In this paper, a novel motor control method is proposed to improve the performance of sensorless drive of BLDC motors. In the terminal voltage sensing method, which is a great portion of sensorless control, a precise rotor position cannot be obtained when excessive input is applied to the drive during synchronous operation mode. Especially in the transient state, the response characteristic decreases. To cope with this problem, the unknown input (back-EMF) is modelled as the additional state of system in this paper. Taking into account the disturbance adopted by the back-EMF, the observer can be obtained by an equation of the augmented system. An algorithm to detect the back-EMF of a BLDC motor using the state observer is constructed. As a result, a novel sensorless drive of BLDC motors that can strictly estimate rotor position and speed is proposed.

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Unknown Input Observer for
a Novel Sensorless Drive of Brushless DC Motors
ABSTRACT:
In this paper, a novel motor control method is proposed to improve the performance of sensorless
drive of BLDC motors. In the terminal voltage sensing method, which is a great portion of
sensorless control, a precise rotor position cannot be obtained when excessive input is applied to
the drive during synchronous operation mode. Especially in the transient state, the response
characteristic decreases. To cope with this problem, the unknown input (back-EMF) is modelled
as the additional state of system in this paper. Taking into account the disturbance adopted by the
back-EMF, the observer can be obtained by an equation of the augmented system. An algorithm
to detect the back-EMF of a BLDC motor using the state observer is constructed. As a result, a
novel sensorless drive of BLDC motors that can strictly estimate rotor position and speed is
proposed.
SOFTWARE:MATLAB/SIMULINK

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BLOCK DIAGRAM:
Fig. 1. Block diagram of BLDC motor drive.

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EXPECTED SIMULATION RESULTS:
Fig. 2. Speed response for the start and transient state. (a) In the proposed sensorless scheme. (b) In the conventional
scheme use sensor.

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Fig. 3. Simulation results of the proposed sensorless scheme at 2000 (rpm). (a) Rotor speed. (b) Rotor position. (c)
Phase current. (d) Line-to-line back-EMF. (e) Commutation function. (f) Commutation signal.

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Fig. 4. Simulation results of the proposed sensorless scheme at 100 (rpm). (a) Rotor speed. (b) Rotor position. (c)
Phase current. (d) Line-to-line back-EMF. (e) Commutation function. (f) Commutation signal.

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CONCLUSION:
In this paper, the unknown input (back-EMF) is modeled as the additional state of system.
Considering disturbance that is adopted by back-EMF, the observer can be obtained effectively
using the equation of augmented system and estimating back-EMF. As a result, an effective
algorithm to estimate rotor position and speed of motor using the state observer is proposed. Use
of sensorless control method can remove problem on manufacture that is happened in circuit to
detect rotor position and speed. Moreover the production of inexpensive motor controller may be
possible because the additional circuit such as encoder is not necessity. In cases using the
proposed sensorless control method, the start-up performance has an almost analogous transient
state characteristic after forced alignment, compared with the conventional method. This method
also provides useful motor control because it is possible to analyze about transient state as well
as steady state unlike various sensorless control methods that have been recently proposed. In
addition, it can be easily applied in industry applications requiring the low-cost style drive of
BLDC motor because actual realization is very simple.
REFERENCES:
[l] T. J. E Miller, “Brushless Permanent-Magnet and Reluctance Motor Drives,” Clarendon
Press, Oxford 1989.
[2] S. Ogasawara and H. Akagi, “An Approach to Position Sensorless Drive for Brushless DC
Motors,” IEEE Trans. Ind. Appl., vol. 27, no. 5, pp. 928-933, Sep./Oct. 1991.
[3] J. C. Moreira, “Indirect Sensing for Rotor Flux Position of Permanent Magnet AC Motors
Operating Over a Wide Speed Range,” IEEE Trans. Ind. Appl., vol. 32, no. 6, pp. 1392-1401,
Nov./Dec. 1996.

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[4] H. R. Andersen and J. K. Pedersen, “Sensorless ELBERFELD Control of Brushless DC
Motors for Energy-Optimized Variable-Speed Household Refrigerators,” EPE Conf. Rec., vol. 1,
pp. 314-318, Sep. 1997.
[5] Hyeong-Gee Yee, Chang-Seok Hong, Ji-Yoon Yoo, Hyeon-Gil Jang, Yeong-Don Bae and
Yoon-Seo Park, “Sensorless Drive for Interior Permanent Magnet Brushless DC Motors,”
Electric Machines and Drives Conf. Record, 1997, IEEE International 18-21 pp. TD1/3.1-
TD1/3.3, May 1997.