Patent ID: 8859157

Claim:
A fuel cell system in a vehicle on which a drive motor is installed, the fuel cell system comprising: a fuel cell that generates electric power using a fuel gas and an oxidizing gas as reaction gases; a secondary battery that is charged by output power of the fuel cell, or that discharges charged electric power; and a controller that is programmed to: control a voltage of the fuel cell to a target voltage value; calculate a necessary heat quantity for the fuel cell system and an output power required for the fuel cell system including an output power required for the drive motor; compare the necessary heat quantity with normal heat generation quantity which is heat generation quantity in a high-efficiency power generation mode in which the fuel cell is caused to generate power at high-efficiency according to the required output power; when the necessary heat quantity is equal to or less than the normal heat generation quantity; based on the necessary heat quantity and the required output power, controlling the fuel cell to operate in the high-efficiency power generation mode in which the fuel cell is caused to generate power at high efficiency; when the necessary heat quantity is greater than the normal heat generation quantity, and the output power required for the drive motor is not 0, controls the fuel cell to operate in a first low-efficiency power generation mode in which a lower limit voltage value is set at a first lower limit voltage value and power generation efficiency is lower than that of the high-efficiency power generation; and when the necessary heat quantity is greater than the normal heat generation quantity, and the output power required for the drive motor is 0, controls the fuel cell to operate in a second low-efficiency power generation mode in which the lower limit voltage value is a second lower limit voltage value that is less than the first lower limit voltage value.