Active filter for reduction of common mode current

• US 20010045863A1
• Filed: 03/23/2001
• Published: 11/29/2001
• Est. Priority Date: 03/28/2000
• Status: Active Grant

• Current Assignee: Infineon Technologies Americas Corp. (Infineon Technologies AG)
• Original Assignee: International Rectifier Corporation (Infineon Technologies AG)
• Inventors: Pelly, Brian R.
• Granted Patent: US 6,636,107 B2
• Time in Patent Office: Days
• US Class Current: 327/552
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 1/123 Suppression of common mode voltage or current
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: H02P 2201/07 DC-DC step-up or step-down converter inserted between the power supply and the inverter supplying the motor, e.g. to control voltage source fluctuations, to vary the motor speed
• CPC Class Codes: H02P 29/50 Reduction of harmonics

Abstract

An active filter reduces the common mode current in the ground wire of a PWM controlled motor drive circuit. The active filter is, in part, integrated into an integrated circuit chip and contains a buffer amplifier which drives two junction type or MOSFET transistors linearly to divert common mode current from a ground wire and through the transistors. The transistors are connected between positive and negative d-c busses which supply d-c power to a PWM inventor which drives an a-c motor, producing the common mode ground current in its grounded frame. A current transformer monitors the common mode current and its output is coupled to the input of the buffer amplifier to control the transistors. An internal power supply for the amplifiers is formed at the nodes between two current sources and two zener diodes which are connected between the d-c bus conductors. Headroom control circuits are disclosed to insure sufficient headroom voltage for each of the transistors under all input a-c voltage conditions.

Claims

1. An active filter for reducing the common mode current in a pulse width modulated motor drive circuit;

said motor drive circuit comprising an a-c source, a rectifier connected to said a-c source and producing a rectified output voltage connected to a positive d-c bus and a negative d-c bus, a PWM inverter having input terminals coupled to said positive d-c bus and negative d-c bus and having a controlled a-c output, a motor driven by said a-c output of said PWM inverter, a ground wire extending from said motor, and a current sensor for measuring the common mode current in said drive circuit in said ground wire, said current sensor producing an output current related to said common mode current;

said active filter comprising a first and second transistor, each having first and second main electrodes and a control electrode, and at least one buffer amplifier;

said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being coupled to said positive d-c bus and said negative d-c respectively;

said at least one buffer amplifier having an input coupled to said output of said current sensor and an output connected to at least one of said control electrodes; and

a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire.

2. The device of

claim 1

, wherein said current sensor is a differential current transformer having first and second windings connected in series with said positive and negative d-c busses respectively and an output winding for producing said output current related to said common mode current.

3. The device of

claim 1

, wherein said current sensor is a current transformer having a primary winding connected in series with said ground wire and a secondary winding for producing said output current related to said common mode current.

4. The device of

claim 2

, wherein said current transformer has a toroidal core.

5. The device of

claim 3

, wherein said current transformer has a toroidal core and wherein said primary winding is a single turn on said toroidal core.

6. The device of

claim 1

, wherein said first and second transistors are complementary NPN and PNP bipolar transistors and their said first electrodes are emitter electrodes.

7. The device of

claim 1

, wherein said first and second transistors are complementary N and P channel power MOSFETs and wherein said first electrodes are source electrodes.

8. The device of

claim 1

, wherein said current sensor is a differential current transformer having first and second windings connected in respective ones of the lines of said a-c source connected to said rectifier and an output winding for producing said output current related to said common mode current.

9. The device of

claim 1

which further includes a headroom voltage control circuit coupled to said first and second transistors for maintaining sufficient voltage between the first and second electrodes of each transistor to permit its linear amplification operation over substantially the full rectified cycle of said a-c source.

10. The device of

claim 9

, wherein said headroom voltage control circuit includes first and second resistors which are respectively connected in parallel with said first and second transistors.

11. The device of

claim 9

, wherein said headroom voltage control circuit comprises respective active clamp circuits connected to said first and second transistors respectively for preventing the reduction of headroom voltage for each of said transistors below a given value.

12. The device of

claim 9

, wherein said headroom control circuit comprises a first circuit for generating a midpoint potential which is the midpoint of the d-c potential between said positive and negative d-c busses and a second amplifier having an input connected to the difference between said midpoint d-c voltage and the voltage at the node of said first and second transistors and an output connected to the input of said first mentioned amplifier for actively regulating the average voltage at said node to said midpoint voltage.

