Transcript Department of Electrical Engineering, Southern Taiwan University

Initial Rotor Position Estimation for
Sensorless Brushless DC Drives
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 4, JULY/AUGUST 2009
Student: G-E Lin
Adviser: Ming-Shyan Wang
Date : 25th-Dec-2009
Department of Electrical Engineering,
Southern Taiwan University
Outline
Abstract
I. INTRODUCTION
II. PROPOSED INITIAL ROTOR POSITION ESTIMATION METHOD
A. Inductance Comparison Process
B. Polarity Determination Process
III. EXPERIMENTAL RESULTS
IV. CONCLUSION
REFERENCES
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Abstract
This paper presents a method for determining the initial rotor position of a
brushless dc machine at standstill without a position sensor.
The key principle of the rotor position estimation is based on the simple de
tection and comparison of phase voltage and current responses relating to t
he stator inductance varied with the position of the rotor magnet.
In the proposed method, only three voltage-pulse injections are applied ,
and a 30◦ resolution can be achieved. Moreover, no knowledge of machine
parameters is required.
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I. INTRODUCTION
brushless dc (BLDC) motors are widely used in a number of industrial
applications because of their high power density, durability, high
efficiency, silent operation, and high starting torque.
An inverter-driven three-phase BLDC motor, as shown in Fig. 1, needs
rotor position information to ensure stable operation by synchronizing
the phase excitation to the rotor position.
Startup is one of the major problems in sensorless BLDC drives, which
are mostly based on back-electromotive-force (EMF) estimation
techniques. The main reason is that the back-EMF voltage disappears
at standstill.
To solve these startup problems, the initial rotor position should
previously be determined. Most popular techniques to estimate the
rotor position are based on the inductance variation, varying with the
rotor position.
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Fig. 1. Inverter-driven three-phase BLDC motor.
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II. PROPOSED INITIAL ROTOR POSITION
STIMATION METHOD
E
The basic principle of estimating rotor position is based on the saturation
effect of the stator core.
The key principle of the proposed method for detecting the rotor position
at standstill is to measure and then compare the stator inductance of each
phase.
The machine parameters are listed in Table I.
Fig. 2 shows the measured current response and calculated inductance
against the actual rotor position.
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TABLE I
PARAMETERS OF THE TESTED BLDC MACHINE
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Fig. 2. Measured current response and calculated equivalent inductance
versus the actual rotor position of a surface-mounted BLDC machine.
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A. Inductance Comparison Process
In this process, a sequence of two voltage pulses is injected to a pair of
selected windings. As shown in Fig. 3, each voltage-pulse injection
consists of two intervals.
The first voltage pulse is injected to the phase-A and phase-B windings
by turning “on” switches AH and BL, as shown in Fig. 3(a).
Therefore, the voltage across the phase-B winding can be detected
through the phase-C terminal and the negative dc bus. Its equivalent
circuit is simplified, as depicted in Fig. 4(a).
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Fig. 3. Switching states for the BLDC drive in Fig. 1 during the first volt
agepulse injection. (a) Pulse-injecting interval. (b) Freewheeling interval.
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Fig. 4. Terminal voltage detection. (a) Pulse-inj
ecting interval of the first
voltage-pulse injection. (b) Freewheeling interv
al of the first voltage-pulse
injection. (c) Pulse-injecting interval of the sec
ond voltage-pulse injection.
(d) Freewheeling interval of the second voltage
-pulse injection.
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B. Polarity Determination Process
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IV. CONCLUSION
A simple initial rotor position estimation method at standstill has been i
ntroduced in this paper. It is based on the stator inductance variation d
ue to the influences of the saturation of the stator iron and the flux d
ue to the position of the rotormagnets.
In the proposed method, only three narrow voltage pulses have been
applied to the phase windings to determine the rotor position, and a 30◦
resolution has been achieved.
Additionally, only one sensing resistor has been added into a typical
BLDC drive. It is particularly suitable for sensorless BLDC drive
applications in which low cost is the major requirement.Moreover, no
machine parameters are required.
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References
[1] STMicroelectronics, Application Note AN1276 BLDC Motor Start Routine
for the ST72141 Microcontroller. [Online]. Available: www.st.com
[2] S. Ogasawara and H. Agaki, “An approach to position sensorless drives for
brushless DC motors,” IEEE Trans. Ind. Appl., vol. 27, no. 5, pp. 928–933,Sep./
Oct. 1991.
[3] P. B. Schmidt, M. L. Gasperi, G. Ray, and A. H. Wijenayake, “Initial rotor a
ngle detection of a non-salient pole permanent magnet synchronous machine,”
in Conf. Rec. IEEE IAS Annu. Meeting, New Orleans, LA, 1997,pp. 459–46
3.
[4] G. H. Jang, J. H. Park, and J. H. Chang, “Position detection and startup
algorithm of a rotor in a sensorless BLDC motor utilizing inductance variation,”
Proc. Inst. Elect. Eng.—Elect. Power Appl., vol. 149, no. 2,pp. 137–142, Mar.
2002.
[5] 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.
[6] Y.-S. Lai, F.-S. Shyu, and S. S. Tseng, “New initial position detection for
three-phase brushless DC motor without position and current sensors,” IEEE
Trans. Ind. Appl., vol. 39, no. 2, pp. 485–491, Mar./Apr. 2003.
[7] J. Sugawara, T. Kaimori, and S. Nichikata, “A novel and simple initial rotor
position detecting method for PMSMs,” in Proc. IEEE PEDS, 2005,pp. 612–61
7.
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Thank you for your attention.
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