1. Robot and Servo Drive Lab. Department of Electrical Engineering Southern Taiwan University of Science and Technology Advanced Servo Control 11/13/2014 Student: T A R Y U D I / 林運昇 Advisor : Prof. Ming Shyan Wang Sensorless Control of BLDC Motor Drive for an Automotive Fuel Pump Using a Hysteresis Comparator Tae-Won Chun, Member, IEEE, Quang-Vinh Tran, Hong-Hee Lee, Senior Member, IEEE, and Heung-Geun Kim, Senior Member, IEEE IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 3, MARCH 2014

2. Department of Electrical Engineering Southern Taiwan University Outline Abstract Introduction Sensorless control using hysteresis comparator Start-up technique Alignment of Rotor Position Start-Up Procedure Hardware and Software Configurations Experimental results Conclusion 2015/10/19 2

3. Department of Electrical Engineering Southern Taiwan University Abstract The brushless dc (BLDC) motor sensorless control system for an automotive fuel pump that are based on a hysteresis comparator and a potential start- up method with a high starting torque. The hysteresis comparator is used to compensate for the phase delay of the back EMFs due to a low-pass filter (LPF) and also prevent multiple output transitions from noise or ripple in the terminal voltages. The rotor position is aligned at standstill for maximum starting torque without an additional sensor and any information of motor parameters. Also, the stator current can be easily adjusted by modulating the pulse width of the switching devices during alignment. Some experiments are implemented on a single chip DSP controller to demonstrate the feasibility of the suggested sensorless and start-up techniques 2015/10/19 3

4. Department of Electrical Engineering Southern Taiwan University Introduction The brushless dc (BLDC) motor is receiving much interest in automotive applications especially on vehicle fuel pumps due to its high efficiency, compact size, and lower maintenance when compared to a brush dc motor [1], [2].12 The requirements: Good reliability wide speed range from 3000 to 9000 rpm fast start up high starting torque. In order to obtain an accurate and ripple-free instantaneous torque of the BLDC motor, the rotor position information for stator current commutation must be known, which can be obtained using hall sensors mounted on a rotor [3], [4]34 This results in a high costs as well as poor reliability, which are serious problems at the vehicle applications. 2015/10/19 4

5. Department of Electrical Engineering Southern Taiwan University Introduction The zero-crossing of the back EMF measured from the stator winding is detected and the commutation points can be estimated by shifting 30° from the zero crossing of the back EMFs [5].5 The performance of the sensorless drive deteriorates with the phase shifter in the transient state. Also, it is sensitive to the phase delay of the low-pass filter (LPF) especially at the high speed. 2015/10/19 5 To cope with the aforementioned restriction, many position sensorless algorithms have been considered as potential solutions Conventional sensorless commutation [30]

6. Department of Electrical Engineering Southern Taiwan University Phase terminal voltage and back EMF waveform [30] 2015/10/19 6

7. Department of Electrical Engineering Southern Taiwan University Introduction Several phase shifters to compensate for phase error induced by the LPF of back EMFs are proposed [6], [7], [8], [9].6789 They require an additional compensation circuit including the timers. The position information is extracted by integrating the back EMF of the silent phase [1], [10], [11].11011 This method has an error accumulation problem at low speed. 2015/10/19 7

8. Department of Electrical Engineering Southern Taiwan University Introduction The sensorless control techniques using the phase-locked loop (PLL) and the third-harmonic back EMF are suggested [12], [13].1213 The motor commutation drifts away from the desired phase angle due to the conduction of the freewheel diode. Furthermore, the drift angle varies as the motor parameters, speed, and load conditions change. The improved sensorless controller by removing the effect of the freewheel diode conduction is suggested [14].14 Access to the motor's neutral point is required, which will complicate the motor structure and increase the cost. 2015/10/19 8

9. Department of Electrical Engineering Southern Taiwan University Introduction Some approaches use the zero crossing points of three-phase line-to- line voltages, so that they coincide to six commutation points [15], [16], [17].151617 Although the commutation signals can be obtained without any phase shifter, the phase delay due to the LPF could not be considered and the multiple output transitions of the comparator may occur from the high frequency ripple or noise in the back EMFs. The zero-crossing point of the back EMF for generating proper commutation control of the inverter is calculated by sampling the voltage of the floating phase without using current and position sensors [18], [19].1819 2015/10/19 9

