Adaptive limitation of standby mode to enhance fuel cell system life

A method for controlling the number of stand-by mode events for a fuel cell stack in a fuel cell system, where the stand-by mode events put the fuel cell stack into a low power condition, said method comprising:

• determining an irreversible voltage loss of the fuel cell stack at predetermined time intervals including estimating a stack polarization curve that defines a relationship between stack current and stack voltage, wherein estimating the stack polarization curve includes estimating the stack polarization curve at a maximum stack current density, and wherein determining the irreversible stack voltage loss includes determining the irreversible stack voltage loss only within a predetermined period of time after a stack voltage recovery process is performed that compensates for a reversible stack voltage loss;
• determining a current stack voltage degradation variable based on the irreversible voltage loss;
• determining if the current stack voltage degradation variable indicates that the fuel cell stack will not meet predetermined stack end-of-life voltage performance requirements;
• calculating a maximum allowed voltage degradation rate of the fuel cell stack that will meet the predetermined stack end-of-life voltage performance requirements if the stack voltage degradation variable indicates that the fuel cell stack will not meet the predetermined stack end-of-life voltage requirements;
• calculating a maximum number of stand-by mode events per unit time that can be allowed to prevent the stack from exceeding the maximum allowed voltage degradation rate;
• and
• controlling the number of stand-by mode events based on the calculated maximum number of stand-by mode events per unit time including comparing the maximum number of stand-by mode events by a current number of stand-by mode events.

A control system for controlling the number of stand-by mode events for a fuel cell stack in a fuel cell system, where the stand-by mode events put the fuel cell stack into a low power condition, said control system comprising:

• means for determining an irreversible voltage loss of the fuel cell stack at predetermined time intervals;
• means for determining a current stack voltage degradation variable based on the irreversible voltage loss;
• means for determining if the current stack voltage degradation variable indicates that the fuel cell stack will not meet predetermined stack end-of-life voltage performance requirements;
• means for calculating a maximum allowed voltage degradation rate of the fuel cell stack that will meet the predetermined stack end-of-life voltage performance requirements if the stack voltage degradation variable indicates that the fuel cell stack will not meet the predetermined stack end-of-life voltage requirements;
• means for calculating a maximum number of stand-by mode events per unit time that can be allowed to prevent the stack from exceeding the maximum allowed voltage degradation rate;
• and
• means for controlling the number of stand-by mode events based on the calculated maximum number of stand-by mode events per unit time.