A hybrid control algorithm for neutral-point voltage balancing in three-level inverters with zero-sequence signal injection and virtual zero-level modulation

This paper proposes a hybrid modulation strategy to suppress the neutral point voltage fluctuation with zero-sequence signal injection (ZSI) and virtual zero-level modulation (VZM) in three-level inverters. The hybrid modulation algorithm proposed in this paper distinguishes itself from traditional strategies by dynamically adjusting its switching point between two modulation types according to fluctuation in the neutral point voltage. This strategy integrates the advantages of hybrid modulation which can achieve neutral point voltage balancing under any power factor, while simultaneously reducing switching loss by decreasing the involvement of virtual zero vector modulation. In addition, this hybrid modulation is simple and easy to implement on digital chips. The simulation verified the effectiveness of the algorithm.