Overview of Hierarchical Control of AC and DC Microgrid

With the widespread application of distributed generation (DG) in microgrids (MG), the concept of hierarchical control (HC) has attracted more attention. According to different time scales, HC includes multiple control levels, which improves the operating efficiency and flexibility of MG. The paper mainly summarizes HC strategies for AC and DC MG. Three layers HC framework of AC and DC MG and the functions of each layer are firstly described. For the first layer, the primary control (PC) requires the fastest time response, and the problems of traditional PC and the corresponding improvement methods are analysed. For the second layer, different control structures (centralized, decentralized and distributed) of the secondary control (SC) are discussed, and the latest control strategy of SC is summarized. For the third layer, the tertiary control (TC) with the slowest time response are analysed in detail. Finally, the possible future research directions of HC of MG are also provided.