Systematic Development Approach for a Hybrid Electric Powertrain Using Fuel-Cell-in-the-Loop Test Methodology

Abstract

A promising approach for defossilization in the transport sector is using the polymer electrolyte membrane fuel cell (PEMFC) as an energy converter for propulsion in combination with green hydrogen. Furthermore, hybridization can bring an additional gain in efficiency. In a hybrid electric vehicle (HEV) powertrain, including FCHEV, at least two power sources (e.g., an FC system (FCS) with a hydrogen storage system and a high-voltage battery (HVB)) provide the required propulsion power. Thus, the powertrain topology and the energy management strategy (EMS) of an FCHEV are more complex than those of a conventional powertrain. To ensure a cost- and time-efficient development process, the FCHEV powertrain concept and its functions must be verified and evaluated early. To this end, this study presents the design and setup of an FC-in-the-Loop (FCiL) test platform as a tool for the systematic development of an FCHEV powertrain under realistic operating conditions. Hence, a medium size FCHEV is modeled with quasistatic sub-models of the powertrain components. The full-vehicle model is validated against measurement data of a commercially available FCHEV on a 4-wheel chassis dynamometer in a driving cycle. Based on the FCiL test methodology, the sizing of the FCS and HVB is demonstrated. It is found that for a low-load driving cycle such as the WLTC, a 110 kW FCS, and a 1.6 kWh HVB can achieve a good result regarding low hydrogen consumption. Furthermore, two different EMS schemes, the power follower strategy (PFS) and the equivalent consumption minimization strategy (ECMS), are implemented and evaluated. With the ECMS, hydrogen consumption can be reduced by 1.6 % compared to the PFS. Moreover, the trade-off behavior between minimum hydrogen consumption and reduced dynamics of the FCS is investigated. Reducing the dynamic operation of the FCS by one-third results in an additional hydrogen consumption of only about 0.8 %.