10. Department of Electrical Engineering Southern Taiwan University Introduction Most sensorless techniques are based on back EMF estimation. However, when a motor is at standstill or very low speed, it is well known that the back EMF is too small to estimate a precise rotor position. Therefore, a specific start-up process in sensorless drive systems is required. 2015/10/19 10

11. Department of Electrical Engineering Southern Taiwan University Introduction The general solution to the problem is the open-loop start-up method named “align and go” [5], [20].520 The procedure is to excite two phases of the three-phase windings for a preset time. The permanent magnet rotor will then rotate to align to a specific position. With a known initial rotor position and a given commutation logic, an open-loop control scheme is then applied to accelerate the motor from a standstill. Although this technique can be applied to certain automotive applications, it causes a large instantaneous peak current and generates a temporary vibration. 2015/10/19 11

12. Department of Electrical Engineering Southern Taiwan University Introduction In addition, the rotor position of the BLDC motor can be identified and driven smoothly from standstill without any position sensors by utilizing the inductance variation technique [21], [22], [23].212223 This is done by monitoring the current responses to the inductance variation on the rotor position. Although these methods can detect a precise rotor position at standstill, they result in a complex control algorithm and an increase of the system costs due to an additional current sensor. Instead of the detection of current, only terminal voltage level is used for detection of the initial position of the permanent magnet [24].24 2015/10/19 12

13. Department of Electrical Engineering Southern Taiwan University Introduction Some drawbacks of the aforementioned sensorless and start-up techniques are restricted in an automotive fuel pump application which requires the good reliability, a wide speed range from 3000 to 9000 rpm, fast start up, and high starting torque for the sensorless BLDC motor drive systems. 2015/10/19 13 To satisfy these requirements, this paper presents a sensorless control based on a hysteresis comparator of terminal voltage and a potential start-up method with a high starting torque. The hysteresis comparator is used to compensate for the phase lag due to the LPF and also to prevent multiple output transitions from noise or ripple in the terminal voltages.

14. Department of Electrical Engineering Southern Taiwan University SENSORLESS CONTROL USING HYSTERESIS COMPARATOR 2015/10/19 14 As only two phases of the BLDC motor are energized at any time, the back EMF can be measured from its terminal voltage in the period of an open phase (60°). During the two-phases conduction period (120°), the only difference between the back EMF and its terminal voltage is a stator impedance voltage drop, which may be considerably small compared with the dc voltage source. Therefore, the waveform of the terminal voltage is nearly the same as that of the back EMF. The terminal voltages can be used to detect the commutation points of the BLDC motor instead of the back EMFs at the proposed sensorless control. Block diagram of sensorless control by using a hysteresis comparator

15. Department of Electrical Engineering Southern Taiwan University Hysteresis Comparator The hysteresis comparator is used to compensate for the phase lag of the back EMFs due to the LPF in order to determine the proper commutation sequence of the inverter according to the rotor position. Also, it can prevent multiple output transitions by high frequency ripples in the terminal voltages. The outputs of the three-phase hysteresis comparators become three commutation signals (Z a,Z b,Z c ), and then six gating signals can be generated through some logic equations. 2015/10/19 15 Block diagram of sensorless control by using a hysteresis comparator

16. Department of Electrical Engineering Southern Taiwan University Plots of phase lag caused by LPF The lag will disturb current alignment with the back EMF and will cause serious problems for commutation at high speed. The phase lag in commutation can produce significant pulsating torques in such drive which may cause oscillations of the rotor speed, and generate extra copper losses. 2015/10/19 16 Plots of phase lag to various rotor speeds under a variation of the cut-off frequency

17. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator The filtered a-phase terminal voltage is applied to the inverting input, and the filtered c-phase terminal voltage is applied via R1 to the non inverting input. where V oa is the output voltage of a-phase hysteresis comparator and resistance ratio n=R 2 /R 1. At V oa = +V sat, the output voltage V oa switches to (-V sat), when the differential voltage V da at (1) is negative, i.e., the following condition is satisfied for the filtered c-phase terminal voltage u cf : (1) 2015/10/19 17 Vda : A differential voltage of a-phase hysteresis comparator

18. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator At V oa =(-V sat ), the output voltage V oa switches back to +V sat, when the differential voltage V da at (1) is positive, i.e., the following condition is satisfied for u cf :(1) 2015/10/19 18 a-phase hysteresis comparator

19. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator The term (1/n)V sat in (2) and (3) is defined as a hysteresis band, which is determined by the output voltage level V sat and resistance ratio n. The right sides of (2) and (3) are the lower threshold voltage V LT and the upper-threshold voltage V UT for the a-phase terminal voltage multiplied by (1+1/n), respectively [25]. Both threshold voltages can be given by(2)(3)(2)(3)25 2015/10/19 19

20. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator When the output voltage is at +V sat and u cf is smaller than V LT, the output voltage switches to -V sat. Then, the output voltage stays at -V sat as long as is below with respect to V UT. When u cf is higher than V UT, the output voltage switches back to +V sat. Because the original commutation signal Z a ′ is generated by the filtered terminal voltages, it lags to the proper commutation point. The a-phase commutation signal Z a extracted from the output of the hysteresis comparator leads to the original commutation signal Z a ’ by time t a. The equation of V LT can be expressed as a function of time as where T s is one period of the terminal voltage, and V p is the peak of the terminal voltage. 2015/10/19 20

21. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator Using (6), the time t c at the cross point between V LT and u cf can be derived as follows:(6) 2015/10/19 21 The time t a is the interval from ( T s /12) to t c as By substituting (7) into (8), the advanced angle θ a can be derived as(7)(8)

22. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator The advanced angle θ a is determined by the values of n, V sat, and V p, where the V p is nearly proportional to the rotor speed. This figure plots of the angle θ a for various rotor speeds under various resistance ratios, when the V sat is +1.2 V. The θ a increases as the resistor ratio decreases or the rotor speed decreases. Therefore, the phase lag by LPF at the overall speed range can be compensated by adjusting the resistance ratio of the hysteresis comparator. The resistance ratio is determined to 1.2 in order that the gating signal can be nearly kept in phase with the back EMF when the motor is at the nominal speed, 6000 rpm. 2015/10/19 22 Plots of advanced angle to various rotor speeds under various resistanceratios.

23. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator This Figure shows the plots of the phase delay due to the LPF with 2.5 kHz cut-off frequency, the advanced angle by the hysteresis comparator with 1.2 resistance ratio, and the phase shift of the terminal voltage after compensating for the phase lag by the hysteresis comparator. It can be seen that although the phase lag by the LPF ranges from −4.5° to −13°, the phase shift after compensation ranges only from −3° to +2°. Thus, the maximum commutation delay at the 9000 rpm rotor speed is significantly reduced from −13° to −3°. 2015/10/19 23 Plot of the phase delay, the advanced angle, and the phase shift after compensation

24. Department of Electrical Engineering Southern Taiwan University The operation of the a-phase hysteresis comparator The logic equations for generating six gating signals of three-phase PWM inverter from three commutation signals can be derived as 2015/10/19 24 Timing diagram for commutation signals and three- phase gating signals relative to the terminal voltages

25. Department of Electrical Engineering Southern Taiwan University The a-phase filtered terminal voltage lags to the unfiltered terminal voltage by the phase θ d. Three commutation signals are advanced by the angle θ a to the commutation points estimated by the three-phase filtered terminal voltages, and they can be compensated for the phase delay θ d by the LPF. Because the waveform of the filtered terminal voltage is nearly the same as that of the filtered back EMF, the gating signal of each phase bridge of the inverter is almost in phase with the each phase of the back EMF. 2015/10/19 25 Timing diagram for commutation signals and three- phase gating signals relative to the terminal voltages

26. Department of Electrical Engineering Southern Taiwan University Block diagram for adjusting Vsat This figure shows the circuit block diagram for adjusting the output voltage of hysteresis comparator V sat linearly to the battery output voltage change in order that the θ a maintains constant. The circuit consists of an inverter amplifier with −0.1amplication ratio, an inverting amplifier with minus unity gain for converting from -V sat to +V sat, and two buffers. 2015/10/19 26 Block diagram for adjusting Vsat linearly to the battery voltage change

27. Department of Electrical Engineering Southern Taiwan University START-UP TECHNIQUE When the motor is at standstill or very low speed, the back EMF is too small to estimate a precise rotor position. Therefore, a specific start- up process in sensorless drive systems is needed 2015/10/19 27 Alignment of rotor position. (a) Switching states of the inverter. (b) Initial rotor position.

