A Novel Multimode Coordination Strategy for Hybrid AC/DC Microgrids Integrated With Distributed Renewable Energy Systems

In the interconnection and optimized operation of the classical hybrid AC/DC microgrids (HMG), the conventional line-frequency transformer cannot block grid faults and comprehensively regulate voltages. A distribution grid fault produces voltage sags, swells, or harmonics, threatening the safe operation of distributed renewable energy generation and user equipment in an HMG. This paper proposes a novel hybrid transformer-interconnected HMG (HT-HMG) and a multimode coordination strategy based on the multiplexing design of a multifunctional converter (MFC). The topology structure and operating principle of the proposed HT-HMG are introduced. A new type of HT, including a three-limb, three-winding line-frequency transformer and an MFC, is proposed for voltage transformation and partial power transmission. The MFC can be operated multimode coordination by flexibly implementing the switches, including shunt, series, island, and standby modes. A hierarchical coordination control strategy, consisting of an energy management layer and a converter control layer, is also designed for the HT-HMG based on its multimode operation. Finally, the accuracy and effectiveness of the proposed HT-HMG are verified through simulations and experiments.