Method for determining membrane protonic resistance of a fuel cell stack

A method for determining a normalized high frequency resistance of a fuel cell stack, said method comprising:

• starting up operation of the fuel cell stack;
• adjusting a cathode air compressor and a water vapor transfer (WVT) unit to increase cell membrane humidification, where the compressor and the WVT unit are adjusted by a controller including a processor and a memory;
• using a water buffer model, calculated in the controller, to estimate a membrane hydration state of the fuel cell stack at humidified conditions, where the water buffer model integrates product water output by the fuel cell stack;
• measuring a high frequency resistance of the fuel cell stack using a high frequency resistance (HFR) sensor electrically coupled to the fuel cell stack;
• identifying, using the controller, a base high frequency resistance of the fuel cell stack at humidified conditions from the high frequency resistance measured by the HFR sensor, including filtering and using data gathered for the base fuel cell stack high frequency resistance at humidified conditions once the water buffer model estimates that the membrane hydration state of the fuel cell stack is within 10% of saturation;
• and
• normalizing the base high frequency resistance of the fuel cell stack against a base high frequency resistance of a reference fuel cell stack to determine the normalized high frequency resistance of the fuel cell stack:
• and
• adjusting the cathode air compressor and the WVT unit, by the controller, to achieve a desired cell membrane humidification based on an estimated relative humidity calculated from the normalized high frequency resistance.