A Symmetric Multi-mode Battery Equalizer Based on Bidirectional DC-DC Converter for Series-Connected Lithiumion Cells

The equalizer with the concentration structure has good compactness and low cost, making it a good choice for the occasion that requires high energy density. However, it is ubiquitous that the performance of the equalizer with the concentration structure in the balancing speed and accuracy is poor. To solve the problem of poor balancing speed and accuracy in the traditional equalizer with the concentration structure, a multi-state and energy path equalizer is proposed, which can realize the inside-to-inside (I2I) charge transfer, outside-to-inside(O2I) and the inside-to-outside (I2O) charge transfer. It allows the proposed equalizer to achieve a faster balancing speed and higher accuracy. A model with four lithium-ion battery cells is built in the Simulink after the rational analysis of the working mode and principle of the proposed equalizer. The results show that the proposed scheme exhibits outstanding balancing performance in speed and accuracy.