A Comparative Study of Different Equalizer for State of Charge Based Droop Control for Distributed Energy Storage Systems

The microgrid in this paper is a low-voltage distribution system composed of photovoltaic equipment, energy storage device, load, power electronic devices and control devices. The control objective of direct-current (DC) microgrid is to maintain the voltage stability of DC bus and equal load sharing in energy storage units. At present, droop control is used in distributed energy storage system to realize energy equilibrium of multiple energy storage units. However, the method causes low current accuracy and imbalance of state of charge (SOC) in multiple energy storage units. In this paper, the performance of different SOC equalizers with large disturbance is investigated, which is determined by response speed and SOC balancing time from the supercapacitors (SCs). The shorter rising time and the anti-jamming performance are obtained by the partial swarm optimization (PSO) SOC equalizer with adaptive fuzzy proportion integral differential (PID) controller. The performance of SOC balancing is obtained in SCs by classic droop SOC equalizer and PID controller.