Patent ID: 7829234
Filing Date: 2010-11-09
Classification: H01M,Y02E

Abstract:
1. A system for controlling the relative humidity of a cathode airflow to a fuel cell stack, said system comprising: a water vapor transfer unit for humidifying the cathode airflow, said water vapor transfer unit receiving a cathode exhaust gas on a cathode exhaust gas line where the water vapor in the cathode exhaust gas provides the humidity for the cathode airflow; a first control valve positioned in the cathode exhaust gas line for controlling the flow of the cathode exhaust gas through the water vapor transfer unit to control the relative humidity of the cathode airflow; a second control valve positioned in a by-pass line for controlling the flow of the cathode exhaust gas by-passing the water vapor transfer unit; and a controller configured to control the position of the first and second control valves, said controller compensating for the non-linearity between the flow resistance and the valve position of the first and second control valves by changing the position of both the first and second control valves when changing the relative humidity of the cathode airflow so that the combined flow resistance of the first and second control valves does not significantly change.