EV BMS with Time-Shared Isolated Converters for Active Balancing and Auxiliary Bus Regulation

Improved utilisation of the total energy storage in Electric Vehicle (EV) battery systems can be achieved through balancing of the series-connected battery units based on parameters such as the terminal voltage and State-of-Charge (SOC). This paper proposes a BMS power architecture where at any given time, an isolated converter connects either a module or one of its constituent sub-modules to the vehicle auxiliary bus, where a 12V lead-acid battery is present. The converters operate in burst-mode with a period of 10 s to simultaneously balance the sub-modules and regulate the auxiliary bus voltage. The use of module and sub-module input modes to the converters enables the supply of high-power auxiliary loads without an increase in converter input current rating. Simulations of one rule-based and one variable-priority control algorithm, both using SOC as the balancing parameter, are shown over a 6 hour load profile and 5% maximum initial SOC imbalance, for a 4 kWh liquid-cooled battery module prototye. Measurements using the same prototype are shown to match the simulation results. The simulation and experimental results highlight the necessary trade-off, in the system control, between auxiliary bus voltage regulation and balancing rate.