A New Balancing Algorithm of Neutral-Point Potential in the Three-Level NPC Converters

The neutral-point (NP) potential of the three-level neutral-point-clamped converters is needed to maintain balanced. Zero-sequence voltage is the only freedom degree when carrier-based PWM is utilized. Appropriate zero-sequence voltage should be identified to control the NP potential. The relationship between the neutral current and injected zero- sequence voltage is studied comprehensively, and a balancing algorithm of NP potential by adopting interpolation method is presented. The theoretical optimum zero-sequence voltage for controlling NP potential can be obtained by the proposed algorithm. Simulation and experimental results are shown to verify the validity and practicability of the algorithm.