Method and control device for controlling a fuel cell or a fuel cell stack

The method involves detecting current-voltage characteristic of fuel cell stack at operation intervals. The pitch with minimum value of each detected voltage-current characteristic, value for minimum of slope, or with minimum of slope related value is determined. The set value is determined for operating point and regulated to desired value by adding predetermined offset value to determined value. Independent claims are included for the following: (1) fuel cell stack; and (2) control device.