Optimal Equivalent Fuel Consumption for Hybrid Electric Vehicles

In this brief, we show that using Pontryagin's minimum principle (PMP) can be a good alternative which achieves near-optimal solutions when the future driving schedule can be known in real-time. The control concept can be solved forward in time when a constant costate value is decided. The constant costate can be interpreted as an equivalent ratio linking fuel usage and electric energy consumption. If the fuel economy is the only objective function to minimize, the control concept based on PMP is near global optimal when the final SOC is close to a desired value. In this brief, a method to calculate the proper costate to sustain the SOC within a reasonable range is suggested. In this method, two parameters, SOCeff and P-mean, which depend on the driving patterns, are used to link the driving cycle to the optimal costate. Simulation results show that we can achieve near optimal control, in which 86% of final SOC values stay within +/- 4% of the desired final value for tested city driving schedules.