Analysis and comparison of optimal power management strategies for a series plug-in hybrid school bus via dynamic programming

This paper examines two optimal power management strategies, i.e., blending (BL) strategy and charge-depleting/charge-sustaining (CD/CS) strategy, for a series plug-in school bus. The minimum fuel consumption results of these two strategies are compared and the pattern of the globally optimal battery state of charge (SoC) trajectories is analysed. Dynamic programming (DP) approach which is able to achieve global optimisation is applied in this study to guarantee a fair comparison. More specifically, to overcome interpolation leakage in traditional DP algorithms, a level-set algorithm is utilised. Simulation results show that: 1) The globally optimal way to control is to linearly deplete the battery SoC to its minimum allowable value when the vehicle reaches to the end of the journey; 2) The difference between the optimal fuel economy that can be achieved by the BL and CD/CS strategies is very marginal for a series plug-in powertrain, which is in the order of 1-2%.