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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 6545(Print), ISSN
0976 6553(Online) Volume 3, Issue 3, October December (2012), IAEME
222
SPEED CONTROL OF ASYNCHRONOUS MOTOR USING SPACE
VECTOR PWM TECHNIQUE
VISHAL RATHORE1, Dr. MANISHA DUBEY2
1(ELECTRAL& ELECTRONIC, TRUBA/ RGPV, BHOPAL, INDIA,
[email protected])2(ELECTRICAL, MANIT/ MANIT, T.T.NAGAR BHOPAL (M.P), INDIA,
ABSTRACT
This paper presents the Space Vector Pulse Width Modulation (SVPWM) approaches
to the problem of speed and torque control of induction motor and induction motor parameter
adaptation. Such problems are commonly encountered in electric drives and many
applications such as robotics, electric vehicles, and so on. The specific contributions of the
paper are new Space Vector Pulse Width Modulation technique flux/speed observer is
developed by delicately introducing some auxiliary variables ( as inverter output voltage,current, torque and speed of induction motor) and a design parameter. Combining the Space
Vector Pulse Width Modulation torque controller, it is thoroughly analyzed the convergence
of the flux/speed observer and the asymptotic stability of the close loop system. Then the
robustness of the proposed Space Vector Pulse Width Modulation observer/controller scheme
is effectively demonstrated by considering the effect of the variation of the rotor resistance,
the stator resistance and the load torque. The SVPWM approach for the speed and torque
control of induction motor is compared with PI and PID controller connected in the feed
forward path of the system .The results are compared on the basis of time response
specification like (Rise time (tr), Peak time (tp), Settling time (ts), Maximum overshoot
(%MP) ).
Keywords:Induction Motor,PI Controller, Park transformation, Space Vector Pulse Width
Modulation (SVPWM), Three-Phase Voltage Source Inverters.
1. INTRODUCTION
Induction motors are most popular machine in AC drives because of its rugged and
inexpensive construction. Therefore much attention is given to their control for various
applications as compare to other rotating machine. An induction machine, especially squirrel
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ISSN 0976 6545(Print)
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Volume 3, Issue 3, October - December (2012), pp. 222-233
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cage, has many advantages when compared with DC machine in terms of cost, construction
and application. Also it is less sensitive to environment variation as compare to DC machine.
Furthermore, it does not require periodic maintenance like DC motors [1]. However, because
of its highly non-linear and coupled dynamic structure, an induction machine requires more
complex control schemes than DC motors. Traditional open-loop control of the induction
machine with variable frequency may provide a satisfactory solution under limitedconditions. However, when high performance dynamic operation is required, these methods
are unsatisfactory [2]. Therefore, more sophisticated control methods are needed to make the
performance of the induction motor comparable with DC motors. Recent developments in the
area of drive control techniques, fast semiconductor power switches, powerful and cheap
microcontrollers made induction motors alternatives of DC motors in industry. The most
popular induction motor drive control method has been the field oriented control (FOC). The
controllers required for induction motor drives can be divided into two major types:
conventional low cost volts per hertz v/f controller and torque controller [1]-[4].
2. MODELING AND DESIGN OF SPACE VECTOR CONTROLLED INDUCTION
MOTOR DRIVE
Induction motors are the most widely used motors in industrial motion control
systems, as well as in home appliances because of their reliability, robustness and simplicity
of control. Until a few years ago the AC motor could either be plugged directly into the mains
supply or controlled by means of the well-known scalar V/f method. When power is supplied
to an induction motor at the recommended specifications, it runs at its rated speed. In this
method, even simple speed variation is impossible and its system integration is highly
dependent on the motor design (starting torque vs. maximum torque, torque vs. inertia,
number of pole pairs). However many applications need variable speed operation. The scalar
V/f method is able to provide speed variation but does not handle transient condition control
and is valid only during a steady state. This method is most suitable for applications without
position control requirements or the need for high accuracy of speed control and leads toover-currents and over-heating, which necessitate a drive which is then oversized and no
longer cost effective. Examples of these applications include heating, air-conditioning, fans
and blowers [9].
