1. Student: Hsin-Feng Tu Professor: Ming-Shyan Wang Date : Dec,29,2010
Commutation Torque Ripple Reduction in a Position Sensorless Brushless DC Motor Drive
Dae-Kyong Kim, Kwang-Woon Lee, and Byung-Il Kwon, Member, IEEE, IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 6, NOVEMBER 2006
Student: Hsin-Feng Tu
Professor: Ming-Shyan Wang
Date : Dec,29,2010

2. Outline Abstract Introduction Sensorless BLDC Motor Control
Commutation Torque Ripple Reduction Strategy
Analysis of Commutation Torque Ripple
Voltage Disturbance Rejection Method
Implementation of the Proposed Strategy
Experimental Results
Conclusion
References

3. Abstract
Presents a novel method to reduce commutation torque ripple in a position sensorless brushless dc (BLDC) motor drive.
Measures commutation interval from the terminal voltage of a BLDC motor.
Calculates a pulsewidth modulation (PWM) duty ratio using the measured commutation interval to suppress the commutation torque ripple.
Implemented in an air conditioner compressor controller reduces not only the pulsating currents but also vibrations of a position-sensorless BLDC motor.

4. Introduction
Permanent magnet brushless dc (BLDC) motors have used wide application due to their power density and ease of control.
Since the proposed method directly measures commutation interval from motor terminal voltage waveforms, it does not require a current sensor and current control loop.
The experimental results show that the proposed method considerably reduces not only current ripples but also the vibrations of the compressor.

5. Sensorless BLDC Motor Control
Commutation points of the inverter can be obtained by knowing
the zero-cross-point (ZCP) of the back-EMF and a speed
dependent period of time delay.
The commutation points are estimated like this
is the zero crossing time of the back-EMF

6. Sensorless BLDC Motor Control
Fig. 1. (a) Configuration of a BLDC motor drive

7. Sensorless BLDC Motor Control
Fig. 1.(b) switching pattern

8. Sensorless BLDC Motor Control
Fig. 1.(c) terminal voltage sensing circuit

9. Sensorless BLDC Motor Control
Fig. 1.(d) terminal voltage waveforms

10. Analysis of Commutation Torque Ripple
Average voltage applied to a non-commutated phase before commutation is

11. Analysis of Commutation Torque Ripple
Fig. 2. Current paths in out-going unipolar PWM scheme when the phase
current is being transferred from phase A to phase B.

12. Analysis of Commutation Torque Ripple
From Fig. 2, the phase voltage equation during commutation is given as

13. Analysis of Commutation Torque Ripple
In case of an out-going phase unipolar PWM ,average voltage applied
to a non-commutated phase is
From (3) and (8), it is apparent that the average voltage of the noncommutationed phase is disturbed by commutation. voltage disturbance generates pulsating current, pulsating
current causes undesirable torque ripple during the commutation.

14. Voltage Disturbance Rejection Method
In order to minimize the pulsating current, the PWM duty ratio during commutation must be modified as (9) in order that the average voltage of the non-commutated phase maintains constant value, that is
If the phase back-EMF assumes constant in the commutation period and
rotational velocity of motor, the phase back-EMF is given as
Equation (9) is adjusted as in

15. Implementation of the Proposed Strategy
Fig. 3. Synchronization of the gating signals.

16. Implementation of the Proposed Strategy
Fig. 4. Configuration of the proposed controller

17. Fig. 5. Configuration of the experimental BLDC motor drive
Experiment Results
Fig. 5. Configuration of the experimental BLDC motor drive

18. Experiment Results
Fig. 6. Single rotary compressor and air conditioner for experimental test

19. Experiment Results

20. Experiment Results
Fig. 7. Measured duration of commutation in the rotary compressor with a BLDC motor

21. Experiment Results
Fig. 8. Simulation results at running frequency (50 Hz).
(a) Conventional control. (b) Proposed control

22. (a) Conventional control. (b) Proposed control
Experiment Results
Fig. 9. Terminal voltage and phase current at running frequency (30 Hz).
(a) Conventional control. (b) Proposed control

23. (a) Conventional control. (b) Proposed control
Experiment Results
Fig. 10. Terminal voltage and phase current at running frequency (75 Hz).
(a) Conventional control. (b) Proposed control

24. Fig. 11. Total vibration measured at the center of the compressor body
Experiment Results
Fig. 11. Total vibration measured at the center of the compressor body

25. Conclusion
This paper has proposed a commutation torque ripple reduction method for a position sensorless BLDC motor drive for he air conditioner.
Since the proposed method uses terminal voltage for measuring the commutation interval, the method does not require current sensors and a current control loop so that it is suitable for a low cost BLDC motor drive.
Experimental results have proved that the proposed control method considerably reduces not only the pulsating currents but also up to 31% of the total vibrations for the BLDC motor.

26. References
[1] Electric Power Research Institute, “Electric Motors; Markets, Trends, and Applications,” Tech. Rep. TR , Jun
[2] R. Calson, M. Lajoie-Mazenc, and J. Fagundes, “Analysis of torque ripple due to phase commutation in brushless dc machines,” IEEE Trans. Ind. Appl., vol. 28, no. 3, pp. 632–638, May/Jun
[3] Y. Murai, Y. Kawase, K. Ohashi, K. Nagatake, and Okuyama, “Torque ripple improvements for brushless dc miniature motors,” IEEE Trans. Ind. Appl., vol. IA-25, no. 3, pp. 441–450, May/Jun
[4] T. M. Jahns and W. L. Soong, “Pulsating torque minimization techniques for permanent magnet ac motor drives-a review,” IEEE Trans. Ind. Electron., vol. 43, no. 2, pp. 321–330, Apr
[5] P. Pillay and R. Krishnan, “Modeling, simulation, and analysis of permanent-magnet motor drives, Part II: The permanent-magnet synchronous drive,” IEEE Trans. Ind. Appl., vol. IA-25, no. 2, pp. 265–273, Mar./Apr

27. References
[6] C. Berendsen, G. Champenois, and A. Bolopion, “Commutation strategies for brushless dc motors: Influence of instant torque,” IEEE Trans. Power Electron., vol. 8, no. 2, pp. 231–236, Apr
[7] K. W. Lee, “Current control algorithm to reduce torque ripple in brushles dc motors,” in Proc. ICPE’98, 1998, vol. 1, pp. 380–385.
[8] X. Zhang, “A new method to minimize the commutation torque ripple in trapezoidal BLDC motor with sensorless drive,” in Proc. PIEMC’00, 2000, vol. 2, pp. 607–611.
[9] T. Endo and F. Tajima, “Microcomputer controlled brushles motor without a shaft mounted position sensor,” in Proc. IPEC’83, Tokyo, Japan, 1983, pp. 1339–1345.
[10] K. Iizuka, “Microcomputer control for sensorless brushless motor,” IEEE Trans. Ind. Appl., vol. IA-27, no. 3, pp. 595–601, May/Jun
[11] K. Rajashekara, A. Kawamaura, and K. Matsuse, Sensorless Control of AC Motor Drives. New York: IEEE Press, 1996.

28. Thanks for your attention!