Field
The present invention relates to a fuel cell system.
Related Art
Various techniques of warming up a fuel cell to a temperature suitable for power generation have been proposed. For example, a fuel cell system described in JP 2009-32605A causes an operating point of a fuel cell to be deviated from an I-V (current-voltage) characteristic curve in a high-efficiency power generation state of the fuel cell and thereby provides a low voltage and high current state. This changes over the power generation state of the fuel cell to a low-efficiency power generation state to warm up the fuel cell.
When the need for warm-up is eliminated, the power generation state of the fuel cell is changed over from the low-efficiency power generation state of low voltage and high current to the ordinary power generation state of high voltage and low current. In the process of changing over the power generation state, an abrupt increase of the voltage in a short time period may cause an excessive current to flow in a DC-DC converter. A gentle increase of the voltage is accordingly preferable in the process of changing over the power generation state. A gentle increase of the voltage is, however, likely to cause the current value to decrease to a target value even when the voltage has not yet increased to a target value and thereby cause a temporary decrease in the output of the fuel cell. Such a decrease of the output may not be negligible in some use condition of the fuel cell system.