The evolution and accumulation of operational experience in the field of fuel cells are opening new perspectives for the use of these technologies in continuous power generation in aviation. In this prospect, the pursuit for high power density and system efficiency becomes essential. This thesis contributes to the initial stage of investigating and modelling auxiliary elements within a fuel cell power system (FCPS), which is intended to become an integral part of the powertrain of a regional hybrid more electric aircraft. Starting from a previous thesis work conducted at the Polytechnic of Turin, where a model of air supply system for the aircraft was developed using a simple layout with the compressor powered by an electric motor, it emerged that the compressor system is the most significantly energy-impacting component among the auxiliary subsystems of the FCPS, powered directly by the fuel cell itself.