CONTROL DEVICE, FUEL CELL SYSTEM, CONTROL METHOD, AND METHOD FOR CONTROL OF FUEL CELL SYSTEM

PROBLEM TO BE SOLVED: To provide a device and method for control of the flow rate of a heat exchange medium, for stabilizing the temperature of a heat exchange medium such as water.SOLUTION: A control device includes: a control section for controlling the flow rate of the heat exchange medium which takes out heat by heat exchange with a heat source by repeating two operation controls of one at a first control rate for a first period and the other at a second control rate that is smaller than the first control rate for a second period; a ratio determination section for determining the ratio of the first period with respect to the sum of the first period and the second period based on the temperature difference between a measured temperature and a target temperature of the heat exchange medium; and a control rate determination section for determining, if the output difference between the previous output result and the current output result is outside a predetermined range, the first and second control rates based on the current output result.