Active Balancing of LiFePO4 Battery Modules using Phase-Shift Type DC-DC Converter for High Voltage Applications

A battery management system (BMS) for electric vehicles is a crucial component that ensures optimal battery pack performance, safety, and longevity. Monitors and manages various aspects of the battery, such as the state of charge, state of health, temperature, and voltage, to prevent overcharging or over-discharging, which can damage the battery. By the estimation of SoC and/or the battery cell/module voltages, active balancing circuits with isolated DC-DC converters enable power exchange between the battery modules for battery balancing. This paper describes a hybrid active battery balancing procedure. The proposed balancing technique includes the implementation of dissipative passive balancing at cell-level and non-dissipative active balancing at the module level. This enhances efficiency while maintaining the cost-effectiveness of the overall battery system. The active balancing part of the proposed system includes an isolated multiport bi-directional half-bridge DC-DC converter with a closed-loop phase-shift control. The proposed phase control algorithm involves generating phase shifts based on the extent of module voltage imbalances, the largest voltage disparity, and the set value of the maximum phase shift. The proposed technique is validated using simulation and experimental analysis.