A Closed-loop Fast Charging Strategy Based on Core Temperature Control for Lithium-ion Battery

Fast charging is one of the main requirements and challenges for electric vehicle batteries. Currently, common charging profiles utilize an open-loop control, which relies on a priori knowledge. It's necessary to use a closed-loop charging technique, where the charging current is controlled by real-time voltage and temperature, particularly when high charging current. Moreover, the massive difference between surface and core temperature leads to thermal issues. Therefore, this paper proposes a closed-loop fast charging strategy (CFCS) based on core temperature control for lithium-ion batteries (LIBs), with an awareness of thermal safety. CFCS includes three modes, i.e., pulse current charging (PCC) mode, constant temperature (CT) mode with a proportional-integral-derivative (PID) controller, and constant voltage (CV) mode. Besides, an extended state observer (ESO) is applied for real-time core temperature estimation, combined with a two-state thermal model. Based on the core temperature control, there is a 40% reduction in charging time compared to the previous method. Meanwhile, core temperature is maintained in a safe range, which keeps the LIB from thermal runaway. The experimental results show the proposed strategy can balance rapidity and security, with a wide application range and strong robustness.