The junction temperature monitoring of power devices in a solid-state power controller(SSPC) plays a vital role in the SSPC reliability. The thermal model method is widely used owing to its contactless measurement and simplicity. However, the aging of the power chip will lead to the degradation of the thermal path, and the junction-to-case thermal resistance of the device will increase. As a result, the actual junction temperature may far exceed the value estimated by the thermal network model, leading to an optimistic estimation of the device's state-of-health. The failure of the solder layer is considered to be one of the main reasons for the aging failure of SSPC power devices. In this paper, the device's aging state is monitored in real time during the life of SSPC, and the thermal model of the power device is adaptively updated online. The thermal impedance taken as an update basis is calculated by measuring the temperature-sensitive electrical parameters which are not affected by the degradation of the solder layer, and the thermal impedance information is associated with the aging state of the solder layer to update the thermal model. Using the proposed method, the thermal model can be updated in real time without affecting the normal operation of SSPC, and experimental results verified the effectiveness of this method.

The diode-rectifer-based high voltage direct current(DR-HVDC) system is a promising low-cost scheme for the connection of offshore wind power, which can deliver wind energy from remote offshore wind farms to onshore power systems. However, the increasing number of offshore DR-HVDC systems may lead to a growing difficulty in controlling wind turbine(WT) converters and a poor system stability. On this basis, a novel grid-formation control method for the connection of DR-HVDC to offshore WT converters is proposed. Two positive-sequence control loops are used to adjust the active power output from WTs and maintain the frequency and voltage of offshore AC grid, in which the first controller can adjust the active power error of each WT to the voltage angle deviation and thus cause frequency changes, and the second controller counteracts frequency changes by adjusting the AC voltage amplitude of WT. The converter's internal current control loop is used to limit the fault current and eliminate high-frequency resonance in the system. Finally, the effectiveness and superiority of the proposed control method are verified by electromagnetic transient simulations in terms of fault crossing, WT power change, reactive power disturbance and WTs shutdown.

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.

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.

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.

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.

The problem of high-order nonlinearity in the transient process of a wireless power transmission system is a difficulty in load measurement and identification. When dealing with beat-frequency signals due to the high-order nonlinearity, there are some problems in the existing analog envelope detection method, such as signal distortion, poor circuit flexibility, and limited measurement range. Aimed at these problems, a digital envelope detection method was proposed based on Hilbert transform, and a digital envelope detector was designed to extract the envelope of the voltage beat-frequency signal. In addition, simulations and experiments were conducted to validate the proposed method. Results show that this method can accurately extract the envelope of the voltage beat-frequency signal with different loads, and it achieved an error of less than 5% in the load resistance range of 1-2 000 Ω. The proposed method extends the contactless load measurement range based on characteristic parameters in the transient process, providing a new idea for measuring the internal resistance of batteries in aircraft such as unmanned aerial vehicles.

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.