Patent ID: 8264234

Claim:
An electric vehicle incorporating a ground fault detecting system, which includes a load, a first ungrounded power supply having a voltage for supplying electric power to the load, a converter having input and output terminals connected between the load and the first ungrounded power supply, and a second ungrounded power supply having a voltage lower than the voltage of the first ungrounded power supply, and which is connected to other input and output terminals of the converter, the ground fault detecting system comprising: a first insulation resistance detector for detecting a first insulation resistance of the first ungrounded power supply with respect to a grounded region; a second insulation resistance detector for detecting a second insulation resistance of the second ungrounded power supply with respect to a grounded region; and a ground fault judging unit for comparing the first insulation resistance or the second insulation resistance with an abnormal detection threshold value, and judging that a ground fault has occurred if either one of the first insulation resistance and the second insulation resistance is smaller than the abnormal detection threshold value; wherein the first insulation resistance detector and the second insulation resistance detector comprise identical circuits, respectively; wherein the first insulation resistance detector charges a first capacitor to a charged voltage (V 01 ) toward the voltage of the first ungrounded power supply for a first given time, discharges the first capacitor, thereafter charges the first capacitor through the first insulation resistance to a charged voltage (V 11 ) toward the voltage of the first ungrounded power supply for a second given time, and calculates the first insulation resistance based on a ratio of the charged voltages (V 01 ), (V 11 ); and wherein the second insulation resistance detector charges a second capacitor to a charged voltage (V 02 ) toward the voltage of the second ungrounded power supply for a third given time, discharges the second capacitor, thereafter charges the second capacitor through the second insulation resistance to a charged voltage (V 12 ) toward the voltage of the second ungrounded power supply for a fourth given time, and calculates the second insulation resistance based on a ratio of the charged voltages (V 02 ), (V 12 ).