Download Department of Electrical Engineering Southern Taiwan University of

Robot and Servo Drive Lab.
A Unified Approach to Zero-Crossing Point Detection
of Back EMF for Brushless DC Motor Drives without Current
and Hall Sensors
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 26, NO. 6, JUNE 2011
By Yen-Shin Lai and Yong-Kai Lin
Professor： Ming-Shyan Wang
Student ： Chih-Hung Wang
Department of Electrical Engineering
Southern Taiwan University of Science and Technology
2017/5/23
Outline
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Introduction
PWM Techniques
Unified Back EMF Detection Approach
Experimental Confirmation
Conclusion
References
2017/5/23
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Southern Taiwan University of Science and Technology
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Abstract
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The main theme of this paper is to present a unified
approach to back electromotive force (EMF) detection of brushless
dc motor (BLDCM) drives without using any current and Hall sensors.
Pulse width modulation (PWM) techniques and theoretical analysis of back
EMF detection are presented, and followed by the proposed unified back
EMF detection method. It will be shown that the back EMF detection
depends upon the PWM techniques and the method is required to be
slightly modified as the PWM technique is changed.
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Experimental results derived from BLDCM drives without using any
current and Hall sensors fully confirm the theoretical analysis.
2017/5/23
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Southern Taiwan University of Science and Technology
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Introduction
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BLDCM is with the advantages of higher power density, and no need of
mechanical commutation mechanism.
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which results in compact and robust structure. In comparison with
induction motor, BLDCM does not have copper losses on the rotor side.
Because of these features, BLDCM becomes more popular for the
applications, where efficiency is a critical issue or spike caused by
mechanical commutation is not allowed.
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Some technical issues for BLDCM control have drawn our attention.
The topics include how to generate commutation signals without using
expensive sensor for the realization of BLDCM drives.
2017/5/23
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Southern Taiwan University of Science and Technology
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Introduction
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For BLDCM drives control, determining the commutation instants for
BLDCM becomes one of the most essential issues.
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One simple way to determine the commutation instant is based upon the
signal of Hall sensors. However, the alignment of Hall sensors and the
related rotor position becomes very important. Misalignment of Hall
sensors will cause significant torque/current ripple and acoustic noise.
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Sensorless control is an alternative way to derive the commutation instants
for BLDCM. However, start-up process and operation range, especially
under low speed region, are two of the concerns.
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PWM Techniques 1
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The performance of the BLDCM drives is decided by the commutation control
techniques.
The high-side power device is controlled by chopper signal every consecutive 120◦
in a fundamental period and the associated low-side control signal is shifted by
180◦, as compared to its high-side one, to clamp the related inverter output to the
negative dc-link rail. The control signals for the other two legs are shifted by 120◦
and 240◦, respectively.
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PWM Techniques 2
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It turns high-side power device ON and lasts for one-sixth fundamental
period.In the following 60◦, the high-side power device is controlled by
chopper signal. The same control signal is applied to the associated lowside power device except 180◦ phase shift.
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PWM Techniques 3
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The high-side power device is chopped in one-sixth fundamental period. In
the following 60◦, the high-side power device is turn ON and clamped to
the positive dc-link rail.
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PWM Techniques 4
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The chop-controlled area for high-side power device is divided into two
parts, each lasts for 30◦. The same control signal is applied to the associated
low-side power device except 180◦ phase shift.
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PWM Techniques 5
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This PWM technique is the same as PWM technique1. However, only
during free-wheeling period, the high-side
power device is clamped to positive dc-link rail, and the low side power
device is with PWM control.
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Definition of terminal voltages of BLDCM
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Since the back EMF is detected from the terminal voltage of
floating phase, the following equations can be derived:
(1)
ip  in io  0
By Kirchhoff’s voltage law
vn  vp   iprs  Ls dip   ep
dt 

 vn   iprp  Ls dip   en
dt 

(2)
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Back EMF and current waveforms of BLDCM.
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Zero-Crossing Point
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The terminal voltage of the floating phase has either rising edge or
falling edge. For both, when the terminal voltage becomes zero, the
zero-crossing point occurs.
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Rising edge
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The terminal voltage of floating phase is analyzed when chopper signal is
“ON.” In the “Chopper ON” period for PWM technique 2, “positive phase”
is connected to positive dc-link rail and “negative” phase is connected to
negative dc-link rail.
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Chopper On
The terminal voltage for the floating phase can be written as
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vo 

