A Neutral-Point Potential Balancing Method for a Three-Level Neutral-Point-Clamped Back-to-Back Converter

In this paper, a neutral-point (NP) potential balancing method based on zero-sequence voltage injection is presented for the traditional three-level neutral-point-clamped (NPC) back-to-back converter. In the control algorithm, make the NP current on the rectifier side follow the reference NP current to adjust the NP potential balancing. The relationship between NP average current and zero-sequence voltage is analyzed in theory. On this basis, choosing several key zero-sequence voltages can reduce the complexity of calculation, and one of the three phases switches will keep unchanged during each switching period, thus the switching loss is reduced, and the NP potential balancing method is optimized. The simulation results show that the optimized zero-sequence voltage injection method can suppress the NP potential fluctuation well, and has little influence on the input current harmonics.