An efficient buck-boost converter for fast active balancing of lithium-ion battery packs in electric vehicle applications

Abstract

This article proposes a fast active cell balancing circuit for lithium-ion battery packs. The proposed architecture incorporates a modified non-inverting buck-boost converter to improve balancing efficiency, an equivalent circuit model technique for battery designing, and an extended Kalman Bucy filter for accurate SOC estimation. The proposed balancing technique analyses a six-series and one parallel (6S1P) battery pack combination in static, charging, and discharging modes. With fewer components, the proposed architecture reduces the losses and improves the balancing performance. The design limitations, balancing principle, loss analysis, and control strategies are thoroughly investigated. The proposed topology is modelled in the MATLAB/Simulink platform to perform energy transformation analysis between stronger and weaker cells. The FPGA-based real-time simulator OPAL-RT (OP5700) validates the balancing performance of the proposed topology. For the 22V, 2200mAh battery pack the proposed topology had an overall balancing efficiency of 97.05% and a balancing speed of 1328s. The proposed topology has a 1.3% deviation in balancing efficiency and a 57s deviation in balancing speed compared to MATLAB and real-time simulation. The proposed active cell balancing architecture considerably increases balancing speed and efficiency.