Electrified vehicle ground fault monitoring system

1. An electrified vehicle charger comprising:

a diode bridge configured to rectify an alternating current (AC) source;

contactors coupling the AC source with a traction battery; and

a controller configured to open the contactors responsive to a magnitude of a potential at an output of the diode bridge, corresponding to a zero crossing of a potential of the AC source, exceeding a threshold that is greater than a defined set point determined by minimum allowed impedance between a positive high voltage DC bus and ground.

2. The electrified vehicle charger of claim 1 further including a voltage sensor coupled across the output of the diode bridge and configured to output the magnitude.

3. The electrified vehicle charger of claim 1 , wherein the zero crossing includes a window of time prior to and after a point in time at which the potential of the AC source transitions between positive and negative.

4. The electrified vehicle charger of claim 3 , wherein the window of time is a percentage of a line period of the AC source.

5. The electrified vehicle charger of claim 4 , wherein the percentage of a line period is determined according to a minimum AC voltage source magnitude, a minimum emulated resistance, and a threshold fault resistance.

6. The electrified vehicle charger of claim 1 further including a current sensor coupled between the AC source and the diode bridge and configured to output a signal indicative of the magnitude.

7. The electrified vehicle charger of claim 1 , wherein the threshold is greater than zero and less than an instantaneous high voltage DC bus differential voltage.

8. The electrified vehicle charger of claim 1 , wherein the AC source is a single-phase AC source or a split-phase AC source configured as a TT grounding network.

9. A method of operating a vehicle charger comprising:

by a controller, disabling the charger responsive to a voltage across a diode of a rectifier for an alternating current (AC) source exceeding a threshold as a potential of the AC source changes sign, wherein the threshold is greater than a defined set point determined by minimum allowed impedance between a positive high voltage DC bus and ground.

10. The method of claim 9 , wherein disabling the charger includes disconnecting contactors between a traction battery and the AC source.

11. The method of claim 9 , wherein an anode of the diode is coupled with a phase terminal of the AC source or a neutral terminal of the AC source.

12. The method of claim 9 , wherein the AC source is a single-phase AC source or a split-phase AC source of a TT network.

13. An electrified vehicle charger comprising:

a diode bridge configured to rectify an alternating current (AC) source, and including a first diode with an anode coupled to a phase terminal of the AC source and a second diode with a cathode coupled to a neutral terminal of the AC source; and

a controller programmed to, responsive to the first diode conducting and the second diode not conducting at a zero crossing of the AC source, disable the charger.

14. The electrified vehicle charger of claim 13 , wherein the first diode conducting is defined by current greater than a threshold flowing through the first diode and the second diode not conducting is defined by current less than the threshold flowing through the second diode.

15. The electrified vehicle charger of claim 13 , wherein a forward voltage applied to the first diode is indicative of the first diode conducting, and a reverse voltage applied to the second diode is indicative of the second diode not conducting.

16. The electrified vehicle charger of claim 13 , wherein the AC source is a single-phase AC source or a split-phase AC source.

17. The electrified vehicle charger of claim 13 , wherein the AC source is configured as a TT grounding network.

18. The electrified vehicle charger of claim 13 , wherein disabling the charger includes disconnecting contactors between a traction battery and the AC source.