Erich Ramschak, Volker Peinecke, Peter Prenninger: AVL List GmbH
Thomas Schaffer, Wolfgang Baumgartner , Viktor Hacker: Graz University of Technology, CD-Laboratory for Fuel Cell Systems
205th ECS Meeting,16.10.2005 - 21.10.2005, Los Angeles
In comparison to state of the art fuel cell stack monitoring techniques, where for reliability and durability reasons either single cell or cell-block voltages are monitored separately, the new approach derives information about critical cell & stack status from the stack sum voltage only. Since the wiring and instrumentation effort as well as the cost are therefore strongly reduced, this new technology has its advantages at high volume applications like FC vehicle fleets or it can be used as a quality management (QM) instrument during the assembly process of stacks.
In this new approach, the fuel cell response (stack voltage) is analysed in comparison to a particular low frequency signal, which is superimposed on the stack current. Critical cell operation occurs, if e.g. a too low air stoichiometry causes a rather sharp voltage drop at a particular cell current. If in such case the current is superimposed by a signal with a specific frequency pattern, then the system response (stack voltage) will be harmonically distorted. Particularly, this means that even if just one single cell is in a critical status, it will cause frequency distortion and occurrence of harmonics in the stack sum voltage. The fractions of harmonics are analyzed in the frequency domain and are compared to the originally superposed frequency pattern, which provides the information that one or some cells are operating in a critical mode.