The integrated control of frequency transient stability of multi-microinverter microgrid is studied, which can effectively control the frequency transient stability of microgrid, improve the control accuracy, and shorten the regulation time. By means of excitation control and power frequency control, a virtual synchronous generator(VSG) control method is constructed to realize the frequency transient stability control of microgrid under a small load disturbance. The improved droop control method is used to realize the frequency transient stability control of microgrid under a large load disturbance. By designing a synchronous voltage controller and a double-loop controller, the free switch between the VSG control method and the improved droop control method is completed, and the transient stability of microgrid frequency under different conditions is controlled comprehensively. Experimental results show that the proposed method can effectively control the frequency transient stability of microgrid under different load disturbances. When switching between the off-grid and grid-connected modes, the control methods are effectively switched, the frequency transient stability of microgrid is accurately controlled, and the regulation time is shortened.

The insulated-gate bipolar transistors (IGBTs) have been widely applied in the modern power electronics technology, and the paralleling of IGBTs has become an economical and feasible method in some working scenarios where one single device cannot meet the design requirements. The paralleling of IGBT modules can simplify the circuit structure, increase the converter output power, and improve the power density of devices. During the operation of IGBTs in parallel, the current imbalance, which may be caused by the difference in IGBTs' characteristics in a static or dynamic mode, the inconsistency of junction temperature, the asymmetry of a drive circuit or power loop, as well as the aging or failure of IGBTs due to long-term use, will affect the system's reliability and stability. The research hotspots of parallel-operating IGBTs at home and abroad are investigated. The principle and influence of static and dynamic current imbalance are summarized, and the difference in the current-sharing control principles is analyzed. The performance characteristics of current-sharing control are summarized and compared from the aspects of power loop current-sharing control and drive circuit current-sharing control. Furthermore, the development of current-sharing technologies for parallel-operating IGBTs in the future is also prospected.

Silicon carbide (SiC) is a promising wide-bandgap semiconductor material owing to its excellent electrical and thermal characteristics. Power metal-oxide-semiconductor field-effect transistors (MOSFETs) based on SiC are suitable for high-power fields, and their high-temperature gate oxide reliability is one of the most concerned characteristics. In this paper, the high-temperature gate oxide reliability of self-developed SiC MOSFETs is compared with that of the foreign SiC MOSFETs of the same specification by positive and negative high-temperature gate bias (HTGB) tests. The negative HTGB test results show that the deviation of threshold voltage of self-developed SiC MOSFETs is almost equal to that of the foreign SiC MOSFETs, and the maximum discrepancy between them is about 4.52%. However, the positive HTGB test results show that the deviation of threshold voltage of self-developed SiC MOSFETs is smaller than that of the foreign SiC MOSFETs, with a maximum discrepancy of 11%. The reason for the better performance of self-developed devices is that an appropriate amount of nitrogen is added to the SiC/SiO2 interface, which can passivate interface defects and reduce the generation of fast interface states, so that the total interface state density is minimized.

To accurately obtain the on-orbit health status of a spacecraft electrical power system, a condition quantitative assessment model for a satellite electrical power system with the fuzzy theory is proposed. First, an index system for evaluating the system condition is established by analyzing the operating characteristics of one satellite electrical power system. Combined with the time-varying characteristics of actual telemetry, the corresponding telemetry pre-processing method for electrical power system and a dimensionless deterioration function are put forward. Then, a hierarchical condition quantitative assessment method for the satellite electrical power system is established through introducing the variable weight theory and fuzzy theory. Finally, the correctness and effectiveness of the proposed condition quantitative assessment method are verified by analyzing the actual on-orbit and simulation data of the satellite and comparing with the traditional method. Moreover, the deteriorated system condition can be assessed by the proposed method two days earlier only based on thresholds.

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.

Aimed at the problems of fast loss and high capacity configuration of battery energy storage equipment in microgrid, an optimal configuration model of battery energy storage capacity of microgrid considering life loss is established in this paper. In addition, a cost calculation method for the battery energy storage life loss based on fixed daily cycle times is also proposed. This method combines the piecewise linearization idea and the scenario analysis method, and it can effectively extend the lifetime by optimizing the discharging depth and daily cycle times of battery energy storage. Moreover, considering the uncertainties in wind power output and load power, a two-stage robust optimization model is introduced, which is further solved by the column-and-constraint generation algorithm. Finally, the effectiveness of the novel model under different uncertainties and different unit prices of battery energy storage is verified by numerical examples.

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.

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.

The circuit topology of a novel three-phase quasi-Z source AC-AC converter is proposed, and the basic working principle and structure of the circuit are analyzed. In addition, the relationship between input voltage and output voltage is also derived. This circuit topology is controlled by a pulse width modulation method, which can achieve the effect of changing the output voltage. MATLAB/Simulink is used to build a simulation model, and the simulation results are analyzed. Finally, an experimental circuit was built on the basis of the simulation model, and experimental results verified the feasibility of the proposed circuit topology and the correctness of circuit analysis.

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.