28. Department of Electrical Engineering Southern Taiwan University A. Alignment of Rotor Position In the BLDC motor, only two phases of the three-phase stator windings are excited at any time by utilizing alternative six excited voltage vectors V1 – V6, That is why the current can flow into only two of the three windings and commutated every 60° of electrical angle. At standstill, the initial rotor position is aligned into one of the six positions that are determined by the six excited voltage vectors to energize two phases of the BLDC motor [20], [26], [27], [28]20262728 2015/10/19 28 Alignment of rotor position. (a) Switching states of the inverter. (b) Initial rotor position.

29. Department of Electrical Engineering Southern Taiwan University A. Alignment of Rotor Position all three stator windings are energized in the case of the proposed start-up scheme by using a specific initial voltage vector (1,0,0). As the rotor is located between voltage vector and, the voltage vector is orthogonal to. It is chosen as the next applied voltage vector in order to achieve maximum starting motor torque at startup. 2015/10/19 29 Alignment of rotor position. (a) Switching states of the inverter. (b) Initial rotor position.

30. Department of Electrical Engineering Southern Taiwan University A. Alignment of Rotor Position It should be noted that the amplitude of the stator current for alignment of the rotor position can be easily adjusted by modulating the pulse width of the switching devices This Figure depicts the three-phase current responses of the BLDC motor, when turning on switch + and modulating the pulse-width of the two switches B− and C− at the same time 2015/10/19 30 Stator currents responses under alignment of rotor position

31. Department of Electrical Engineering Southern Taiwan University A. Alignment of Rotor Position This Figure shows minimum, maximum, and average values of the a-phase stator current with a variation of the duty cycles of PWM signals when a switching period is 100 μs. Obviously, the magnitude of the stator current can be easily governed by adjusting the duty cycle, which can be decided by considering the initial torque required at alignment. This method can prevent a surge of current that may damage the motor as in the case of utilizing the conventional method, and also it is robust with motor parameter changes. 2015/10/19 31 Magnitude of stator current to various duty cycles

32. Department of Electrical Engineering Southern Taiwan University B. Start-Up Procedure After aligning the rotor position, the start-up procedure is considered for accelerating the BLDC motor from standstill up to a specific speed, 3000 rpm which is a minimum speed at the automotive fuel pump application. As the sensorless scheme is not self-starting, the motor should be started and can be brought to a certain speed at which the zero- crossing point of the back EMF can be detected. The v/f starting method is used at this paper, which is suitable for the BLDC motor drive. The open loop starting based on / control is accomplished by producing the rotating electric field with a specific relationship to the reference voltage in terms of a rotor speed. 2015/10/19 32

33. Department of Electrical Engineering Southern Taiwan University B. Start-Up Procedure As the frequency is gradually increased, the rotor speed also increases. The magnitude of a reference voltage is adjusted as proportional to the rotor speed. A phase angle can be obtained from integrating the rotor speed and the pulse width of the gating signals is modulated with the reference voltage magnitude. The six PWM signals with 60° phase displacement are generated corresponding to the phase angle without any rotor position information. When the rotor speed reaches at 3000 rpm, the back EMF can be sensed to provide the rotor position information and the system is switched to the sensorless control. 2015/10/19 33

34. Department of Electrical Engineering Southern Taiwan University Experimental Setup 2015/10/19 34 Experimental setup. (a) Hardware configuration. (b) Photograph of the experimental setup (a) (b) The control system is implemented by a 16-bit DSP type TMS320LF2406 operating with a clock frequency of 40 MHz and the sampling interval is 50 μs for both the start-up and sensorless controls. The DSP generates six PWM signals and also measures a rotor speed by using the three- phase commutation signals. The reference speed can be changed from the host computer through a RS232 C serial port. a 12-bit 4-channel D/A converter and displayed on an oscilloscope.

