A fast SOC balancing control strategy for distributed energy storage system based on sinusoidal signal injection

• A fast state of charge (SOC) balancing strategy for distributed energy storage system (DESS) based on injected sinusoidal signals is proposed. • A novel SOC balance control is designed on the current closed loop, and two acceleration factors are designed to ensure the fast convergence in the whole process of SOC balancing. • Using the phase difference between the injected sinusoidal signals to achieve output current sharing according to the capacity, thus getting rid of the constraints of the framework of droop control. • Compared with the previous control strategy, the proposed strategy in this article can achieve SOC equalization more quickly. In this paper, a fast state-of-charge balancing strategy for distributed energy storage system based on injected sinusoidal signals is proposed, which solves the problems of unbalanced state-of-charge, unreasonable load current sharing, and unstable direct current bus voltage. Firstly, the state-of-charge of distributed energy storage unit is directly combined with the reference current of the current closed-loop by using the arc-sin function, and two acceleration factors are set to realize rapid state-of-charge balance. Secondly, the frequency of the injected sinusoidal signals is constructed to be inversely proportional to the direct current output current of the distributed energy storage unit, which frees from the constraints of the framework of droop control and overcomes the limitations of conventional droop control. Then, the phase difference between the injected sinusoidal signals forms a reactive power circulation, which enables the output current of the distributed energy storage unit to be proportionally shared by its capacity without communication, reducing the cost of system communication. In addition, the bus voltage can be effectively compensated by designing the limiter link and virtual negative impedance. Finally, the feasibility and effectiveness of the proposed strategy are verified by experiments.