1. Department of Electrical Engineering, Southern Taiwan University 1 A current ripple reduction of a high-speed miniature brushless direct current motor using instantaneous voltage control Student: Wei-Ting Yeh Adviser: Ming-Shyan Wang Date : Dec,17,2010 D.-H. Lee and J.-W. Ahn, Published in IET Electric Power Applications

2. Department of Electrical Engineering, Southern Taiwan University 2 Outline  Abstract  Introduction  Torque ripple analysis of a high-speed BLDCM  The proposed control system for a high-speed miniature BLDCM  Simulation and experimental results  Conclusions  References

3. Department of Electrical Engineering, Southern Taiwan University 3 Abstract High-speed miniature brushless direct current motor (BLDCM) is used in robots and medical applications because of its high-torque and high-speed characteristics The authors propose a simple instantaneous source voltage and phase current control for torque ripple reduction of a high-speed miniature BLDCM. To reduce the switching current ripple, instantaneously controlled source voltage is supplied to the inverter system according to the motor speed and the load torque.

4. Department of Electrical Engineering, Southern Taiwan University 4 Introduction In contrast with the general BLDCM, a high-speed miniature BLDCM has a low electrical time-constant to realise high-speed drive with a low source voltage. The current ripple during conduction period is much higher than the general one, which is operated under 10 000 rpm. In the proposed control system, the instantaneous voltage controller adjusts the source voltage of the inverter, and a fast hysteresis current controller keeps the phase current within a limited band to reduce the torque ripple.

5. Department of Electrical Engineering, Southern Taiwan University 5 Torque ripple analysis of a high-speed BLDCM Fig. 1. General inverter for three-phase BLDCM Figure

6. Department of Electrical Engineering, Southern Taiwan University 6 Torque ripple analysis of a high-speed BLDCM where are the phase voltages (V); are the phase resistance and inductance, respectively; are the phase currents (A); is the back-EMF of each phase (V).

7. Department of Electrical Engineering, Southern Taiwan University 7 Torque ripple analysis of a high-speed BLDCM Fig. 2. Operating modes of BLDCM during a. Turn-on period

8. Department of Electrical Engineering, Southern Taiwan University 8 Torque ripple analysis of a high-speed BLDCM b. Turn-off period

9. Department of Electrical Engineering, Southern Taiwan University 9 Torque ripple analysis of a high-speed BLDCM The voltage equation can be expressed during conduction period as follows where is the rotation speed (rad/s) and is the back-EMF constant (V/rad/s). In (2), denotes the switch conditions, = 1 means turn-on period and = － 1 means turn-off period.

10. Department of Electrical Engineering, Southern Taiwan University 10 Torque ripple analysis of a high-speed BLDCM Fig. 3. Phase and DC-link current according to switching pattern

11. Department of Electrical Engineering, Southern Taiwan University 11 Torque ripple analysis of a high-speed BLDCM The supplied voltage of phase winding can be obtained as follows. Even if the phase voltage is determined by the current controller, the average phase voltage in the steady state can beobtained from back-EMF,, and demanded current,, at each rotor position as follows.

12. Department of Electrical Engineering, Southern Taiwan University 12 Torque ripple analysis of a high-speed BLDCM The duty ratio,, and turn-on time can be obtained from bipolar PWM control method as follows. The current and torque ripple of BLDCM can be calculated with an assumption that voltage drop of switching devices is zero in the inverter as follows

13. Department of Electrical Engineering, Southern Taiwan University 13 Torque ripple analysis of a high-speed BLDCM Fig. 4. Maximum torque ripple according to switching frequency and speed

14. Department of Electrical Engineering, Southern Taiwan University 14 Torque ripple analysis of a high-speed BLDCM Fig. 5. Maximum torque ripple according to load current and speed with 100 kHz switching frequency

15. Department of Electrical Engineering, Southern Taiwan University 15 The proposed control system for a high-speed miniature BLDCM The reference voltage of non-inverting amplifier with power OP-amp can be calculated as follows

16. Department of Electrical Engineering, Southern Taiwan University 16 The proposed control system for a high-speed miniature BLDCM Fig. 6. High-speed hysteresis current controller and switching signals a. High-speed hysteresis current controller

17. Department of Electrical Engineering, Southern Taiwan University 17 The proposed control system for a high-speed miniature BLDCM b. PWM signal generation

18. Department of Electrical Engineering, Southern Taiwan University 18 The proposed control system for a high-speed miniature BLDCM c. Switching signals according to Hall-sensor signals

19. Department of Electrical Engineering, Southern Taiwan University 19 The proposed control system for a high-speed miniature BLDCM Fig. 7. Block diagram of the proposed high-speed BLDC speed control

20. Department of Electrical Engineering, Southern Taiwan University 20 Simulation and experimental results Table 1 The specifications of a Prototype BLDCM

21. Department of Electrical Engineering, Southern Taiwan University 21 Simulation and experimental results Fig. 8. Comparison of simulation results at 5000 rpm with 100 kHz switching frequency a. General case b. Proposed case a b

