Pontryagin's Minimum Principle-Based Power Management of Plug-In Hybrid Electric Vehicles to Enhance the Battery Durability and Thermal Safety

Temperature affects the battery aging and stability, bringing about significant effects on the electric vehicle's economy, reliability, and safety. Therefore, it is necessary to consider the battery thermal condition when designing the power management scheme. In this article, an optimal power management strategy (PMS) for plug-in hybrid electric vehicles is proposed based on Pontryagin's minimum principle (PMP). Two situations, normal operation and cooling system failure, are considered. The impacts of battery aging and temperature rise are characterized based on the durability analysis model and thermal model. The temperature variation rate of the battery is incorporated into the Hamiltonian function, and the correlation between the cost optimization and temperature rise is disclosed by a shooting method. Then, the optimal costate variables in different cases are determined. Based on the above efforts, the PMP-based multiobjective optimal control strategy is proposed and evaluated based on the temperature statistical data in Shenyang, China. The results show that the proposed method can improve the durability of the battery and inhibit the excessive temperature rise. In the case of the cooling system failure, it can realize the tradeoff between safety and economy to reduce the risk of battery thermal runaway.