35. Department of Electrical Engineering Southern Taiwan University BLDC Parameter 2015/10/19 35

36. Department of Electrical Engineering Southern Taiwan University Software Flowchart The rotor is aligned to the initial position for a time interval of 80 ms with constant duty cycle, and then the motor is accelerated to 3000 rpm by the proposed start-up method. When the rotor speed is greater than 3000 rpm, a sensorless control scheme for the BLDC motor is applied 2015/10/19 36

37. Department of Electrical Engineering Southern Taiwan University Experiment results This Figure shows the a-phase and c-phase filtered terminal voltages, Za, and a stator current at the light load condition when the rotor speed is 3000 (a) and 6000 (b) 2015/10/19 37

38. Department of Electrical Engineering Southern Taiwan University Experiment results This Figure shows the a-phase and c-phase filtered terminal voltages, Za =10.7º, and a stator current at the light load condition when the rotor speed is 9000 rpm (c) 2015/10/19 38 Plot of the phase delay, the advanced angle, and the phase shift after compensation

39. Department of Electrical Engineering Southern Taiwan University Experiment results This figure shows the unfiltered and filtered a-phase terminal voltages and gating signals of the a-phase switching devices at = 6000 rpm. Although the filtered terminal voltage lags the nonfiltered terminal voltage, A+ and A− both are nearly in phase with the actual terminal voltage 2015/10/19 39 A-phase terminal voltages and gating signals at ωr = 6000 rpm.

40. Department of Electrical Engineering Southern Taiwan University Experiment results This Figure shows the unfiltered and filtered a-phase terminal voltages and stator current at heavy load when the rotor speed is 6000 rpm. The stator current is increased and the conducting period of the freewheeling diode is extended a little bit. 2015/10/19 40 Terminal voltages and stator current at heavy load when the rotor speed is 6000 rpm

41. Department of Electrical Engineering Southern Taiwan University Experiment results The switching device A+ is always conducted and both switches B− and C− are modulated by 7% and 15% duty cycles, respectively. The average values of stator current are about 0.8 and 4 A when the duty cycle is 7% and 15%, respectively. 2015/10/19 41 PWM signals and stator current response under aligning rotor position. (a) At 7% duty cycle. (b) At 15% duty cycle

42. Department of Electrical Engineering Southern Taiwan University Experiment results It can be seen that both of average values of stator current are similar with those as shown in this Figure and the magnitude of stator current can be easily controlled by the duty cycle for aligning a rotor position. 2015/10/19 42 Magnitude of stator current to various duty cycles

43. Department of Electrical Engineering Southern Taiwan University Experimental result 2015/10/19 43 Start-up currents with a variation of the initial angle between stator and rotor fluxes under the light load condition. (a) At initial angle = 90 ◦. (b)At initial angle = 60 ◦. (c) At initial angle = 0 ◦.

44. Department of Electrical Engineering Southern Taiwan University Experimental result 2015/10/19 44 Start-up currents with a variation of the initial angle between stator and rotor fluxes under the light load condition. (c) At initial angle = 0 ◦. The system is switched from the start-up mode to the sensorless control mode, when the rotor speed reaches at 1500 rpm. It can be seen that the start-up current at the initial angle = 90° is lowest, and the start-up current increases as the initial angle decreases to 0° under both load conditions. The start-up current at the same angle is higher under the heavy load condition

45. Department of Electrical Engineering Southern Taiwan University Experimental result 2015/10/19 45 Start-up currents with a variation of the initial angle between stator and rotor fluxes under the heavy load condition. (a) At initial angle = 90 ◦. (b) At initial angle = 60 ◦. (c) At initial angle = 0 ◦.

