A Sigmoid-Weighted-Consensus for Balancing Multiple Battery Energy Storage Systems

In this article, a weighted-consensus strategy for state-of-charge (SoC) balancing, voltage regulation and accurate current sharing in a dc microgrid (MG) composed of battery energy storage systems (BESSs) is presented. The consensus strategy is applied in association with a S-shape function known as sigmoid function, a common activation function in neural networks. By a neighbor-to-neighbor communication, each BESS exchange its SoC information to achieve faster SoC balancing and uses only its capacity for accurate current sharing. The sigmoid functions ensure continuity and differentiability of the system around the charging/discharging of the BESSs and guarantee the SoC balancing even if the graph becomes disconnected by communication failures or if the consensus is switched-off. As each BESS uses its own information in the weighted-consensus, the resilience against attacks and communication time-delays is increased. When all SoCs are within operational limits, the strategy avoids circulating currents in the MG by forcing all BESSs either charge or discharge simultaneously. However, if the SoC limits are violated, simultaneous charge and discharge among BESSs in a low rate is allowed to satisfy the limits. Experimental tests show the feasibility of the proposed approach and its faster SoC balancing in relation to advanced methods in the literature.