ISSN: 2348-0033 (Online) ISSN : 2249-4944 (Print)
IJEAR Vol. 4, Issue Spl-1, Jan - June 2014
SVPWM Based Three Phase Inverter Fed BLDC Drive
1
1,2,3
Dr. P. V. V. Rama Rao, 2P. Devi Kiran, 3A. Sireesha
Dept. of EEE, Shri Vishnu Engineering College for Women, Bhimavaram, AP, India
Abstract
In high power, high torque and low torque applications BLDC
motors are widely used because of high efficiency, simple
construction, low cost less maintenance and high torque or high
output power per unit volume. For driving the BLDC motor we
required inverter. PWM inverter which gives good performance.
In two level inverters there is a problem of harmonics distortion,
heating of rotor shaft, voltage spikes across the motor terminals
etc. The use of space vector modulation PWM technique can
give better results when compared with the ordinary PWM
techniques. In this paper SVPWM controlled inverter is used to
feed the BLDC motor drive. Simulation is carried out using matlab
/ simulink, validating the steady state and dynamic performance
of the drive.
Keywords
Brushless DC (BLDC) Drive, PWM, Space Vector Pulse Width
Modulation (SVPWM).
I. Introduction
In recent years, industry has begun to demand higher power
equipment. Three phase inverters have been increasing attention
for power conversion in high-power applications due to their lower
harmonics, higher efficiency, and lower voltage stress compared
to single phase inverters [1].
The Brushless DC (BLDC) motor is the perfect choice for
applications that require high reliability, high efficiency, and high
power-to-volume ratio. Generally, a BLDC motor is considered
to be a high performance motor that is capable of providing large
amounts of torque over a vast speed range. BLDC motors are a
derivative of the most commonly used DC motor, the brushed
DC motor, and they share the same torque and speed performance
curve characteristics. The major difference between the two is the
use of brushes. BLDC motors do not have brushes (hence the name
“brushless DC”) and must be electronically commutated [2]. A sensorless speed permanent magnet synchronous motor (PMSM)
with direct torque control (DTC) using single DC-link voltage and
current sensors is proposed. In this paper prediction is based on
the dynamic motor model, the inverter switches states adjustment
and the measured DC-link current. Then whole system is then
incorporated into a speed sensorless DTC scheme and the rotor
speed is estimated [3]. In fact, a DTC scheme achieves the closedloop control of the motor stator flux and the electromagnetic
torque without using any current loop or shaft sensor [4]. Many
researchers are interested in this control technique because of
its wide area applications used with various ac machine types as
induction motor, PMSM [5], PM Brushless [6], and reluctance
motor [7].
In this paper modelling of BLDC Drive and simulation of SVPWM
based BLDC Drive is presented using MATLAB/ Simulink
tool.
II. Brush Less DC Drive
A brushless DC motor is similar to that Brush DC motor in that it
has an internal shaft position feedback that tells which windings
to switch on at which exact moment. This internal feedback
gives linear speed-torque curves which are well suited for speed
28
International Journal of Education and applied research
and position control and high starting torque for both the brush
DC motor and the brushless DC motor. The internal feedback
is accomplished in a brush type DC motor with the mechanical
commutator (a series of copper bars which are insulated from each
other) and the mechanical brushes through which the current is
fed into the commutator bars and switched sequentially into the
appropriate winding in the armature. In a BLDC motor, the internal
feedback is accomplished by a shaft position feedback sensor of
some type which gives the required shaft position information to
the drive electronics. The drive electronics in turn switches on the
appropriate windings at exactly the right moment. This internal
shaft position feedback also gives the BLDC characteristics which
are similar to the characteristics of a DC motor like linear speedtorque characteristics and high starting torque. The power supplied
to a BLDC motor can be DC power but it can also be AC if the
drive electronics has the necessary circuitry to convert the AC
power to DC. Fig. 1 shows the block diagram of the brushless
dc drive.
The mathematical modelling of a BLDC drive is developed with
the help of following equations. These equations are used to
develop the simulink model of BLDC drive. So that the simulation
of the said Space Vector Pulse Width Modulation (SVPWM)
Fig. 1: Block Diagram of the Brushless dc Drive
(1)
Where Va, Vb, Vc are the phase voltages ia, ib, ic are the phase
currents, Ea, Eb, Ec are the phase back-EMF waveforms, R is
the phase resistance, L is the self inductance of each phase and
M is the mutual inductance between any two phases. So the
electromagnetic torque can be obtained as:
(2)
where ωr is the mechanical speed of the rotor and T is the
electromagnetic torque. The equation of motion is:
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ISSN: 2348-0033 (Online) ISSN : 2249-4944 (Print)
(3)
B is the damping constant, J is the moment of inertia of the drive
and Tl is the load torque. The electrical frequency related to the
mechanical speed for a motor with P numbers of poles is:
A. Advantages
1. High Speed Operation: A BLDC motor can operate at speeds
above 10,000 rpm under loaded and unloaded conditions.
