Hydrogen Fuel Cell Aiming at Vehicle Propulsion: Onboard or Off-Board Electricity Generation?

Abstract

In response to the global energy crisis and climate change, hydrogen has been pointed out as promising fuel to be part of the green energy transition. Thus, countries worldwide have released policies to support and increase the hydrogen industry. Therefore, investigations regarding how hydrogen can be utilized best as a fuel should be addressed to evaluate its potential applications. Since transportation is responsible for 37% of the carbon emissions from the end-use sectors, it is of interest to consider hydrogen fuel for vehicle propulsion. There are two main alternatives that might be considered for the electricity generation from hydrogen: 1) a hydrogen fuel cell onboard the electric vehicle or 2) a hydrogen fuel cell off-board powering the electric vehicle.Therefore, in this work, we propose the modeling and simulation from hydrogen fuel to wheels of the two different systems using the WLTP as the driving cycle reference. For the onboard system, the following components were considered: the vehicle dynamics, the gear, the motor, the inverter, the battery, and the fuel cell system on board (fuel cell vehicle powertrain). For the off-board system, the following components were considered: the vehicle dynamics, the gear, the motor, and the inverter for the battery electric vehicle powertrain, followed by the charger, the grid, and the fuel cell system off-board. The components were modeled as further described.The vehicle dynamics were modeled mathematically and the weight difference between the vehicles was taken into account. The gear was a single-step gear. The motor was an eight-pole PMSM and the inverter three-phase IGBT. The battery for both was modeled as a lithium-ion battery with different sizes, with the battery for the fuel cell vehicle being much smaller. Capacity values similar to commercialized vehicles were used (4 and 300 Ah). The fuel cell was modeled as a commercialized fuel cell with 63% peak efficiency. For the fuel cell vehicle, a control strategy was implemented to split the power demand between the fuel cell and the battery. The control strategy was based on the state of charge of the battery and the power demand for each point of the cycle.The simulation results have shown a slightly higher efficiency and lower hydrogen consumption for the onboard system compared to the off-board system. Even though there were more losses associated with the battery and the fuel cell in the onboard system, the losses associated with vehicle weight and the off-board power electronics related to the off-board system were more significant to the overall energy consumption. Thus, the results suggest that if hydrogen is available as a fuel aimed at vehicle propulsion using it onboard is more efficient than using it off-board.