Adaptive Energy Management Strategy for Hybrid Vehicles Based on Pontryagin’s Minimum Principle 2020-01-1191
The energy management strategies (EMS) for hybrid electric vehicles (HEV) have a great impact on the fuel economy (FE). The Pontryagin's minimum principle (PMP) has been proved to be a viable control strategy for HEV. The optimal costate of the PMP control can be determined by the given information of the driving conditions. Thus various methods are proposed to estimate the optimal costate of PMP by the prediction of the driving cycle. But in practice, full knowledge of future driving conditions is not available. In most studies, the design of EMS without the prediction of driving conditions is determined by the upper and lower bounds of the PMP costate, which is changed by the state of batteries. However, the predefined bounds of the PMP costate limits the scope of application, and cannot achieve best FE performance in all driving conditions. To solve this issue, this paper proposed a dynamic optimization method for PMP costate from the view of energy. It is known that the lower fuel consumption the method yields, the more efficiently the engine works. The selection of costate is designed to make the engine work in the high efficiency range. Compared with the rule-based control, the proposed method by the principle of Hamiltonian, can make engine working points have more opportunities locating in the middle of high efficiency range, instead of on the boundary of high efficiency range. Besides a hard and soft constraints of battery SOC is defined to balance the control of optimal costate and the working state of battery. Simulations based on the standard driving cycles are conducted to verify the FE performance. The results are compared with other control strategies to show the effect of proposed method in unknown driving condition.