2. Responsiveness & Quick Acceleration: Inner rotor Brushless
DC motors have low rotor inertia, allowing them to accelerate,
decelerate, and reverse direction quickly.
3. High Power Density: BLDC motors have the highest running
torque per cubic inch of any DC motor.
4. High Reliability: BLDC motors do not have brushes, meaning
they are more reliable and have life expectancies of over
10,000 hours. This results in fewer instances of replacement
or repair and less overall down time for your project.
III. PWM Techniques
The DC-AC inverters usually operate on Pulse Width Modulation
(PWM) technique. The PWM is a very advance and useful
technique in which width of the Gate pulses are controlled by
various mechanisms. PWM inverter is used to keep the output
voltage of the inverter at the rated voltage (depending on the
user’s choice) irrespective of the output load. In a conventional
inverter the output voltage changes according to the changes in
the load. To nullify this effect of the changing loads, the PWM
inverter correct the output voltage by changing the width of the
pulses and the output AC depends on the switching frequency and
pulse width which is adjusted according to the value of the load
connected at the output so as to provide constant rated output.
There are four basic PWM techniques.
A. Single Pulse Width Modulation,
B. Multiple Pulse Width Modulation,
C. Sinusoidal Pulse Width Modulation. and
D. Space Vector Pulse Width Modulation.
A. Single Pulse Width Modulation
In this modulation there is an only one output pulse per half cycle.
The output is changed by varying the width of the pulses. The
gating signals are generated by comparing a rectangular reference
with a triangular reference. The frequency of the two signals is
nearly equal.
IJEAR Vol. 4, Issue Spl-1, Jan - June 2014
be modulated in such a way so that the average voltage waveform
corresponds to a pure sine wave. The simplest way of producing
the SPWM signal is through comparing a low power sine wave
reference with a high frequency triangular wave. This SPWM
signal can be used to control switches. Through an LC filter,
the output of Full Wave Bridge Inverter with SPWM signal will
generate a wave approximately 13 equal to a sine wave. This
technique produces a much more similar AC waveform than that of
others. The primary harmonic is still present and there is relatively
high amount of higher level harmonics in the signal.
D. Space Vector Pulse Width Modulation
The most common and popular technique for generating True
sine Wave is Pulse Width Modulation (PWM). Space vector
pulse width modulation (SVPWM) is an optimum pulse width
modulation technique for an inverter used in a variable frequency
drive applications. It is computationally rigorous and hence limits
the inverter switching frequency. In SVPWM methods, the voltage
reference is provided using a revolving reference vector. In this case
magnitude and frequency of the fundamental component in the line
side are controlled by the magnitude and frequency, respectively,
of the reference voltage vector. Space vector modulation utilizes dc
bus voltage more efficiently and generates less harmonic distortion
in a three phase voltage source inverter.
A three phase inverter can be controlled so that at no time are both
switches in the same leg turned on or else the DC supply would
be shorted. This requirement may be met by the complementary
operation of the switches within a leg. i.e. if A+ is on then A− is
off and vice versa. This leads to eight possible switching vectors
for the inverter, V0 through V7 with six active switching vectors
and two zero vectors.
Space vector modulation as shown in fig. 2 has a reference signal
Vref sampled with a frequency fs (Ts = 1/fs). The reference signal
may be generated from three separate phase references using the
αβγ transform. The reference vector is then synthesized using a
combination of the two adjacent active switching vectors and one or
both of the zero vectors. Various strategies of selecting the order of
the vectors and which zero vector(s) to use exist. Strategy selection
will affect the harmonic content and the switching losses.
B. Multiple Pulse Width Modulation
In this modulation there are multiple number of output pulse per
half cycle and all pulses are of equal width. The gating signals are
generated by comparing a rectangular reference with a triangular
reference. The frequency of the reference signal sets the output
frequency and carrier frequency.
