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Energy Education Science and Technology Part A: Energy Science and Research
2011 Volume (Issue) 27(2): 455-466
Brushless direct current (BLDC)
motor driving experimental set
Yasin Bektas, N. Fusun Oyman Serteller
*
*
Marmara University, Kadikoy , Istanbul, Turkey
Received 28 November 2010; accepted 29 December 2010
Abstract
The aim of the present study is to familiarize students with the parameters of a brushless direct
current (BLDC) motor and its driving circuits, with particular emphasis on the dynamic motor
behavior from stable working to the transient operating phase. A BLDC motor experimental set and
MATLAB real time simulation program are designed and improved to control a BLDC motor’s
parameters in a laboratory environment. The characteristics of the operating parameters are
mathematically and graphically presented in a trial. BLDC motor driving characteristics are given in
detail to support students’ theoretical understanding. This study is intended to provide to students with
all the necessary theoretical knowledge including MATLAB real time simulation program, with the
best practical observation on the subject. Furthermore, the driving circuit card is designed and
constructed to provide to the students simple, clear and easily understood data for a general overview
of BLDC motors.
Keywords: BLDC motor; Driving circuit design; Experiment set; MATLAB
© Sila Science. All rights reserved.
1. Introduction
Conventional direct current (DC) motors are highly efficient and they can effectively be
used as motors. However, due to the presence of commutation and brushes it is subjected to
mechanical wear and hence requires maintenance. As time passed the functions of
commutation and brushes were implemented by solid-state (semi-conductor) switches, thus
maintenance-free motors were realized. These motors on further development gave birth to a
special electrical machine known as brushless dc motors. Actually, the usability of BLDC
motor has increased for last ten years due to rapid development in semi-conductor and
permanent magnetic material technology. The BLDC motors increasingly are being used in
computer, automotive, industrial and household products because of its high power density,
compactness, high efficiency, low maintains and its common control technology.
In this paper
the subjects are explained that students are familiar with the basic knowledge of electric
motor, driving circuits and computer using skills.
_______________
*
Corresponding author. Tel.: + 90-216-336-5770; Fax: + 90- 216-337-8583.
E-mail address: fserteller@marmara.edu.tr (N. F. Oyman Serteller).
456 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
The brushless direct current motor is constructed with three stator or armature windings and
a set of pole paired permanent magnet on the rotor (fig. 1(a) and (b)). As the BLDC motor is
inherently electronically controlled it is required control and driving unit. The motor drive unit
regulates the switching of the direct current supply voltage to the stator winding of the motor.
Basically, the motor requires a driving system to supply commutated current to the motor
stator windings synchronized to the rotor position. Rotor position is knowable with or without
sensor. In these study hall sensors are used [1-5]. In general, BLDC motors are started through
two kinds of driver unit, like other small and medium-sized powerful motors: bipolar and
unipolar. Some applications a bipolar driver is suggested such as loaded starting. But some
application unipolar drive is needed such as high speed requirements. Also some application
two circuit driving feature can be needed. In this paper all of them have been taken into
consideration. These circuits are quite complex and puzzling to understand electronic devices
and their features. In this study both drive application are implemented in the same electronic
card to prove and compare the circuit’s features in the laboratory environment. The developed
driving circuit card has a capability so that it can be used either unipolar or bipolar or both
together to understand the each driving effect on the BLDC motor [8].
The laboratory studies in electric machines courses have a great importance because of
constructing an active and permanent learning environment. The purpose of this study is to
determine encountered difficulties during matching knowledge of electric machines
laboratory with electrical machine theoretical information. The purpose of this study is to
determine encountered difficulties. A new driving design requirement is prepared to
overcome the difficulties of complex theoretical knowledge of BLDC motor faced by students
using evaluation of experiences of the teacher, observation of lecturer and background
information from students [6, 9, 10].
