Study on neutral-point balancing for three-level space voltage vector pulse-width modulation inverter

This paper analyzed the neutral-point balancing problem of the neutral-point-clamped (NPC) three-level space voltage vector pulse-width modulation (SVPWM) inverter and the influence of each vector to the neutral-point voltage. Based on the normal control strategies to solve the neutral-point balancing problem, including the open-circuit passive control strategy, the hysteresis-band control strategy, and the active control strategy, this paper presents one kind of control strategy which integrates open-circuit passive control with hysteresis-band control. In this strategy, utilizing the predominance that the action time of small vectors does not affect the quality of the output waveform in the open-circuit passive control strategy, it implements the first step balance adjustment to neutral-point, and then by a simple hardware circuit, the precise balance adjustment of hysteresis-band control neutral-point is realized. For this scheme, the circuit structure is simple, handled easily, and practical. It is a convenient method in actual project. At last, the experiments verify the validity of the argumentation.