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The Proportional Current Control Strategy for Equalization Circuits of Series Battery Packs

In renewable energy power generation system, the battery storage unit is necessary for suppressing voltage fluctuations and ensuring stable operation. However, the cost of the battery storage unit is very expensive, and the life time of batteries is limited. In order to extend the service life as much as possible, rapid equalization circuits are needed for the series battery packs. Unfortunately, the equalization currents are almost small and uncontrollable. Based on Buck-Boost equalization circuit, this paper introduces the proportional current control strategy for equalization circuits of series battery packs. The state of charge (SOC) of each battery is considered in the strategy. The differences between the practical SOC values and the average SOC value are used to calculate the reference equalization currents to charge or discharge batteries. The improved current control strategy determines the duty cycle of the switches, while the voltage control loop determines the equalization direction of series packs. The derived strategy could realize accuracy control of equalization currents, and simultaneously, could achieve rapid equalization process. Experimental results verify the validity of the proposed control strategy.