Fuel cell system and method for controlling fuel cell system

A method for controlling a fuel cell system that includes a fuel cell provided with a fuel-electrode passage configured to supply a fuel gas to be supplied from a fuel-gas supply passage to a fuel electrode, an oxidizing-electrode passage configured to supply an oxygen-containing gas to an oxidizing electrode, and a cooling-water passage isolated from at least either the fuel-electrode passage or the oxidizing-electrode passage by a conductive porous material,

• a cooling-water tank having a cooling-water supply port to which a cooling-water supply pipe coupled at one end to a cooling-water inlet manifold provided in an upstream inlet of the cooling-water passage is coupled at the other end, a first oxygen-containing-gas discharge pipe coupled at one end to an air outlet manifold provided on a downstream side of the oxidizing-electrode passage being coupled to the cooling-water tank at the other end, the cooling-water tank being configured to supply cooling water from the cooling-water inlet manifold, and
• a pressure-loss part to which a second oxygen-containing-gas discharge pipe coupled at one end to an air discharge port of the cooling-water tank is coupled at the other end, and to which a fuel-gas discharge pipe coupled at one end to a fuel-outlet manifold provided in a downstream outlet of the fuel-electrode passage is coupled at the other end,
• the method comprising adjusting a differential pressure between a water-pressure in the cooling-water inlet manifold and an air-pressure in an air outlet manifold provided on a downstream side of the oxidizing-electrode passage by an amount of discharge from the cooling-water passage.