1. Department of Electrical Engineering Southern Taiwan University of Science and Technology Robot and Servo Drive Lab. 2015/12/6 Professor ： Ming-Shyan Wang Student ： Chih-Hung Wang Pulse-width Modulation Technique for BLDCM Drives to Reduce Commutation Torque Ripple without Calculation of Commutation Time IEEE TRANSACTIONS ON POWER ELECTRONICS, 978-1-4244-5287-3/10/$26.00 ©2010 IEEE By Yen-Shin Lai and Yong-Kai Lin

2. Department of Electrical Engineering Southern Taiwan University of Science and Technology 2015/12/6 Robot and Servo Drive Lab. 2 Outline Introduction Proposed commutation torque reduction PWM techniques Proposed commutation period detection circuit Experimental results Conclusion References

3. Department of Electrical Engineering Southern Taiwan University of Science and Technology 2015/12/6 Robot and Servo Drive Lab. 3 Abstract This paper presents a three-phase pulse-width modulation technique for brushless DC motor drives to reduce the commutation torque the presented technique doesn’t require any torque observer and calculation of commutation time which may be sensitive to motor parameters and require more calculation time. The commutation time for the presented technique is determined by a detection circuit which consists of simple comparator circuit. Experimental results derived from an FPGA-based controlled BLDCM drive show that the commutation current ripple can be significantly reduced by the presented PWM technique.

4. Department of Electrical Engineering Southern Taiwan University of Science and Technology Introduction(1/2) Fig. (A) shows the ideal waveforms of back-EMF and phase current of BLDCM. As shown in Fig. (A), the current is with flat waveform which is in phase with the back-EMF and thereby giving smooth torque. 2015/12/6 Robot and Servo Drive Lab. 4

5. Department of Electrical Engineering Southern Taiwan University of Science and Technology Introduction(2/2) Due to the limitation of current slew rate and commutation of inverter, the current waveform is not flat as shown in Fig. (B). And this fact gives significant torque ripple which can be up to 50% of average torque. 2015/12/6 Robot and Servo Drive Lab. 5

6. Department of Electrical Engineering Southern Taiwan University of Science and Technology PWM Techniques A new three-phase pulse-width modulation technique for brushless DC motor drives to reduce the commutation torque is proposed. As compared to previous approaches, the presented technique doesn’t require any torque observer and calculation of commutation time which may be sensitive to motor parameters and require more calculation time. The commutation time for the presented technique is determined by a detection circuit which consists of simple comparator circuit. 2015/12/6 Robot and Servo Drive Lab. 6

7. Department of Electrical Engineering Southern Taiwan University of Science and Technology Basic idea Using phase “a” as the non-commutation phase, phase “b” as the outgoing phase” and phase “c” as the incoming phase”. 2015/12/6 Robot and Servo Drive Lab. 7

8. Department of Electrical Engineering Southern Taiwan University of Science and Technology Three-phase PWM control for commutation torque reduction 2015/12/6 Robot and Servo Drive Lab. 8

9. Department of Electrical Engineering Southern Taiwan University of Science and Technology Tn. Tc1. Tc2 During non-commutation period (CP = “L”), the required turn- on time, “tn”, is applied to PWM control, and two-phase PWM control is retained during this period. “tn” can be derived from a control loop, such as speed control loop and torque control loop In contrast, turn-on times, “tc1” and “tc2”, are used during commutation period (CP = “H”) and three-phase PWM control 2015/12/6 Robot and Servo Drive Lab. 9

10. Department of Electrical Engineering Southern Taiwan University of Science and Technology x = non-commutation phase y = outgoing phase z = incoming phase 2015/12/6 Robot and Servo Drive Lab. 10

11. Department of Electrical Engineering Southern Taiwan University of Science and Technology Chop on Kirchhoff”s Voltage Law: (1) (2) (3) The central tap voltage: (4) 2015/12/6 Robot and Servo Drive Lab. 11

12. Department of Electrical Engineering Southern Taiwan University of Science and Technology Current slew rate 2015/12/6 Robot and Servo Drive Lab. 12 Substituting (4) to (1)-(3),the current slew rate: (5) (6) (7)

