Coordinated sectional droop charging control for EV aggregator enhancing frequency stability of microgrid with high penetration of renewable energy sources

For microgrids with high penetration of renewable energy sources (RESs) and electric vehicles (EVs), the stochastic charging/discharging of the EVs would result in a large impact on the secure and stable operation of the microgrids. Therefore, the coordinated control between EVs and RESs becomes an important challenge for keeping the microgrid stable. In this paper, a coordinated sectional droop charging control (CSDCC) strategy is proposed for an EV aggregator that participates in the frequency regulation of the microgrids with high penetration RESs. All EVs are controlled as grid-friendly loads, and the CSDCC strategy operates as a virtual synchronous generator by only controlling the charging power of the EVs. Because the discharging of an EV is not required, the CSDCC strategy has no detrimental effects on the EV battery life. The inertia damping characteristic of a synchronous generator is modelled as a virtual inertia factor, which can eliminate charging power vibration, and can improve the system inertia. Finally, the validity of the proposed strategy in enhancing frequency regulation is verified by demonstrating a set of comparative cases.