22. Department of Electrical Engineering, Southern Taiwan University 22 Simulation and experimental results Fig. 9. Experimental configuration

23. Department of Electrical Engineering, Southern Taiwan University 23 Simulation and experimental results Fig. 10. Comparison of experimental results at 500 rpm with 100 kHz switching frequency a. General case b. Proposed case ab

24. Department of Electrical Engineering, Southern Taiwan University 24 Simulation and experimental results Fig. 11. Comparison of experimental results at 7500 rpm with 100 kHz switching frequency a. General case b. Proposed case a b

25. Department of Electrical Engineering, Southern Taiwan University 25 Simulation and experimental results Fig. 12. Comparison of experimental results at 30 000 rpm with 100 kHz switching frequency a. General case b. Proposed case ab

26. Department of Electrical Engineering, Southern Taiwan University 26 Simulation and experimental results Figure 13 Experimental result with speed reference change from 2000 to 20 000 rpm

27. Department of Electrical Engineering, Southern Taiwan University 27 Conclusions Because of the low electrical time-constant, the phase current and torque ripple of a high-speed miniature BLDCM are very high in the conduction period. To overcome these problems, a fast instantaneous source voltage controller using power OP-amp and hysteresis current controller are proposed. The proposed instantaneous source voltage controller supplies the proper DC-link voltage of a three-phase inverter according to motor speed and load current.

28. Department of Electrical Engineering, Southern Taiwan University 28 References [1] PILLAY P., KRISHNAN R.: ‘Application characteristics of permanent magnet synchronous and brushless DC motor for servo drives’. IEEE IAS Annual Meeting, 1987, pp. 380–390 [2] BIANCHI N., BOLOGNANI S., LUISE F.: ‘Analysis and design of high speed brushless motors’. Power Electronics Intelligent Motion Conf. Rec., PCIM03, Nurnberg(D),Germany, May 20–22, 2003. CD–ROM [3] BOULES N.: ‘Impact of slot harmonics on losses of highspeed permanent magnet machines with a magnet retaining ring’, Elect. Mach. Electromech., 1981, 6, (6), pp. 527–539 [4] JABBAR M.A., KHAMBADKONE A.M., YANFENG Z.: ‘Development of a high-speed AC brushless appliance motor’. Proc. Electrical Electronic Technology 2001, (TENCON 2), pp. 792–795 [5] CALRSON R., LAJOIE-MAZENC M., FAGUNDES J.C.S.: ‘Analysis of torque ripple due to phase commutation in brushless DC machines’. IEEE Conf. IAS Annual Meeting, 1990, pp. 287–292 [6] CROS J., VINASSA J.M., CLENET S., ASTIER S., LAJOIE-MAZENC M.: ‘A novel current control strategy in trapezoidal EMF actuators to minimize torque ripples due to phases commutations’. Eur. Power Electron. Conf., 1993, vol. 4, pp. 266–271

29. Department of Electrical Engineering, Southern Taiwan University 29 References [7] HANSELMAN D.C.: ‘Minimum torque ripple, maximum efficiency excitation of brushless permanent magnet motors’, IEEE Trans. IE, 1994, 41, (3), pp. 292–300 [8] JAHNS T.M., SOONG W.L.: ‘Pulsating torque minimization techniques for permanent magnet AC motor drives – a review’, IEEE Trans. Ind. Electron., 1996, 43, (2),pp. 321–330 [9] JEROUG H., BOUKAIS B., SAHAOUI H.: ‘Analysis of torque ripple in BDCM’, IEEE Trans. Magn., 2002, 38, (2), pp. 1293–1296 [10] YONEZAWA H., TANIGUCH K., LEE H.W.: ‘Suppression method for torque ripple of PM synchronous motor’, J. Power Electron., 2005, 5, (14), pp. 264–271 [11] UTSMI Y., HOSHI N., OGUCHI K.: ‘Comparison of FPGA-based direct torque controller for permanent magnet synchronous motors’, J. Power Electron., 2006, 6, (2), pp. 114–120 [12] MURAI Y., KAWASE Y., OHASHI K., NAGATAKE K., OKUYAMA K.: ‘Torque ripple improvement for brushless DC miniature motors’, IEEE Trans. Ind. Appl., 1989, 25, (3), pp. 441–450

30. Department of Electrical Engineering, Southern Taiwan University 30 References [13] BECERRA R.C., EHSANI M.: ‘High-speed torque control of brushless permanent magnet motors’, IEEE Trans. Ind. Electron., 1988, 35, (3), pp. 402–406 [14] MARIAH I.H., WAHSH S.A.: ‘Comparative study of high speed brushless dc motor fed from various inverter types’. Proc. 35th SICE Annu. Conf., 1996, pp. 1401–1405 [15] BIANCHI N., BOLOGNANI S., LUISE F.: ‘Analysis and design of a PM brushless motor for high-speed operation’, IEEE Trans. Energy Conv., 2005, 20, (3), pp. 629–637

31. Department of Electrical Engineering, Southern Taiwan University 31 Thanks for your attention!