CHARACTERIZATION OF FUEL CELLS POWER DEMAND IN VEHICLES. HYBRID POWER SPLITTING STRATEGY

Abstract

The alternatives to internal combustion vehicles have arisen attention over the last years.Hydrogen, as an energy vector has multiple advantages, especially in heavy-duty vehicles.However, there is no simulator available to simulate the operation of fuel-cell (FC) vehicles. Thus, DLR-TT has devoted time to developing a phenomenological simulator for computing the power demand of a vehicle to accomplish a selected drive cycle and to calculate the FC unit power specifications. The developed phenomenological model and simulator consider a hybrid FC / lithium-ion battery (LiB) power system, where the FC unit provides mostly steady state power, and the lithium-ion battery unit provides mostly dynamic power. Besides estimating the power demand,this model allows for the testing of different operating and design parameters concerning stability and power performance. The model was implemented in python in a well-structured manner to create in-house simulator. In this thesis, the simulator was useful to run different drive cycles and find the most representatives for heavy-duty vehicles operating in Europe. Also, the properties of the vehicles, such as the powertrain efficiency, the aerodynamic characteristic, and the rotational inertia factor, were studied and it was possible to confirm that these are the parameters with the strongest effect on the power demand. The power split between FC and LiB units was also studied. Another important point in this thesis was the evaluation of the power splitting strategy. The developed simulator was run to assess the optimum power contribution of the FC unit to the vehicle; the power was stepwise increased or decreased. It was concluded that for short cycles (ca. 1 h), there are advantages on having an increased capacity of the LiB unit.