Investigating the impact of degradation on the energy management of a hybrid hydrogen-battery powertrain for the railway transport

The goal of this work is to evaluate the effect of the degradation of the components of a hybrid battery-fuel cell power unit on the operation of a train using hydrogen as its fuel. To this aim, it was decided to create a program written in the MATLAB environment that takes into account both fuel cell and battery degradation, and that allows to evaluate at every moment in the operating life of the train the state of aging of the two components of the power train, while tracing its impact on fuel consumption. The analysis is applied to a real case of a hybrid hydrogen train running on the Brescia-Iseo-Edolo line, a mountainous line located in northern Italy. The expected result is that by controlling the dynamic constraints of the fuel cell it will be possible to determine which strategy is the most suited for prolonging the fuel cell life, which one is best for the battery life and which one represents the best compromise between the two. The possible strategies vary in between two extremes, one using the fuel cell as a range extender, operating at fixed power and whose aim is only to recharge the battery and guarantee its state of charge never goes below a limit value, and one using the fuel cell in load following mode, with power variations dependent on the instantaneous power demand coming from the electric motor. In the first case, the battery manages all the power demand variations, while in the second case it only supplies the power that the fuel cell, due to its dynamic constraints and its size, is not able to provide. In both cases, the battery also allows for power recovery during braking. Although in the discussed case the characteristics of the power unit of the train are fixed, the program can also be used to perform an analysis of the impact of the power of the fuel cell and of the size of the battery on the degradation of the two components and on fuel consumption. The results of such study could then be used to determine which is the best dimensioning of the components and which is the best management strategy with a chosen criterion, for example an economic one of reduction of the total cost of ownership. However, such an analysis is out of the scope of this work, which is restrained to creating a tool useful to evaluate the degradation of powertrain components. Obviously, the ambition of this study is neither to exactly represent reality, nor to foresee the future, as some criticalities are present: first of all, as already seen, there is no consensus about the correct way of modeling fuel cell and battery degradation, and the adopted models come from articles found in literature. As such, they are validated for the specific components and conditions described in said articles, and may prove inaccurate for other cases. The coefficients representing degradation have been rescaled to the size of the components employed in the case object of study, but the best approach would be to repeat their calculation for the real components. That would require the right experimental setup, a great amount of time and the availability of batteries and fuel cells that would probably be destroyed in the process