Conceptual design of fuel-cell vehicle powertrains

As worldwide interest on fuel-cell vehicles increases, the automotive manufacturers work harder on their vehicle designs. Clearly, one major topic in this field is the optimization of powertrain designs. The typical design process in engineering is a multistep iterative process, which begins from the general conceptualization and goes through multiple detailed design steps to a final decision. The product that arises at the end of this process, needs to meet the expectations of both the manufacturer and the potential customer best. However, due to several trade-offs in the design, it would be non-realistic to expect a single solution that fulfills all design objectives ultimately. Therefore it needs to be assured that all technological possibilities, which lead to an extremely high number of design candidates, are considered and the decision is made based on an extensive analysis. In order to increase the accuracy of this costly design process, it is necessary to define and use systematical approaches already at the early conceptualization. A few computer aided engineering tools, which require extensive information about components, to analyze vehicle powertrains are commercially available and, unfortunately, they are more suitable for solving specific problems in detailed design powertrains. Similarly, in the literature it is not possible to identify a suitable approach that can be used in conceptualization of fuel-cell vehicle powertrains. In this work, a new methodology for conceptual design of fuel-cell vehicle powertrains to analyze and evaluate a wide search space by considering the design expectations of all parties is proposed and demonstrated. A fuel-cell vehicle powertrain is mostly based on a hybrid structure, combining an electrical energy storage system with the FC system. The degree of hybridization in terms of power and energy capacity distribution between these two drivelines is an important design variable, which needs to be decided in the light of an optimized energy management strategy. Additionally, a hydrogen storage unit and at least one electric machine unit are required. The sizing, topology and management of these components have a great influence on vehicle characteristics. Therefore, the proposed methodology simultaneously and accurately analyzes the effects of these individual aspects on the system as a whole. In order to achieve this, scalable component models and a new universal energy management strategy are developed within this work. Furthermore, several simulation-aided analytical models are developed in order to increase the computational efficiency. The results of these models are evaluated according to the design objectives that are relevant for a potential customer’s decision by using several methods, which are introduced for multiobjective decision making. Finally, the proposed methodology is demonstrated in two case studies, where the optimum fuel-cell powertrain for a typical long-range vehicle is sought and the plug-in capability for the same vehicle is evaluated.