| CPC G01R 31/14 (2013.01) | 4 Claims |
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1. An insulation monitor for a high-voltage onboard electrical system of a motor vehicle, wherein the onboard electrical system comprises a high-voltage (HV) battery and is galvanically isolated from a vehicle earth, wherein there is a respective insulation resistance between a positive potential of the HV battery and the vehicle earth and between a negative potential of the HV battery and the vehicle earth as a result of parasitic effects, and wherein a respective Y-capacitor arranged between the positive potential and the vehicle earth and between the negative potential and the vehicle earth, the insulation monitor comprising:
a current source or a voltage source configured to recharge the Y-capacitors, wherein the current source is connected between the vehicle earth and one of the positive and negative potentials;
a voltmeter configured to measure at least one of the positive and negative potentials,
wherein the current or voltage source is configured to balance the positive and negative potentials,
wherein the insulation monitor is configured to
apply a negative current using the current source when the positive potential measured by the voltmeter exceeds a predefined upper value and to impress a positive current by using the current source when the positive potential measured by the voltmeter falls below a predefined lower value, wherein the current is limited to a maximum permissible contact current in case of an insulation fault, and a magnitude of the insulation resistances is inferable using the voltage measured by the voltmeter and using the recharging current that has been fed in,
after a voltage measurement, determine a distribution of the positive and negative potentials using the voltmeter to start the onboard electrical system,
first produce a distribution of the positive or negative potential that is balanced with respect to the vehicle earth by applying a current to determine a constant current applied by the current source and at which the balanced potential distribution is maintained for a subsequent calculation of the insulation resistances, and
to effect, based on the balanced distribution of the positive or negative potentials, a smaller recharging of the positive and negative potentials by a smaller positive or negative value around the balanced distribution by feeding in a further additive current from the current source.
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