Battery module equalizer based on state of charge observation derived from overall voltage variation

Abstract

Growth in the electric vehicle industry has resulted in considerable chemical battery waste, which requires special recycling processes. The power and recharging capacities of waste batteries are insufficient for the operation of traction motors. However, such batteries can be reused as power sources in residential renewable energy systems because household energy demands are much lower than those of electric vehicles. To enable this reuse, a battery pack should be equipped with an equalizer. Hence, in this study, we propose a battery module equalizer that adjusts the state of charge (SOC) of each battery module to the same point using a generation control circuit (GCC). By strategically changing the duty ratio of the GCC while detecting the overall voltage of the entire battery pack, the relative SOC of each battery module can be observed while the battery system is in operation. Although this approach uses only two sensors, it enables SOC observation for the entire battery pack, leading to reduced implementation costs and form factor. The equalization current is further regulated based on the observed relative SOC. The simulation and experimental results demonstrate the rapid equalization capability of the proposed GCC-type equalizer during the discharging process.