Patent ID: 11921167
Assignee: YAZAKI CORPORATION
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 6:
7. An earth fault detection apparatus to be connected with a non-grounded battery and for calculating an insulation resistance of a system including the battery, the earth fault detection apparatus comprising:
a capacitor configured to be operated as a flying capacitor;
a switch group configured to switch between a first measurement path, a second measurement path, and a third measurement path, the first measurement path including the battery and the capacitor, the second measurement path including the battery, a negative-side insulation resistance that is an insulation resistance between a negative-side line of the battery and ground, and the capacitor, the third measurement path including the battery, a positive-side insulation resistance that is an insulation resistance between a positive-side line of the battery and the ground, and the capacitor; and
a control unit configured to calculate a reference value based on each charging voltage of the capacitor in each of the first to third measurement paths, and configured to calculate the insulation resistance with reference to a predetermined conversion map, wherein
the conversion map includes conversion maps corresponding to capacitances of the capacitor and including a standard conversion map,
the control unit is configured to use charging voltages of the capacitor in the first, second and third measurement paths in order to perform determination whether or not there is a possibility that the insulation resistance is decreased,
upon determining that there is a possibility that the insulation resistance is decreased, the control unit is configured to estimate the capacitance of the capacitor, and to calculate the insulation resistance by referring to the conversion map corresponding to the capacitance of the capacitor that has been estimated, and
upon determining that there is no possibility that the insulation resistance is decreased, the control unit is configured to calculate the insulation resistance by referring to the standard conversion map.