Optimal Discontinuous Space Vector PWM for Zero-Sequence-Circulating Current Reduction in Two Paralleled Three-Phase Two-Level Converter

Abstract

This article proposes an optimal discontinuous pulsewidth modulation (ODPWM) strategy to reduce the zero-sequence circulating current (ZSCC) for paralleled three-phase two-level converters. While existing methods generally entail a tradeoff between the ZSCC peak and the switching losses, this article fully explores the redundancy in the vector sequences to further improve both objectives. First, we derive eight candidate vector sequences for 60° sectors, each sequence with minimal switching times and ZSCC changing rate. Second, we divide each 60° sector into 12 subsectors, each is equipped with one of the eight candidates. The comparisons show that the proposed method maintains the same maximum ZSCC peak of existing best methods while using the minimal switching times, or effectively reducing the switching loss by up to 50%; the ZSCC of the proposed method is minimal across the major modulation regions, guaranteeing a smaller loss of the common mode inductor and further reducing the semiconductor losses. We implement the proposed optimal vector sequences in a carrier-based modulation scheme, the references of which depends on the subsector. Despite the complex geometry of the subsectors, the decision procedure is simple. Finally, the experimental results confirm the effectiveness of the proposed ODPWM.