Design o a Hierarchical Energy Management Strategy for a Range-Extender Electric Delivery Truck

In this work we propose an on-line implementable hierarchical strategy merging heuristic and locally optimal features for the energy management of a range-extender electric vehicle. This class of vehicles can operate as pure electric as well as hybrid, with a range-extender internal combustion engine working as a generator. Standard energy management strategies, such as Charge Depleting/Charge Sustaining and Equivalent Consumption Minimization Strategy (ECMS), show several limitations when applied to range-extender electric powertrains. These limitations can include excessive engine start/stops, potential cold starts, distance from optimal fuel consumption, inefficient usage of the grid energy. Therefore, in this work the energy management problem has been split over two levels: at the higher level, a heuristic rule-based controller is used to decide when to operate the vehicle as pure electric; at the lower level, the ECMS is implemented to locally manage the powertrain energy flows whenever the vehicle is in hybrid mode. The lower level controller is implemented in three different variants in the effort of finding a trade-off between fuel consumption, emissions, drivability and efficient battery recharge. The performance of the hierarchical energy management strategy is numerically evaluated for a range-extender Class 6 delivery truck and compared to pure ECMS. The results show the ability of the proposed approach to ensure near-optimal fuel economy with an acceptable number of start/stops of the range-extender.