolar devices is alleviated and the conduction current density of devices per unit area is improved. The effects of P-pillar concentration, N-pillar width and N-pillar concentration of super junction JBS diode on the forward conduction and reverse blocking characteristics are analyzed using a numerical method. The forward conduction and reverse blocking mechanism of super junction JBS diode is analyzed using the theory of electric field coupling effect, and a super junction JBS diode with 300 V is designed.

In view of the fact that the existing methods cannot identify all the effective power supply paths for voltage over-limit, which leads to problems of poor real-time performance and unobvious suppression effect in the voltage over-limit identification in distribution network, the voltage over-limit identification in distribution network with photovoltaic (PV) power supply is studied based on a regulation function, so as to improve the corresponding real-time performance and effectiveness. First, an external characteristic model of PV power supply is constructed by using its physical mechanism, based on which a simulation model of PV power supply is built in the Matlab/Simulink software. According to the power relationship in distribution network with PV power supply, the voltage variation at the grid-connected point before and after the integration of PV power supply is calculated, and the mechanism of voltage over-limit is analyzed, so as to design the equivalent circuit of distribution network with PV power supply. All the effective power supply paths for voltage over-limit are specified, a candidate set of voltage over-limit regulation strategies for distribution network with PV power supply is set up in an decreasing order by means of the regulation function, and the candidate strategies are selected from the candidate set of regulation strategies to realize the voltage over-limit identification. The analysis results of an example show that the proposed method can effectively adjust the voltage of distribution network with PV power supply to a normal state with less iteration times and a short execution time, indicating a high practicability.

A modeling data and optimization algorithm driven electrothermal behavior model of gallium nitride high electron mobility transistor (GaN HEMT) is proposed to facilitate the quantitative analysis of problems caused by high speed switching, such as turn-on overvoltage, false turn-on, oscillation and EMI noise. Compared with the traditional behavior models of GaN HEMT, the proposed model can precisely depict the electrothermal characteristics of GaN HEMT in a wide temperature range in both the first and third quadrants by only two compact equations. Meanwhile, the nonlinear parasitic capacitances of GaN HEMT can be accurately modeled by one compact equation. In addition, an optimization algorithm combing the genetic algorithm and Levenberg-Marquardt algorithm is put forward, and a one-step extraction of modeling parameters is realized based on this optimization algorithm and modeling data, which can reduce the modeling time and work load to a certain degree. Results show that the proposed modeling method can precisely model multiple types of GaN HEMT devices manufactured by different companies. Finally, the correctness and effectiveness of the proposed modeling method was verified by the well-matched simulated dynamic waveforms and experimental measurement data.

The HT-6M Tokamak Reconstruction is an international project of cooperation between China and Thailand for responding to the Belt and Road Initiative. The function of pulse power supply for heating field is to breakdown and produce plasma, and the corresponding power supply scheme adopts the form of capacitor energy storage pulse discharge. To calculate the parameters of power supply that meet the requirements, the discharging process of pulse power supply for heating field is analyzed mathematically, and the core devices are designed and developed according to working parameters of power supply equipment. To verify the theoretical analysis of discharging process, a set of small capacitor energy storage pulse power supply was developed. At the same time, a turn-off experiment on a high-power solid-state circuit breaker was carried out.

Since the existing distribution network technology increases the active power loss of distribution network system, problems such an increase in the network loss value and a lower penetration rate will arise. To solve these problems, the research on the optimal control method for the flexible soft switch in distribution network considering demand-side response is proposed. First, a demand-side response model and an optimal control model of flexible soft switch are established. Then, the particle swarm optimization algorithm is used to solve these models, and the design of load transfer in distribution network is completed. Finally, the constraint conditions such as the operation of flexible soft switch, power flow in distribution network system and output from renewable energy power generation are set, thereby realizing the optimization of the control of flexible soft switch in distribution network. Experimental results show that after the application of the proposed method, the load of distribution network system can be effectively transferred, the active power loss of distribution network system and the overall network loss can be greatly reduced, and the penetration rate of distribution network system and the consumption of renewable energy power generation can be improved. As a result, the operation optimization of distribution network system is realized, providing a guarantee for its safe and economic operation.

The traditional nearest level modulation (NLM) has advantages of simple control and low switching frequency. However, when the number of output levels is small, the harmonic distortion rate of output waveform from a modular multilevel converter(MMC) under the NLM modulation will be large. In this paper, a full-bridge auxiliary sub-module is added to each arm of the traditional three-phase six-leg MMC topology, and the capacitance voltage of the auxiliary sub-module is half of that of the half-bridge sub-module. Aimed at this MMC topology, an improved hybrid modulation strategy is proposed, which can realize the balance control of half-bridge and auxiliary sub-module, reduce the harmonic distortion rate of MMC AC-side output current, and reduce the switching frequency and system loss of the full-bridge sub-module. A detailed simulation model is built in MATLAB/Simulink, and simulation results verify the effectiveness of the proposed MMC topology and the improved hybrid modulation strategy.

Aimed at the particularity of an isolated DC/DC converter when it is applied in a space radiation environment, the isolated magnetic feedback circuit is usually used to improve the feedback accuracy and stability. The working principles for several commonly used amplitude modulation magnetic feedback circuits are introduced, and a forward-flyback amplitude modulation bidirectional magnetic feedback circuit is introduced and optimized to solve the problem of the need for an additional secondary power supply voltage. Under the premise of realizing the same function, a two-winding transformer is used to replace the three-winding transformer, which effectively reduces the volume of the magnetic core and simplifies the circuit structure. The working principle for the circuit and the design method for a pulse sampling circuit and a magnetic feedback transformer are analyzed in detail. In addition, based on the magnetic feedback circuit, a DC/DC converter prototype with 100 W output was built. Simulation and experimental results show the effectiveness of the proposed isolated magnetic feedback circuit, providing a theoretical guidance for engineering design.

The conventional Buck-type power factor correction (PFC) converter has a disadvantage of high harmonic current, which limits its applications. A Buck-type single-switch integrated PFC converter is proposed and analyzed. This converter is composed of a Buck-type PFC converter and a Buck-Boost PFC converter, and they are integrated by only one active switch, thereby simplifying the control. Under the constant on time (COT) control, the dead zone of input current in the Buck-type PFC converter is eliminated. With advantages of Buck and Buck-Boost converters, this converter can achieve a high power factor and a high efficiency in universal-input applications. The circuit structure, working principle, steady-state characteristics and design considerations of the proposed converter are introduced and analyzed. Finally, a 56 W prototype was built, and experimental results verified the analysis results.