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

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

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.

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.

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

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

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

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

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

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

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.

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

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.

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

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

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

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

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

Experiment Results

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

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

(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

(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

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

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.

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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. 1993. [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. 1985. [11] K. Rajashekara, A. Kawamaura, and K. Matsuse, Sensorless Control of AC Motor Drives. New York: IEEE Press, 1996.

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