ACTIVE FILTER FOR REDUCTION OF COMMON MODE CURRENT

• US 20080180164A1
• Filed: 03/26/2008
• Published: 07/31/2008
• 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 7,583,136 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 for reducing the common mode current in a pulse width modulated drive circuit driving a load, said 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 load driven by said a-c output of said PWM inverter, a ground wire extending from said load, 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, and an amplifier circuit driving said transistors; 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 amplifier circuit having an input coupled to said output of said current sensor and having an output connected to 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 wherein said current sensor is a current transformer having a primary winding connected in series with said ground wire and a secondary winding connected as the signal input to the amplifier circuit.

Claims

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

said 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 load driven by said a-c output of said PWM inverter, a ground wire extending from said load, 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, and an amplifier circuit driving said transistors;

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 amplifier circuit having an input coupled to said output of said current sensor and having an output connected to 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

wherein said current sensor is a current transformer having a primary winding connected in series with said ground wire and a secondary winding connected as the signal input to the amplifier circuit.

2. The device of claim 1, wherein said current transformer has a toroidal core and wherein said primary winding is a single turn on said toroidal core.

3. The device of claim 1, wherein said dc isolating capacitor is connected to said ground wire between said primary winding of said current transformer and a connection for said load device.

4. The device of claim 1, wherein said primary winding of said current transformer is disposed between said connection for said load device and a common node connecting said dc isolating filter capacitor and said ground wire.

5. The device of claim 1, wherein said common node between said DC isolating capacitor and said ground wire is disposed between said primary winding of said current transformer and said connection for said load device.

6. The device of claim 1, wherein said primary winding of said current transformer is disposed between said common node between said DC isolating filter capacitor and said ground wire and said connection for said load device.

7. The device of claim 1, further including 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 linear amplification operation of each transistor over substantially the full rectified cycle of said a-c source.

8. An active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load;

said 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 load driven by said a-c output of said PWM inverter, a ground wire extending from said load, 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, and an amplifier circuit driving said transistors;

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 amplifier circuit having an input coupled to said output of said current sensor and having an output connected to 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;

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

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

9. An active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load;

said 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 load driven by said a-c output of said PWM inverter, a ground wire extending from said load, 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, and an amplifier circuit driving said transistors;

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 amplifier circuit having an input coupled to said output of said current sensor and having an output connected to 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

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

10. An active filter for reducing a common mode current in a PWM switched power supply, said power supply comprising an AC source, a rectifier connected to said AC source which produces a rectified output voltage between a positive DC bus and a negative DC bus a PWM inverter having input terminals coupled to said positive DC bus and negative DC bus and having a controlled AC output adapted to be connected to a load device, a ground wire adapted for connection to the load device, and a current sensor which measures a common mode current, and produces an output current related to the common mode current;

said active filter comprising;

first and second transistors, each having first and second electrodes providing a controlled current path and a control electrode, and

a DC isolating capacitor, wherein;

said first electrodes of said first and second transistors are connected to a common node;

said second electrodes of said first and second transistors are connected to said positive DC bus and said negative DC respectively;

said DC isolating capacitor is connected between said common node and said ground wire; and

said current sensor output is coupled to at least one of said control electrodes; 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 linear amplification operation of said transistors over substantially the full rectified cycle of said AC source;

further including a reduced voltage positive filter bus coupled to said DC bus;

said second electrodes of said first and second transistors being connected to said reduced voltage positive filter DC bus and said negative DC bus respectively.

11. The device of claim 10 further including a series connected resistor and zener diode connected between said positive and negative DC busses;

said positive DC filter bus being connected to the node between said resistor and said zener diode.

12. The device of claim 10 further including a first and second series connected capacitor'"'"'s connected across said positive and negative DC busses and wherein said DC filter bus is connected to the node between said first and second capacitors.

13. An active filter for reducing a common mode current in a PWM switched power supply, said power supply comprising an AC source, a rectifier connected to said AC source which produces a rectified output voltage between a positive DC bus and a negative DC bus a PWM inverter having input terminals coupled to said positive DC bus and negative DC bus and having a controlled AC output adapted to be connected to a load device, a ground wire adapted for connection to the load device, and a current sensor which measures a common mode current, and produces an output current related to the common mode current;

said active filter comprising;

first and second transistors, each having first and second electrodes providing a controlled current path and a control electrode, and

a DC isolating capacitor, wherein;

said first electrodes of said first and second transistors are connected to a common node;

said second electrodes of said first and second transistors are connected to said positive DC bus and said negative DC respectively; and

said DC isolating capacitor is connected between said common node and said ground wire; and

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

a reduced voltage filter bus coupled to said DC bus; and

further wherein;

said second electrode of said first transistor is connected to said reduced voltage filter bus;

said reduced voltage filter bus has a reduced positive voltage bus and a reduced negative voltage bus; and

one of said reduced positive voltage bus and said reduced negative voltage bus is connected in common with a corresponding one of said positive DC bus and said negative DC bus.

14. The device of claim 13, further including a series connected resistor and zener diode connected between said positive and negative DC busses, said positive DC filter bus connected to the node between said resistor and said zener diode.

15. The device of claim 13, further including first and second series connected capacitors connected across said positive and negative DC busses;

and wherein said DC filter bus is connected to the node between said first and second capacitors.

16. An active filter for reducing a common mode current in a PWM switched power supply, said power supply comprising an AC source, a rectifier connected to said AC source which produces a rectified output voltage between a positive DC bus and a negative DC bus a PWM inverter having input terminals coupled to said positive DC bus and negative DC bus and having a controlled AC output adapted to be connected to a load device, a ground wire adapted for connection to the load device, and a current sensor which measures a common mode current, and produces an output current related to the common mode current;

said active filter comprising;

first and second transistors, each having first and second electrodes providing a controlled current path and a control electrode, and

a DC isolating capacitor, wherein;

said first electrodes of said first and second transistors are connected to a common node;

said second electrodes of said first and second transistors are connected to said positive DC bus and said negative DC respectively;

said DC isolating capacitor is connected between said common node and said ground wire; and

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

and further comprising;

a reduced voltage filter bus coupled to said DC bus, wherein;

said second electrode of said first transistor is connected to said reduced voltage filter bus;

said reduced voltage filter bus has a reduced positive voltage bus and a reduced negative voltage bus; and

one of said reduced positive voltage bus and reduced negative voltage bus is connected in common with a corresponding one of said positive DC bus and negative DC bus.

17. The device of claim 16, further including a series connected resistor and zener diode connected between said positive and negative DC busses, and wherein said positive DC filter bus is connected to the node between said resistor and said zener diode.

18. The device of claim 16, further including first and second series connected capacitors connected across said positive and negative DC busses;

and wherein said DC filter bus is connected to the node between said first and second capacitors.