Method and device for obtaining internal side, external side insulation resistances of relay, and battery management system

1. A method for obtaining internal side and external side insulation resistances of a relay, wherein the method is applied to a circuit comprising a battery pack, a main relay and a pre-charge circuit, the main relay comprises a main positive relay and a main negative relay, the pre-charge circuit comprises a pre-charge relay and a pre-charge resistor and is connected in parallel to both sides of the main positive relay, an insulation resistance obtaining circuit is connected between the battery pack and the main positive relay, wherein the insulation resistance obtaining circuit comprises two sampling points, wherein the method comprises:

controlling the insulation resistance obtaining circuit to output a low-frequency AC signal;

when both the main relay and the pre-charge relay are switched off, obtaining a first phase shift of the low-frequency AC signal between the two sampling points according to first collected electrical signals;

obtaining an internal side insulation resistance of the main relay according to the first collected electrical signals and the first phase shift;

controlling the pre-charge relay to be switched on;

when the main relay is switched off and the pre-charge relay is switched on, obtaining a second phase shift of the low-frequency AC signal between the two sampling points according to second collected electrical signals; and

obtaining an external side insulation resistance of the main relay according to the second collected electrical signals and the second phase shift.

2. The method according to claim 1 , wherein the controlling the pre-charge relay to be switched on comprises:

detecting whether the internal side insulation resistance of the main relay is greater than a first preset alarm threshold;

when the internal side insulation resistance of the main relay is greater than the first preset alarm threshold, controlling the pre-charge relay to be switched on.

3. The method according to claim 1 , wherein the low-frequency AC signal is a sinusoidal signal.

4. The method according to claim 2 , wherein the method further comprises:

detecting whether the external side insulation resistance of the main relay is greater than a second preset alarm threshold;

when the external side insulation resistance of the main relay is greater than the second preset alarm threshold, ending the detecting.

5. The method according to claim 4 , wherein the ending the detecting comprises:

controlling the main negative relay to be switched on, so as to pre-charge a load;

when the pre-charging of the load ends, controlling the pre-charge relay to be switched off; and

controlling the main positive relay to be switched on.

6. A device for obtaining internal side and external side insulation resistances of a relay, comprising an insulation resistance obtaining circuit and a processor,

wherein the insulation resistance obtaining circuit is configured to output an AC signal and collecting an electrical signal, wherein the insulation resistance obtaining circuit comprises two sampling points;

wherein the processor is configured to:

control the insulation resistance obtaining circuit to output the AC signal;

when both the main relay and a pre-charge relay are switched off, obtain a first phase shift of the low-frequency AC signal between the two sampling points according to first collected electrical signals;

obtain an internal side insulation resistance of the main relay according to the first collected electrical signals and the first phase shift;

control the pre-charge relay to be switched on;

when the main relay is switched off and the pre-charge relay is switched on, obtain a second phase shift of the low-frequency AC signal between the two sampling points according to second collected electrical signals; and

obtain an external side insulation resistance of the main relay according to the second collected electrical signals and the second phase shift.

7. The device according to claim 6 , wherein processor is configured to:

detect whether the internal side insulation resistance of the main relay is greater than a first preset alarm threshold; and

control the pre-charge relay to be switched on when the internal side insulation resistance of the main relay is greater than the first preset alarm threshold.

8. The device according to claim 6 , wherein processor is configured to:

control the insulation resistance obtaining circuit to output a low-frequency AC signal, wherein the low-frequency AC signal is a sinusoidal signal.

9. The device according to claim 7 , wherein processor is further configured to:

detect whether the external side insulation resistance of the main relay is greater than a second preset alarm threshold; and

when the external side insulation resistance of the main relay is greater than the second preset alarm threshold, end detecting.

10. The device according to claim 9 , wherein processor is configured to:

control the main negative relay to be switched on, so as to pre-charge a load;

when the pre-charging of the load ends, control the pre-charge relay to be switched off; and

control the main positive relay to be switched on.

11. A battery management system (BMS) comprising the device for obtaining the internal side and external side insulation resistances of a relay according to claim 6 .