Simple carrier-based pulse-width modulation scheme for three-phase four-wire neutral-point-clamped inverters with neutral-point balancing

Neutral-point-clamped (NPC) three-level inverters can drive a combination of single- and three-phase loads or non-linear in a three-phase four-wire distribution system. However, an intrinsic problem with NPC three-level inverters is the fluctuation in the neutral-point (NP) voltage. In this study, a dynamic model of the NP voltage in a three-phase four-wire system will be analysed and developed. On the basis of this model, a simple carrier-based pulse-width modulation scheme for NP balancing is proposed. The proposed scheme decouples the NP voltage balancing from the necessity to control phase voltages, and controls the NP voltage without introducing zero-sequence voltage, thus the scheme can be applied to a general NPC voltage source inverter. The effectiveness of the proposed modulation scheme is verified by both simulation and experimental results. Finally, these results are compared with those reported in the literature.