Magnetic flux sensor and method

• US 20030071609A1
• Filed: 09/20/2002
• Published: 04/17/2003
• Est. Priority Date: 12/13/1999
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Inventors: Blakely, John H.
• Granted Patent: US 6,774,618 B2
• Time in Patent Office: Days
• US Class Current: 324/127
• CPC Class Codes: G01R 15/183 using transformers with a magnetic core
• CPC Class Codes: H01F 2003/106 Magnetic circuits using combinations of different magnetic materials

Abstract

A device comprises a first magnetically conductive structure, a second magnetically conductive structure, and a circuit coupled the first and second magnetically conductive structures. The circuit senses information pertaining to a permeability of the first magnetically conductive structure relative to a permeability of the second magnetically conductive structure. The device may be used for various flux sensing and control applications, such as in current sensors.

Claims

1. A device comprising:

(A) a first magnetically conductive structure;

(B) a second magnetically conductive structure;

(C) a circuit coupled to the first and second magnetically conductive structures that senses information pertaining to a permeability of the first magnetically conductive structure relative to a permeability of the second magnetically conductive structure.

2. A device according to claim 1, wherein the circuit includes first, second and third windings, the first winding being wound around the first magnetically conductive structure and not the second magnetically conductive structure, the second winding being wound around the second magnetically conductive structure and not the first magnetically conductive structure, and the third winding being wound around both the first and second magnetically conductive structures.

3. A device according to claim 1, wherein the circuit includes a feedback control circuit that controls an amount of magnetic flux in the first and second magnetically conductive structures based on the information pertaining to the permeability of the first magnetically conductive relative to the permeability of the second magnetically conductive structure.

4. A device according to claim 3, further comprising a configurable polarity circuit, the configurable polarity circuit monitoring stability of the feedback control circuit and adjusting operation of the feedback control circuit upon detecting that a direction of a magnetic flux produced in the first and second magnetically conductive structures by the feedback control circuit should be reversed in order to avoid saturation of the first and second magnetically conductive structures.

5. A device according to claim 3, wherein the feedback control circuit includes a transfer function offset circuit that provides the circuit with first and second stable operating points, the first and second stable operating points being provided by an offset that is introduced in an error signal produced by the feedback control circuit, the error signal being produced as a function of the permeability of the first magnetically conductive structure relative to the permeability of the second magnetically conductive structure.

6. A device according to claim 5, wherein the circuit is a sensor that generates information pertaining to a parameter of interest, and wherein the circuit further comprises a compensation circuit that adjusts a signal representing the parameter of interest to compensate operation of the transfer function offset circuit.

7. A device according to claim 1, further comprising an excitation source, the excitation source providing an excitation signal that tends to cancel a low frequency component of a magnetic flux in the first and second magnetically conductive structures.

8. A device according to claim 1, wherein the device is a current sensor, and wherein the current sensor produces information pertaining to a current flowing in a winding that is wound around at least one of the first and second magnetically conductive structures based on the information pertaining to the permeability of the first magnetically conductive structure relative to the permeability of the second magnetically conductive structure.

9. A device according to claim 1, wherein the circuit further comprises

an excitation winding, the excitation winding being wound around at least one of the first and second magnetically conductive structures,

an excitation source, the excitation source being coupled to the excitation winding and applying an excitation signal to the excitation winding, and

a sense winding, the sense winding being wound around at least one of the first and second magnetically conductive structures, and the sense winding producing a sense signal in response to the excitation signal, and the sense signal having a characteristic that is indicative of the permeability of the first material relative to the second material.

10. A device according to claim 1, wherein a ratio of (1) an amount of the magnetic flux which flows through the first magnetically conductive structure to (2) an amount of the magnetic flux which flows through the second magnetically conductive structure varies as a function of a total amount of the magnetic flux flowing through the first and second magnetically conductive structure;

and

wherein the circuit senses the information pertaining to the permeability of the first magnetically conductive structure relative to the permeability of the second magnetically conductive structure by sensing information indicative of the ratio.

