Practical sensorless control for inverter-fed
BDCM compressors
CHEN H.C., CHANG Y.C., HUANG C.K.: ‘Practical sensorless control for inverterfed BDCM compressors’, IET Electric Power Appl., 2007, 1, (1), pp. 127–132
Student: Chien-Chih Huang
Teacher: Ming-Shyan Wang
Date : 2011.04.27
Department of Electrical Engineering,
Southern Taiwan University
Outline
Abstract
Introduction
System configuration
Sensorless circuits
Terminal-voltage analysis
Design of sensorless circuits
Design results
Sensorless-commutation table
Sensorless control
Starting strategy
Limitations
Practical sensorless control
Experiment Results
Conclusion
References
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Abstract
Brushless DC motors (BDCMs) possess higher efficiencies
than the conventional induction motors and BDCMs have
therefore been used widely in inverter-fed compressors.
Since the Hall position sensors cannot work well in the
high-temperature environment of refrigerants,sensorless
control schemes play an important role in the application
of inverter-fed BDCM compressors.
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Abstract
The sensorless circuits used have been analysed in detail to
find the design rules of the circuit parameters for various
compressor motors.
The limitations of sensorless control are discussed to develop
a practical speed controller for BDCM compressors.
The developed starting strategy and sensorless algorithms are
presented and digitally implemented.
Some experimental results are displayed to demonstrate the
proposed sensorless speed control for BDCM compressors.
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Introduction
During the last decades, more and more researchers have
focused their attention on energy-saving technology and
promoted the development of high-efficiency products.
It has been concluded that inverter-fed compressors (or
called variable-speed compressors) are the key to increasing
system efficiency and reducing energy consumption.
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Introduction
To commutate the motor current adequately, the actual
rotor positions are required in normal BDCM operation.
Unfortunately, in the refrigeration application,hightemperature refrigerants will surround the compressor
motor and commonly used rotor-position sensors such as
Hall elements cannot be used to sense the positions.
To solve this problem, many sensorless control methods
have been proposed.
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System configuration
Fig. 1 System configuration of the sensorless speed control
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System configuration
Fig. 2 Waveforms of the BDCM operation
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Terminal-voltage analysis
As shown in Fig. 1, we can express the terminal voltagesVx as
VX = VN + EX + iXZX = VN + EX + VZX
X=U，V，W (1)
Since｜VZX ｜is generally smaller than ｜EX｜ in motor operation
VZX can be neglected and thus (1) can be rewritten as
VXN = VX － VN ≒ EX
X=U，V，W (2)
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Design of sensorless circuits
Fig. 3 Sensorless circuits
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Design of sensorless circuits
The transfer function between the terminal voltage VU and the
new signal vU can be derived as
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Design of sensorless circuits
Note that the near-90°phase shifting occurs at a frequency ten times
higher than the cut-off frequency of the lowpass filter.
The DC-filtering stage designed here is to prevent the DC and lowfrequency components from appearing in the filtering signals.
The main function of the last PWM-filtering stage is to attenuate
the high-frequency component in signals. Thus, its cut-off
frequency fcut3 must be placed far smaller than the PWM frequency
f PWM and larger than the highest frequency (PωrHigh/120).
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Design results
The PWM switching frequency is fpwm = 8 kHz and the 4P BDCM
compressor is operating during the speed range between 1000
rev/min (=ωrLow) and 6000 rev/min (=ωrHigh) to yield variable
cooling capability.
It is sensible to select the individual resistor and capacitor values as
follows to meet the design rules (8)–(10).
