UC Davis

Heavy-duty electric and hybrid electric vehicles are potential means to reduce the emissions of the transportation sector. However, the lithium batteries needed to power these vehicles can be cost and weight prohibitive, and battery degradation adds to the lifetime cost of these vehicles. Buses in particular are considered throughout this work—their frequent stopping and starting makes them prime candidates for electrification or hybridization, yet that same stopping and starting can be a source of significant battery wear. This work explores methods to improve battery lifespan and improve the overall economic feasibility of heavy-duty alternative powertrain vehicles.Four studies are carried out to this effect; simulation is used in all cases due to the slow rate of battery degradation and the expense associated with destructive testing. First, an electric bus is fitted with an on-board photovoltaic system. A full model for on-board photovoltaics is developed and it is shown that the power provided by the modules reduce the battery discharge depth to a sufficient degree to improve battery lifespan. Bus rooftop photovoltaics are shown to have a positive return on investment. Next, aging-aware control of a hybrid energy storage system is considered. Hybrid energy storage pairs an ultracapacitor with the conventional lithium battery to reduce large current spike and improve battery aging. A new energy management strategy that incorporates ultracapacitor aging is shown to be a more effective means of control than existing literature. The third and fourth studies concern robust energy management. The third considers the robustness of aging-aware energy management to aging model variations and methods of improving the robustness of aging-aware strategies are proposed. The fourth study introduces a new energy management concept that incorporates elements of minimax dynamic programming. This new strategy is first shown to improve robustness of a series hybrid bus to driving condition uncertainty, then second it is shown to improve the performance of aging-aware control of an electric vehicle with hybrid energy storage.