11. A method of sensing a parameter comprising acquiring information indicative of a permeability of a first material relative to a permeability of a second material, the permeability of the first material relative to the permeability of the second material being indicative of the parameter.

12. A method according to claim 11, wherein the first material forms a first magnetic path, wherein the second material forms a second magnetic path, and wherein the acquiring step is performed by a sensing circuit that comprises a first winding and a second winding, the first winding being wound around the first magnetic path and not the second magnetic path, and the second winding being wound around the first magnetic path and the second magnetic path.

13. A method according to claim 11, wherein the first material forms a first magnetic path, wherein the second material forms a second magnetic path, wherein the acquiring step is performed by a sensing circuit that comprises a first winding, a second winding, and a third winding, the first winding being wound around the first magnetic path and not the second magnetic path, the second winding being wound around the second magnetic path and not the first magnetic path, and the third winding being wound around the first magnetic path and the second magnetic path.

14. A method according to claim 13, wherein the parameter is magnetic flux flowing through the first and second materials, and wherein the method further comprises producing information pertaining to a current that is flowing in a primary winding, the primary winding being wound around the first and second magnetic paths.

15. A method according to claim 13, further comprising implementing a feedback control circuit, the feedback control circuit utilizing as feedback information produced by at least one of the first and second windings, and the feedback control circuit being operative to generate a control signal that tends to cause the first and second materials to avoid saturation.

16. A method according to claim 11, further comprising implementing a feedback control of an amount of magnetic flux in the first and second magnetically conductive structures based on the information pertaining to the permeability of the first magnetically conductive relative to the permeability of the second magnetically conductive structure.

17. A method according to claim 16, further comprising detecting that a direction of a magnetic flux produced in the first and second magnetically conductive structures by the feedback control should be reversed in order to avoid saturation of the first and second magnetically conductive structures, and in response reversing the direction of the magnetic flux produced by the feedback control.

18. A method according to claim 16, wherein the feedback control has first and second stable operating points, the first and second stable operating points being provided by an offset that is introduced in an error signal produced by the feedback control, and the error signal being produced as a function of the permeability of the first magnetically conductive structure relative to the permeability of the second magnetically conductive structure.

19. A method according to claim 18, further comprising generating a signal indicative of an additional parameter of interest based on the sensed parameter, and adjusting the a signal that represents the parameter of interest to compensate for the offset.

20. A method according to claim 11, wherein a reluctance of the first magnetic path varies with respect to a reluctance of the second magnetic path by an amount that is dependent on a total amount of magnetic flux carried by the first and second magnetic paths.

21. A system comprising:

a magnetically conductive structure;

a feedback control circuit that controls an amount of magnetic flux in the magnetically conductive structure, the feedback control circuit comprising a sensing circuit that acquires information indicative of the relative permeability of first and second magnetic flux paths that form at least a part of the magnetically conductive structure, the sensing circuit producing a signal that is usable by the feedback control circuit to control the amount of flux in the magnetically conductive structure.

22. A system according to claim 21, wherein the sensing circuit comprises a first winding and a second winding, the first winding being wound around the first magnetic path and not the second magnetic path, and the second winding being wound around the first magnetic path and the second magnetic path.

23. A system according to claim 21, wherein the sensing circuit comprises a first winding, a second winding, and a third winding, the first winding being wound around the first-magnetic path and not the second magnetic path, the second winding being wound around the second magnetic path and not the first magnetic path, and the third winding being wound around the first magnetic path and the second magnetic path.

24. A system according to claim 21, wherein a reluctance of the first magnetic path varies with respect to a reluctance of the second magnetic path by an amount that is dependent on a total amount of magnetic flux carried by the first and second magnetic paths.

25. A system according to claim 21, wherein the feedback control circuit further comprises a configurable polarity circuit, the configurable polarity circuit monitoring stability of the feedback control circuit and adjusting operation of the feedback control circuit upon detecting that a direction of a magnetic flux produced in the magnetically conductive structure by the feedback control circuit must be reversed in order to avoid saturation of the magnetically conductive structure.