The experiment set has been developed as possible as simple and understandable and
motor parameters have been analyzed to give the ideas for motor operation performances,
control and command. In addition all the relationship of the motor parameters is given and an
experiment set are realized to show all the control effects on motor [14].
2. Mathematical explanations of driving of a BLDC motor
Here, a three phase, star connected and sole wound BDCM was utilized and its required
plate values were given Table 1. The BLDC motor uses three winding stator structure and
permanents magnets mounted on the rotor (Fig.1 (a) and (b), respectively). The detailed
explanation for stator and rotor windings is given in section 3 and 4. The rotor or rotating part
of the BLDC motor has high resistivity of both magnet and stainless steel.
Table 1. Specifications and parameters of BLDC motor
Working Voltage 220 V
Power 550 W
Working current 2 A
Number of phases 3 -
Insulation class F -
Return direction Clockwise/ visaverse -
Stator 3 Phased Star con. 2p=4 -
Rotor 4 Piece and 2p=4 Ferrit -
Weight 6.5 kg
The basic equations of the BLDC motor equations can be explained as follows:
457 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
aT
IKT
(1)
Eaa
KRIV
(2)
V
R
K
R
KK
T
a
T
a
ET
(3)
where
T
K ,
E
K ,
a
R ,
a
I ,
and V are torque constant, back emf (electro-motive force) constant,
resistance and current of the energized windings, rational speed and supplied voltage
respectively[5,16]. Table 2 shows the major variables of the BLDC motor driven by a bipolar
or unipolar drive in the case of the application same voltage.
(a)
(b)
Fig. 1. BLDC motor stator winding (a) and permanent magnet rotor (b).
It shows the major variables relationship of the BLDC motor driven by a bipolar or unipolar
in the case of the application same voltage which is of 33V.
Table 2. motor design variables of a BLDC motor operated by unipolar and bipolar
Motor parameters Bipolar Drive Unipolar Drive
Torque constant
K
T
(1/2) K
T
Resistance
R
a
(1/2) R
a
Torque-speed relation
V
R
K
R
K
T
a
T
a
T
2
V
R
K
R
K
T
a
T
a
T
2
2
Starting torque
V
R
K
a
T
V
R
K
a
T
No-load speed
T
K
V
T
K
V2
458 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
Torque constant and back emf constant of a unipolar drive are half of those of a bipolar
drive. This makes the unipolar drive has an advantage over the bipolar drive in the high speed
applications. Whereas if the same voltage is applied to motor and operates in the linear range
the former input current is larger and the starting torque of the unipolar drive is much smaller
than that of the bipolar drive in practice[16].
3. Experimental set of the driving circuit of the BLDC motor
The realized education tool of the BLDC motor is shown schematically in Fig. 2. The real
set is shown in Fig.3 (a) and (b). The development and prevalence of computer technology and
usability for multi purpose aims provides not only speed and economy but also visual and
sound opportunity. Especially learning the difficult concepts like motor and motor driving, it
is important to use the visual materials effectively, besides educational strategies such as
seeing, hearing and talking [17-19].
Fig. 2. Schematic diagram of the BLDC motor with its driving circuit and other auxiliaries.
The experiment set of BLDC motor including the loading equipment as an educational tool
is presented in Fig.2. Computer assistant learning is a method used to increase the efficiency
of traditional educational approaches (lecturers, exercises and laboratories) it is used in a great
number of applications in electrical machine education and training [20]. The simulation is
used in this study as a type of computer assistant. Simulations provide a model in which the
students play a role and interact with the computer. Simulations provide a model in which the
student plays a role and interacts with the computer. They are applicable to any field however
it is very vital for teaching electric machine drive and can be of significant help in illustrating
concepts, in helping students to develop problem solving techniques or in allowing students to
explore complex interactions [26-28]. Here, MATLAB software program and PCI data
acquisition card (PCI-1711) are used to simulate and to run the motor operating parameters. It
also controls motor speed rate and current oscillation as a computer assistant [30 -35]. The
developed flow diagram is given in Appendix. Fig. 3 (a) shows complete part of the
experiment set and Fig. 3 (b) shows the main components of the experiment set.
