A three-phase Vienna rectifier is taken as the research object in this paper. In view of the difficulty in selecting the weight factor when the finite control set model predictive control realizes the neutral-point potential balance control, as well as the problem of large current ripple on grid-side caused by the action of one single vector during the sampling period, an unweighted factor model predictive control strategy based on double vectors is proposed. First, a single-objective cost function based on power prediction is constructed, and the efficiency of single optimization is improved by sector division and unweighted factor. According to the fluctuation of neutral-point potential on DC side, the redundant small vector is selected to realize the unweighted factor neutral-point potential balance control. Then, based on the obtained optimal vector, the double-vector fixed switching frequency control is realized by combining with the zero vector. Finally, the proposed control strategy is verified on a hardware-in-the-loop platform based on RT-LAB from the aspects of steady state, transient state and neutral-point potential fluctuation, and results effectively prove its correctness and effectiveness.

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.

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.

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.

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.

Aimed at the problem that the influencing mechanism of configuration size of a differential pressure channel in proton exchange membrane fuel cell(PEMFC) for the cell's electrochemical performance is unclear, the influences of channel height and rib width on the oxygen concentration, water concentration distribution characteristics, current density, power density, and pressure drop of a differential pressure channel and a straight channel are studied, and a comparative analysis of the two kinds of channels is performed. Results show that channel height has little effect on both channels, but the differential pressure channel has an obvious advantage when its rib width is 1.25 mm or 1.5 mm. The influence of pressure converter area on the performance of the differential pressure channel is further studied, and results show that its peak power density is the highest when the height and length of the pressure converter area are 0.05 mm and 1.5 mm, respectively. With the comprehensive consideration of influences on power density and pressure drop, the differential pressure channel with a height of 0.4 mm, width of 1.25 mm, rib width of 1.25 mm, and a pressure converter area with a length of 1.5 mm and height of 0.05 mm is selected. In this case, its peak power density is 0.366 1 W/cm², which is 6.3% higher than that of the straight channel.

The phenomenon of dynamic avalanche occurring during the IGBT turn-off process is one of the important reasons for its failure. To study the dynamic avalanche failure mechanism of IGBT, the Silvaco software was used to simulate and analyze this mechanism. Through the simulation and analysis of the breakdown mechanism, current density distribution and temperature distribution of dynamic avalanche, it is concluded that dynamic avalanche can generate moving current filaments and dead filaments which are either moving slowly or fixed. However, the failure of the device is caused by the dead filaments formed by dynamic avalanche. The dead filaments will lead to a sharp increase of local temperature in the IGBT, and the IGBT will eventually fail because the local temperature is too high to burn the device. On this basis, the causes of dead filaments are analyzed, and specific measures to prevent the dynamic avalanche failure of IGBT are also put forward.

The development of power modules towards high temperature, high power and high density raises higher requirements for the packaging structures of modules. Compared with the traditional wire-bond structure, the double-sided structure has attracted more and more attention owing to its characteristics such as high heat dissipation capacity and low parasitic inductance. However, the mismatch of thermal expansion coefficient between materials used in the double-sided structure makes the structure suffer tremendous thermo-mechanical stress, thus reducing the reliability of power module. Therefore, to develop double-sided bi-directional modules with low thermo-mechanical stress, the effects of chip layouts on the heat dissipation performance of modules and the parasitic inductance were analyzed by simulations at first. Then, a flexible buffering spacer with low Young's modulus is proposed accordingly. The feasibility of reducing the thermo-mechanical stress and improving the reliability of the module was preliminarily proved by simulation and experimental results.

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.

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.