A simple neutral-point voltage balancing control method for three-level NPC PWM VSI inverters

Abstract

Based on the space vector PWM (SVPWM) strategy, this paper mainly focuses on the control method of neutral-point voltage balancing problem in three-level NPC PWM VSI inverter. A comprehensive mathematic model of three-level inverter is set up. Then, a simple neutral-point voltage balancing control method, which only requires the direction information detection of each phase leg's current and neutral-point voltage ripple, is proposed in this paper. According to the information, the control method selects the appropriate SVPWM switching states sequences to drive three-level NPC inverter. The scheme is easy to implement. As a result, the neutral-point voltage imbalance is limited without increasing the switching loss and the dv/dt of output voltage. The experimental results verify the correctness and feasibility of the proposed control scheme.