One of the most powerful aspects of MATLAB functions is to present useful functions
package which are called toolbox. Toolbox covers wide range of application areas such as
mathematics, analysis, modeling, data collection, control, signal and image processing and
cost modeling so on. These are additional functions and enable us to run in real time on our
laptop PC for rapid prototyping or hardware-in-the-loop simulation of control system.
Since control technology of BLDC motor is predominantly explained in this study, special
interest is given to driving circuit. It can be explained in three main parts in general. In the
first section, a controller that processes the position information coming from the sensors is
available with electronic component (MC33035). The position information processed by the
controller is used to trigger the six switching element (IRF720) for the bipolar working mode
459 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
(a)
(b Card Socket)
Fig. 3(a). The whole experimental set which includes loading equipment and other
auxiliaries, (b) BLDC motor with its driving unit.
and three switching (in some cases this number can be increased) that can be named as second
section. The third section in the circuit consists to ensure the insulation of MOSFET drive
circuit elements (IR2113) between the section that belongs to the keying elements where the
high source voltage is available and the section that belongs to the controller where low
voltage is available [21-25] and hall sensors to define rotor position(S
A
, S
B,
S
C
).
Terminal voltage is distributed to the motor over the switching elements (MOSFETs)
determined and triggered by the controller according to the position of the rotor (Fig. 4).
3. 1. Bipolar and unipolar circuit driving system
Three- phase stator windings (A, B, C) star -connected BLDC motors (Figs. 5 and 6) can
be categorized as bipolar or unipolar driving systems like identical other type of motors.
Unipolar and bipolar driving methods energize one phase and two phases out of three phases
at each commutation period, respectively. Their commutation periods are 60 and 120
electrical degrees, respectively. The unipolar driving system has fewer electromagnetic
switches (Fig 1) and a simpler driving circuit and the commutation frequency is half that of
BLDC
MOTOR
FUKO LOADING
EXPERIMENT SET
The driver circuit
(Uni-Polar/Bi-Polar)
FLUKE125
PCI Data
Acquisition
Current
Probe
Speed Sensor
HostPC
Tar
g
etPC
460 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011 455-466
Fig. 4. Driving card of the BLDC motor with its all equipments.
the bipolar driving circuit. A unipolar drive appears to offer advantageous over the bipolar
drive. However, during start up operation, magnetic saturation appears due to huge current
values, and this causes high torque ripple and lower starting torque. Additionally, it has dead
spots like a single phase motor, because the direction of current flows through the phase
windings can not be inverted so that it needs more switches to overcome the problems which
is being explained next section [16, 29].The current flow direction and current values are
given Figs. 6(b) and 7(b). The graphical results of speed of concerning driving circuits are
given with comparison in section 4.
3. 2.
Hybrid (Bipolar- starting and unipolar-running) driving system
The bipolar-starting and unipolar-running method is used to provide high speed with high
starting torque, especially when the motor is loaded. As a result, a bipolar starting and
unipolar-running driving circuit is thought to combine advantages of bipolar and unipolar
driving. In Fig. 7 shows another topology of a unipolar drive with six switches (transistors).
Since the unipolar drive use three switches and they can’t invert the direction of the current
flow with the application of two additional switches current flow can be inverted. These two
switches (N
+
and N
-
) are connected to a neutral point and they are off using bipolar drive
(stating time). In the case of operating unipolar drive two additional switches play role on
flowing the positive or negative current in the given single phase.
The graphical results are given in Section 4. Although hybrid driving has more electronic
switches than other configurations, it is more stabile and more convenient for various
application (Figs. 8 (a) , (b) ,(c),(d) and 9). In particularly, a BLDC motor operating at load
regime, using hybrid driving looks more effective [16, 30-33].
