An Online Extremum Seeking Optimization Strategy for Warm-up of Lithium Batteries

The durability and efficiency of lithium batteries are impaired in low temperature environments, in which it is necessary to heat them to a suitable temperature before normal operation. Self-heating by discharging battery current is an efficient and economical method, whose discharge current rate dramatically affects the heating time and the capacity decay. In the paper, a warm-up strategy based on extremum seeking is proposed to obtain the optimal discharging current. Firstly, the models are constructed by analyzing the electrical and thermal characteristics of lithium battery. Then, the loss function is formulated by combining capacity fade and heating efficiency. The extremum seeking algorithm is utilized to calculate the optimal heating current based on the real-time internal resistance state. The proposed strategy realizes the balance between heating time and energy loss, and reduce the required energy for heating battery.