Optimized Modulation for Three-Level Boost Converters with ZVS under Unbalanced Load

Three-level boost (TLB) converters with voltage balance capability are promising to serve as the interface in bipolar DC microgrids. With different power of the positive and negative DC buses in bipolar DC microgrids, conventional modulation methods of TLB converters fail to zero voltage switching (ZVS) for all switches, and the peak current is also high, leading to inductor saturation. In this paper, an optimized modulation method is proposed to achieve ZVS for all switches even under unbalanced loads. The modulation degree of freedom of TLB converters is analyzed in detail, and the advantages of the proposed modulation method are compared with its counterparts. The effectiveness and advantages of the optimized modulation method is validated by experiments.