Fuel cell device

A fuel cell device comprising:

• a cell stack comprising a plurality of fuel cells electrically coupled to generate power with a fuel gas and an oxygen-containing gas;
• a fuel gas supply unit to supply the fuel gas to the plurality of fuel cells;
• and
• a controller configured to control the amount of electrical current that is generated by the plurality of fuel cells and that is supplied to the external load,
• wherein the controller is further configured to:
• linearly increase a rate of fuel utilization (Uf (%)) of the plurality of fuel cells with increasing the electric current when the fuel gas flow is below a minimum fuel gas flow necessary to maintain a temperature of the plurality of fuel cells above a predetermined temperature;
• non-linearly increase the rate of fuel utilization (Uf (%)) from a point of minimum fuel gas flow with increasing the electric current during a partial load operation;
• and
• maintain the rate of fuel utilization (Uf (%)) constant with increasing the electric current during a rated operation.

A fuel cell device comprising:

• a cell stack comprising a plurality of fuel cells electrically coupled to generate an electric current (I) from a reaction of a fuel gas and an oxygen-containing gas in one of at least a first range defining a partial load operation and a second range defining a rated operation;
• a fuel gas supply unit to supply the fuel gas to the plurality of fuel cells at a fuel gas flow rate from a raw fuel supply unit;
• and
• a controller configured to:
• control the reaction of the fuel gas and the oxygen-containing gas and
• control the fuel gas flow rate to:
• linearly vary a rate of fuel utilization (Uf (%)) of the plurality of fuel cells in direct proportion to the electric current when the fuel gas flow is below a minimum fuel gas flow, wherein the minimum fuel gas flow is defined as a minimum fuel gas flow sufficient to maintain a temperature of the plurality of fuel cells above a predetermined temperature;
• non-linearly vary the rate of fuel utilization (Uf (%)) as a function of the current when the fuel gas flow is above the minimum fuel gas flow and the current is in the first range;
• and
• maintain the rate of fuel utilization (Uf (%)) constant when the current is in the second range.