Active EMI filter having no inductive current sensing device

• US 20040246751A1
• Filed: 06/03/2004
• Published: 12/09/2004
• Est. Priority Date: 06/04/2003
• Status: Active Grant

• Current Assignee: Infineon Technologies Americas Corp. (Infineon Technologies AG)
• Original Assignee: International Rectifier Corporation (Infineon Technologies AG)
• Inventors: Honda, Jun
• Granted Patent: US 6,920,053 B2
• Time in Patent Office: Days
• US Class Current: 363/39
• 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 1/15 using active elements
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters

Abstract

An active EMI filter senses current in a ground line as a voltage across a capacitor coupled to the ground line. The EMI filter senses common mode voltage and determines a difference between the common mode voltage and noise to provide an output to the ground line to reduce the difference.

Claims

1. A filter for an electrical power system, comprising:

an error amplifier coupled to system lines in said system, to obtain voltages related to currents in the respective lines, and operable to output a signal based on a difference in current between a pair of said lines;

the output signal being coupled to one of said lines;

wherein the output signal influences said difference in said voltages between said pair of system lines to decrease the voltage difference.

2. The circuit according to claim 1, wherein the error amplifier is coupled to said system lines by at least one capacitor.

3. The circuit according to claim 1, wherein at least one system line is an AC power line, and at least one other system line is a ground line.

4. The circuit according to claim 1, wherein said AC power line is a neutral line.

5. The circuit according to claim 1, further comprising:

a power supply to the error amplifier for powering the error amplifier; and

the power supply being coupled to one or more input lines in the electrical power system.

6. The circuit according to claim 3, wherein the error amplifier is referenced to said power line and has a first input which receives said voltage from said ground line.

7. The circuit according to claim 6, wherein the error amplifier outputs said output signal to said ground line.

8. The circuit according to claim 6, wherein said error amplifier has a second input which receives said output signal for controlling headroom of said error amplifier.

9. The circuit according to claim 8, wherein said error amplifier has a third input which receives said output signal from said ground line for controlling frequency response of said error amplifier.

10. The circuit according to claim 6, wherein said error amplifier has another input which receives said output signal from said ground line for controlling frequency response of said error amplifier.

11. The circuit according to claim 1, further comprising a high-pass filter at an input of the error amplifier.

12. The circuit according to claim 1, wherein said error amplifier comprises an input circuit and a transresistance amplifier.

13. The circuit according to claim 12, further comprising a buffer circuit which receives an output of said transresistance amplifier and delivers said output signal.

14. The circuit according to claim 1, further comprising a buffer circuit which delivers said output signal.

15. A method for reducing EMI in an electrical power circuit with an active EMI filter, comprising:

sensing a voltage on at least one of an input and ground line related to current through the line;

sensing voltage in at least another of the input and ground line;

comparing the sensed voltages and providing a voltage signal based on differences between the voltages; and

applying the voltage signal to at least one of the input and ground lines to thereby reduce the voltage difference.

16. The method according to claim 15, further comprising amplifying the voltage difference to obtain a closed loop feedback control.

17. An active EMI filter, comprising:

an error amplifier for amplifying an error signal;

a capacitor coupled to an input of the error amplifier for developing a voltage related to a sensed current;

a second capacitor coupled to a second input of the error amplifier for developing a voltage related to a sensed current; and

an output capacitor coupled to an output of the error amplifier and at least one of the first and second capacitors;

wherein the error amplifier is operable to detect a difference in voltages developed across the first and second capacitors and supply a voltage to the output capacitor to compensate the difference in voltages between the first and second capacitors.