Comparison and Improvement of ZVS Operation Under Different Modulation Strategies for Modular Multi Active Bridge Converters

Modular multi active bridge (MMAB) converter, which is the core of high-frequency-link-based power electronic transformers, can provide multiple dc ports for flexible interconnection among regional power grids with different voltage levels and forms. Besides merits of galvanic isolation and exceptional scalability, MMAB converters have inherent zero-voltage-switching (ZVS) turn-on operation under phase-shift modulation, which substantially reduces switching losses and leads to high efficiency. However, ZVS characteristics of the converters cannot be guaranteed under traditional single phase-shift modulation. Therefore, modulation techniques with additional control degrees of freedom, such as common phase-shift and universal phase-shift modulation strategies, are introduced to improve the ZVS performance of the converters over a wide operation range. A comparison of ZVS operation under diverse modulation strategies is analyzed in detail, and experimental results with tested efficiencies under extreme conditions have verified the ZVS analysis and improved effects.