IMPLEMENTATION OF DSP BASED SENSORLESS CONTROL WITH
DIRECT BACK-EMF DETECTION METHOD FOR BLDC MOTOR

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ACKNOWLEDGEMENTS
I am greatly indebted and respectful to my supervisor and advisor, Dr. K.S. Rama Rao,
for his guidance and support throughout the completion of this thesis. His rigorous
attitude to do the research and inspiring thinking to solve problems are invaluable for
my professional career.
I would like to express my heartfelt thanks to Dr Soib Taib for his time and
efforts he spent as my co-supervisor. I am also grateful to the faculty and staff
members of Universiti Sains Malaysia, for their help.
I would like to express my appreciation to my fellow graduate students in USM.
To me, the friendship with the members of USM is a big treasure. Their hardworking,
perseverance, sharing, and self-motivation have always inspired me.
ABSTRAK
Projek ini mempersembahkan satu kaedah baru untuk mengesan voltan balikkan EMF
tanpa sensor untuk sistem pacuan BLDC dengan mengaplikasikan kawalan digital
DSP (digital signal processor). Dengan kaedah ini voltan neutral motor tidak diperlukan
untuk mengesan EMF balik. Sebaliknya, kaedah ini menggunakan rangkaian A/D
berkelajuan tinggi yang terdapat pada pengawal DSP. EMF balikan yang sebenar bagi
lingkaran motor yang terapung dapat dikesan ketika masa tutup PWM kerana voltan
terminal bagi motor adalah bertindak secara terus dengan fasa EMF balik pada ketika
ini. Voltan EMF balik juga dirujukkan pada sambaungan bumi tanpa sebarang kesan
hingar. Dengan itu, kaedah pengesanan EMF balik ini tidak dipengaruhi oleh hangar
pensuisan PWM. Justeru itu, peningkatan dan penapisan isyarat tidak diperlukan.
Simulasi untuk projek ini telah diimplementasi dengan mengunakkan perisian
Simulink Matlab. Dalam simulasi, elemen utama seperti kelajuan, “torque’, arus fasa,
voltan terminal, dan voltan EMF balik diperhati. Model simulasi untuk motor BLDC,
marangkumi penyelesaian mengunakan keadah pengamiran bergantung kepada input
kepada motor dan konstan simulasi. Model matematik bagi system pacuan telah dibina
untuk menganalisis keupayaan system pacuan yang direkebentuk.
Sistem pacuan ini menggunakan sistem digital DSP, yang telah diprogramkan
dengan program kawalan tanpa sensor untuk system pacuan motor BLDC.
Implementasi melalui bahasa program DSP telah megurangkan bilangan komponen
dan mempercepatkan respon dari pengawal. DSP berpretasi tinggi yang digunakkan
telah mengurangkan masa lingkaran kawalan. Pengubahsuaian dapat dilakukan
dengan mudah pada struktur kawalan dengan memprogram perisian baru ke dalam
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pengawal. Kesahihan system pacuan yang direkabentuk telah diperiksa melalui
keputusan ujian kaedah simulasi dan pembinaan prototaip. Prototaip yang dibina
mempunyai julat operasi pada 24V, 5A. Berdasarkan analisis yang dijalankan
keputusan prototaip menyamai keputusan simulasi.
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IMPLEMENTATION OF DSP BASED SENSORLESS CONTROL WITH
DIRECT BACK-EMF DETECTION METHOD FOR BLDC MOTOR
ABSTRACT
This thesis presents a back EMF sensing scheme, direct back EMF detection, for
sensorless Brushless DC (BLDC) motor drives with a DSP based controller. Using this
scheme, the motor neutral voltage is not needed to measure the back EMF. Instead the
method utilizes the high-speed A/D converter channels, which are available on a DSP
controller. The true back EMF of the floating motor winding is detected during the off
time of PWM because the terminal voltage of the motor is directly proportional to the
phase back EMF during this interval. Also, the back EMF voltage is referenced to
ground without any common mode noise. Therefore, the developed back EMF sensing
method is immune to switching noise and common mode voltage. As a result,
attenuation and filtering is not necessary for the back EMF sensing.
The simulation of the BLDC motor drive system is implemented in SIMULINK
MATLAB software. The simulation of the system for important characteristics such as
speed, torque, phase current, terminal voltage, and Back EMF (BEMF) are monitored.
The simulation modeling involves solving many simultaneous differential equations,
each depending upon the inputs to the motor and the simulation constants.
A mathematical model of the drive system is also developed to analyze the
performance of the proposed driver.
The system is implemented developing the hardware, using a digital signal
processor (dsPIC30F), which is programmed with sensorless control for BLDC motor.
The implementation through assembly language programming of DSP has resulted in
reduced hardware and fast response of the controller. The high performance of digital
signal processors (DSPs) minimizes the control loop delays. Also further modifications
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in control structure are easily possible by changing the software. The implemented
hardware can support speed range up to 3500 rpm of the BLDC motor, with reduced
back EMF noise. The validity of the proposed BLDC motor drive system is verified
through simulation and hardware results such as phase current, back EMF signal
waveforms and speed. The experimental results on a 3-phase, 24 V, 120 W BLDC
motor using dsPIC30F (DSP) based digital controller closely agree with the simulation
results.
CHAPTER I
INTRODUCTION TO BRUSHLESS DIRECT CURRENT (BLDC) MOTOR
1.0 Research Objective
The objective of this thesis is to present the design of a 3-phase sensorless
brushless dc (BLDC) motor control with back-EMF (electromotive force) zero-crossing
sensing using an AD converter. It is based on Microchip dsPIC30F3010 DSP which is
dedicated for motor control applications. The system is designed as a motor drive system
for 3-phase BLDC motors and is targeted for applications in both industrial and appliance
fields. The reference design incorporates both hardware and software parts of the system
including details of hardware layout. This thesis also includes the basic motor theory,
simulation implementation concept, hardware implementation and software design.
1.1 Research Methodology
The research methodology of this thesis involves a number of different tasks that
are needed to lead towards completion. The first task is to define the objective of the
research in which the target specification of end product is defined. This followed by the
literature review where all the theoretical information regarding the research is gathered
and a comparison of previous similar research is discussed. A brief description on the
BLDC motor theory and performance is then presented. The advantage of the proposed
back-EMF detection scheme for sensor-less control is compared with the conventional
back-EMF detection schemes. Next in this thesis, the simulation of the targeted controller
implementation for the drive system using MATLAB SIMULINK software tools is discussed.
The simulation waveforms of voltages, phase currents and speed response are obtained to
compare with the results from proto-type hardware drive system. The next task is to design
the hardware for the target controller, based on the application target. The component
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ratings and type were selected. Once the hardware design is completed the software
implementation is carried out. The software code matching the hardware design is
developed in this stage. The next step is to integrate the software code and the hardware
to debug any failures. This task is implemented with ICD2 [15] debugging software. The
following task is to analyze the test results obtained with the controller and motor to
determine the performance, and also the waveforms of critical parameters captured during
this stage. The final stage is to conclude the research findings and the thesis write up.
Figure 1.1 shows the flow chart of the research methodology of this thesis.