Control analysis of an ejector based fuel cell anode recirculation system

An ejector based recirculation system is incorporated on the anode side of the fuel cell to address anode flooding. The objective of the recirculation system is to regulate anode humidity with recirculating flow, while safeguarding the membrane and supporting the electric load. These objectives can be achieved by a control system that uses two actuators, namely the fuel supplied from the fuel source and a back pressure valve placed in the recirculation path. For these actuators, the control analysis presented in this paper identifies anode pressure, along with either return manifold pressure or recirculation flow rate, as variables to be tracked in order to facilitate meeting of the control objectives, while assuring internal stability. Feedback regulation of these variables with a minimum number of pressure sensors is addressed by identifying appropriate sensor locations. The sensor selection and corresponding observer design for the system are treated from the points of view of the observability requirements and robustness to sensor noise. The performance of various sensor combinations shows that measurement of anode pressure is adequate for a full order observer based state feedback controller.