A state-of-charge balance method for distributed energy storage units in microgrid

When distributed energy storage units (DESUs) in islanded ac microgrid are controlled by conventional P-f droop control, the state-of-charge (SOC) of DESUs becomes unbalanced due to the inconsistent line impedances and initial SOC. In order to achieve SOC balancing, an improved droop control is presented in this paper. The SOC balancing of DESUs and frequency regulation can be realized by adding a SOC balancing factor to conventional P-f droop control. The advantage of this scheme is that frequency can maintain within the specified range in the process of SOC balancing. Finally, simulation and experimental results in different conditions show the effectiveness of the proposed scheme.