Robustness of ECMS-based Optimal Control in Parallel Hybrid Vehicles

Control algorithms for hybrid vehicles have undergone extensive development leading to near-optimal techniques being employed and demonstrated over the previous decade. The different optimal controllers are inevitably linked through the assumed knowledge of the powertrain. For alternative fuelled engines, this assumed knowledge becomes circumspect due to composition variability, leading to uncertainty in the models used by the hybrid powertrain controller. The robustness of a map-based optimal controller using an equivalent charge maintenance strategy (ECMS) is consequently investigated in terms of theoretical fuel consumption losses under certain restrictive assumptions. The potential real world impact of variable composition fuels in hybrid powertrains is also assessed through two case studies involving significantly different prototype flex fuel hybrid vehicles.