2.1Field Orientated Control (FOC)
The Field Orientated Control (FOC) consists of controlling the stator currents
represented by a vector. This control is based on projections which transform a three phase
time and speed dependent system into a two co-ordinate (d and q co-ordinates) time invariant
system. These projections lead to a structure similar to that of a DC machine control. Field
orientated controlled machines need two constants as input references the torque component
(aligned with the q co-ordinate) and the flux component (aligned with d co-ordinate). As
Field Orientated Control is simply based on projections the control structure handlesinstantaneous electrical quantities. This makes the control accurate in every working
operation (steady state and transient) and independent of the limited bandwidth mathematical
model. The FOC thus solves the classic scheme problems, in the following ways [8]. The
ease of reaching constant reference (torque component and flux component of the stator
current).The ease of applying direct torque control because in the (d,q) reference frame the
expression of the torque is:
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1By maintaining the amplitude of the rotor flux ( ) at a fixed value we have a linearrelationship between torque and torque component isq. We can then control the torque by
controlling the torque component of stator current vector.
2.1.1 Space Vector Definition and ProjectionThe three-phase voltages, currents and fluxes of AC-motors can be analyzed in terms
of complex space vectors. With regard to the currents, the space vector can be defined as
follows. Assuming that ia, ib, icare the instantaneous currents in the stator phases, then the
complex stator current vector is defined by:
is = ia + ib + 2ic 2
And represent the spatial operators.
Fig.1Stator current space vector and its component in (a,b,c).
This current space vector depicts the three phase sinusoidal system. It still needs to be
transformed into a two time invariant co-ordinate system. [8] This transformation can be split
into two steps: (a,b,c)(,) (the Clarke transformation) which outputs a two co-ordinatetime variant system. (,)(d,q) (the Park transformation) which outputs a two co-ordinatetime invariant System. The space vector can be reported in another reference frame with onlytwo orthogonal axis called (,). Assuming that the axis-a and the axis- are in the samedirection we have the following vector diagram. The projection that modifies the three phase
system into the (,) two dimension orthogonal system is presented below: 3
4
We obtain a two co-ordinate system that still depends on time and speed.
Fig.2Stator current space vector and its components in (,)
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 6545(Print), ISSN
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2.1.2 The (,)(d,q) Projection.This is the most important transformation in the FOC. In fact, this projection modifies
a two phase orthogonal system (,) in the d-q rotating reference frame. If we consider the daxis aligned with the rotor flux, the next diagram shows, for the current vector, the
relationship from the two reference frame:
Fig.3Stator current space vector and its component in (,
) and in the d, q rotating reference frame.
is the rotor flux position. The flux and torque components of the current vector are
determined by the following equations:
5 6
These components depend on the current vector (,) components and on the rotor fluxposition, if we know the right rotor flux position then, by this projection, the d,q component
becomes a constant. We obtain a two co-ordinate system
with the following
characteristics: two co-ordinate time invariant system with iSd (flux component) and iSq
(torque component) the direct torque control is possible and easy.
2.1.3 The (d,q)( ,) Projection.Here, we introduce from this voltage transformation only the equation that modifies
the voltages in d-q rotating reference frame in a two phase orthogonal system:
7 8
The outputs of this block are the components of the reference vector that we call Vr,Vr isthe
voltage space vector to be applied to the motor phases.
2.2 The Basic Scheme for the FOCTwo motor phase currents are measured. These measurements feed the Clarke
transformation module. The outputs of this projection are designated iSand iS.
