Hysteresis-band control based PWM strategy of three-level neutral-point balance

A new method of neutral-point balance based on hysteresis-band control for NPC three-level inverters is proposed in this paper. The neutral-point is balanced by PWM control according to the direction of neutral-point current and the state of neutral-point voltage. The neutral-point current direction is got by output current of each phase and PWM group. The state of neutral point voltage is decided by hysteresis-band control. PWM group is regrouped when it goes against the neutral point potential balance. Being independent of PWM mode, this scheme can be used in any PWM mode for neutral-point balance control. The amplitude of neutral point voltage ripple and the switch times of IGBT can be adjusted by regulating the width of hysteresis-band. The method is verified by simulation and experiment of three-level converter with SHEPWM control scheme.