Ground fault detecting system and electric vehicle with ground fault detecting system
When a malfunction of an ungrounded drive electric system including first and second ungrounded power supplies, an inverter, and a motor which is energized by the first and second ungrounded power supplies through the inverter, i.e., an erroneous opening of switches of a battery, is detected, switches of an insulation resistance detector are opened to insolate the insulation resistance detector from the ungrounded drive electric system.
1. A ground fault detecting system for detecting a ground fault in an ungrounded drive electric system including an ungrounded power supply, a drive circuit, and a motor which is energized by the ungrounded power supply through the drive circuit, comprising:
a ground fault detector for measuring a resistance value of an insulation resistor of the ungrounded power supply with respect to a ground;
the ground fault detector including switches connected between the ungrounded power supply and circuit components of the ground fault detector and between the ungrounded power supply and the ground; and
a circuit breaking controller for opening the switches to isolate the ground fault detector from the ungrounded drive electric system when a malfunction or a shutdown of the ungrounded drive electric system is detected.
2. A ground fault detecting system according to claim 1 , wherein the ungrounded power supply includes a first ungrounded power supply for generating a voltage and a second ungrounded power supply for generating a voltage lower than the voltage generated by the first ungrounded power supply; and
the circuit breaking controller opens the switches when a failure which disconnects only the second ungrounded power supply from the ungrounded drive electric system is detected.
3. An electric vehicle incorporating a ground fault detecting system, the ground fault detecting system detecting a ground fault in an ungrounded drive electric system including an ungrounded power supply, a drive circuit, and a motor which is energized by the ungrounded power supply through the drive circuit, the ground fault detecting system comprising:
a ground fault detector for measuring a resistance value of an insulation resistor of the ungrounded power supply with respect to a ground;
the ground fault detector including switches connected between the ungrounded power supply and circuit components of the ground fault detector and between the ungrounded power supply and the ground; and
a circuit breaking controller for opening the switches to isolate the ground fault detector from the ungrounded drive electric system when a malfunction or a shutdown of the ungrounded drive electric system is detected.
4. A ground fault detecting system according to claim 1 , wherein the switches include a first switch, a second switch, a third switch, a fourth switch, and a fifth switch;
the circuit components include a first resistor and a capacitor; and
the ground fault detector includes:
the first switch and the second switch which have respective ends connected to positive and negative terminals, respectively, of the ungrounded power supply;
the first resistor having an end connected to another end of the first switch;
the capacitor having an end connected to another end of the first resistor;
the third switch having an end connected to the other end of the first resistor;
the fourth switch having an end connected to the other end of the first resistor;
the fifth switch having an end connected to a common junction between another end of the capacitor and another end of the second switch;
a voltage sensor connected between another end of the fourth switch and the ground;
a second resistor connected between another end of the third switch and the ground; and
a third resistor connected between another end of the fifth switch and the ground.
5. A ground fault detecting system according to claim 4 , further comprising an opening and closing timing controller for controlling times at which the first switch, the second switch, the third switch, the fourth switch, and the fifth switch are opened and closed.
6. A ground fault detecting system according to claim 5 , further comprising an insulation resistance calculator to be controlled by the opening and closing timing controller for measuring, with the voltage sensor, a first charged voltage across the capacitor when the first and second switches are closed for a first given time to charge the capacitor from a state in which the first through fifth switches are open, then opening the first through third switches and closing the fourth and fifth switches to discharge the capacitor for a time, measuring, with the voltage sensor, a second charged voltage across the capacitor when the first, fourth, and fifth switches are opened and the second and third switches are closed for a second given time to charge the capacitor through the insulation resistor and the second resistor, opening the first through fifth switches, and determining the resistance value of the insulation resistor based on a ratio of the first and second charged voltages.
7. A ground fault detecting system according to claim 2 , wherein the first ungrounded power supply comprises a fuel cell and the second ungrounded power supply comprises an electric energy storage.