Patent ID: 8795908

Claim:
A fuel cell humidity determining method comprising: determining an absolute voltage difference between an average cell voltage for a plurality of individual cells of a fuel cell stack and a minimum cell voltage value for a voltage output by the individual cells; comparing the absolute voltage difference with a first preset value; selectively changing a flow rate of an oxidizer gas to change humidity in the fuel cell based on a comparison between the absolute voltage difference and the first preset value, the changing the flow rate of the oxidizer gas based on the comparison between the absolute voltage difference and the first preset value being prohibited when the absolute voltage difference is less than the first preset value so that the flow rate of the oxidizer gas is maintained, and the changing the flow rate of the oxidizer gas based on the comparison between the absolute voltage difference and the first preset value occurring when the absolute voltage difference greater than or equal the first preset value; determining a humidity state in the fuel cell stack based on a change in the absolute voltage difference due to the change in the humidity in the fuel cell after the flow rate of the oxidizer gas has been changed, such that a change in the humidity state indicates whether the fuel cell is becoming excessively humid or insufficiently humid depending on the change in the flow rate of the oxidizer gas, wherein in the excessive humidity state, the flow rate of the oxidizer gas is increased and liquid in the fuel cell is dispersed; and at least one of the following: comparing the absolute voltage difference with a second preset value, which is greater than or equal to the first preset value, after the flow rate of the oxidizer gas has been increased, and determining the humidity state in the fuel cell stack being in an insufficiently humid state when the absolute voltage difference is greater than or equal to the second preset value; and comparing the absolute voltage difference with the second preset value after the flow rate of the oxidizer gas has been increased, and determining the humidity state in the fuel cell stack being either in an excessive humid state or in an insufficient oxygen state when the absolute voltage difference is less than the second preset value.