Neutral-Point Voltage Balancing Strategy for Three-Level Neutral Point Clamped Inverter Based on On-line Calculating Redundant Vector Duty Cycles

This paper analyzes the principle of neutral-point (NP) voltage balancing control for three-level neutral point clamped (NPC) inverter by distributing redundant small vector duty cycles (RVDC) firstly, then the calculation formulas of RVDC to control the NP voltage unbalanced value of each modulation period to be zero are derived and the controllable regions of NP balance corresponding to different modulation index and power factors are discussed. On this foundation, a NP balancing strategy based on on-line calculating RVDC is proposed, which can control the NP voltage balancing without designing hysteresis parameters. The strategy is verified by the results of simulation.