R1 = 470 kΩ， R2 = 47 kΩ， R3 = 30 kΩ
R4 = 470Ω， C1 = C2 = 2.2μF， C3 = 0.47μF
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Design results
Fig. 4 Responses of resulting sensorless circuits for different values of resistor R4
(a) Amplitude response (b) Phase response
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Sensorless-commutation table
Table 1: Sensorless-commutation table
ABC D E FA
Fig. 2 Waveforms of the BDCM operation
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Starting strategy
Fig. 5 Timing diagram of proposed starting strategy
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Starting strategy
The period Tn of each commutation state in starting strategy
is obtained as
and the synchronous speed orsyn can be formulated as
Then, (12) can be rewritten as
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Limitations
Fig. 6 Limitations of the sensorless controlled BDCM
(a) Torque against speed
(b) Power against speed
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Practical sensorless control
Fig. 7 Proposed sensorless speed controller for actual BDCM compressors
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Practical sensorless control
The BDCM speed or in revolutions per minute is obtained from
the period TU of signal HU through counting in the MCU timer:
The above limiting lines Tmin will be considered in our sensorless
speed controller. After obtaining the frontend input current iin
through the current transformer (CT) and the A/D peripherals shown
in Fig. 1, we can estimate the input power estimate P . Then, the
estimated power P will be co-ordinated in Fig. 6b to decide the
speed limit or;lim it as shown in Fig. 7
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Experimental results
Fig. 8 Voltage and current waveforms at 5400 rev/min withdifferent values of R4
(a) R4=2kΩ
(b) R4=470Ω
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Experimental results
Fig. 9 Critical waveforms at different speeds
(a) 900 rev/min
(b) 1800 rev/min
(c) 2700 rev/min
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Experimental results
Fig. 9 Critical waveforms at different speeds
(d) 3600 rev/min
(e) 4500 rev/min
(f) 5400 rev/min
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Experimental results
Table 2: Experimental data of developed BDCMcompressor
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Conclusion
This paper develops a sensorless controller for BDCM
compressors where the operating limitations of inverter-fed
BDCM compressors and sensorless control are considered.
To improve the current waveforms, the sensorless circuits are
designed and implemented.
The control algorithms, including the starting strategy, the
sensorless commutation table and the speed-control loops, are all
implemented digitally in MCU.
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References
1 Murakami, H., Honda, Y., Kiriyama, H., Morimoto, S., and Takeda, Y.: ‘The
performance comparison of SPMSM, IPMSM and SynRM in use as airconditioning compressor’. Proc. IAS’99, 1999, pp. 840–845
2 Soong, W.L., Kliman, G.B., Johnson, R.N., White, R.A., and Miller, J.E.:
‘Novel high-speed induction motor for a commercial centrifugal compressor’,
IEEE Trans. Ind. Appl., 2000, 36, (3), pp. 706–713
3 Llzuka, K., Uzuhashi, H., Kano, M., Endo, T., and Mohri, K.:
‘Microcomputer control for sensorless brushless motor’, IEEE Trans. Ind.
Appl., 1985, 21, (4), pp. 595–601
4 Moreira, J.C.: ‘Indirect sensing for rotor flux position of permanent magnet
AC motors operation in a wide speed range’. Proc. IAS’94, 1994, pp. 401–407
5 Ogasawara, S., and Akagi, H.: ‘An approach to position sensorless drive for
brushless DC motors’, IEEE Trans. Ind. Appl., 1991, 27, (5), pp. 928–933
6 Chen, H.C., and Liaw, C.M.: ‘Current-mode control for sensorless BDCM
drive with intelligent commutation tuning’, IEEE Trans. Power Electron.,
2002, 17, (5), pp. 747–756
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References
7 Chen, Z., Tomita, M., Doki, S., and Okuma, S.: ‘An extended electromotive
force model for sensorless control of interior permanentmagnet synchronous
motors’, IEEE Trans. Ind. Electron., 2003, 50, (2), pp. 288–295
8 Shao, J., Nolan, D., and Hopkins, T.: ‘Improved direct back EMF detection
for sensorless brushless DC (BLDC) motor drives’. Proc. APEC’03, 2003, pp.
300–305
9 Chen, H.C., Chang, Y.C., Lin, S.P., Huang, C.M., Chen, Y.C., and Liang,
K.Y.: ‘Sensorless control for DC inverter-fed compressors’. Proc. APEC’04,
2004, pp. 1106–1110
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Thanks for your attention!
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