C. Sinusoidal Pulse Width Modulation
In this modulation technique there are multiple numbers of output
pulse per half cycle and pulses are of different width. The width
of each pulse is varying in proportion to the amplitude of a sine
wave evaluated at the centre of the same pulse. The gating signals
are generated by comparing a sinusoidal reference with a high
frequency triangular signal. Sinusoidal Pulse Width Modulation
is the best technique for this. This PWM technique involves
generation of a digital waveform, for which the duty cycle can
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Fig. 2: Space Vectors Modulation Representation
All eight possible switching vectors for a three-leg inverter using
space vector modulation. An example Vref is shown in the first
sector. Vref_MAX is the maximum amplitude of Vref before non-linear
over modulation is reached. Space Vector PWM (SVPWM) method
is an advanced; computation intensive PWM method and possibly
International Journal of Education and applied research 29
ISSN: 2348-0033 (Online) ISSN : 2249-4944 (Print)
IJEAR Vol. 4, Issue Spl-1, Jan - June 2014
the best techniques for variable frequency drive application.
SVPWM is a different approach from PWM modulation, based
on space vector representation of the voltages in the α-β plane. The
α-β components are found by Clark’s transformation. SVPWM
refers to a special switching sequence of the upper three power
transistors of a three-phase power inverter. It has been shown
to generate less harmonic distortion in the output voltages and/
or currents applied to the phases of an AC motor and to provide
more efficient use of dc input voltage. Because of its superior
performance characteristics, it has been finding widespread
application in recent years.
Space Vector PWM is superior as compared to Sinusoidal pulse
width modulation in many aspects like, higher Modulation Index,
more output voltage, less current and torque harmonics etc.
2. 5
2
1. 5
1
0. 5
0
-0. 5
-1
-1. 5
-2
-2. 5
1. 6
1. 65
1. 7
1. 75
1. 8
Time
1. 85
1. 9
1. 95
2
Fig. 5: BLDC Drive Current Waveform
line voltages
IV. Simulation and Results
The simulation diagram and the obtained waveforms of space vector
pulse width modulation technique applied three phase inverter fed
brushless dc drive are shown below. Fig. 3 shows simulink diagram
of Space Vector Pulse Width Modulation developed in MATLAB/
Simulink environment. Fig.4 shows the simulink model of svpwm
three phase inverter fed BLDC drive.
120
100
80
60
40
20
+
- v
+v
-
E
g
m
0. 4
0. 6
0. 8
1
Time
1. 2
1. 4
1. 6
1. 8
2
+ -i
1. 2
+ -i
1. 15
+ -i
1. 1
line voltages
g
C
E
E
E
1. 05
g2
m
g6
m
g
C
g4
m
0. 2
[g2]
C
[g6]
g
[g4]
E
E
m
g5
0
Fig. 6: Speed Curve of Brushless dc Motor Drive
+v
-
C
C
C
g3
m
g1
0
+v
-
[g5]
g
[g3]
g
[g1]
1
control circuit
0. 95
0. 9
Fig. 3: Simulink Diagram of SVPWM Technique
0. 85
1. 6
powergui
+ v
g
C
E
+
v
-
E
g5
m
E
m
g
[g5]
g3
m
g1
C
g
[g3]
C
[g1]
S tep
+ -i
+
SS1
Tm
+ i
-
A
<>
m
B
cvs
s
-
+ -i
g
G oto9
SS2
G oto10
<>
SS3
G oto11
C
g
<>
sc
E
m
E
emf _abc
Decoder
C
g2
m
E
g6
m
g4
H all
Permanent Magnet
Synchronous Machine
[g2]
C
g
[g6]
C
[g4]
t
S ubsystem
-K -
<R otor s peed wm (rad/s )>
ra d2rpm
P ID
C onsta nt
P ID
100
s
ra d2rpm1
-1
Fig. 4: Simulation of SVPWM Inverter Fed BLDC Drive
The current waveform of SVPWM inverter fed BLDC drive is
shown in fig. 5. It is observed that the output currents are showing
the effectiveness of SVPWM Technique. Speed curve of SVPWM
inverter fed BLDC drive shown in fig. 6. fig. 7 shows the torque
response of SVPWM inverter driven BLDC drive. Fig. 8 shows
the output voltage waveform of SPWM.
30
1. 7
1. 75
1. 8
Time
1. 85
1. 9
1. 95
2
Fig. 7: Torque of Brushless dc Motor
Discrete,
Ts = 1e-005 s.
+ v
-
1. 65
International Journal of Education and applied research
V. Conclusion
This paper presented the BLDC drive control using SVPWM in
MATLAB/ Simulink. SVPWM has many advantages over the
other PWM techniques. The SVPWM technique results better
performance of the BLDC drive. This SVPWM control scheme
is very much useful for high power low torque applications.
The simulink model and the simulation results presented in the
paper demonstrate that the satisfactory performance of the BLDC
drives.
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ISSN: 2348-0033 (Online) ISSN : 2249-4944 (Print)
IJEAR Vol. 4, Issue Spl-1, Jan - June 2014
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