1. Department of Electrical Engineering, Southern Taiwan University 1 A novel sensorless control method for brushless DC motor Student: Wei-Ting Yeh Adviser: Ming-Shyan Wang Date : Jan,14,2010 H.-B. Wang and H.-P. Liu, Published in IET Electric Power Applications

2. Department of Electrical Engineering, Southern Taiwan University 2 Outline  Abstract  Introduction  Model of inductance of IPM BLDCM  Principle of the proposed method  Analysis of the sensitivity of the proposed method  Experimental results  Conclusions  References

3. Department of Electrical Engineering, Southern Taiwan University 3 Abstract The authors present the theory and implementation of a novel sensorless control method for the interior permanent magnet (IPM) brushless DC motor (BLDCM). The proposed new sensorless technique can accurately detect the zero-cross point (ZCP) of back electromotive force (BEMF), which is based on a comparison of the terminal voltage of the unconducting phase during the first and second part of a pulse width modulation (PWM) cycle

4. Department of Electrical Engineering, Southern Taiwan University 4 Introduction Brushless DC motor (BLDCM) can be broadly categorised into interior permanent magnet (IPM) motors and surfacemounted permanent magnet (SPM) motors. This study presents a novel sensorless position detection technique for IPM BLDCM that can detect equal selfinductance of the energised phases by using measurements of the instantaneous voltage across the unconducting phase.

5. Department of Electrical Engineering, Southern Taiwan University 5 Model of inductance of IPM BLDCM Fig. 1. Inverter topology and equivalent circuit of the BLDCM

6. Department of Electrical Engineering, Southern Taiwan University 6 Model of inductance of IPM BLDCM Fig. 2. BEMF waveforms

7. Department of Electrical Engineering, Southern Taiwan University 7 Model of inductance of IPM BLDCM where is the mechanical speed of a motor, is the BEMF constant. Equation (1) gives relationship between the A-phase BEMF and rotor position. Similar equations can be found for the B-phase and the C-phase BEMF.

8. Department of Electrical Engineering, Southern Taiwan University 8 Model of inductance of IPM BLDCM The stator selfinductances of IPM motor can be approximately expressed as The stator-to-stator mutual inductances are

9. Department of Electrical Engineering, Southern Taiwan University 9 Model of inductance of IPM BLDCM Equation (4) gives exact relationships among rotor positions, self-inductances, mutual inductances and BEMF.

10. Department of Electrical Engineering, Southern Taiwan University 10 Principle of the proposed method Fig. 4. Equivalent circuit during the PWM on time

11. Department of Electrical Engineering, Southern Taiwan University 11 Principle of the proposed method The circuit equations of Fig. 4 are

12. Department of Electrical Engineering, Southern Taiwan University 12 Principle of the proposed method where is the inverter switch on-state voltage drop. Substituting (6) and (7) into (5) gives where is at or. So the potential of C-phase is

13. Department of Electrical Engineering, Southern Taiwan University 13 Principle of the proposed method Fig. 5. Equivalent circuit during the PWM off time

14. Department of Electrical Engineering, Southern Taiwan University 14 Principle of the proposed method The circuit equations of Fig. 5 are

15. Department of Electrical Engineering, Southern Taiwan University 15 Principle of the proposed method where is the inverter diode on-state voltage drop. Substituting (11) and (12) into (10) gives where is at or. Substituing (4) into (13), the potential of C-phase, can be represented as

16. Department of Electrical Engineering, Southern Taiwan University 16 Principle of the proposed method Comparing (9) with (14) gives

17. Department of Electrical Engineering, Southern Taiwan University 17 Analysis of the sensitivity of the proposed method According to Fig. 4, combining (5), (6) and (7), we get According to Fig. 5, combining (10), (11) and (12), we get

18. Department of Electrical Engineering, Southern Taiwan University 18 Analysis of the sensitivity of the proposed method Fig. 6. The A-phase current waveform in a H_PWML_PWM period

19. Department of Electrical Engineering, Southern Taiwan University 19 Analysis of the sensitivity of the proposed method According to similar triangle principle, Fig. 6 can give approximately The voltage difference (T) between (t=2) and ((t+t T)/2) can be represented as

20. Department of Electrical Engineering, Southern Taiwan University 20 Analysis of the sensitivity of the proposed method Substituting (8), (13), (16), (17), (18) into (19) gives From (2), we have

21. Department of Electrical Engineering, Southern Taiwan University 21 Analysis of the sensitivity of the proposed method If the difference of is ignored, substituting (21) into (20) gives The direct and the quadrature axis inductance are

22. Department of Electrical Engineering, Southern Taiwan University 22 Analysis of the sensitivity of the proposed method It is assumed that the IPM BLDCM has low saliency ratio. Therefore comparing (24) with (25) and neglecting the last term of (25), we obtain

23. Department of Electrical Engineering, Southern Taiwan University 23 Analysis of the sensitivity of the proposed method Substituting (26) into (20) gives Similarly, when A-phase is open, we get When B-phase is open, we obtain

