Patent ID: 8071232

Claim:
A method of controlling voltage conversion of a hybrid fuel cell system in which a fuel cell and an electricity storage device are connected via a voltage converter provided with a plurality of phases, the method comprising: measuring a value equivalent to power passing through the voltage converter; changing a number of phases of operation of the voltage converter in accordance with the measured equivalent value such that changing the number of phases of operation switches the converter between a single phase drive mode and a multiple phase drive mode; and for each of the phases in the voltage converter, handling an alternating current and having a different phase shift with respect to the other phases, wherein when the changing of the number of phases used by the voltage converter occurs, the changing of the number of phases is conducted in a synchronized manner, the operation is switched to the single phase drive mode during the multiple phase drive mode when the equivalent value becomes smaller than a first value, and the operation is switched to the multiple phase drive mode during the single phase drive mode when the equivalent value is larger than a second value that is larger than the first value, and the first and second values are both set less than a threshold value at which a total loss of the voltage converter for the single phase drive mode surpasses a total loss of the voltage converter for the multiple phase drive mode.