An Integrated Series-Parallel Microgrid Structure and its Unified Distributed Control

This paper presents an integrated series-parallel microgrid(MG), where a few distributed generation(DG) units in series type are used to form a DG string, then DG strings supply power to the common load in parallel type. With this structure, low-voltage devices could be integrated into MG without DC-DC boost converters. It provides a more flexible and efficient way to form higher voltage level MG. But it is difficult to find a decentralized control method to achieve power balance for this integrated system because of the difference between power transmission characteristics of parallel and series converter system. For this proposed MG in island mode, a unified distributed control strategy is proposed. With low bandwidth communication, accurate power sharing can be realized by exchanging information between the first converters connected to the bus of adjacent DG strings and between adjacent converters inside each DG string. Because the central controller is not used, the communication pressure of the system is reduced and the reliability is guaranteed. Simulation test has verified the feasibility and validity of the proposed control strategy.