A Resilient Control for Distributed Energy Storage Units in an Islanded AC Microgrid

A high number of charge/discharge cycles results in premature aging of distributed energy storage units (DESUs). Since classical droop control does not consider this issue and leads to microgrid (MG) voltage and frequency fluctuations in steady state, controls, such as state of charge (SoC) synchronization control, are used to minimize the number of DESUs in charge/discharge cycles. Few methods in the literature, however, investigate frequency and voltage (
$f$
and
$V$
) restoration while ensuring a functional SoC equalization control in both charge and discharge modes. In this article, an adaptive frequency droop based on the virtual power (AFDVP) method is proposed to achieve DESU’s SoC equalization to prolong their lifespan while ensuring MG voltage and frequency regulation. In addition, the AFDVP strategy ensures optimal use of second-life batteries since they are naturally less solicited due to the decrease in their capacity. DESU’s SoC equalization is achieved thanks to virtual active powers using a proportional–integral (PI) controller. A complete stability analysis is provided to choose optimal parameters for the proposed distributed control. Experimental tests are performed to check the performance of the AFDVP technique in several study cases. A comparison is also performed with an SoC equalization strategy from the literature.