EMI filter and method

• US 5,483,136 A
• Filed: 05/27/1994
• Issued: 01/09/1996
• Est. Priority Date: 05/27/1994
• Status: Expired due to Term

• Current Assignee: Emerson Electric Company
• Original Assignee: Emerson Electric Company
• Inventors: Marcinkiewicz, Joseph G.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/250,158
• Time in Patent Office: 592 Days
• Field of Search: 318/254, 318/558, 318/722, 318/801, 363/37, 363/44, 363/45, 363/47, 324/613, 336/155, 336/170, 336/180, 333/25, 333/32, 333/170, 333/181
• US Class Current: 318/558
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters

Abstract

An improved EMI filter design is provided for an inverter operated dynamoelectric machine. A lossy balun wound choke is connected between a power supply in the form of a bridge rectifier and the inverter. The choke acts as a source resistance. Using the choke as the source resistance, an equiripple approximation to linear phase filter is derived. The filter is placed on the input side of the bridge rectifier. A method of designing an EMI filter for use in conjunction with an inverter operated dynamoelectric machine.

Claims

1. In a control system for a dynamoelectric machine including a stator assembly having a plurality of windings, a rotor assembly mounted for rotation with respect to said stator assembly, an inverter operatively connected to said windings to supply the electrical energy to said windings in a predetermined manner, a bridge rectifier electrically connected to a source of power, said bridge rectifier having an input side and an output side, said rectifier defining on its output side first and second rails, said inverter being operatively connected between said first and second rails on its input side and to said dynamoelectric machine at its output side, the improvement comprising an electromagnetic interference filter for reducing electromagnetic interference associated with said control system and said dynamoelectric machine, said filter including a lossy core inductor having magnetically coupled first and second coils, one each of said first and second coils being serially connected in one each of said first and said second rails on the output side of said rectifiers;

and a fourth order filter having 0.5 degree equiripple approximation to linear phase operatively connected on the input side of said bridge rectifier.

2. The improvement of claim 1 further includes a logic control operatively connected to said inverter.

3. The improvement of claim 2 further including rotor position sensing means operatively connected to said logic control.

4. The improvement of claim 3 wherein said rotor position sensing means comprises Hall effect sensors.

5. The improvement of the previous claim 4, further including a voltage doubler means operatively connected on the output side of said bridge rectifier.

6. The improvement of claim 3, wherein said rotor position sensing means is accomplished by monitoring an electrical characteristic of the dynamoelectric machine.

7. A control for an electrical device comprising;

a dynamoelectric machine including a stator assembly and a rotor assembly, said stator assembly including a core and a plurality of stator windings associated with said core, said rotor assembly including a rotor mounted for rotation with respect to said stator assembly;

a bridge rectifier having an input side and an output side, said bridge rectifier being operatively connected to an ac source on said input side, the output side of said rectifier defining first and second rails of dc potential;

an inverter having an input side and an output side, the input side of said inverter being connected in parallel between said first and said second rails of said bridge rectifier, the output side of said inverter being operatively connected to said stator windings for energizing said windings in a predetermined sequence; and

a filter for reducing EMI transmissions during operation of said control, said filter including a lossy core inductor having magnetically coupled first and second coils, one each of said first and said second coils being operatively connected in series in respective ones of said first and said second rails on the output side of said bridge rectifier, and a linear phase filter designed with the lossy core inductor as a source impedance operatively connected on the input side of said bridge rectifier.

8. The control of claim 7 further includes a logic control operatively connected to said inverter.

9. The control of claim 8 further including rotor position sensing means operatively connected to said logic control.

10. The control of claim 9 wherein said rotor position sensing means comprises at least one Hall Effect sensor.

11. A method of designing an EMI filter for a control of an inverter operated dynamoelectric machine including a source of dc voltage, said voltage source having an input side and an output side, the output side defining first and second rails, and an inverter having a first side connected between said rails and a second side connected to said dynamoelectric machine comprising the steps of:

inserting a lossy core inductor having first and second coils on the output side of said source of voltage, between said source and said inverter;

determining the impedance of said lossy core inductor;

designing an EMI filter using the impedance so determined as the source impedance; and

inserting said EMI filter on the input side of said source of dc voltage.

12. The method of claim 11, including the step of using an EMI test set up as a load impedance.

13. A method of claim 12, further including the step approximating the load impedances as much greater than the source impedance.

14. The method of claim 12, including the step of approximating the source impedance as much greater than the load impedance.

15. The method of claim 12 wherein the source of dc voltage is a full wave bridge rectifier.