METHOD FOR DETECTING AN ISOLATION FAULT

The present disclosure relates to a method for detecting an isolation fault in an isolation resistance between a positive and negative high-voltage bus rail (5, 6) and a vehicle chassis on a high-voltage propulsion side (3) of a high-voltage system of an electric or hybrid-electric vehicle. The high-voltage system is split into a high-voltage battery side (1) and the high-voltage propulsion side (3) by means of first and second high-voltage contactors (7, 8) located in the positive and negative high-voltage bus rails (5, 6), respectively. The high-voltage propulsion side (3) comprises a first and second capacitors (9, 10) connected in series across the positive and negative high-voltage bus rails (5, 6), wherein a common junction (11) of the first and second capacitors (9, 10) is connected to the chassis. The method comprising: ensuring that first and second high-voltage contactors (7, 8) are set in an open state; operating an isolated DC/DC converter (13) for converting a supplied high-voltage (14) from a high-voltage battery (2) of the high-voltage battery side (1) to a low-voltage output (15) on the high-voltage propulsion side (3); supplying the low-voltage output (15) to the positive and negative high-voltage bus rails (5, 6) for simultaneous charging of the first and second capacitors (9, 10); registering a charging current, voltage level or energy level of the first and second capacitors (9, 10); and determining, based in the registered charging current, voltage level or energy level of the first and second capacitors (9, 10), whether an isolation fault between the positive and/or negative high-voltage bus rail (5, 6) and the vehicle chassis on the high-voltage propulsion side (3) of the high-voltage system is present. The present disclosure also relates to a corresponding high-voltage circuit of an electric or hybrid-electric vehicle.