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

Abstract

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 MG voltage and frequency fluctuations in steady state, controls such as State of Charge (SoC) synchronization control are used to minimize DESUs number of charge/discharge cycles. However, few methods in the literature investigate frequency and voltage (f & V) restoration while ensuring a functional SoC equalization control in both charge and discharge modes. In this paper, an Adaptive Frequency Droop based on Virtual Power (AFDVP) method is proposed to achieve DESUs SoC equalization to prolong their lifespan while ensuring MG voltage and frequency regulation. In addition, AFDVP strategy ensures optimal use of second life batteries, since they are naturally less solicited due to the decrease in their capacity. DESUs SoC equalization is achieved thanks to virtual active powers using a 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 a SoC equalization strategy from the literature.