13. The device of

claim 1

, which further includes a reduced voltage positive filter bus coupled to said d-c bus;

said second electrodes of said first and second transistors connected to said reduced voltage positive filter d-c bus and said negative d-c bus respectively.

14. The device of

claim 13

which further includes a series connected resistor and zener diode connected between said positive and negative d-c busses;

said positive d-c filter bus connected to the node between said resistor and said zener diode.

15. The device of

claim 13

which further includes a first and second series connected capacitor connected across said positive and negative d-c busses;

and said d-c filter bus connected to the node between said first and second capacitors.

16. The device of

claim 15

, wherein said rectifier comprises a voltage doubler circuit which includes two series connected diodes connected across said positive and negative d-c Busses and in parallel with said first and second capacitors;

and said a-c source connected to the nodes between said diodes and said capacitors.

17. The device of

claim 1

, wherein said buffer amplifier has at least first and second power supply inputs, and a power supply circuit for applying bias voltages to said buffer amplifier inputs;

said power supply circuit comprising first and second current sources and first and second zener diodes;

the anode of said first zener diode connected to the cathode of said second zener diode at a first node;

said cathode of said first zener diode connected to one terminal of said first current source;

said anode of said second zener diode connected to one terminal of said second current source;

the second terminal of said first and second current sources being coupled to said positive and negative d-c busses respectively;

the node between said first current source and said first zener diode connected to said first power supply input; and

the node between said second current source and said second zener diode connected to said second power supply input.

18. The device of

claim 3

, wherein said common node between said d c isolating capacitor and said ground wire is disposed between said primary winding of said current transformer and said motor.

19. The device of

claim 3

, wherein said primary winding of said current transformer is disposed between said common node between said d-c isolating filter capacitor and said ground wire and said motor.

20. The device of

claim 1

, wherein said first and second transistor and said buffer amplifier are formed in a common integrated circuit chip.

21. The device of

claim 9

, wherein said first and second transistors and said buffer amplifier and said headroom control circuits are formed in a common integrated circuit.

22. The device of

claim 14

, wherein said first and second transistors and said buffer amplifier and said series connected resistor and a zener diode are formed in a common integrated circuit.

23. The device of

claim 17

, wherein said first and second transistors and said buffer amplifier and said power supply circuit are formed in a common integrated circuit.

24. The device of

claim 1

, wherein said current sensor is connected in said ground wire.

25. The device of

claim 1

, wherein said current sensor comprises a current transformer having at least one primary winding and a secondary winding;

said secondary winding being connected to said input of said buffer amplifier;

said at least one primary winding connected between said positive d-c bus and said second electrode of said first transistor, thereby to define a feedback architecture.

26. The device of

claim 1

, wherein said current sensor comprises a current transformer having at least one primary winding and a secondary winding;

said secondary winding being connected to said input of said buffer amplifier;

said at least one primary winding connected between one of said input terminals of said inverter and said second electrode of said first transistor, thereby to define a feed forward architecture.

43. The device of

claim 2

, wherein said current transformer has a toroidal core and wherein said first and second windings are each a single turn.

44. The device of

claim 3

, wherein said common node between said d c isolating capacitor and said ground wire is disposed between said primary winding of said current transformer and said motor.

45. The device of

claim 3

, wherein said primary winding of said current transformer is disposed between said common node between said d-c isolating filter capacitor and said ground wire and said motor.

46. The device of

claim 1

, which further includes a reduced filter voltage bus coupled to one of said positive or negative voltage bus;

said second electrodes of said first and second transistors connected to said reduced filter voltage bus.

47. The device of

claim 46

, wherein said reduced filter voltage bus is connected to said negative voltage bus.

48. The device of

claim 26

, wherein said first and second transistors are MOSFETs;

and which further includes a quiescent bias current circuit coupled to one of said control electrode of one of said first and second transistors, and a regulation circuit connected to said bias current circuit for regulating the quiescent bias current to maintain the quiescent gate voltage of said MOSFET transistors at their threshold voltage, thereby to eliminate cross-over distortion of the output current of said MOSFETs.

27. An active filter for reducing the common mode current in a pulse width modulated motor drive circuit;

said motor drive circuit comprising an a-c source, a rectifier connected to said a-c source and producing a rectified output voltage connected to a positive d-c bus and a negative d-c bus, a PWM inverter having input terminals coupled to said positive d-c bus and negative d-c bus and having a controlled a-c output, a motor driven by said a-c output of said PWM inverter, a ground wire extending from said motor, and a current sensor for measuring the common mode current in said drive circuit, said current sensor producing an output current related to said common mode current;

said active filter comprising a first and second transistor, each having first and second main electrodes and a control electrode, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being directly connected to said positive d-c bus and said negative d-c bus respectively; and

a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire;

said current sensor comprising a differential current transformer having first and second windings connected in series with said positive and negative d-c busses respectively and an output winding for producing said output current related to said common node current;

said output winding is being coupled to said control electrodes;

said circuit having the architecture of a feed forward system with unity amplification by said current transformer and said transistors.

