Novel Back EMF Zero Difference Point Detection Based Sensorless Technique for BLDC Motor

ELECTRICAL PROJECTS USING MATLAB/SIMULINK
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Novel Back EMF Zero Difference Point
Detection Based Sensorless Technique for
BLDC Motor
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.

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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.

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Fig.3. Steady state operation at the low speed of 600 rpm.
Fig.4. performance of proposed sensorless scheme at 17000 rpm

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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.

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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.

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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.
[5] J. R. Frus and B. C. Kuo, “Closed-loop control of step motors using waveform
detection,” in Proc. Int. Conf. Stepping Motors and Systems, Leeds, U.K., 1976, pp. 77–
84.

Novel Back EMF Zero Difference Point Detection Based Sensorless Technique for BLDC Motor

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