Seamless switching power sharing control method in a hybrid DC‐AC microgrid by the isolated two‐stage converter based on SST

To facilitate the application of various renewable generations as well as diversified loads, hybrid DC/AC microgrids have aroused widespread interest; however, direct access of different types of sources and loads to the utility through multiple converters may be inefficient. In addition, with the complexity growth of the system, the stable and efficient operation puts forward new requirements for the isolation protection and more intelligent control. Facing these problems, the isolated two-stage converter topology based on solid state transformer (SST) is designed and the automatic seamless switching power sharing control strategy is proposed. The proposed topology replaces the conventional passive transformer with dual-active-bridge converter (DABC) to realize voltage matching and galvanic isolation for higher controllability and less volume occupation. Constant ratio control method is adopted for DABC to operate as an ideal DC transformer. Further, AC frequency and DC voltage are measured as characterizations of power level to adjust the transferred power of the converter. Through the non-directional strategy, bidirectional power support and decentralized cooperation are realized, and the capacity and sensitivity of microgrids are considered. The stability of the proposed control strategy is analyzed and the feasibility is verified by several real-time hardware-in-loop experiments.