Fuel cell system and method for controlling the same

A method for controlling a fuel cell system, the system comprising:

• a reformer provided with a reform reaction flow channel for generating anode gas containing hydrogen from reform-subject fuel;
• a fuel cell provided with an anode flow channel to which the hydrogen contained in the anode gas is supplied by supplying the anode gas from the reform reaction flow channel, a cathode flow channel to which a cathode gas containing oxygen is supplied, and an electrolytic body arranged between the cathode flow channel and the anode flow channel;
• a fuel pump for supplying the reform-subject fuel to the reform reaction flow channel;
• supplied fuel quantity detecting means for detecting a supplied fuel quantity, which indicates a quantity of the reform-subject fuel supplied by the fuel pump;
• a cathode pump for supplying the cathode gas to the cathode flow channel;
• supplied cathode gas quantity detecting means for detecting a supplied cathode gas quantity, which indicates a quantity of the cathode gas supplied by the cathode pump;
• generated power quantity detecting means for detecting a generated power quantity in the fuel cell;
• and
• a control device for controlling a delivery of the reform-subject fuel by the fuel pump and a delivery of the cathode gas by the cathode pump so that the generated power quantity may be equal to a requested generation power quantity which is necessary to operate a load utilizing power generated by the fuel cell, wherein:
• a cathode offgas line for sending the cathode offgas released from the cathode flow channel to the reform reaction flow channel is connected to the cathode flow channel;
• and
• the method comprising:
• a reformed carbon quantity calculation step for obtaining a reformed carbon quantity C, which indicates a quantity of carbon supplied to the reform reaction flow channel, based on the supplied fuel quantity detected by the supplied fuel quantity detecting means;
• a reformed oxygen quantity calculation step for obtaining a consumed oxygen quantity, which indicates a quantity of oxygen contained in the cathode gas consumed to generate power in the fuel cell, from the generated power quantity detected by the generated power quantity detecting means and also obtaining a supplied oxygen quantity, which indicates a quantity of oxygen supplied to the cathode flow channel, from the supplied cathode gas quantity detected by the supplied cathode gas quantity detecting means and then obtaining the residual oxygen quantity in the cathode offgas by subtracting the consumed oxygen quantity from the supplied oxygen quantity and obtaining a reformed oxygen quantity O, which indicates a quantity of oxygen supplied to the reform reaction flow channel, based on the residual oxygen quantity;
• and
• a reformed carbon quantity correction step for correcting the reformed carbon quantity C by changing only the delivery of the fuel pump so that O/C, which is a proportion of the reformed oxygen quantity O against the reformed carbon quantity C, may be kept in a target range.