Diode neutral point clamped (NPC) three-level converters have been widely used in recent years. Aiming at the problems of the high device failure rate and unstable neutral point potential of NPC three-level converters, an NPC three-level circuit with fourth bridge arm redundancy is proposed based on the traditional NPC three-level converter. The redundant fourth bridge arm is used to realize the function of stabilizing voltage when there is no fault and replacing the fault half-bridge arm to maintain the continuous operation of the converter when there is a fault. By analyzing the working principle of space vector pulse width modulation (SVPWM) and the power loss of the switch, it is of particular significance to the design and control of NPC three-level converters in the future. Matlab/Simulink verifies the feasibility of the fault-tolerant circuit structure.

Renewable energy sources are connected to the grid through inverters, resulting in reduced grid inertia and poor stability. Traditional grid-connected inverters do not have the function of voltage and frequency regulation and can no longer adapt to the new development. The virtual synchronous generator (VSG) has the function of voltage and frequency regulation and has more outstanding advantages than the traditional inverter. Based on the principle of the VSG, the relationship between energy storage capacity, frequency response and output power of the VSG is derived, and the relationship between the virtual inertia coefficient, damping coefficient and frequency characteristics of the VSG and output power is revealed. The mathematical model is established and modeled using the Matlab/Simulink simulation software, and the simulation results verify the relationship between energy storage capacity and frequency response and the output power of the VSG.