A vector-splitting method for neutral-point voltage regulation in a three-level inverter

Neutral-point voltage regulation is one of the critical issues of a three-level inverter. This problem adversely affects the reliability of the power semiconductor. Zero-sequence voltage (ZSV) can be useful to regulate the neutral-point voltage in a three-level inverter. However, the regulating performance can be impeded by the change of the modulation index and the power factor. In this paper, a novel method is proposed to improve ZSV-based regulation. By aptly splitting a reference vector, the available range of the neutral-point current can be further stabilized at each operating point. It is detailed how to combine vector splitting with ZSV-based regulation. After the proposed method is discussed with simulation results for the entire first quadrant operation of an induction motor, its effectiveness is validated with experimental results under harsh operating conditions. As a result, the proposed method could effectively regulate the neutral-point voltage at various operating points and, in particular, could reduce neutral-point voltage ripples by 72.6% even under the worst condition.