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0976 6553(Online) Volume 3, Issue
Fi
Fig.6Referenc
Where T4and T6are the times
during which the zero vectors ar
Park transformation) and the spossible to determine the uncert
Under these constraints the loc
vertices are formed by the tip
waveforms are symmetrical with
Fig.7
ngineering and Technology (IJEET), ISSN 0976 65
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.5SVPWM, vectors and sectors
vector as a combination of adjacent vectors
uring which the vectors V4,V6 are applied an
e applied. When the reference voltage (output
ample periods are known, the following sysinties T4,T6and T0:
s of the reference vector is the inside of a he
s of the eight vectors. The generated space
respect to the middle of each PWM period.
Pattern of SVPWM in the sector 3
5(Print), ISSN
T0the time
of the inverse
em makes it
9
10
xagon whose
vector PWM
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The following diagram shows
inputs for the SVPWM are the
Fig.8
reference vector components
relevant sector limiting vectors.
3. COORDINATE TRANSFO
Coordinate transformati
their inverse transformation.Clar
three-phase AC system to two-
transformation, as shown in: Q
Conversely, change the 2-phasetransformation, also called
transformation Change the tw
transformation. The program is s
To the Y-connected winding wit
Conversely, change the DC syst
ngineering and Technology (IJEET), ISSN 0976 65
3, October December (2012), IAEME
228
he pattern of SVPWM for each sector In c
Hexagon of SVPWM, pattern [4]
) and the outputs are the times to appl
MATION
n includes Clarke transformation, Park transf
ke transformation and inverse transformation C
hase system is called Clarke transformation, a
=
AC system to 3-phase AC system is called i2/3 transformation. Park transformation
-phase AC system to rotating DC system i
hown in Fig.11:
=
hout the central line, there is:
Fig.11Program of Park
m to AC system is called inverse Park transfor
5(Print), ISSN
nclusion, the
y each of the
ormation and
hange the
lso called 3/2
verse Clarkeand inverse
called Park
15
ation.
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3.1 Speed Controller
Speed controller adopts PI controller. The program is shown in Fig.12. The input of
the PI controller is the difference between the given speed * and the practical speed r.
Saturation control link is to limit the output amplitude.
Fig.12Program of speed controller
3.2 Flux Observer Module
The property of vector control frequency converter system is decided by theestimating precision of rotors flux observer to a great extent. Flux observer module contains
an amplitude calculation of rotors flux sub-module and a flux angle calculation sub-module.
The former is used to calculate torque current component ist, and the latter is used in the
coordinate transformation. The latter is more difficult. So here only discusses the sub-module
of the rotor flux angle [1,4].
is calculated by integrating the sum of the angular speed of practical measurement and the
slip angular frequency.
s dt 16Where is the angular speed that could be measured directly, s is the slip frequency scould
be calculated by,
s LmistTrr
17
Where Tr LrRr
is the leakage flux coefficient. The program of the calculation of rotor flux
angle is shown in Fig.13 Signal measurement module is composed of Machine Measurement
Demux in Simulink library power system block sets.
Fig.13Sub-module of the rotor flux angle
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4. SIMULATION RESULTS
To accelerate the dynamic speed of the simulation module, a first-order delay-link 1/z is
adopted in feedback transmission function. Link up the above modules, the total simulating
module could be got, as shown in Fig.14 The induction motor parameters are as follows:
PN=500W, UN =650V, f=50Hz, RS =4.495, Rr =5.365 , LM =0.149H, Lr =0.162H,LS=0.206H.
4.1 Proportional Integral (PI) Controller
In this speed and theta calculation are done with PI controller. The error signal of
speed fed to PI controller and generates reference torque value. The reference theta value
with PI controller use error signal of current (Iq), speed (wm), and flux (phir). The whole
SVPWM control technique in simulation diagram is denoted by the control block. The
simulation with PI controller is shown in Fig.14.
Fig.14Simulation for PI controller
The output voltage of inverter with PI controller is shown in Fig.15. The output voltage is
mainly control by SVPWM pulses are generated by control block.
