Fuel cell system

A fuel cell system, comprising:

• a fuel cell;
• a voltage detector configured to detect an output voltage of the fuel cell;
• a current detector configured to detect an output current of the fuel cell;
• an alternating current signal supply unit configured to supply an alternating current signal to electrodes on both ends of the fuel cell;
• a phase difference calculation unit configured to calculate, based on a detected alternating voltage that is detected by the voltage detector and a detected alternating current that is detected by the current detector, a phase difference between the detected alternating current and the detected alternating voltage;
• and
• a controller programmed to estimate, in accordance with the phase difference, an electric power generation distribution feature amount representing an electric power generation distribution in a cell surface of the fuel cell, with use of a predetermined relationship between the electric power generation distribution feature amount and the phase difference, wherein
• the electric power generation distribution feature amount includes a value indicating a difference between a maximum value and a minimum value of local current density in the cell surface.