DC‐link capacitor voltage balance strategy of independent double three‐phase common bus five‐level NPC/H‐bridge inverter based on finite control set

Abstract

This study aims at the DC-link capacitor voltage imbalance problem of independent double three-phase common bus five-level neutral point-clamped/H-bridge inverter, which is applied to an electromagnetic launch system under instant high-power and high-current conditions. First, the traditional method of voltage balance strategy based on redundant vectors is described, and the key factors leading to the DC-link capacitor voltage fluctuation is analysed in detail. Second, the objective function is constructed to predict the variation trend of DC-link capacitance voltage difference. Third, an optimised voltage balance strategy is proposed. At first, the optimised strategy calculates the variation trends of the voltage difference for all three-phase switch vector combinations. Then, the results make up a voltage balance finite control set. At last, compare the results in the set to select the vector combination corresponding to the minimum variation for output. Finally, tested by the semi-physical real-time simulation platform, and the proposed optimised voltage balance strategy is verified effective for improving DC-link capacitor voltage imbalance and inhibiting the voltage difference fluctuation.