Observability Analysis of PEM Fuel Cell Systems with Anode Recirculation

The optimal control of gas partial pressures in fuel cell systems is a key part to increase the efficiency and the lifetime of the fuel cell. In automotive applications, the nitrogen and hydrogen gas partial pressures are not measurable with actual sensors. Therefore an observer is required to determine the gas partial pressures in the fuel cell system. In this paper we present an observability analysis for PEM fuel cell systems with anode recirculation for an automotive application. The fuel cell stack voltage and the total gas pressure in front of the fuel cell are assumed as measurable outputs. The opening of the input valve and purge valve as well as the total pressure at the cathode are inputs. The fuel cell stack current is a measurable disturbance. It is shown that the hydrogen and nitrogen partial pressures in front of the fuel cell, inside the fuel cell, and behind the fuel cell are globally differentially observable as long as the fuel cell system is not in idle mode. As a result, asymptotic and finite time observers can be used to observe the total pressures and partial hydrogen pressures in an fuel cell system with anode recirculation.