26. A system according to claim 23, wherein the feedback control circuit includes a transfer function offset circuit that provides the circuit with first and second stable operating points, the first and second stable operating points being provided by an offset that is introduced in an error signal produced by the feedback control circuit, the error signal being produced as a function of the permeability of the first magnetic path relative to the permeability of the second magnetic path.

27. A device according to claim 26, wherein the system is a sensor that generates information pertaining to a parameter of interest, and wherein the circuit further comprises a circuit that adjusts a signal representing the parameter of interest to compensate operation of the transfer function offset circuit.

28. A system comprising:

(A) a magnetically first magnetically conductive structure formed of a first material;

(B) a second magnetically conductive structure formed of a second material, the second material having a different permeability than the first material;

(C) a first winding that is wound around the first magnetically conductive structure and not the second magnetically conductive structure; and

(D) a second winding that is wound around the second magnetically conductive structure and not the first magnetically conductive structure;

(E) a third winding that is wound around both the first magnetically conductive structure and the second magnetically conductive structure; and

(F) processing circuitry coupled to the first, second and third windings to receive information pertaining to a permeability of the first material relative to a permeability of the second material, and the processing circuitry generating information pertaining to a parameter of interest based upon the relative permeability of the first and second materials.

29. A system according to claim 28, wherein the processing circuitry includes a feedback control circuit that controls an amount of magnetic flux in the first and second magnetically conductive structures.

30. A system according to claim 28, wherein the sensor is a current sensor, wherein the first structure is a first transformer core and the second structure is a second transformer core, wherein the sensor further comprises a primary winding that is wound around the first and second transformer cores and that receives a primary current that is measured by the sensor.

31. A method of sensing a parameter, comprising:

(A) acquiring information pertaining to a permeability of a first material relative to a permeability of a second material, the first and second materials forming first and second magnetically conductive paths in a magnetically conductive structure;

(B) generating an excitation signal based on the information pertaining to the permeability of the first material relative to a permeability of the second material, the excitation signal being operative to adjust the total amount of magnetic flux in the magnetically conductive structure.

32. A method according to claim 31, wherein the acquiring step is performed using a first winding that is wound around both the first magnetically conductive path and the second magnetically conductive path and a second winding that is wound around only one of the first magnetically conductive path and the second magnetically conductive path.

33. A method according to claim 31, wherein the acquiring step is performed using a first winding that is wound around both the first magnetically conductive path and the second magnetically conductive path, a second winding that is wound around the first magnetically conductive path and not the second magnetically conductive path, and a third winding that is wound around the second magnetically conductive path and not the first magnetically conductive path.

34. A system comprising:

a magnetically conductive structure;

a feedback control circuit including

a sense winding, the sense winding being wound around the magnetically conductive structure;

an excitation winding, the excitation winding being wound around the magnetically conductive structure;

wherein the feedback control circuit acquires feedback information pertaining to a voltage across the sense winding, and wherein the feedback control circuit provides an excitation signal to the excitation winding to control the amount of flux in the magnetically conductive structure.

35. A system according to claim 34, wherein the feedback control circuit comprises an integrator circuit, the integrator circuit being coupled between the sense winding and the excitation winding, the integrator circuit receiving the information pertaining to the voltage across the sense winding as an error signal.

36. A system according to claim 35, wherein the error signal is compared with a flux setpoint signal, and the feedback control circuit is operative to control flux in the magnetically conductive structure in accordance with the flux setpoint signal.

37. A system according to claim 34, wherein the feedback control circuit implements linear feedback control.

38. A system according to claim 34, further comprising a primary winding, the primary winding being wound around the magnetically conductive structure, wherein the excitation winding is coupled to a burden resistor, wherein the excitation signal provided by the feedback control circuit results in a current that flows through the excitation winding, wherein at least a portion of the current that flows through the excitation winding also flows through the burden resistor, and wherein the flow of the current through the burden resistor produces a voltage that is indicative of a current through the primary winding.