Influence of stack voltage window, driving cycle, and HVAC strategy on hydrogen consumption in a fuel cell electric bus

This study investigates the energy efficiency and operational behaviour of a hydrogen fuel cell electric bus (FCEB) under different fuel cell stack voltage windows, driving cycles, and heating, ventilation and air-conditioning (HVAC) operating modes. A one-dimensional MATLAB/Simulink model coupling a proton exchange membrane fuel cell (PEMFC) stack, a traction battery, an electric drive and an HVAC subsystem was developed and validated against measured speed data from a real intercity route between Incheon and Seoul, reproducing the measured speed with a coefficient of determination above 0.99 and a maximum local deviation of about 5 %. Two stack voltage windows — Scenario 1 (420–480 V) and Scenario 2 (440–500 V) — were evaluated over three driving cycles: Braunschweig (urban), the World Harmonized Vehicle Cycle (WHVC, mixed) and the European Transient Cycle (ETC, transient heavy-duty), under hot summer (35 °C, 74–75 % relative humidity) and cold winter (−7 °C, 59 % relative humidity) conditions. Of the three factors, the driving cycle had the largest effect: hydrogen consumption over the 700 s window ranged from 0.139 kg in WHVC to 0.257 kg in Braunschweig, a difference of about 85 %, or about 55 % when normalised by the distance covered. The stack voltage window had the smallest effect, Scenario 1 reducing hydrogen consumption by 2.7 %, 2.2 % and 0.9 % for the three cycles while keeping the battery state of charge (SOC) within a narrow band and avoiding deep discharge. HVAC operation fell between the two: under summer conditions at full load it accounted for 22–35 % of the total hydrogen demand with recirculation on and for 14–23 % with fresh-air operation, the latter lowering cumulative HVAC energy by 40–45 %. The results show that auxiliary thermal management influences hydrogen consumption an order of magnitude more strongly than the stack voltage window, and that fuel economy optimisation in fuel cell buses should therefore be treated as an integrated control problem rather than a component-level one.