Patent ID: 8644045

Claim:
A voltage conversion device having a DC-DC converter which comprises a reactor which can temporarily accumulate energy using a direct current from a direct current power supply, and a switching element, and which converts, using the energy accumulated in the reactor, direct current power from the direct current power supply to a direct current power of a different voltage value utilizing a switching operation of the switching element and outputs the converted power, a capacitor which is provided at an input side of the DC-DC converter and in parallel with the direct current power supply, and a cooling unit which cools the capacitor with a cooling medium, the voltage conversion device comprising: a cooling medium temperature detecting unit which detects a temperature of the cooling medium for cooling the capacitor; a switching frequency setting unit which sets a switching frequency of the switching element based on both the temperature of the cooling medium for cooling the capacitor and a temperature of the switching element; and a switching controller which controls the switching operation of the switching element by the set switching frequency, to control a voltage conversion ratio of the DC-DC converter, wherein: the switching frequency setting unit sets the switching frequency of the switching element to a first frequency or a second frequency which is lower than the first frequency, based on the temperature of the switching element, and when the temperature of the cooling medium for cooling the capacitor detected by the cooling medium temperature detecting unit is higher than a set temperature T 1 , the switching frequency setting unit sets the switching frequency of the switching element to the first frequency regardless of the temperature of the switching element.