46. Department of Electrical Engineering Southern Taiwan University Experimental result 2015/10/19 46 Start-up currents with a variation of the initial angle between stator and rotor fluxes under the heavy load condition.(c) At initial angle = 0 ◦. The system is switched from the start-up mode to the sensorless control mode, when the rotor speed reaches at 1500 rpm. It can be seen that the start-up current at the initial angle = 90° is lowest, and the start-up current increases as the initial angle decreases to 0° under both load conditions. The start-up current at the same angle is higher under the heavy load condition

47. Department of Electrical Engineering Southern Taiwan University Experimental result The responses of the reference and rotor speeds, reference voltage, and -phase current in order to verify the start-up technique. At first, the rotor is aligned to the initial position for a time interval of 80 ms by adjusting the duty cycle to 15%. Then, the motor is accelerated to 3000 rpm by the proposed start-up method. Subsequently, a sensorless control scheme for the BLDC motor is applied for speeding up the motor to 6000 rpm. The start-up time is about 1.2 s, which is acceptable for vehicle fuel pump application. 2015/10/19 47 Fig. 19. Transient responses from the start- up mode to the sensorless mode

48. Department of Electrical Engineering Southern Taiwan University CONCLUSION The maximum commutation phase lag is significantly reduced from −13° to −3° by adjusting both the resistance ratio and the output voltage level of the hysteresis comparator, The commutation signal is nearly in phase with the back EMF. If a peak of ripple voltage in the terminal voltage is within the hysteresis band +1 V regardless of magnitude of the terminal voltage, it can prevent multiple output transitions at a hysteresis comparator by high frequency ripples in the terminal voltage. 2015/10/19 48

49. Department of Electrical Engineering Southern Taiwan University CONCLUSION After aligning the rotor position for achieving the maximum starting torque, the BLDC motor accelerates from a standstill up to a nominal speed within 1.2 s. The magnitude of the stator current for aligning the rotor position can be easily controlled by modulating the pulse width of specific switching devices. Through the experimental results, it can be seen that the proposed sensorless and start-up techniques are ideally suited for the automotive fuel pump application. 2015/10/19 49

50. Department of Electrical Engineering Southern Taiwan University Reference [1] J. Shao, “An improved microprocessor-based sensorless brushless DC (BLDC) motor drive for automotive applications,” IEEE Trans. Ind. Appl., vol. 42, no. 5, pp. 1216–1221, Sep./Oct. 2006. [2] J. Gao and Y. Hu, “Direct self-control for BLDC motor drives based on three-dimensional coordinate system,” IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 2836–2844, Aug. 2010. [3] J. Fang, X. Zhou, and G. Liu, “Instantaneous torque control of small inductance brushless DC motor,” IEEE Trans. Power Electron., vol. 27, no. 12, pp. 4952–4964, Dec. 2012. [4] J. Fang, X. Zhou, and G. Liu, “Precise accelerated torque control for small inductance brushless DC motor,” IEEE Trans. Power Electron., vol. 28, no. 3, pp. 1400–1412, Mar. 2013. [5] N. Matsui, “Sensorless PM brushless dc motor drives,” IEEE Trans. Ind. Electron., vol. 43, no. 2, pp. 300–308, Apr. 1996. [6] K. Y. Cheng and Y. Y. Tzou, “Design of a sensorless commutation IC for BLDC motors,” IEEE Trans. Power Electron., vol. 18, no. 6, pp. 1365–1375, Nov. 2003. [7] Y.Wu, Z. Deng, X.Wang, X. Ling, and X. Cao, “Position sensorless control based on coordinate transformation for brushless DC motor drives,” IEEE Trans. Power Electron., vol. 25, no. 9, pp. 2365–2371, Sep. 2010. [8] G. J. Su and J. W. McKeever, “Low-cost sensorless control of brushless DC motors with improved speed range,” IEEE Trans. Power Electron., vol. 19, no. 2, pp. 296–302, Mar. 2004. [9] D. H. Jung and I. J. Ha, “Low-cost sensorless control of brushless DC motors using a frequency-independent phase shifter,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 744–752, Jul. 2000. [10] R. C. Becerra, T. M. Jahns, and M. Ehsani, “Four-quadrant sensorless brushless ECM drive,” in Proc. IEEE- APEC’91 Conf., 1991, pp. 202–209. [11] T. M. Jahn, R. C. Becerra, and M. Ehsani, “Integrated current regulation for a brushless ECM drive,” IEEE Trans. Power Electron., vol. 6, no. 1, pp. 118–126, Jan. 1991. [12] J. X. Shen, Z. Q. Zhu, andD.Howe, “Sensorless flux-weakening control of permanent-magnet brushless machines using third-harmonic back-EMF,” IEEE Trans. Ind. Appl., vol. 40, no. 6, pp. 1629–1636, Nov./Dec. 2004. [13] M. Fraq and D. Ishak, “A new scheme sensorless control of BLDC motor using software PLL and third harmonic back-EMF,” in Proc. IEEE Symp. Ind. Electron. Appl., 2009, pp. 861–865. [14] J. X. Shen and S. Iwasaki, “Sensorless control of ultrahigh-speed PM brushless motor using PLL and third harmonic back EMF,” IEEE Trans. Ind. Electron., vol. 53, no. 2, pp. 421–427, Apr. 2006. 2015/10/19 50

