Robust Integral Voltage Tracking Control for PEM Fuel Cell Systems Under Varying Operating Current

This paper presents a robust controller design approach for nonlinear PEM fuel cell systems in a linear parameter varying system representation. The magnitude bounds on variations of the elements of system matrices corresponding to variational operating current are identified and addressed during control law construction via numerically tractable linear matrix inequality algorithms. In order to achieve voltage control with diminishing tracking error, integration of the tracking error is considered as an additional state and included in the fuel cell control system design. For a desired magnitude of voltage tracking command, the allowable magnitude constraints on gas flowrate are specified accordingly. The upper bound of the energy ratio between voltage tracking error and command is minimized in terms of optimization. In time response simulation based on the parameters of a Ballard 5 kW PEM fuel cell, both constant step and variational sinusoid tracking commands are considered for verification. The situation of a sudden change of load resistance and output current is also included in the simulation study. As demonstrated, the proposed robust controller design can achieve the desired voltage tracking performance for the tracking command and gas flowrates with specified magnitude while the operating current varies within its specified range.