Ground fault detection apparatus

A ground fault detection apparatus connected to a high-voltage battery and configured to detect lowering of insulation resistance of a system provided with the high-voltage battery, the apparatus comprising:

• a detection capacitor which operates as a flying capacitor;
• a control unit configured to measure fully charged voltage of the detection capacitor;
• a first switch and a first resistor configured to connect a positive electrode side of the high-voltage battery to a positive-electrode-side end of the detection capacitor in series;
• a second switch and a second resistor configured to connect a negative electrode side of the high-voltage battery to a negative-electrode-side end of the detection capacitor in series;
• a third switch configured to connect the positive-electrode-side end of the detection capacitor to a ground;
• a fourth switch configured to connect the negative-electrode-side end of the detection capacitor to the ground;
• a positive-electrode-side termination resistor configured to connect the positive electrode side of the high-voltage battery to the ground;
• and
• a negative-electrode-side termination resistor configured to connect the negative electrode side of the high-voltage battery to the ground,
• wherein the control unit is configured to:
• compare a first charge voltage (Vp) of the detection capacitor, which is measured with the first switch and the fourth switch turned on, with a second charge voltage (Vn) of the detection capacitor, which is measured with the second switch and the third switch turned on;
• and,
• if the first charge voltage (Vp) is smaller and when degree of the smallness of the first charge voltage (Vp) is greater than a predetermined reference, then determine that the positive-electrode-side insulation resistance is lowered, and if the second charge voltage (Vn) is smaller and when degree of the smallness of the second charge voltage (Vn) is greater than a predetermined reference, determine that the negative-electrode-side insulation resistance is lowered.