VDC  ipRON   ipRON   eo
2
VDC
 eo
2
(3)
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Chopper Off
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The terminal voltage for the floating phase can be written as
Vo 
 VD  ipRON   eo
(4)
2
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Falling edge
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the terminal voltage of flowing phase for the case of falling
edge. In the “Chopper ON” period for PWM technique 2.
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Chopper ON
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The terminal voltage for the floating phase can be written as
vo 
VDC  ipRON   ipRON   eo
VDC

 eo
2
2
(5)
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Chopper Off
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The terminal voltage for the floating phase can be written as
vo 
VDC  ipRON   VDC  VD   eo
2

2VDC  VD  ipRON 

 eo
2
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Back EMF Detection Method for PWM Techniques
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Experimental Confirmation
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The block diagram of the experimental system,which consists of an FPGA
controller, inverter, BLDCM, and the proposed unified back EMF detection
circuit. To confirm the back EMF detection algorithm, neither current nor
Hall sensor is required. The BLDCM used in this paper is with power
rating of 70 W, eight poles, and rated speed = 2500 r/min. The dclink
voltage and switching frequency of inverter are 24 V and 20kHz.
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Southern Taiwan University of Science and Technology
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Experimental Confirmation
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Southern Taiwan University of Science and Technology
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Experimental Confirmation
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Southern Taiwan University of Science and Technology
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Experimental Confirmation
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Southern Taiwan University of Science and Technology
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Experimental Confirmation
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Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
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Experimental Confirmation
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Southern Taiwan University of Science and Technology
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Experimental Confirmation
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Conclusion
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The contribution of this paper is summarized as follows.
1.Propose a unified back EMF detection method for wide
speed control of sensorless BLDCM drives. The methods
of zero-crossing point detection of back EMF for various
PWM techniques are presented to give low-speed and
high-speed operation. Therefore, the proposed back EMF
detection method is useful for wide speed range.
2017/5/23
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Conclusion
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2.Investigate the dependency of back EMF detection method upon PWM
techniques.
3.Confirmation of theoretical analysis by experimental results.
The experimental results derived from BLDCM drive confirm that the
proposed method works well for various PWM techniques and wide speed
range. Moreover, it is shown that the back EMF detection method is
required to be modified, as the PWM control method is changed, and the
modification to the back EMF detection method includes reference voltage
and sampling instants (Chopper ON or Chopper OFF) of terminal voltage.
Experimental results derived from BLDCM drives without using any
current and Hall sensors fully confirm the theoretical analysis.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
29
References
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[1] K.W. Lee, D. K Kim, B. T. Kim, and B. I. Kwon, “A novel startingmethod
of the surface permanent-magnet BLDC motors without position sensor
for reciprocating compressor,” IEEE Trans. Power Electron., vol. 44,
no. 1, pp. 85–92, Jan./Feb. 2008.
[2] J. Dixon, M. Rodriguez, and R. Huerta, “Position estimator and simplified
current control strategy for brushless-DC motors, using DSP technology,”
in Proc. IEEE IECON Conf., 2002, pp. 590–596.
[3] J. P. M. Bahlmann, “A full-wave motor drive IC based on the backEMF sensing principle,” IEEE Trans. Consum. Electron., vol. 35, no. 3,
pp. 415–420, Aug. 1989.
[4] T. Nagate, A. Uetake, Y. Koike, and K. Tabata, (Seiko Epson Co.), “Brushless
DC motor without position sensors and its controller,” European
Patent, EP0553354-A1–19930804, 1993.
[5] K. Nishimura, “Sensorless motor drives,” U.S. Patent 6 111 372, 2000.
2017/5/23
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Southern Taiwan University of Science and Technology
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Thanks for listening
2017/5/23
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Southern Taiwan University of Science and Technology
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