Aging Rate Equalization Strategy for Battery Energy Storage Systems in Microgrids

It is urgent to reduce the maintenance burden and extend the service life of recycled batteries used in microgrids. However, the corresponding balancing techniques mainly focus on the state of health (SOH) balancing for unique converter structures or with complex SOH estimators. This paper proposes an aging rate equalization strategy for microgrid-scale battery energy storage systems (BESSs). Firstly, the aging rate equalization principle is established based on the relationship among throughput, state of charge (SOC), and injected/output power of a BESS, which is obtained according to the semi-empirical life model of the battery. Second, based on the established principle, the droop coefficients of energy storage systems (ESUs) are designed in the lower-level control, which can ensure the aging rate equalization of ESUs in one. The upper-level control optimizes the output of multiple microgrids. Then, the stability of the proposed aging rate equalization strategy is proven by a small-signal analysis. The performance analysis shows that the proposed aging rate equalization can also realize SOC balance. Finally, the RTLAB hardware-in-the-loop tests are carried out to illustrate the outstanding performance of the proposed strategy for extending the battery service life and ensuring microgrid operation stability.