Lithium-ion battery equalization circuit and control strategy for photovoltaic energy storage applications

Solar photovoltaic (PV) is considered a very promising technology, and PV-lithium-ion battery energy storage is widely used to obtain smoother power output. In this paper, we propose a battery equalization circuit and control strategy to improve the performance of lithium-ion batteries. In the equalization circuit, the passive equalization and active equalization circuits are combined, and the active equalization circuit used is simple and has high performance, while in the equalization strategy, since the system works 24h a day, the equalization speed is sacrificed to obtain a smaller temperature rise by adjusting the duty cycle of the passive equalization metal-oxide-semiconductor field-effect transistors (MOSFETs), and by calculating the state of charge (SOC) instead of the voltage to obtain better performance. The proposed circuit and strategy can not only achieve the goal of battery equalization, while turn on 4 batteries at the same time and the temperature rise of passive equalization is only 1°C for about 1.5h, compared with the traditional equalization control strategy with 8mV voltage error, the proposed strategy is only 3mV, which has better performance.