Odd harmonics reduction of phase angle controlled loads

• US 6,614,197 B2
• Filed: 06/30/2001
• Issued: 09/02/2003
• Est. Priority Date: 06/30/2001
• Status: Expired due to Fees

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Berringer, Kenneth A.
• Primary Examiner(s): Ro, Bentsu
• Assistant Examiner(s): Duda, Rina I.
• Application Number:
  US09/896,534
• Publication Number:
  US 20030002302A1
• Time in Patent Office: 794 Days
• Field of Search: 318/629, 318/632, 318/798, 318/799, 318/807, 318/808, 318/809, 318/811, 318/245, 323/235, 363/39, 363/41, 363/45, 363/57, 363/85, 363/96, 363/135
• US Class Current: 318/245
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 5/2576 with digital control
• CPC Class Codes: H02P 23/186 of one shaft by controlling the prime mover

Abstract

The present invention relates generally to the reduction of odd harmonics of phase angle controlled loads. One embodiment relates to an apparatus for reducing odd harmonic currents introduced into an alternating current (AC) supply by a load having a zero crossing detector and a processor coupled to the zero crossing detector. The zero crossing detector is coupled to the AC current supply for measuring voltage zero crossings of the AC current supply. The processor receives a user control signal for controlling the load, such as, for example, a speed control, determines phase angles required at the voltage zero crossings of the AC current supply to implement the user control signal, and selectively modulating the phase angles when they are in a predetermined range of undesired phase angles in order to selectively reduce odd harmonics within the AC current supply.

Claims

1. Apparatus for reducing odd harmonic current introduced into an alternating current supply by a load, comprising:

zero crossing detection means coupled to the alternating current supply for measuring voltage zero crossings of the alternating current supply; and

processing means coupled to the zero crossing detection means, the processing means receiving a user control signal for controlling the load, the processing means determining phase angles required at the voltage zero crossings of the alternating current supply to implement the user control signal, and selectively modulating the phase angles when the phase angles are within a predetermined range of an undesired phase angle, the selectively modulating reducing odd harmonics within the alternating current supply.

2. The apparatus of claim 1 wherein the load is a motor and the user control signal is a speed control signal for controlling speed of the motor.

3. The apparatus of claim 1 wherein the undesired phase angle is approximately ninety degrees to significantly minimize a third harmonic of the alternating current supply.

4. The apparatus of claim 1 wherein the predetermined range comprises a range substantially within 30 to 60 degrees wide.

5. The apparatus of claim 1 further comprising:

a thyristor for receiving a load control signal from the processing means.

6. The apparatus of claim 1 wherein the processing means selectively modulates by subtracting a predetermined correction phase angle from a phase angle within the predetermined range and determining an error phase, the error phase being added to a subsequent phase angle within the predetermined range to average modification of the phase angle.

7. The apparatus of claim 1 wherein the processing means further comprises a microcontroller unit (MCU) and the load is a universal motor.

8. A method for reducing odd harmonics in an alternating current supply, comprising:

receiving a user command to control a load;

determining a phase angle at each zero crossing of the alternating current supply required to implement the user command;

identifying a predetermined range of phase angles to modulate around;

not modifying the phase angle if the phase angle is less than the predetermined range of phase angles;

modifying the phase angle by performing one of selectively adding and selectively subtracting a predetermined phase from the phase angle if the phase angle is within the predetermined range of phase angles;

calculating an error in response to modifying the phase angle;

adding the error to a subsequent phase angle so that an average phase angle equals required phase angle modification required to implement the user command; and

not modifying the phase angle if the phase angle is greater than the predetermined range of phase angles.

9. The method of claim 8 further comprising implementing the predetermined range of phase angles as substantially between sixty degrees and one hundred twenty degrees.

10. The method of claim 8 further comprising implementing the predetermined range of phase angles as a range centered substantially around ninety degrees to substantially reduce third harmonics in the alternating current supply.

11. The method of claim 8 further comprising implementing the user command as a speed control signal and implementing the load as a motor.

12. The method of claim 8 further comprising:

coupling modified or non-modified phase angles to a thyristor to control switching of the alternating current supply to the load.

13. A computer readable medium storing software for reducing odd harmonics in an alternating current introduced by a load, the computer readable medium comprising:

at least one instruction for determining a phase angle at each zero crossing of the alternating current required to implement a user command to control the load;

at least one instruction for determining if the phase angle at each zero crossing is within or outside a predetermined range of phase angles to modulate around and not changing the phase angle if the phase angle is outside of the predetermined range; and

at least one instruction for changing the phase angle by forming a differential between a predetermined phase angle and the phase angle if the phase angle is within the predetermined range, for calculating an error value associated with the phase angle, and for adding the error value to a subsequent phase angle so that an average of two successive phase angles will accurately implement the user command.

14. The computer readable medium of claim 13 further comprising implementing the predetermined range substantially around ninety degrees to minimize third harmonics.

15. The computer readable medium of claim 13 further comprising implementing the load as a motor and processing the user command to variably change motor speed.

16. The computer readable medium of claim 13 wherein the computer readable medium is an embedded memory within a system for controlling the load.

17. A system for reducing odd harmonic current introduced into an alternating current supply by a load, comprising:

a zero crossing detector coupled to the alternating current supply for measuring voltage zero crossings of the alternating current supply; and

a processor coupled to the zero crossing detector, the processor receiving a user control signal for controlling the load, the processor determining phase angles required at the voltage zero crossings of the alternating current supply to implement the user control signal, and selectively modulating the phase angles when the phase angles are within a predetermined range of an undesired phase angle, the selectively modulating reducing odd harmonics within the alternating current supply.

18. The system of claim 17 wherein the load is a motor and further comprises:

a triac coupled in series between the motor and the alternating current supply, the triac being controlled by the processor to switch a neutral phase of the alternating current supply to the motor in response to selectively modulating the phase angles.

19. The system of claim 17 further comprising:

a speed control device coupled to the processor, the speed control device providing the user control signal to the processor for controlling speed of the load.

20. The system of claim 17 further comprising:

a memory coupled to the processor, the memory storing software that when executed by the processor implements selective modulation of phase angles by the processor.