Cell equalizer for recycling batteries from hybrid electric vehicles

Abstract

The rise of electric vehicles (EVs) and hybrid electric vehicles (HEVs) has resulted in increases in battery toxic waste. Although the powering and capacity characteristics of batteries deteriorate after use in EVs and HEVs, they usually retain enough potential for reuse as power sources in home energy systems, whose power requirements are much lower than those of EVs and HEVs. This study proposes an active cell equalizer that balances the state of charge (SOC) of nickel–metal hybrid (NiMH) batteries recycled from HEVs. In the proposed cell equalizer, two different circuits, e.g., a generation control circuit (GCC) and a power-decoupling circuit are integrated. Excessive energy is automatically transferred from a high-SOC cell to a low-SOC cell through the GCC. The power-decoupling circuit lowers the power pulsation caused by the single-phase DC/AC inverter. This reduces the low-frequency ripple current flowing into the battery pack, ensures safe operation and prolongs the lifecycle of the batteries. A prototype circuit with a three-stage battery pack is implemented in the discharging state and the obtained experimental results are analyzed to verify the equalizer functionality.