Claims
- 1. An active EMI filter for reducing common mode noise current in a circuit comprising a rectifier coupled to an AC network, the rectifier supplying DC power to a DC bus, the DC bus feeding an inverter stage for providing AC power to a load, the load having a ground return line to a ground connection of the AC network, the active filter comprising:
a transistor switching stage comprising two transistors coupled across the DC bus; a current sensor coupled to the DC bus for sensing the common mode noise current flowing in the DC bus, said current sensor comprising a current transformer having a primary connected in series with a respective leg of said DC bus; the current sensor having an output coupled to the transistor switching stage, the transistor switching stage being driven by said current sensor such that said transistors are each switched on and off in response to the direction of common mode current in said DC bus; a capacitor coupling said transistor switching stage and said ground return line; said capacitor providing a cancellation current to said ground return line from said transistor switching stage to substantially cancel the common mode current in the ground return line; said two transistors of said transistor switching stage being coupled such that respective main electrodes of said two transistors are coupled to respective legs of said DC bus, another corresponding main electrode of each transistor being coupled by a respective secondary of said current transformer to a common node, and wherein the control electrode of each of said transistors is coupled by another respective secondary of said current transformer to said common node.
- 2. The filter of claim 1, wherein said current sensor and said switching stage are coupled in a feed forward arrangement whereby the switching stage is coupled across said DC bus between said rectifier and said current sensor, said transistor switching stage and said current sensor having an amplitude gain of approximately unity.
- 3. The filter of claim 1, wherein the two transistors are MOSFETs.
- 4. The active filter of claim 3, wherein said MOSFETs are of the same type.
- 5. The active filter of claim 1, wherein said capacitor couples said ground return line to the common node of said transistors.
- 6. The active filter of claim 1, wherein said other secondaries of said current transformer provide bias circuits for applying respective bias voltages to the control electrodes of said two transistors.
- 7. The active filter of claim 1, wherein said primary and said secondary of said current transformer have the same number of turns.
- 8. The active filter of claim 7, wherein said primary and said secondary of said current transformer each have a single turn.
- 9. The active filter of claim 7, wherein said other secondary has a greater number of turns than said primary.
- 10. An active EMI filter for reducing common mode noise current in a circuit comprising a rectifier coupled to an AC network, the rectifier supplying DC power to a DC bus, the DC bus feeding an inverter stage for providing AC power to a load, the load having a ground return line to a ground connection of the AC network, the active filter comprising:
a transistor switching stage comprising two transistors coupled across the DC bus; a current sensor coupled to the DC bus for sensing the common mode noise current flowing in the DC bus; the current sensor having inputs coupled to respective legs of the DC bus and an output driving the transistor switching stage, the transistor switching stage comprising two transistors driven by said output of the current sensor such that said transistors are each switched off and on in response to the direction of common mode current in said DC bus; a capacitor coupling said transistor switching stage and said ground return line; said capacitor providing a cancellation current to said ground return line from said transistor switching stage to substantially cancel the common mode current in said ground return line; said current sensor comprising a first current transformer having a primary connected in series with a respective leg of said DC bus, and a second current transformer having a primary coupled to a secondary of the first current transformer; said two transistors of said transistor switching stage each having two main electrodes and one control electrode, one main electrode of each transistor being coupled in common to one end of a secondary of said second current transformer, a control electrode of each transistor being coupled in common to another end of the secondary of said secondary current transformer.
- 11. The active filter of claim 10, wherein the two transistors are bipolar transistors.
- 12. The active filter of claim 11, wherein the emitters of the two transistors are connected together.
- 13. The active filter of claim 10, wherein the two transistors are complementary.
- 14. The active filter of claim 13, wherein the emitters of the two transistors are connected together.
- 15. The active filter of claim 10, wherein said current sensor and said switching stage are coupled in a feed forward arrangement whereby the switching stage is coupled across said DC bus between said rectifier and said current sensor, said transistor switching stage and said current sensor having an amplitude gain of approximately unity.
- 16. The active filter of claim 10, wherein said capacitor connects said ground return line in common to the control electrodes of said two transistors.
- 17. The active filter of claim 10, further comprising third and fourth transistors, each having two main electrodes, one main electrode of each of said third and fourth transistors being connected in common to one end of said secondary of said first current transformer, and each having a control electrode, said control electrodes being connected in common to another end of said secondary of said first current transformer.
- 18. The active filter of claim 17, wherein the other main electrodes of said third and fourth transistors are connected across a DC supply voltage which is lower than said DC bus voltage.
- 19. The active filter of claim 10, wherein said first current transformer has a step-up turns ratio and said second current transformer has a step-down turns ratio.
- 20. An active EMI filter for reducing common mode noise current in a circuit comprising a rectifier coupled to an AC network, the rectifier supplying DC power to a DC bus, the DC bus feeding an inverter stage for providing AC power to a load, the load having a ground return line to a ground connection of the AC network, the active filter comprising:
a transistor switching stage comprising two transistors coupled across the DC bus; a current sensor coupled to the DC bus for sensing the common mode noise current flowing in the DC bus, said current sensor comprising a current transformer having a primary connected in series with a respective leg of said DC bus; the current sensor having an output coupled to an amplifier, the transistor switching stage being driven by said amplifier such that said transistors are each switched on and off in response to the direction of common mode current in said DC bus; a capacitor coupling said transistor switching stage and said ground return line; said capacitor providing a cancellation current to said ground return line from said transistor switching stage to substantially cancel the common mode current in the ground return line; and further comprising: a floating bias circuit coupled to said current sensor for receiving a signal representative of said common mode noise current, rectifying said signal and supplying a DC bias voltage to said amplifier.
- 21. The filter of claim 20, wherein said current sensor and said switching stage are coupled in a feedback arrangement whereby the switching stage is coupled across said DC bus between said current sensor and said inverter, said transistor switching stage, said amplifier and said current sensor having a high amplitude gain.
- 22. The filter of claim 20, wherein said current sensor and said switching stage are coupled in a feed forward arrangement whereby the switching stage is coupled across said DC bus between said rectifier and said current sensor, said transistor switching stage, said amplifier and said current sensor having an amplitude gain of approximately unity.
- 23. The filter of claim 22, wherein said floating bias circuit and said amplifier are both connected to a secondary of said circuit transformer.
- 24. The filter of claim 20, wherein said floating bias circuit and said amplifier are both connected to a secondary of said circuit transformer.
- 25. The filter of claim 20, wherein said floating bias circuit and said amplifier are coupled respectively to a first and a second secondary of said current transformer.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims priority of U.S. Provisional Application Serial No. 60/376,643 filed Apr. 30, 2002 (IR-2166), and U.S. Provisional Application Serial No. 60/378,201 filed May 3, 2002 (IR-2222/2224), the disclosures of which are incorporated by reference herein.
Provisional Applications (2)
|
Number |
Date |
Country |
|
60376643 |
Apr 2002 |
US |
|
60378201 |
May 2002 |
US |