An ESS charge balancing method based on current allocation with multi-source power converters for electric microcars

Batteries are one of the most costly components in electric vehicles (EVs) yet they also limit the performance and lifespan of the vehicles. Voltage imbalance between series connected battery cells worsens the limitations but is inevitable due to the manufacturing tolerance of capacity and deviations of environmental and batteries´ parameters. Industries have developed a wide range of solutions to keep cell voltage equalized including adding balancing circuits and specialized chargers to improve the battery capacity utilization and to extend the lifespan of whole battery pack. However, these methods are generally ineffective for the energy storage systems (ESSs) in EVs. Instead of developing circuitries for cell balancing, this study would like to investigate the effectiveness of battery charge balancing by load/charge allocation with multi-source power converters such as multilevel voltage source inverters (VSIs) that directly connect the batteries in ESSs as sources. A simulation model with an 11-level cascaded H-bridge inverter (CHBI) was employed to examine the proposed switching scheme. The simulation result is encouraging that voltage sources were balanced by utilizing a significant amount of the load/charging current as balancing current; the sources attained equal voltage within a short period in simulation environment.