Control strategies in AC microgrid: A brief review

Increasing energy demand led to shifting the focus to the use of the renewable and sustainable energy sources. Microgrids (MGs), mainly inverter based, is gaining more importance as they can accommodate various types of renewable energy effectively. Their control is one of the most challenging research areas. In the last few years, many control strategies have been developed. In this paper, the control strategies for AC Microgrids based on hierarchical structures are introduced in different aspects. The control strategies in AC microgrid can be classified into three layers: firstly inner and outer control layer that controls the output current and manages the output active and reactive power of renewable energy sources (RESs), secondly, power sharing control layer that adjusts the amplitude and frequency of the voltage reference values and provides these reference values to inner and outer loops, finally supervisory control layer that restores voltage and frequency with controls the output active and reactive power between utility grid and MG, this control layer can be classified depending on operating mode into two levels: 1. MG supervisory control level or secondary control level, 2. Grid supervisory control level or tertiary level.