SOC Dynamic Balance Strategy Based on Adaptive Droop Control with Variable Regulating Factor

Energy storage device can provide the support to the DC microgrid to resist the disturbance from the distributed new-energy source and load. However, the energy storage device with a lower or higher initial State Of Charge (SOC) among multiple energy storage devices may delay or advance the discharge or charge due to the uneven power distribution, which affects the system stability. This paper proposes an adaptive droop control by relating the droop coefficient of the energy storage devices to a arccotangent function of the battery SOC, so as to achieve the dynamic equalization of SOCs. Accordingly, the charge and discharge speed of the energy storage device are adaptively changed. However, SOC equalization speed decreases when the SOC difference between energy storage devices is small. This paper further proposes a variable-factor droop control by further adjusting the factor in the arccotangent function dynamicly according to the SOC. Compared with the droop control with the fixed factors in the arccotangent function, the SOC equalization speed can be maintained as the SOC difference between energy storage devices continues to decrease. In addition, a voltage compensation link is added into the droop control to compensate the DC-bus voltage drop caused by the changed droop coefficient. Finally, the variable-factor droop control simulation model with the voltage compensation is established. It is verified by simulation results that the proposed adaptive droop control can realize the dynamic SOC equalization of multiple energy storage devices and the dynamic SOC adjustment speed. And the DC-bus voltage is stable during during all the charging or discharging periods of the energy storage device.