Cost-optimal integration of innovative powertrain technologies into rail vehicles

Zusammenfassung

Railway is an essential transportation mode in nowadays society, both for passengers and goods. Considering that the relation between the carried passenger activity and the derived pollutant emissions is lower than in road transport, railway becomes an essential stakeholder in the path towards transport decarbonization. During the last decades, a significant effort to electrify railway lines has been carried out globally. However, due to its high cost, electrification is not always cost-efficient. Consequently, 65% of rail tracks are not electrified yet, and diesel still accounts for 53% of the global railway sector energy use. This demonstrates the importance of searching for cleaner alternatives also in the railway sector. Recent techno-economic developments have pushed the use of greener technologies such as batteries and fuel cells in various transport applications, including railway vehicles. Due to their technical limitations, hybrid architectures such as the diesel-battery or the fuel cellbattery become the most promising options, or even the only feasible ones, in many cases. This hybridization involves additional complexity compared to traditional architectures. In essence, the main challenge consists of obtaining a cost-efficient solution compared to conventional vehicles, which will also enable a cleaner transportation. With the aim of obtaining that cost-efficient solution, this Ph.D. Thesis focuses on the design of the powertrain of railway vehicles. Important features to be considered during the powertrain design include the selection of the technologies to be integrated into the powertrain, the size of the powertrain elements, and the energy management strategy. Traditionally, these features are defined ad-hoc for a specific context (i.e., for a particular driving cycle or economic framework), but this is a time-consuming process, and the replicability of the conclusions is limited. Therefore, evaluating the impact that the different features of the specific context have on the optimal powertrain design can help simplify the efforts of the design approach. In order to overcome all these challenges, this Ph.D. Thesis proposes and implements a holistic design methodology to achieve a cost-optimal integration of fuel cell and battery systems in railway vehicles. The holistic design methodology is based on a complete analysis of the Life Cycle Cost, which is composed of several steps. Firstly, the cost of integrating different powertrain sizes, battery technologies and energy management strategies is compared. Secondly, the obtained conclusions are evaluated in different frameworks, including multiple railway routes and economic contexts. For the development of this analysis, a power flow-based simulation model is set. This model is based on the Itiner tool previously developed by CAF I+D, and it is fed with the data provided by CAF Power & Automation. This will allow using realistic vehicle and route data to develop the mentioned Life Cycle Cost analysis. Moreover, within the development of this analysis, this Ph.D. Thesis also proposes several innovative energy management strategies and a novel chemistry-dependent battery lifetime estimation model. Once the holistic design methodology is explained in detail, the methodology and the whole Life Cycle Cost analysis are implemented in two case studies. Each of the case studies of this Ph.D. Thesis is based on one of the railway vehicle topologies mentioned above: (1) the diesel-battery hybrid topology, and (2) the fuel cell-battery hybrid topology. The development of the two case studies will provide valuable conclusions for the design of railway vehicle powertrains that integrate battery and fuel cell systems. These conclusions are claimed to be especially helpful for railway manufacturers to make decisions regarding the powertrain design of hybrid diesel-battery or fuel-cell battery vehicles