Fuel cell operation to minimize RH cycles to improve durability

A method for controlling a relative humidity of a cathode exhaust gas from a fuel cell stack in a fuel cell system, said method comprising:

• providing sensor signals indicative of operating parameters of the fuel cell system;
• calculating a minimum sustainable relative humidity of the cathode exhaust gas based on the sensor signals;
• determining if the calculated minimum sustainable relative humidity is less than a predetermined percentage;
• providing a relative humidity set-point above 100% if the calculated minimum sustainable relative humidity is greater than the predetermined percentage;
• providing a relative humidity set-point below 100% if the calculated minimum sustainable relative humidity is less than the predetermined percentage;
• and
• controlling fuel cell system components based on the relative humidity set-point to attempt to maintain the relative humidity of the cathode exhaust gas at the set-point.

A method for controlling a relative humidity of a cathode exhaust gas from a fuel cell stack in a fuel cell system, said method comprising:

• providing sensor signals indicative of operating parameters of the fuel cell system;
• maintaining the cathode exhaust gas relative humidity in a wet operating mode if the operating parameters of the fuel cell system are able to sustain the cathode gas relative humidity above a first predetermined value;
• and
• maintaining the cathode exhaust gas relative humidity in a dry operating mode if the operating parameters of the fuel cell system are able to sustain the cathode gas relative humidity below a second predetermined value.