Degradation Avoiding Start Up and Shut Down of Fuel Cell Stacks for Automotive Application Using Two Plant Model Predictive Control

Exposure of fuel cell membranes to open circuit voltage results in the dissolution of the platinum in the catalyst layer, as well as corrosion of the carbon support. It is, therefore, important that the cells' potential inside a fuel cell stack be brought to zero at the start of the inactive phase. A shut down procedure to avoid open circuit voltage for fuel cell stacks is presented. The air supply is shut off first and a dummy current used to consume all the remaining oxygen reducing the voltage to zero ending up with nitrogen and water only. The hydrogen supply is then shut off leaving some hydrogen in the anode. Two zero dimensional models are developed: one (nonlinear) describes the fuel cell stack during normal operation and the second (linear) describes the system during shut down or start up. A model predictive control algorithm is employed to track the power demand during operation using the first model and to perform the shut down / start up procedure using the second model ensuring avoidance of open circuit voltage as well as the air/hydrogen front which causes severe degradation. Different criteria (maximum/minimum dummy current, supply shut off speed, final anode pressure level) can be incorporated into the controller to adapt its performance to any particular stack.