Modeling and Control of Neutral-point Voltage Balancing Problem in Three-level NPC PWM Inverters

This paper explores the mathematic model and control method of neutral-point voltage balancing problem in three-level NPC inverter. A comprehensive mathematic model of three-level inverter is established. Then, based on the space vector PWM strategy, a simple neutral-point voltage balancing control method, which depends on the direction information detection of each phase leg current and neutral-point voltage ripple, is proposed in this paper. According to the direction information, the control method selects appropriate switching states sequences to drive three-level NPC inverter. As a result, the neutral-point imbalance is restrained in a small bound, while the switching loss and the dv/dt of output voltage will not increase. The experimental results verify the correctness and feasibility of the proposed control scheme