An SOC Coordinated Control of the Hybrid Energy Storage System in DC Microgrids

Hybrid energy storage systems (HESS) are extensively employed in DC microgrids to alleviate power fluctuations resulting from renewable energy sources and loads. The state-of-charge (SOC) of the HESS components affects their operation performance and lifespan. To prevent HESS from overcharging and overdischarging, the SOC of batteries and supercapacitors needs to be adjusted in real time. In this paper, an SOC coordinated control is proposed, which combines a second-order filter with an improved voltage reference SOC coordinated control. The frequency division response of the battery and supercapacitor is realized through the second-order filter, allowing the supercapacitor to recover its SOC after a transient response. In addition, the SOC of the battery is introduced into the voltage reference so that the battery output power can be adjusted according to its SOC level, and thus achieving battery SOC equalization without communication. A parallel HESS was established in MATLAB/Simulink to verify the performance and effectiveness of the proposed SOC coordinated control. The feasibility of the proposed control is further verified in the real-time laboratory (RT-Lab).