Fig.15Inverter output voltage waveform with PI controller
Discrete,
Ts = 2e-006 s.
v+-
Voltage measurement
Vab
z
1
g
A
B
C
+
-
Three-phase Inverter
Step
Scope6
Scope5
Scope4
Scope3
Scope2
Scope1
Manual
Switch
0
MULTIMETER
Load Torque
step
Tm
mA
B
C
Induction
Motor
m
is_abc
wm
Te
Demux
DC
650 Volts
120
Constant
In1
In2
In3
Out1
CONTROL
BLOCK
Inv erter Output Voltage
Stator currents Is_abc
Speed wm
Speed wm
Torque Tm
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The three phase current Iabcof motor are vary with torque value or speed controlled value.
The wave form for Iabc for speed controlled value with PI controller is shown in Fig.16.
Fig.16Currents (Iabc) waveform with PI controller
Fig.17Currents (Ia) waveform with PI controller
The waveform of speed control with PI controller shown in Fig.18. At starting the speed
gradually increased up to peak value (more than reference speed) within 1.1 sec, with PI
Controller. And it takes 4.4 sec, to achieve reference value. The parameters with PI controller
given in table-1.
Fig.18Waveform for speed with PI controller.
0 0.5 1 1.5 2 2.5 3-250
-200
-150
-100
-50
0
50
100
150
200
250
Time (sec)
Iabc(Amps)
Iabc with PI Controller
0 0.5 1 1.5 2 2.5 3-200
-150
-100
-50
0
50
100
150
200
250
Time (sec)
Ia(Amp)
Ia with PI controller
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S.No. Parameters PI
1 Rise time (tr) 1.1 sec
2 Peak time (tp) 1.4 sec
3 Settling time (ts) 4.4 sec
4 Maximum
overshoot
(%MP)
23.05 %
Table.1Comparison of parameters with PI and controller
5. CONCLUSION
The simulating results indicate space vector control system has good static and
dynamic properties. It is a stable control method. The two speed control techniques with PIcontroller and with PID controller were used The SVPWM approach for the speed and torque
control of induction motor is compared with PI and PID controller connected in the feed
forward path of the system .The results are compared on the basis of time response
specification like Rise time (tr), Peak time (tp), Settling time (ts) and Maximum overshoot
(%MP).It is found that the results with SVPWM with PID controller are quite satisfactory as
compared to the PI controller. The results indicate the coincidence of the dynamic simulating
process and the practical mobile process as well. So it verifies the correctness of the
simulating model based on the mathematic model combining with Matlab/Simulink.
REFERENCES
[1]
Wu Tao, Zhao Liang, Simulation of vector control frequency converter of inductionmotor based on matlab/Simulink, 2011 Third International Conference on Measuring
Technology and Mechatronics Automation, 2011 IEEE, pp. 265268.
[2] E. Hendawi, Analysis, simulation and implementation of space vector pulse width
modulation inverter, Proceedings of the 9th WSEAS International Conference on
Applications of Electrical Engineering, 2009 IEEE, pp. 124-131.
[3] Chintan Patel, Fast direct torque control of an open-end induction motor drive using 12-
sided polygonal voltage space vectors, IEEE Transactions On Power Electronics, vol.
27, 2012 IEEE, no. 1, pp. 0885-0889.
[4] R. Arulmozhiyal, Space vector pulse width modulation based speed control of induction
motor using fuzzy PI controller, International Journal of Computer and Electrical
Engineering, vol. 1, no. 1, April 2009, pp. 1793-1798.
[5]
Tao Wu, Yi-Lin , Yu Guo, Chao Xu, Simulation of FOC vector control of inductionmotor based on lab view, 2009 IEEE.
[6]
Dr. Rami A. Mahir, Dr. Ziadm M. Ahmed and Mr. Amjad J. H., Indirect field
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2008,pp. 265-277.
[7] M. Menaa, O. Touhami, R. Ibtiouen, M. Fadel, Speed sensorless vector control of an
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