13. Department of Electrical Engineering Southern Taiwan University of Science and Technology Chop off 2015/12/6 Robot and Servo Drive Lab. 13 Kirchhoff”s Voltage Law: (8) (9) (10) The central tap voltage: (11)

14. Department of Electrical Engineering Southern Taiwan University of Science and Technology Current slew rate 2015/12/6 Robot and Servo Drive Lab. 14 Substituting (11) to (8)-(10),the current slew rate: (12) (13) (14)

15. Department of Electrical Engineering Southern Taiwan University of Science and Technology commutation period detection circuit When the commutation period comes to the end, the status of “Dyp” becomes low and thereby indicating the commutation period. As commutation period, indicated by “CP” comes to its end, the duty is changed to the required turn-on time,”tn”, and two-phase PWM control is resumed. 2015/12/6 Robot and Servo Drive Lab. 15

16. Department of Electrical Engineering Southern Taiwan University of Science and Technology Experimental Results DC-link current is fed back for current control. DC-link voltage and switching frequency of inverter are 24 V and 20 kHz. 2015/12/6 Robot and Servo Drive Lab. 16

17. Department of Electrical Engineering Southern Taiwan University of Science and Technology Experimental Results the rotating speed of BLDCM is calculated by sensing Hall signals. The chop signal “chopdn” which is used for generating PWM signals when “CP” = “L”. As “CP“ becomes “H”, the chop signal “chopdc” is used for generating PWM signals. 2015/12/6 Robot and Servo Drive Lab. 17

18. Department of Electrical Engineering Southern Taiwan University of Science and Technology Experimental Results 2015/12/6 Robot and Servo Drive Lab. 18

19. Department of Electrical Engineering Southern Taiwan University of Science and Technology Experimental Results 2015/12/6 Robot and Servo Drive Lab. 19

20. Department of Electrical Engineering Southern Taiwan University of Science and Technology Experimental Results 2015/12/6 Robot and Servo Drive Lab. 20

21. Department of Electrical Engineering Southern Taiwan University of Science and Technology Conclusion This paper presents a three-phase pulse-width modulation technique for brushless DC motor drives to reduce the commutation torque. The presented technique doesn’t require any torque observer and calculation of commutation time which may be sensitive to motor parameters and require more calculation time. The commutation time for the presented technique is determined by a detection circuit. Experimental results derived from an FPGA-based controlled BLDCM drives show that the commutation current ripple can be significantly reduced by the presented PWM technique. 2015/12/6 Robot and Servo Drive Lab. 21

22. Department of Electrical Engineering Southern Taiwan University of Science and Technology References [1] R. Carlson, M. Lajoie-Mazenc, and J. C. D. S. Fagundes, “Analysis of torque ripple due to phase commutation in brushless DC machines,” IEEE Trans. on Industry Applications, Vol. 28, No. 3, pp. 632-638, 1992. [2] C. T. Pan and E. Fang, “A phase-locked-loop-assisted internal model adjustable-speed controller for BLDC motors,” IEEE Trans. On Industrial Electronics, Vol. 55, No. 9, pp. 3415-3425, 2008. [3] K. Y. Nam, W. T. Lee, C. M. Lee and J. P. Hong, “Reducing torque ripple of brushless DC motor by varying input voltage,” IEEE Trans. on Magnetics, Vol. 42, No. 4, pp. 1307- 1310, 2006. [4] J. Cao, B. Cao, P. Xu, S. Zhou, G. Guo and X. Wu, “Torque ripple control of position- sensorless brushless DC motor based on neural network identification,” in Proc. of IEEE ICIEA, pp. 752-757, 2008. [5] X. Xiao, Y. Li, M. Zhang and M. Li, “A novel control strategy for brushless DC motor drive with low torque ripples,” in Proc. of IEEE IECON, pp.1660-1664, 2005. 2015/12/6 Robot and Servo Drive Lab. 22

23. Department of Electrical Engineering Southern Taiwan University of Science and Technology Thanks for listening 2015/12/6 Robot and Servo Drive Lab. 23