Combined Sizing and EMS Optimization of Fuel-Cell Hybrid Powertrains for Commercial Vehicles 2019-01-0387

During the last years, fuel-cell-based powertrains have been attracting a lot of attention from commercial vehicle manufacturers for reducing vehicle-related Greenhouse Gas (GHG) emissions. Compared to Battery-Electric Vehicles (BEV), fuel-cell-based powertrains has the strong advantage of dealing with range-anxiety, which is crucial for commercial vehicle with high duty-cycle energy requirements. Amongst the different fuel-cell types, Proton Exchange Membrane Fuel-Cells (PEMFC) have the greatest potential for utilization in automotive applications, due to their relatively high technical readiness, market availability and utilization of hydrogen (H₂) fuel. In addition, Solid Oxide Fuel-Cells (SOFC) show good potential due to existing re-fueling infrastructure for light hydrocarbon fuels or heavier hydrocarbon fuels (e.g. diesel). This study focuses on the application of both PEMFCs and diesel-fueled SOFCs in Fuel-Cell Hybrid Electric Vehicle (FCHEV) architectures for commercial vehicles. Delivery vans in the 2.5 t-3.5 t weight range, coach buses and 3-axle tractor-type long-haul trucks are considered energy-driven types and highly suitable for fuel-cell systems, which offer high energy density values. Due to the high number of vehicle application types and system configurations, and due to the complexity of such hybrid architectures, powertrain design loops can be very time-consuming and model-based systems engineering becomes necessary. This study proposes a combined model-based component sizing process with Energy Management Strategy (EMS) optimization for determining powertrain performance and total system costs. In the suggested approach, the initially considered design space is reduced to a lower number of feasible power source combinations based on initial estimations, fixed component efficiencies and vehicle performance requirements. An optimization algorithm is then utilized for all the feasible combinations on different drive-cycles, i.e. the time-based WLTP drive-cycle for delivery vans and modified distance-based VECTO drive-cycles for coach buses and long-haul trucks, with more detailed component performance characteristics, for vehicle sub-categories defined based on the market in the United Kingdom. The suggested design approach for FCHEV powertrain architectures is analyzed and presented.