Decentralized Droop Control Strategies for Parallel-Connected Distributed Generators in an AC Islanded Microgrid: A Review

This paper reviews the different decentralized droop control strategies in an AC microgrid. Microgrids are made up of parallel-connected distributed generators (DGs), storage devices and loads operating with coordinated control. They often integrate Renewable Energy Sources (RES) as DGs. The grid can operate in grid-connected and autonomous modes. Due to the intermittent nature of RES, the imbalance between power demand and power supply, the presence of different types of loads and line impedance mismatch, effective sharing of active and reactive power, as well as the regulation of frequency and voltage become imperative in the islanded mode of operation in order to ensure system stability. Droop control is preferred over other control strategies for sharing active and reactive power because it does not require communication channels. This paper review presents the merits and demerits of decentralized droop control methods. Furthermore, possible suggestions for improvement on active and reactive power sharing for parallel-connected DGs are presented including voltage and frequency regulation in an AC islanded microgrid.