Fuzzy Logic Control of External Heating System for Electric Vehicle Batteries at Low Temperature

Abstract

The reduction in driving range and the degradation of vehicle performance in cold weather has become one of the challenges in vehicle electrification in recent years. The root cause of this phenomenon is the property of lithium-ion batteries with capacity and power capability reduction at low temperatures. In this study, an external battery heating system was developed by employing an electrothermal film affixed to the surface of each cell, and the heating process was performed during driving. An equivalent circuit model combined with a thermal model was established for the simulation and control design. A fuzzy logic control strategy was developed to optimize the external heating power provided by the battery pack, and to achieve the maximum range by the end of discharge. A global optimal control strategy obtained by dynamic programming and a constant maximum power heating strategy were used for comparison. Simulation and experimental validations show that the proposed fuzzy logic control algorithm can achieve a 3.6% to 5.3% improvement in driving range than the maximum power heating method, and has close performance to the global optimal solution. Furthermore, the vehicle equipped with the proposed heating system can have up to 150.4% of the range recovery under different driving conditions.