24. Department of Electrical Engineering, Southern Taiwan University 24 Experimental results Fig. 7. Block diagram representation showing the implementation of the proposed system

25. Department of Electrical Engineering, Southern Taiwan University 25 Experimental results Fig. 8. Three-phase terminal voltage and HALL commutation signal

26. Department of Electrical Engineering, Southern Taiwan University 26 Experimental results Fig. 9. The process of estimating ZCP of unconducting phase

27. Department of Electrical Engineering, Southern Taiwan University 27 Experimental results Fig. 10. A- and B-phase terminal voltages, the ZCP and estimated commutation signal

28. Department of Electrical Engineering, Southern Taiwan University 28 Experimental results Fig. 11. A- and B-phase terminal voltages, the commutation signal from Hall sensor and the estimated commutation signal

29. Department of Electrical Engineering, Southern Taiwan University 29 Experimental results Figure 12 The real A-phase current waveform and corresponded PWM waveform

30. Department of Electrical Engineering, Southern Taiwan University 30 Conclusions The process of estimating ZCP is implemented by the software, and so this method does not need any sensor. Moreover, the parameter in the software is important to commutation error. This method does not need to know the exact parameter of the motor, such as self-inductance, mutual inductance and its inertia, because it only needs to know when self-inductances of energised phases are equal. The special PWMscheme, H_PWM-L_PWM, is used in this method, which will result in higher switch losses when compared with the conventional PWMmodulation scheme.

31. Department of Electrical Engineering, Southern Taiwan University 31 References [1] ACARNLEY P.P., JOHN F.: ‘Review of position sensorless operation of brushless permanent magnet machines’, IEEE Trans. Ind. Electr., 2006, 53, (2), pp. 352–362 [2] JOHNSON J.P., EHSANI M., GUZELGUNLER Y.: ‘Review of sensorless methods for brushless DC’. Industry Applications Conference, 1999, 34th IAS Annual Meeting. Conference Record of the 1999 IEEE 1999, vol. 1, pp. 143–150 [3] CHEN C.-H., CHENG M.-Y.: ‘A new sensorless control scheme for brushless DC motors without phase shift circuit’. Proc. 6th IEEE It. Conf. Power Electronics and Drive Systems, KL, Malaysia, 2005, pp. 1084–1089 [4] IIZUKA K., UZUHASHI H., KANO M., ENDO T., MOHRI K., IIZUKA, ET AL.: ‘Microcomputer control for sensorless brushless motor’, IEEE Trans. Ind. Appl., 1985, 27, pp. 595–601 [5] KANG Y., LEE S.B., YOO J.: ‘A microcontroller embedded AD converter based low cost sensorless technique for brushless DC motor drives’, IEEE Trans. Power Electron., 2004, 19, (6), pp. 1601–1607

32. Department of Electrical Engineering, Southern Taiwan University 32 References [6] SHAO J., NOLAN D., TEISSIER M., SWANSON D.: ‘A novel microcontroller-based sensorless brushless DC (BLDC) motor drive for automotive fuel pumps’, IEEE Trans. Ind. Appl., 2003, 39, (6), pp. 1734–1740 [7] CHEN H.C., CHANG Y.C., HUANG C.K.: ‘Practical sensorless control for inverter-fed BDCM compressors’, IET Electric Power Appl., 2007, 1, (1), pp. 127–132 [8] SCHROEDL M.: ‘Sensorless control of AC machines at low speed and standstill based on the “INFORM” method’. Conf. Rec. IEEE-IAS Annu. Meeting, 1996, vol. 1, pp. 270–277 [9] KULKARNI A.B., EHSANI M.: ‘A novel position sensor elimination technique for the interior permanent magnet synchronous motor drive’, IEEE Trans. Ind. Appl., 1992, 28, (1), pp. 144–150 [10] CORLEY M.J., LORENZ R.D.: ‘Rotor position and velocity estimation for permanent magnet synchronous machine at standstill and high speed’. Conf. Rec. IEEE-IAS Annu.Meeting, 1996, vol. 1, pp. 36–41

33. Department of Electrical Engineering, Southern Taiwan University 33 References [11] NOGUCHI T., KOHNO S.: ‘Mechanical sensorless permanent magnet motor drive using relative phase information of harmonic currents caused by frequency-modulated threephase PWM carriers’, IEEE Trans. Ind. Appl., 2003, 39, (4), pp. 1085–1092 [12] SHEN J.X., TSENG K.J.: ‘Analyses and compensation of rotor position detection error in sensorless PM brushless DC motor drives’, IEEE Trans. Energy Conv., 2003, 18, (1), pp. 87–93 [13] KULKAMI A., EHSANI M.: ‘A novel position sensor elimination technique for the interior permanent magnet synchronous motor drive’, IEEE Trans. Ind. Appl., 1992, 28, pp. 144–150246

34. Department of Electrical Engineering, Southern Taiwan University 34 Thanks for your attention!