Differential current detection

• US 20050259371A1
• Filed: 05/21/2004
• Published: 11/24/2005
• Est. Priority Date: 05/21/2004
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (General Motors Company)
• Inventors: Henze, Christopher P., Tirumala, Rohit K.
• Granted Patent: US 7,224,559 B2
• Time in Patent Office: Days
• US Class Current: 361/44
• CPC Class Codes: B60L 3/0023 Detecting, eliminating, remedying or compensating for drive train abnormalities, e.g. failures within the drive train
• CPC Class Codes: B60L 3/0069 relating to the isolation, e.g. ground fault or leak current
• CPC Class Codes: H02H 3/332 with means responsive to dc component in the fault current

Abstract

A detection circuit detects a difference between a source current and a return current. The detection circuit includes a constantly biased magnetic core through which conductors of the source and return currents extend, and a sense winding around the core. The sense winding carries an AC signal. A sensing circuit connected with the sense winding senses a change in small signal impedance of the sense winding relative to the core. This detection circuit can be used to protect people and equipment against accidental contact with high-voltage DC systems.

Claims

1. A detection circuit that detects a difference between a source current and a return current, the detection circuit comprising:

a constantly biased magnetic core through which conductors of the source and return currents extend;

a sense winding around said core, said sense winding carrying an AC signal; and

a sensing circuit connected with said sense winding that senses a change in small signal impedance of said sense winding relative to said core.

2. The detection circuit of claim 1 further comprising a bias winding around said core, said bias winding biased by a DC signal.

3. The detection circuit of claim 2 wherein said core is biased near saturation.

4. The detection circuit of claim 1 wherein said sensing circuit comprises a capacitor that receives said AC signal.

5. The detection circuit of claim 1 wherein said sensing circuit comprises a capacitor in series with said sense winding.

6. The detection circuit of claim 1 wherein said core comprises a first core, said sense winding comprises a first sense winding, and said sensing circuit comprises:

a second constantly biased magnetic core through which conductors of the source and return currents extend, said second core opposedly biased relative to said first core;

a second sense winding around said second core, said second sense winding carrying said AC signal; and

a pair of capacitors that provide a differential voltage in response to said change in small signal impedance.

7. The detection circuit of claim 6 further comprising a pair of opposedly wound bias windings around said cores, each bias winding biased by a DC signal.

8. The detection circuit of claim 6 further comprising a controller that eliminates an initial difference voltage across said capacitors.

9. A detection circuit that detects a difference between a source current and a return current, the detection circuit comprising:

a pair of magnetic cores through which conductors of the source and return currents extend;

a bias winding and a sense winding around each said core, said bias windings carrying opposed DC signals, said sense windings carrying an AC signal; and

a sensing circuit driven by the AC signal that senses a shift in at least one operating point set by at least one said DC signal relative to at least one of said cores.

10. The detection circuit of claim 9 wherein at least one of said cores is biased near saturation.

11. The detection circuit of claim 9 wherein said sensing circuit comprises at least one capacitor that receives said AC signal.

12. The detection circuit of claim 11 wherein said capacitor is in series with one of the sense windings.

13. The detection circuit of claim 9 wherein said sensing circuit comprises a pair of capacitors that generate a differential voltage in response to said shift in at least one operating point.

14. The detection circuit of claim 13 further comprising a controller that eliminates an initial difference voltage across said capacitors.

15. A detection circuit that detects a difference between a source current and a return current, the detection circuit comprising:

a magnetic core through which conductors of the source and return currents extend;

a bias winding and a sense winding around said core, said bias winding carrying a DC signal, said sense winding providing a small signal impedance to said core; and

a sensing circuit that senses a change in the small signal impedance.

16. The detection circuit of claim 15 wherein said DC signal biases said core near saturation.

17. The detection circuit of claim 15 wherein said sensing circuit comprises a capacitor that receives said AC signal.

18. The detection circuit of claim 15 wherein said sensing circuit comprises a capacitor in series with the sense winding.

19. The detection circuit of claim 15 wherein said core comprises a first core, said bias winding comprises a first bias winding, said sense winding comprises a first sense winding, and said sensing circuit comprises:

a second magnetic core through which conductors of the source and return currents extend;

a second bias winding and a second sense winding around said second core, said second bias winding biased opposedly to said first bias winding, said second sense winding carrying said AC signal; and

a pair of capacitors that provide a differential voltage in response to said change in said small signal impedance.

20. The detection circuit of claim 19 further comprising a controller that eliminates an initial difference voltage across the capacitors.

21. A method of detecting a difference between a source current and a return current, comprising:

conducting the source and return currents through a pair of opposedly biased magnetic cores;

generating a small signal impedance in a sense winding around one of the cores; and

sensing a change in the small signal impedance.

22. The method of claim 21 further comprising using DC current to bias the cores in opposed directions.

23. The method of claim 21 further comprising conducting DC current through bias windings around the cores in opposed directions.

24. The method of claim 21 further comprising selecting an operating point for one of the cores based on a B-H curve for the one of the cores.

25. The method of claim 21 further comprising sensing a voltage across a capacitor in series with the sense winding;

and

using the voltage to detect said change in the small signal impedance.

26. A vehicle comprising a detection circuit that detects a difference between a source current and a return current in an electrical circuit of the vehicle, said detection circuit comprising:

a magnetic core through which conductors of the source and return currents extend;

a bias winding and a sense winding around said core, said bias winding biased by a DC signal, said sense winding carrying an AC signal; and

a sensing circuit connected with said sense winding that senses a shift in an operating point set by said DC signal relative to said core.

27. The vehicle of claim 26 wherein said core is biased near saturation.

28. The vehicle of claim 26 wherein said sensing circuit comprises a capacitor that receives said AC signal.

29. The vehicle of claim 26 wherein said sensing circuit comprises a capacitor in series with said sense winding.

30. The vehicle of claim 26 wherein said core comprises a first core, said bias winding comprises a first bias winding, said sense winding comprises a first sense winding, and said sensing circuit comprises:

a second magnetic core through which conductors of the source and return currents extend;

a second bias winding and a second sense winding around said second core, said second bias winding biased opposedly to said first bias winding, said second sense winding carrying said AC signal; and

a pair of capacitors that provide a differential voltage in response to said shift in operating point.

31. The vehicle of claim 30 wherein said detection circuit further comprises a controller that eliminates an initial difference voltage across said capacitors.