Flatness-based Trajectory Planning for the Battery State of Charge in Hybrid Electric Vehicles

Abstract

In this contribution an energy management framework for hybrid electric vehicles (HEV) is presented. Particularly, the energy management strategy is extended by a trajectory planning level for the battery state of charge (SoC). For the design of the SoC reference trajectory generator the differential flatness property of the system is exploited to formulate a nonlinear static optimization problem. Its performance is evaluated in combination with the Equivalent Consumption Minimization Strategy (ECMS) which is a commonly applied technique for the fuel consumption optimization of hybrid electric vehicles. Therefore, we apply an adaptation law for the equivalence factor, relating electric energy to fuel consumption, which requires a SoC reference value as input. Compared to the case when ECMS assumes a constant SoC reference, the application of a time varying SoC reference, as introduced in this work, improves the overall performance of the energy management controller on the considered driving cycle.