Maximum Current Limit Equalization by Phase Shift Control of Multi-Active Half-Bridge Equalizer

For improved utilization, Lithium-ion batteries are operated with currents close to the design current of the battery, demanding fast voltage equalization. Active multicell-to-multicell equalizers can achieve fast equalization by simultaneous and efficient charge transfer from all the overcharged cells to all the undercharged cells. Phase-Shifted Multi-Active Half-Bridge(PS-MAHB) equalizer is a multicell-to-multicell equalizer with open-loop control that offers faster equalization by maintaining high equalization currents throughout the equalization. For the PS-MAHB equalizer, a dynamic phase-shift-based control algorithm is proposed to maximize the equalization currents to the design limit and enhance the equalization rate. A significant increase in the rate of equalization with the proposed control algorithm is verified in the simulation. The convergence of Li-ion cell voltages into a narrow band of 10mV verifies equalization operation with the developed compact hardware operating at 1MHz. The impact of peculiar step-response of the Li-ion cell voltage on the voltage-sensing-based equalization control algorithm and simple modifications brought in the control algorithm to reduce this impact are discussed.