A Brief Review of the Application and Control Strategies of Alternating Current Microgrids in the Power System

Alternating current (AC) microgrids have occupied a central position in research since the evolution of the microgrid concept. In this article, a brief review of control and scientific strategies for AC microgrids is presented. AC microgrids consist of distributed energy sources and different loads, which are connected to a synchronous machine using an AC bus and through a power electronic converter. The mixed structure of alternating current microgrid reduces inertia, which increases frequency deviation and frequency change rate, and makes the overall stability of the power system more sensitive to disturbances. For constant production of all production units, a proper control method is needed. Applying appropriate hierarchical control makes the system flexible, so that it is possible to integrate more distributed power units in the system. Hierarchical control strategy is widely used in all three types of microgrids. Centralized control, decentralized control and distributed control are three basic control strategies based on the communication method. The main problem in control schemes based on communication channels is poor reliability in case of communication link failure. Also, two working modes of the microgrid connected to the network and island are mentioned. The correct control of the microgrid in both operating modes faces different challenges. This study will be useful for the comparative analysis and development of control strategies for AC microgrids for future research.