Control of the air supply system of a PEM fuel cell with guaranteed stability properties

Fuel cells are widely regarded as potential future stationary and mobile power sources. In this paper, the study is concentrated on the air subsystem and, in particular, on the problem of providing tuning rules for controllers ensuring stability of the overall system. Proceeding from a reduced order nonlinear model, that preserves the main features of the (by-now classical) 9-th order model, we suggest a natural decomposition into interconnected subsystems where one of them is strictly passive, and the other one depends on the controller parameters. The proposed tuning methodology consists then on enforcing the required passivity property of the feedback loop. Thus, the feedback operator is linearized. Then, Kharitonov-based robust positive realness (PR) conditions are imposed to determine the allowable ranges for the controller gains. We illustrate the methodology with a classical cascaded loop controller structure with an outer loop feedback linearizing controller and an inner loop PI regulator. Simulation results are presented to illustrate the conservativeness of the analysis as well as the performance improvement obtained with a suitable tuning.