## 4 Conclusions  
The literature review and the co-simulations between MATLAB/SIMULINK and GT-SUITE underlined that two types of fuel cells are really promising for transportation application: the PEMFC and the SOFC. The first one is a fuel cell operating at 80 \({}^{\circ}\)C, which allows a fast and simple start-up. Nevertheless, in this operating condition, the compressor must be powered by the stack, which decreased the useful power transmitted to the wheels. The use of a turbine, coupled with the compressor, reduced the power that the air supply system required by 45.8%, on average. As a result, the driving range of the vehicle increased by 3.5% and reached 706 km with an average electric efficiency of 32.1%. This was 11.5% better than the single-stage configuration's electric efficiency. However, to deal with the compactness of the PEMFC stack, the two-stage compressor emerged as a real asset. By increasing the maximum pressure ratio from 2.8 bar to 4.0 bar, it decreased the number of cells that were necessary to reach the same output power by 12.5%. Unfortunately, this downsising operation had an impact on voltage losses. Finally, the two-stage compressor reached a similar driving range to the single-stage configuration. It can be interesting to compare these results with a roots compressor, such as the one used by Toyota for their FCVs. The second one is a fuel cell operating between 550-1000 \({}^{\circ}\)C. The low power density (about 9.3 kg\(\cdot\)kW\({}^{-1}\)) and the impossibility of a quick start-up make the use of this technology as a pure propulsion system irrelevant at the moment. Nevertheless, the high operating temperature allows combining a SOFC stack and a gas turbine together into a hybrid system. The use of this technology as a range extender for an electric vehicle is truly promising. It allows extending the driving range by 252%. The driving range, with an initial SOC of 100% and a 6.2-kg tank full of pure hydrogen, reached more than 600 kilometres. It must be noticed that this result depended on the power management strategy. With an optimisation of the driving range per charge cycle, the vehicle reached 626 kilometres. A different strategy can also be used to optimise the driving range per tank of hydrogen. In this case, it reached 759 km due to five charge cycles from 60% to 100%. The use of PEMFC and SOFC technologies are fundamentally different. The first is used as a propulsion system, whereas the second is used as a range extender. The development and the optimisation of the latter is more complex in term of power management. Plus, the driving range really depends on the driver's behaviour on the road and the frequency at which the battery is charged. In 2015, the kWh European average price was 0.205 \(\upcels\)[44]. In 2017, the kilogram of hydrogen price was 15 \(\upcels\) in an Air Liquide station [45]. As a result, the first strategy of power management described in the previous paragraph leads to a price of 0.166\(\upcels\) per kilometre for a SOFC/electric hybrid vehicle, whereas the optimised driving range per tank of hydrogen leads to 0.135 \(\upcels\) per kilometre. For a PEMFC vehicle using an E-turbocharger, the price per kilometre is 0.119 \(\upcels\). This difference is partially due to the consumed hydrogen into the burner to warm the inlet air through the heat exchanger. As a result, it could be interesting to evaluate the performances of a vehicle using a PEMFC stack as a range exender instead of a SOFC one. This result matches with most of the fuel cell vehicles using the PEMFC technology, which is simpler and cheaper to use. However, this result must be nuanced, since the production of hydrogen is not as developed as power generation, which explains the high price of the fuel. [PERSON] was the student who carried out the modelling effort at Brunel University London and his work was checked by [PERSON], also a research student at Brunel, who also drafted the paper.