4. Discussion and result
This research has prepared the effects of the computer assistant method and laboratory work
on students’ success in teaching of the subject of a BLDC motor and it’s driving in the
Electrical machine course of electrical education. The BLDC equipment set and computer
461
Y. Bektas, N. F. Oyman. Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
(a)
(b)
Fig. 5. Bipolar driver circuit and stator windings of motor (a), stator current values for phase
A (b).
(a)
(b)
Fig. 6. Unipolar driver circuit and stator windings of motor (a) stator current values for phase
A(b).
462 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
(a)
(a)
(b)
Fig. 7. Hybrid driver circuit and stator windings of BLDC motor (a), bipolar starting unipolar
running driver current variation (b).
visualization was found very effective in teaching the features of the driving units of a BLDC
motor. Operation of the drive system can be observed on a PC monitor and can be modified
by choosing appropriate functions. The contents of the control functions do not change while
the program is running [16, 20]. Figs. 8 (a), (b), (c) show results of the experiment on the
relationship between speeds versus time (ms). The graphs indicate that the experimental
results are almost in good agreement with the simulation results (reference results). The
experiment was realized of 33V at load of 0.5 Nm.
A detailed understanding of these driving circuits and motor parameter’s role for motor
operation is an essential first step towards improved performance. This paper clearly shows
that students can easily understand the operation of the driving circuit and can conclude that
the hybrid method has low torque ripple when the motor is running at high speed and large
starting torque which provides advantages over the bipolar and unipolar drives (see the
comparion of Figs. 8 (b), (c), (d))[18,30-33] .
5. Class assignments
This experimental set was prepared and implemented for graduate level students, so it was
therefore assumed that students already know the basic principles of the motor technology,
power electronics and computer software. The developed experiment set was designed to
463 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
(a) (b)
(c)(d)
Fig. 8. Experimental and Simulation results: (a) no load hybrid driving circuit; (b) bipolar
starting hybrid driving circuit at 0.5 Nm ;(c) unipolar driving circuit at 0.5 Nm ;(d)
Bipolar driving circuit.
encourage students to learn the concepts of the methods presented at lectures, based on the
standard textbooks, and information about the lesson provided by the lecturer. The electrical
machine’s course module progresses should be planned so that the new technologies included
into the course such as BLDC motor. The course should therefore be divided into two parts,
dealing with conventional and new technologies, respectively. At the end of each theoretical
section of the course, students test their knowledge on the experiment sets [34]. During
laboratory work, the students should be divided into the smallest possible groups, such as a
maximum of two persons and each student has his computer and student is watched and
guided while working with the computer to effectively improve their knowledge.
Assignments should also be set, to test students’ knowledge themselves. In the meantime,
their questions are answered and assistance is given when required. The authors believe that
this study demonstrates highly effective results in assisting students to understand the course
content [26-28, 35-39].
6. Conclusion
The presented brief, graduate level driving methods and their experimental results are of
value for teaching the control of brushless motor designs, driving circuit features and analysis,
which are necessary for students to develop knowledge of electrical machines and driving
464 Y. Bektas, N. F. Oyman Serteller / EEST Part A Energy Science and Research 27 (2011) 455-466
circuits. Implementations and suggestions are offered within the trial, to teach students the
concepts step by step.
In this paper, a basic knowledge, precluding complex algorithms, of BLDC motor
performance and driving circuits are explained. Students are particularly encouraged when
they can observe the open circuit, control the motor themselves and use the real time
simulation program; since they have all the necessary theoretical and practical data, they can
perform quite complex tasks, achieved from the experimental experience.
Acknowledgements
This work was supported by the Scientific Research Project Commission of Marmara
University Project No FEN-C-YLP- 0105080100.
We thank to the Scientific Research Project
Commission so that we have achieved a chance to study at laboratory environment.
Appendix
MatlabProgramme
FH2: Brand code of the loading unit.
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