A Real-Time Capable Humidity Model for a Polymer Electrolyte Membrane Fuel Cell Electric Vehicle

Abstract

In polymer electrolyte membrane fuel cells, hydrogen and oxygen are converted into electrical energy, with water as the main product. However, uneven water distribution, particularly close to the gas inlets, can lead to local membrane dry-outs, reducing performance and long-term durability. To prevent this, external humidification of inlet gases is often applied. In fuel cell electric vehicles (FCEVs), membrane humidification is preferred as it involves low energy losses and is independent of external water supply. Effective water management requires precise, real-time capable models to support advanced control strategies. In this study, a novel real-time capable crossflow membrane humidifier model was developed and combined with a fuel cell stack model, focusing on water transport. The proposed humidifier model employs a solution-diffusion approach, utilising a piecewise linear approximation of membrane water content and a simplified diffusion coefficient, which enables real-time applications as an explicit function. Coupling both models reduces sensor requirements, as boundary conditions can be estimated internally. The complete humidity model is validated on a full-scale, vehicle-specific test bench, showing strong agreement with experimental data. This enables its application in model-based control to improve the efficiency and lifespan of FCEVs.