A design method for small and medium-power DC/DC converters suitable for low-orbit commercial aerospace is given in this paper. A synchronous rectifier flyback topology and surface mounted devices are adopted, which can meet the demands for common single-and multi-output DC/DC converters applied in aerospace, with advantages of low cost, high performance, high reliability, and mass production. To further improve the conversion efficiency and power density, gallium nitride(GaN) FETs are also used. In addition, the losses of main power devices in the topology under different operating conditions are calculated and compared. Finally, a DC/DC converter with a wide range of input voltage (23-47 V) and output of 5 V and 30 W was built for verification.

Aimed at the problem of DC voltage fluctuations caused by load switching, power fluctuations and dou-ble-frequency injection in DC microgrids, a dynamic compensation control strategy for a Buck-type bidirectional DC-DC converter based on model predictive control (MPC) is proposed. First, the corresponding discrete state space matrix is es-tablished, and the input current is used as the disturbance. Second, the model-based inner-loop current predictive control and outer-loop voltage control of the Buck-type bidirectional DC-DC converter is designed. Third, a dynamic compensa-tion control structure based on a residual generator is designed for the current disturbance, and the dynamic compensa-tion controller Q(z) is solved. At the same time, the recursive least squares algorithm is used for parameter identification to reduce the influence of model uncertainty on the dynamic compensation control strategy. Finally, a comparative ex-periment was designed on the PSCAD/EMTDC simulation platform to verify the effectiveness of the proposed control strategy. Experimental results show that the compensation control structure can effectively solve the problem of DC bus voltage fluctuations and enhance the robustness of the entire system without changing the original predictive control.

Aimed at the low conversion efficiency and all the load power that needs to be processed by converters at different stages in the two-stage architecture of a DC transformer cascaded PWM converter, a quasi single-stage DC-DC conversion method with partial power active regulation based on a split-sigma structure is proposed. By splitting the output port of the DC transformer into two ports, the power of one port is directly transmitted to load without being processed by the back-stage PWM converter, thus realizing the quasi single-stage power conversion equivalently. In addition, the power capacity and loss of the PWM converter are effectively reduced, and the system efficiency is improved. The principle and circuit implementation method for the split-sigma structure are analyzed in detail, and the principle and characteristics of system output voltage regulation are also studied. One of the circuits is taken as an example, and its working principle, voltage regulation characteristics and design method for key parameters are analyzed. Finally, experimental results verified the effectiveness and correctness of the proposed scheme.

The three-port converter studied in this paper includes three ports, i.e., power supply, energy storage and load, in which the load can directly obtain electric energy from the power supply or the energy storage port. First, a mathematical model of Euler-Lagrange form is established, a passivity-based controller is designed, and the simulation of passivity-based control (PBC) is carried out. The PBC strategy has advantages of strong global stability and strong robustness to system parameter deviation and external disturbance in the nonlinear system. Based on the PBC theory, the passivity of the three-port converter system is demonstrated. Through the PBC and single-phase-shift control of dual-active-bridge (DAB), the energy transfer between the three ports is realized. Finally, simulation results in Matlab/Simulink are given, which proves that the load in the device can directly obtain electric energy from the energy storage port and run safely, stably and reliably.

Aimed at the problems of complex topologies, high total standing voltage of switches, and unbalanced series capacitor voltages in the existing multilevel inverters, a novel seven-level inverter based on switched-capacitor is proposed. By adopting the phase disposition pulse width modulation strategy, three capacitors are reasonably controlled in series/parallel with the DC source, so that the seven-level output with a triple boost gain is realized. The proposed inverter uses only one single DC source, so it has advantages such as a simple structure, fewer components, high boost gain and self-balanced capacitor voltage. In addition, it does not use the H-bridge to change the polarities of output levels, thus reducing the total standing voltage of switching devices. The topology, working principle, capacitor voltage self-balance, modulation strategy, capacitor parameter and current stress are analyzed, and five aspects including the numbers of switches, diodes and capacitors, the total standing voltage and the boost gain are compared with those of the existing topologies, which fully proves the practicality of the proposed topology. Finally, the feasibility of this topology was verified by experimental results.

