A charging method for Lithium-ion battery using Min-max optimal control

Abstract

Overheat of the Lithium-ion battery during the charge process lead to decrease in capacity of the battery, cycle life, and charge efficiency. Safe and reliable charging methods require control of the battery temperature. In this paper, a min-max charging strategy based on a nonlinear equivalent circuit-Thermal model a Lithium-ion battery is proposed. The min-max optimal problem of specifying the optimal charging current is defined and the constraints such as current, temperature, and voltage limits are intended. The object of min-max optimal control is minimizing maximum irreversible heat that is generated by electrical current flow through the battery. Charging current is calculated by solving min-max optimal control problem. The employment of such current in charging system is difficult according to its fast variations. To solve this problem, the calculated current injected into the battery has been limited to some specified levels. The proposed charging strategy is compared with constant current-constant voltage method and simulated in MATLAB software to verify its validity. The minmax strategy is capable of reducing the heat generation and time of charging by 37.5% and 43 % respectively.