Method for controlling an electric motor to reduce EMI

• US 20050225275A1
• Filed: 06/09/2005
• Published: 10/13/2005
• Est. Priority Date: 04/30/2002
• Status: Active Grant

• Current Assignee: Infineon Technologies Americas Corp. (Infineon Technologies AG)
• Original Assignee: International Rectifier Corporation (Infineon Technologies AG)
• Inventors: Eskritt, James B., Kuehner, Joel E.
• Granted Patent: US 7,202,622 B2
• Time in Patent Office: Days
• US Class Current: 318/437
• CPC Class Codes: B62D 5/065 characterised by specially adapted means for varying pressurised fluid supply based on need, e.g. on-demand, variable assist
• 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
• CPC Class Codes: H02M 7/53875 with analogue control of three-phase output
• CPC Class Codes: H02P 23/04 specially adapted for damping motor oscillations, e.g. for reducing hunting
• CPC Class Codes: H02P 23/26 Power factor control [PFC]
• CPC Class Codes: H02P 29/50 Reduction of harmonics

Abstract

A method for reducing EMI emissions in the control of an electric motor supplied by a switching inverter fed by a DC bus comprising controlling a phase advance of a conduction angle period during which a phase of the motor is fed power by the inverter to control the conduction angle to control the speed of the motor, thereby to reduce the number of switching operations of the inverter and thereby reduce EMI.

Claims

1. A method for reducing EMI emissions in the control of an electric motor supplied by a switching inverter fed by a DC bus comprising:

controlling a phase advance of a conduction angle period during which a phase of the motor is fed power by the inverter to control the conduction angle to control the speed of the motor, thereby to reduce the number of switching operations of the inverter and thereby reduce EMI.

2. The method of claim 1, further comprising:

providing the motor with a sensor for determining a switching instant for a switch of the inverter controlling the conduction angle;

receiving an output signal of the sensor; and

advancing a switching-on time of a switch of the inverter coupling the dc bus voltage to a motor phase by a phase angle prior to the next output signal of the sensor to provide said phase advance.

3. The method of claim 2, wherein the step of controlling the phase advance comprises increasing the conduction angle by the amount of said phase angle.

4. The method of claim 3, wherein the phase angle comprises a fixed phase angle amount and a variable phase angle amount to control the speed of the motor.

5. The method of claim 4, wherein the variable phase angle increases the conduction angle and the fixed phase angle shifts the conduction time temporally.

6. The method of claim 1, further comprising pulse width modulating the switch during the conduction angle.

7. The method of claim 4, wherein two alternately conducting switches arranged in a half bridge are provided and further comprising advancing a switching-on time of each switch by the phase angle.

8. The method of claim 7, wherein the motor is a three phase motor and three half bridges are provided, each comprising two alternately conducting switches, one comprising a high side switch and the other a low side switch and further comprising advancing a switching-on time of each switch by the phase angle.

9. The method of claim 8, wherein the conduction angle varies between 120°

and 180°

, and the variable phase angle varies between 0° and

60°

.

10. The method of claim 9, wherein the fixed phase angle advance equals approximately 15°

.

11. The method of claim 4, wherein the fixed phase angle is provided so that a turn-off instant for the switch is aligned with a transition of the sensor output independently of the amount of conduction angle.

12. The method of claim 1, further comprising pulse width modulating during the conduction angle at a duty cycle of 100%.

13. The method of claim 1, further comprising selecting between the two following options a) and b) to control the motor speed:

a) varying the phase angle and 100% duty cycle pulse width modulation during the conduction angle; and

b) zero phase angle and varying they duty cycle by pulse width modulation during the conduction angle.

14. The method of claim 13, further comprising selecting option b) if a desired speed can be reached at 120°

conduction angle and less than 100% duty cycle.

15. The method of claim 13, further comprising selecting option b) if a current drawn by the motor exceeds a predetermined limit with 120°

conduction angle and 100% duty cycle.

16. The method of claim 13, further comprising selecting option a) if a desired motor speed cannot be reached with 120°

conduction angle and 100% duty cycle and the current drawn by the motor is below a predetermined limit.

17. The method of claim 1, wherein the step of controlling comprises controlling a brushless DC motor.