Aimed at the problems of current spikes and voltage fluctuations in the charging process of existing multi-level inverters, a novel quasi-resonant five-level inverter is proposed in this paper. A carrier-stacked pulse width modulation scheme is adopted, and the switched capacitor technology is combined with the traditional five-level inverter, which reduces the accumulated level at the previous stage and realizes the output of five-level voltage. In addition, the capacitor charging process and the series inductance resonate to eliminate current spikes and voltage fluctuations, while reducing the heating problem of the capacitor and prolonging the service life of the circuit. Finally, simulation verification is carried out, and results prove the correctness and feasibility of the scheme for the proposed inverter structure.

A single-phase transformerless inverter for photovoltaic power generation is proposed, which has a common ground between its input and output and thus eliminates the common-mode current in the photovoltaic system. Meanwhile, its voltage gain is higher than that of the traditional single-phase quasi-Z-source inverter. In addition, the use of thin film capacitor makes the inverter more reliable and prolongs its service life. The working principle of this inverter is also analyzed in detail. Finally, a 140 W prototype was built, and results verified the correctness of the proposed inverter topology and the effectiveness of the control strategy in islanding and grid-connected operation modes.

The advantages of a Boost-APFC circuit operating in critical conduction mode are introduced. Aimed at the disadvantages of the traditional single-phase CRM-Boost APFC voltage mode control method, such as a long PI parameter debugging time, a poor adjustment effect and increasing unstable factors, a single-phase CRM-Boost APFC voltage mode control method with a static operating point is proposed, and the advantages of this method are verified by PSIM simulations. Considering the shortcomings of the novel interleaved control method, such as a long PI parameter debugging time, increasing unstable factors and the need to use an additional voltage-controlled current source, an improved two-phase interleaved parallel CRM-Boost APFC voltage mode control method is put forward, and the PSIM simulations are completed, with a power factor as high as 99.96%. A 4 kW two-phase interleaved parallel CRM-Boost APFC experimental prototype was made, and it was experimentally debugged, with a power factor of 99.66% and an efficiency of 98.02%.

A virtual synchronous generator (VSG) can provide inertia and damping for the grid connection of new energy by simulating the characteristics of a synchronous generator. However, a circuit breaking fault may occur in the process of high-frequency switching of power electronic switching devices, which will lead to a serious distortion of output current waveform and affect the safe and stable operation of power grid. In this paper, a VSG fault-tolerant model predictive control strategy based on neutral point voltage equalization is proposed to solve the fault problem of neutral point clamped (NPC) three-level VSG bridge arm. The operation mechanism of NPC three-level VSG single-phase bridge arm after fault is analyzed. The DC-side capacitor forms a virtual bridge arm after the switching device fault, which is reconstructed as a VSG bridge arm fault-tolerant structure. Under fault conditions, a current predictive model is established, and the space voltage vector in a fault state is reconstructed. The neutral point capacitor voltage on the DC-side is introduced into the cost function of fault-tolerant model to reduce capacitor voltage fluctuations and realize the fault-tolerant operation of VSG bridge arm. Experimental results show that the NPC three-level VSG can operate continuously after the switching device fault, which verifies the effectiveness of the proposed model predictive fault-tolerant control strategy and improves the operation reliability of VSG.

The large grid inductance in weak grid may cause a grid-connected converter to be unstable. Therefore, an impedance model of grid-connected converter is built at first, and the influence of grid inductance on the stability of grid-connected converter is analyzed according to the impedance ratio criterion. Then, aimed at the problem of low adaptability of the grid-connected converter to inductive grid impedance, a virtual impedance control strategy based on band-pass filter is proposed, and the influence of virtual resistance value on the adaptability of grid-connected converter to weak grid is studied. Furthermore, a selection principle for the virtual resistance value is also given. Finally, a system simulation model is built, and simulation results verify the correctness of theoretical analysis and the effectiveness of the proposed control strategy.