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A novel sensorless control method for
brushless DC motor
H.-B. Wang and H.-P. Liu, Published in IET Electric Power Applications
Student: Wei-Ting Yeh
Adviser: Ming-Shyan Wang
Date
: Jan,14,2010
Department of Electrical Engineering,
Southern Taiwan University
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Outline
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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
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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
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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.
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Model of inductance of IPM BLDCM
Fig. 1. Inverter topology and equivalent circuit of the BLDCM
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Model of inductance of IPM BLDCM
Fig. 2.
BEMF waveforms
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Model of inductance of IPM BLDCM
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.
where
is the mechanical speed of a motor,
BEMF constant.
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is the
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Model of inductance of IPM BLDCM
The stator selfinductances of IPM motor can be approximately
expressed as
The stator-to-stator mutual inductances are
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Model of inductance of IPM BLDCM
Equation (4) gives exact relationships among rotor positions,
self-inductances, mutual inductances and BEMF.
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Principle of the proposed method
Fig. 4. Equivalent circuit
during the PWM on time
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Principle of the proposed method
The circuit equations of Fig. 4 are
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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
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Principle of the proposed method
Fig. 5. Equivalent circuit
during the PWM off time
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Principle of the proposed method
The circuit equations of Fig. 5 are
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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
potential of C-phase,
. Substituing (4) into (13), the
can be represented as
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Principle of the proposed method
Comparing (9) with (14) gives
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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
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Analysis of the sensitivity of the
proposed method
Fig. 6. The A-phase current waveform in a H_PWML_PWM period
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Analysis of the sensitivity of the
proposed method
According to similar triangle principle, Fig. 6 can give
approximately
The voltage difference
(T) between
((t+t T)/2) can be represented as
(t=2) and
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Analysis of the sensitivity of the
proposed method
Substituting (8), (13), (16), (17), (18) into (19) gives
From (2), we have
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Analysis of the sensitivity of the
proposed method
If the difference of
(20) gives
is ignored, substituting (21) into
The direct and the quadrature axis inductance are
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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
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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
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Experimental results
Fig. 7. Block diagram representation showing the implementation of the
proposed system
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Experimental results
Fig. 8. Three-phase terminal voltage and HALL commutation signal
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Experimental results
Fig. 9. The process of estimating ZCP of unconducting phase
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Experimental results
Fig. 10. A- and B-phase terminal voltages, the ZCP and
estimated commutation signal
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Experimental results
Fig. 11. A- and B-phase terminal voltages, the commutation signal
from Hall sensor and the estimated commutation signal
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Experimental results
Figure 12 The real A-phase current waveform and
corresponded PWM waveform
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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.
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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
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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
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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
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Thanks for your attention!
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