51. Department of Electrical Engineering Southern Taiwan University [17] A. Halvaei, A. Vahedi, and H. Moghbelli, “A novel position sensorless control for a four-switch, brushless DCmotor drive without phase shifter,” IEEE Trans. Power Electron., vol. 23, no. 6, pp. 3079–3087, Nov. 2008. [18] Y. S. Lai andY. K. Lin, “Novel back-EMF detection technique of brushless DC motor drives for wide range control without using current and position sensors,” IEEE Trans. Power Electron., vol. 23, no. 2, pp. 934–940, Mar.2008. [19] Y. S. Lai and Y. K. Lin, “A unified approach to zero-crossing point detection of back-EMF for brushless DC motor drives without current and hall Sensors,” IEEE Trans. Power Electron., vol. 26, no. 6, pp. 1704–1713,Jun. 2011. [20] S. Ogasawara and H. Akagi, “An approach to position sensorless drive for brushless DCmotors,” IEEE Trans. Ind. Appl., vol. 27, no. 5, pp. 928–933, Sep./Oct. 1991. [21] G. H. Jang, J. H. Park, and J. H. Chang, “Position detection and start-up algorithm of a rotor in a sensorless BLDC motor utilizing inductance variation,” IEE Proc., Electr. Power Appl., vol. 149, no. 2, pp. 137–142,2002. [22] W. J. Lee and S. K. Sul, “A new starting method of BLDC motors without position sensor,” IEEE Trans. Ind. Appl., vol. 42, no. 6, pp. 1532–1538, Nov./Dec. 2006. [23] P. Champa, P. Somrisi, P. Wipasuramonton, and P. Nakmahachalasint, “Initial rotor position estimation for sensorless brushlessDCdrives,” IEEE Trans. Ind. Appl., vol. 45, no. 4, pp. 1318–1324, Jul./Aug. 2009. [24] Y. S. Lai, F. S. Shyu, and S. S. Tseng, “New initial position detection technique for three-phase brushlessDCmotor without position and current sensors,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 485–491, Mar./ Apr.2003. [25] R. F. Coughlin and F. F. Driscoll, Operational Amplifiers and Linear Integrated C0ircuit. Englewood Cliffs, NJ, USA: Prentice-Hall, 2007. [26] L. Zhang,W. Xiao, andW. Qu, “Sensorless control of BLDCmotors using an improved low-cost back-EMF detection method,” in Proc. IEEE Power Electron. Spec. Conf., 2006, pp. 1–7. [27] K. W. Lee, D. K. Kim, B. T. Kim, and B. I. Kwon, “A novel starting method of the surface permanent-magnet BLDC motors without position sensor for reciprocating compressor,” IEEE Trans. Ind. Appl., vol. 44,no. 1, pp. 85–92, Jan./Feb. 2008. [28] M. Ku and Y. Li, “A novel sensorless starting method of BLDC motor for large inertia system,” in Proc. IEEE Electron. Mech. Eng. Inf. Technol., 2011, pp. 3449–3452. [29] Z. Wang, K. Lu, and F. Blaabjerg, “A simple startup strategy based on current regulation for back-EMF-based sensorless control of PMSM,” IEEE Trans. Power Electron., vol. 27, no. 8, pp. 3817–3825, Aug. 2012. [30] Ming Shyan Wang “ BLDC Motor (2) “,Hand out lecturer Advanced Servo Control, 2014 2015/10/19 51

52. Department of Electrical Engineering Southern Taiwan University Thank you for your attention 2015/10/19 52