ABSTRACT
In this paper a novel position sensorless scheme named
Back EMF Zero Difference Point (ZDP) detection has been proposed for six-switch
VSI converter fed permanent magnet BLDC motor. This technique is based on the
comparison of back EMFs and detection of the points in the back EMF waveforms
where they cross each other or in other words they are equal. Commutation point
is achieved exactly at the same instant when the difference of back EMFs of any
two phases becomes zero. The simulation study has been carried out for the proposed
sensorless scheme. The proposed sensorless scheme has the excellent performance
from zero to the extra high speed. The method needs no additional delay circuit
as used for calculation of commutation point from back EMF ZCP and involves
less calculation burden. The method is fault tolerant and accurate even in the
case of noise in measurement (or estimation) of phase back EMFs. A nonzero
threshold value proportional to input voltage (or reference speed) is used for
overcoming the problem due to quantization and sampling for digital
implementation. This method proves to be excellent substitute of hall sensing scheme
as it also senses at zero speed.
KEYWORDS:
1.
BLDC motor
2.
Back EMF ZDP
3.
Commutation
4.
Sensorless control
5.
Zero difference point.
SOFTWARE: MATLAB/SIMULINK
CIRCUIT
DIAGRAM:
Fig.1 VSI fed BLDC motor with indirect
Back EMF detection scheme
EXPECTED SIMULATION RESULTS:
Fig.2.
Phase Back EMF ZDPs, switching signals, counter output and triggering sequence
signals.
Fig.3.
Steady state operation at the low speed of 600 rpm.
Fig.4.
performance of proposed sensorless scheme at 17000 rpm
Fig.5.
Noise immune performance during steady state operation for reference speed of
17000rpm.
Fig.6.
sensing fault occurs at 0.5 second in the measurement of phase-B back EMF.
Fig.7.
speed increases when sensing fault occurs (here phase-B sensing fault
CONCLUSION
In
the proposed Back EMF Zero Difference Point (ZDP) detection method, the very
first commutation signal is achieved at starting itself i.e. one step before
the ZCP method, which proves the superiority of the method. The back EMF for
the proposed scheme can be applied to various existing back EMF detection or
estimation techniques. This technique is insensitive to the inherent noise in
measurement (or estimation) of back EMF. This method does not need extra circuitry
as needed for delay after ZCP for getting commutation point, thereby less
computational complexity is involved. The speed (or input voltage) proportional
threshold used for avoiding uncertainty in the zero difference of back EMF,
sets its scope of wide usability in precise operation from zero to extra high
speed. Operation at initial zero back EMF is the main strength of this method
and it doesn’t necessitate separate starting techniques. Speed response at
transient period is 0.15 ms faster than previous methods for identical motor
parameters.
REFERENCES
[1] M.V.Kesava
Rao, Department of Electrical technology, IISc Bangalore, ‘‘Brush Contact Drops
in DC machines’’, Accepted 25-6-1934, Bangalore Press.
[2] Y.S. Jeon, H.S. Mok, G.H. Choe, D.K. Kim, J.S.
Ryu, “A New Simulation Model of BLDC Motor with Real Back EMF waveform”, 7 th
workshop on Computers in power Electronics , 2000 (COMPEL 2000), page 217- 220.
[3] Padmaja
yedmale, “Brushless DC (BLDC) Motor Fundamentals”, AN885, 2003 Microchip
Technology.
[4] S. Tara , Syfullah Khan Md “Simulation of
sensorless operation of BLDC motor based on the zero cross detection from the
line voltage” International Journal of Advanced Research in Electrical
Electronics and Instrumentation Engineering, vol 2, issue 12 , December 2013,
ISSN 2320-3765.
J. R. Frus and B. C. Kuo, “Closed-loop control
of step motors using waveform detection,” in Proc. Int. Conf. Stepping Motors
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