Observer-Based Air Excess Ratio Control of a PEM Fuel Cell System via High-Order Sliding Mode

This paper deals with a high-order sliding mode (HOSM) approach to the observer-based output feedback control of a proton exchange membrane (PEM) fuel cell (FC) system consisting of a compressor, a supply manifold, an FC stack, and a return manifold. The treatment is based on a lumped parameter nonlinear modeling of the PEM FC system under study. The suggested scheme assumes the availability for measurements of readily accessible quantities such as the compressor angular velocity, the load current, and the supply and return manifold pressures. The control task is formulated in terms of regulating the oxygen excess ratio (which is estimated by a nonlinear finite-time converging HOSM observer) to a suitable set-point value by using, as adjustable input variable, the compressor supply voltage. The proposed observer embeds an original synergic combination between second-and third-order sliding mode (SM) algorithms. The controller also uses a second-order SM algorithm complemented by a novel tuning procedure, supported by local linearization and frequency-domain arguments, which allows the designer to enforce a practical SM regime with some prespecified and user-defined characteristics. Thoroughly discussed simulations results certify the satisfactory performance of the proposed approach.