1. Department of Electrical Engineering Southern Taiwan University Robot and Servo Drive Lab. 2015/9/18 Pulsewidth Modulation Technique for BLDCM Drives to Reduce Commutation Torque Ripple Without Calculation of Commutation Time Yong-Kai Lin and Yen-Shin Lai IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 47, NO. 4, JULY/AUGUST 2011 1786-1793 學生 : 劉哲維 指導教授 : 王明賢 教授

2. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 2 Outline 1.Abstract 2.Introduction 3.Proposed Commutation Torque Reduction PWM Techniques a.Basic Idea b.Derivation of and During the Commutation Period c.Proposed Commutation Period Detection Circuit 4.Experimental Results 5.References

3. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 3 Abstract This paper presents a three-phase pulsewidth modulation (PWM) technique for brushless dc motor (BLDCM) drives to reduce the commutation torque ripple. As compared to previous approaches, the presented technique does not require any torque observer and calculation of commutation time which may be sensitive to motor parameters and may require more calculation time. The commutation time for the presented technique is determined by a detection circuit which consists of simple comparator circuit.

4. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 4 Introduction Fig.1(a) shows the ideal waveforms of the back EMF and phase current of BLDCM. As shown in Fig.1 (a), the current is with a flat waveform which is in phase with the back EMF, thereby giving a smooth torque. However, due to the limitation of current slew rate and commutation of inverter, the current waveform is not flat, as shown in Fig.1 (b). Fig. 1.

5. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 5 Basic Idea Fig. 3. Basic idea of the proposed technique (|dib/dt| = |dic/dt|). Phase “a” as the noncommutation phase Phase “b” as the outgoing phase Phase “c” as the incoming phase The basic idea is to retain the same magnitude of current slew rate while with opposite sign for the incoming and outgoing phases. This basic idea can be achieved by controlling the duty during commutation. Fig. 2 shows the block diagram of BLDCM drives

6. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 6 Basic Idea Fig. 4. Fig. 4 shows the proposed commutation control patent. During noncommutation period (CP = “Low”), the required turnon time “ ” is applied to PWM control, and two-phase PWM control is retained during this period. “ ” can be derived from a control loop such as speed control loop, torque control loop, etc. In contrast, turn-on times “ ” and “ ” are used during the commutation period (CP = “High”), and three-phase PWM control is applied, as shown in Fig. 4. “ ” and “ ” will be derived in the next section.

7. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 7 Derivation of tc1 and tc2 During the Commutation Period “x,” “y,” and “z” to represent the noncommutation, outgoing, and incoming phases, respectively. Fig. 5. Circuit of BLDCM during the commutation period at Sector 2.(a) Chop on. (b) chop off. Fig. 5.

8. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 8 Derivation of tc1 and tc2 During the Commutation Period Fig. 6. Equivalent circuit of Fig. 5. (a) Chop on. (b) Chop off. Fig. 6. If the winding resistor is neglected,as shown in Fig. 6(a), (1)–(3) can be derived by Kirchhoff’s voltage law (1) (2) (3) Central-tap voltage of three-phase winding with respect to the negative dc-link. Current of the noncommutation phase, Current of the outgoing phase. Current of the incoming phase.

9. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 9 Derivation of tc1 and tc2 During the Commutation Period Fig. 6. By (1)–(3), the central tap voltage can be derived as (4) Substituting (4) into (1)–(3), the current slew rate of each phase can be written as (5) (6) (7)

10. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 10 Derivation of tc1 and tc2 During the Commutation Period Fig. 6. As shown in Fig. 6(b), (8)–(10) can be derived by Kirchhoff’s voltage law (8) (9) (10) Central-tap voltage of three-phase winding with respect to the negative dc-link. Current of the noncommutation phase, Current of the outgoing phase. Current of the incoming phase.

11. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 11 Derivation of tc1 and tc2 During the Commutation Period Fig. 6. By (8)–(10), the central tap voltage can be derived as (11) Substituting (4) into (1)–(3), the current slew rate of each phase can be written as (12) (13) (14)

12. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 12 Derivation of tc1 and tc2 During the Commutation Period The average current slew rate of each phase can be written as (15) (16) (17) where “ ” is the duty ratio during the commutation period of Sector 2, and it can be defined as (18). In the succeeding equation, “ ” represents the switching period (18)

13. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 13 Derivation of tc1 and tc2 During the Commutation Period In order to retain the same magnitude of current slew rate while with opposite sign for the incoming and outgoing phases,the following equation can be derived: (19)

14. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 14 Derivation of tc1 and tc2 During the Commutation Period Moreover, the on-time “ ” during the commutation period can be derived as Assuming, (20) can be rewritten as Similarly, the on-time “ ” during the commutation period of Sector 3 can be written as Assuming, (22) can be rewritten as Back EMF = dc-limk voltage Back EMF constant Rotor speed of BLDCM (20) (21) (22) (23)

15. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 15 Proposed Commutation Period Detection Circuit Fig. 7. Proposed commutation period detection circuit. (a) Circuit. (b) Nonzero current @ chop off,, and Sector = 2, 4, and 6. (c) Zero current @ chop off, ( = floating) <, and Sector = 2, 4, and 6. Fig. 7. Fig. 8. Experimental result of the commutation period detection circuit. Ch1 =, Ch2 = chop y−, Ch3 =, and Ch4 = CP.

16. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 16 Experimental Results Fig. 10. FPGA-based experimental system. Fig. 11. Block diagram in FPGA. The chop signal “ ” is used in generating PWM signals when “CP” = “Low.” As “CP” becomes “high,” the chop signal “ ” is used in generating PWM signals according to Fig. 4.

17. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 17 Experimental Results Ch1 =,Ch2 =, and Ch3 = CP. (a) Without the proposed method. (b) With the proposed method. Fig. 12 Fig. 13 Fig. 14

18. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 18 Experimental Results Fig. 15 shows the measurement system with load cell Kistler 4503A for the measurement of torque ripple. 3φ BLDCM, L = 0.6 mH, R = 0.33 Ω, Prated = 70 W, and = 3 A. Fig. 16. Measured torque ripple (I ∗ PN = 0.5 p.u.). (a) Without the torque ripple reduction method. (b) With the torque ripple reduction method. Fig. 16.

19. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 19 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. Ind. Appl., vol. 28, no. 3, pp. 632–638, May/Jun. 1992. [2] C. T. Pan and E. Fang, “A phase-locked-loop-assisted internal model adjustable-speed controller for BLDC motors,” IEEE Trans. Ind. Electron., vol. 55, no. 9, pp. 3415–3425, Sep. 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. Magn., vol. 42, no. 4, pp. 1307–1310, Apr. 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. IEEE ICIEA, 2008, pp. 752–757. [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. IEEE IECON, 2005, pp. 1660–1664. [6] D. K. Kim, K. W. Lee, and B. I. Kwon, “Commutation torque ripple reduction in a position sensorless brushless dc motor drive,” IEEE Trans. Power Electron., vol. 21, no. 6, pp. 1762–1768, Nov. 2006. [7] H. Lu, L. Zhang, and W. Qu, “A new torque control method for torque ripple minimization of BLDC motors with un-ideal back EMF,” IEEE Trans. Power Electron., vol. 23, no. 2, pp. 950–958, Mar. 2008. [8] Y. Liu, Z. Q. Zhu, and D. Howe, “Commutation-torque-ripple minimization in direct-torque-controlled PM brushless dc drives,” IEEE Trans. Ind. Appl., vol. 43, no. 4, pp. 1012–1021, Jul./Aug. 2007. [9] S. S. Bharatkar, R. Yanamshetti, D. Chatterjee, and A. K. Ganguli, “Reduction of commutation torque ripple in a brushless dc motor drive,” in Proc. IEEE PECon, 2008, pp. 289–294. [10] Y. S. Lai and Y. K. Lin, “Quicken the pulse,” IEEE Ind. Appl. Mag., vol. 14, no. 5, pp. 34–44, Sep./Oct. 2008. [11] Y. S. Lai, F. S. Shyu, and Y. K. Lin, “Novel PWM technique without causing reversal dc-link current for brushless dc motor drives with bootstrap driver,” in Conf. Rec. IEEE IAS Annu. Meeting, 2005, vol. 3, pp. 2182–2188. [12] Y. S. Lai and Y. K. Lin, “Assessment of pulse-width modulation techniques for brushless dc motor drives,” in Conf. Rec. IEEE IAS Annu. Meeting, 2006, vol. 4, pp. 1629–1636.

20. Department of Electrical Engineering Southern Taiwan University 2015/9/18 Robot and Servo Drive Lab. 20 Thanks for your listening!