28. The device of

claim 27

, wherein said current transformer has a toroidal core

29. The device of

claim 27

which further includes a headroom voltage control circuit coupled to said first and second transistors for maintaining sufficient voltage between the first and second electrodes of each transistor to permit its linear amplification operation over substantially the full rectified cycle of said a-c source.

30. The device of

claim 27

, wherein further includes a reduced voltage positive filter bus coupled to said d-c bus;

said second electrodes of said first and second transistors connected to said reduced voltage positive filter d-c bus and said negative d-c bus respectively.

31. The device of

claim 27

, wherein said first and second transistors are formed in a common integrated circuit chip.

32. The device of

claim 27

, wherein said first and second transistors and said headroom control circuits are formed in a common integrated circuit.

33. An active filter for reducing the common mode current in a pulse width modulated motor drive circuit;

said motor drive circuit comprising an a-c source, a rectifier connected to said a-c source and producing a rectified output voltage connected to a positive d-c bus and a negative d-c bus, a PWM inverter having input terminals coupled to said positive d-c bus and negative d-c bus and having a controlled a-c output, a motor driven by said a-c output of said PWM inverter, a ground wire extending from said motor, and a current sensor for measuring the common mode current in said drive circuit, said current sensor producing an output current related to said common mode current;

said active filter comprising a first and second transistor each having first and second main electrodes and a control electrode, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being directly connected to said positive d-c bus and said negative d-c respectively;

said current sensor output coupled to at least one of said control electrodes; and

a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire; and

a headroom voltage control circuit coupled to said first and second transistors for maintaining sufficient voltage between the first and second electrodes of said transistors to permit their linear amplification operation over substantially the full rectified cycle of said a-c source

34. The device of

claim 33

, wherein said headroom voltage control circuit includes first and second resistors which are respectively connected in parallel with said first and second transistors.

35. The device of

claim 33

, wherein said headroom voltage control circuit comprises respective active clamp circuits connected to said first and second transistors respectively for preventing the reduction of headroom voltage for each of said transistors below a given value.

36. The device of

claim 33

, which further includes a reduced voltage positive filter bus coupled to said d-c bus;

said second electrodes of said first and second transistors connected to said reduced voltage positive filter d-c bus and said negative d-c bus respectively.

37. The device of

claim 36

which further includes a series connected resistor and zener diode connected between said positive and negative d-c busses;

said positive d-c filter bus connected to the node between said resistor and said zener diode.

38. The device of

claim 36

which further includes a first and second series connected capacitor connected across said positive and negative d-c busses;

and said d-c filter bus connected to the node between said first and second capacitors.

39. An active filter for reducing the common mode current in a pulse width modulated motor drive circuit;

said motor drive circuit comprising an a-c source, a rectifier connected to said a-c source and producing a rectified output voltage connected to a positive d-c bus and a negative d-c bus, a PWM inverter having input terminals coupled to said positive d-c bus and negative d-c bus and having a controlled a-c output, a motor driven by said a-c output of said PWM inverter, a ground wire extending from said motor, and a current sensor for measuring the common mode current in said drive circuit, said current sensor producing an output current related to said common mode current;

said active filter comprising a first and second transistor, each having first and second main electrodes and a control electrode, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being coupled to said positive d-c bus and said negative d-c respectively;

said current sensor output being coupled to at least one of said control electrodes;

a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire; and

a reduced voltage positive filter bus coupled to said d-c bus;

said second electrode of said first transistor being connected to said reduced voltage positive filter bus.

40. The device of

claim 39

which further includes a series connected resistor and zener diode connected between said positive and negative d-c busses;

said positive d-c filter bus connected to the node between said resistor and said zener diode.

41. The device of

claim 39

which further includes a first and second series connected capacitor connected across said positive and negative d-c busses;

and said d-c filter bus connected to the node between said first and second capacitors.

42. The device of

claim 41

, wherein said rectifier comprises a voltage doubler circuit which includes two series connected diodes connected in parallel with said first and second capacitors;

and said a-c source connected to the nodes between said diodes and said capacitors.