Fuel cell system for motor vehicle and control method of same

A fuel cell system for a motor vehicle, the fuel cell system comprising:

• a fuel cell stack configured to supply power to an electric motor for driving a vehicle as well as generating power by an electrochemical reaction between a fuel gas and an oxidant gas;
• a discharge circuit having a plurality of resistance elements and a plurality of switching elements switching connection relationships between the plurality of resistance elements, and capable of forming a plurality of discharge paths through which power generated in the fuel cell stack is discharged by the plurality of switching elements switching the connection relationships between the plurality of resistance elements;
• and
• a discharge control circuit configured to control turning on and off of the plurality of switching elements wherein
• the discharge control circuit has:
• a discharge starting unit configured to start the discharge through a first discharge path by forming the first discharge path in the discharge circuit when a discharge instruction signal indicating instructions to discharge power generated in the fuel cell stack is input;
• a voltage detection unit configured to detect a detected voltage corresponding to an output voltage of the fuel cell stack;
• and
• a path switching unit configured to form a second discharge path whose resistance value is smaller than the resistance value of the first discharge path and to switch the discharge through the first discharge path to discharge through the second discharge path when the detected voltage that is detected by the voltage detection unit is lower than a predetermined threshold voltage during the discharge through the first discharge path, wherein
• the discharge circuit has:
• a first resistance element, to one end of which one terminal of the fuel cell stack is connected;
• a second resistance element one end of which is connected to the other end of the first resistance element;
• a third resistance element, to one end of which the other terminal of the fuel cell stack is connected;
• a first switching element arranged between the other end of the second resistance element and the other end of the third resistance element;
• a second switching element arranged between one end of the first resistance element and the other end of the second resistance element;
• and
• a third switching element arranged between one end of the second resistance element and one end of the third resistance element,
• the first discharge path is formed by the first resistance element, the second resistance element, and the third resistance element connected in series by turning on the first switching element while maintaining the second switching element and the third switching element in the off state, and
• the second discharge path is formed by the first resistance element, the second resistance element, and the third resistance element connected in parallel by turning on the first switching element, the second switching element, and the third switching element.