Charging and discharging spaces-based current allocation in parallel-connected battery systems

Abstract

Battery cells or modules are usually connected in parallel to build up large current and to increase system reliability. However, charge imbalance among parallel-connected battery cells or modules is very common and results in circulating current, which increases energy loss, shortens battery life, and even incurs fire hazard. Thus, charge balance or equalization among battery cells or modules is important. For parallel-connected battery modules, we first define the charging space and discharging space. Then the module charge imbalance can be gradually reduced by allocating larger charging (discharging) current to the module with larger charging (discharging) space. Motivated by this idea, we propose the current allocation method based on charging and discharging spaces (CDSs). In the proposed CDS-based current allocation, control parameters are provided to facilitate the flexible control of system performance, such as total power loss and module state of charge (SOC) range. In addition, the current allocation in proportion to module SOCs reported in recent studies can be viewed as a special case of the proposed CDS-based current allocation. Finally, simulation results illustrate these properties and advantages of the proposed CDS-based current allocation.