2. SEMINAR
ON
SPEED CONTROL OF SPACE VECTOR
MODULATED INVERTER DRIVEN
INDUCTION MOTOR
SUBMITTED BY
M.AGNIVESH (08UK1A0212)
Prof.B.V ENUGOPAL REDDY N.MAHENDER Prof.K.PRAKASH
Guide Asst.Prof. Head of the dept.
Co-ordinator
3. ABSTRACT
In this paper, v/f control of Induction motor is simulated for both open
loop and closed loop systems. The induction motor (IM) is fed from
three phase bridge inverter which is operated with space vector
modulation (SVM) Technique. Among the various modulation
strategies Space Vector Modulation Technique is the efficient one
because it has better spectral performance and output voltage is more
closed to sinusoidal. The performance of SVM technique and Sine
triangle pulse width modulation (SPWM) technique are compared for
harmonics, THD, dc bus utilization and Output voltage and observed
that SVM has better performance. These techniques when applied for
speed control of Induction motor by v/f method for both open loop
and closed loop systems it is observed that the induction motor
performance is improved with SVM.
4. CONTENTS
INTRODUCTION
INDUCTION MOTOR AND IT’S MODELLING
DIFFERENT SPEED CONTROL METHODS
VOLAGE SOURCE INVERTER(VSI)
DIFFERENT PWM TECHNIQUES
5. INTRODUCTION
With the development in power electronic switches and
low cost computational hardware ac induction motor drives
now compare favorably to DC motors on considerations
such as power to weight ratio, acceleration performance,
maintenance, operating environment, and higher operating
speed without the mechanical commutator, cost and
robustness of the machine, and perhaps control flexibility
are often reasons for choosing induction machine drivers in
small to medium power range applications.
Up to date, due to the improvement of fast-switching
power semiconductor devices and machine control
algorithm, more precise PWM (Pulse Width Modulation)
method finds particularly growing interest. A large variety
of methods for PWM exists on which a survey was recently
given.
6. For the ac machine drive application, full utilization of the
dc bus voltage is extremely important in order to achieve
the maximum output torque under all operating conditions.
In this aspect, compared with any other PWM method for
the voltage source inverter, the PWM method based on
voltage space vectors results in excellent dc bus utilization.
Moreover as compared to sine triangle PWM method, the
current ripple in steady state operation can minimized in
this method.
The speed or torque of an induction machine can be
controlled by various modulation strategies for inverter. In
this paper v/f control of IM for both open loop and closed
loop systems using the best modulation strategy known as
SVM technique is simulated and compared with the
conventional SPWM technique and shown that IM
performance is improved.
7. INDUCTION MOTOR AND IT’S MODELLING
AN INDUCTION MOTOR IS A ELCRTICAL MACHINE WHICH
IS USED TO CONVERT THE INPUT ELECTRICAL POWER TO
OUTPUT MECHANICAL POWER.
THE INDUCTION MOTOR WORKS ON THE PRINCIPLE OF
PRODUCTION OF “ROTATING MAGNETIC FIELD”.
THE INDUCTION MOTOR CAN BE TREATED AS A ROTATING
TRANSFORMER.
BASICALLY THERE ARE 2 TYPES OF INDUCTION MOTORS
DEPENDING ON THE TYPE OF THE INPUT
1.SINGLE PHASE INDUCTION MOTORS
2.THREE PHASE INDUCTION MOTORS
8. FOR LOW POWER APPLICATIONS AND DOMESTIC PURPOSE
WE USE SINGLE PHASE INDUCTION MOTORS.
FOR HIGH POWER APPLICATIONS SUCH AS INDUSTRAIL
APPLICATIONS WE USE THREE PHASE INDUCTION MOTORS
BASICALLY THE INDUCTION MOTOR CONSISTS OF A
STATOR AND ROTOR.
STATOR CONSISTS OF A THREE PHASE BALANCED
WINDING WHICH PRODUCES ROTATING MAGNETIC FIELD
WHEN IT IS EXCITED BY THREE PHASE SUPPLY.
ROTOR IS ROTATING PART OF THE INDUCTION MOTOR
WHICH WILL BE CONNECTED TO THE MECHANICAL LOAD
TO SUPPLY THE MECHANICAL ENERGY.
DEPENDING ON THE CONSTRUCTION OF ROTOR THE
INDUCTION MOTORS ARE CLASSIFIED AS
1.SQUIRREL-CAGE INDUCTION MOTOR
2.SLIP RING OR WOUND ROTOR INDUCTION MOTOR
9. PRINCIPLE OF OPERATION OF INDUCTION MOTOR
When the stator is powered with 3 phase supply
there will be production of rotating magnetic field which
rotates with the synchronous speed.
As the magnetic field through the rotor is changing
(rotating) and the rotor has windings in the form of
closed loops of wire. The rotating magnetic flux induces
currents in the windings of the rotor as in a transformer.
According to Lenz's law the rotor windings will try to
oppose the cause of production of induced current in the
rotor.
The cause of induced current in the rotor is the
rotating stator magnetic field, so to oppose this the rotor
will start to rotate in the direction of the rotating stator
magnetic field to make the relative speed between rotor
and rotating stator magnetic field zero, thus the motor
will start.
10. For these currents to be induced, the speed of the physical
rotor must be lower than that of the stator's rotating
magnetic field ( Ns).
Thus induction motor will not rotate at synchronous speed
but it will rotate at a speed lower than the synchronous
speed. That’s why an induction motor can be called as
asynchronous motor.
As the speed of the rotor drops below synchronous speed,
the rotation rate of the magnetic field in the rotor increases,
inducing more current in the windings and creating more
torque.
The ratio between the rotation rate of the magnetic field as
seen by the rotor (slip speed) and the rotation rate of the
stator's rotating field is called "slip". Under load, the speed
drops and the slip increases enough to create sufficient
torque to turn the load.
slip=(Ns – Nr)/Ns
11. INDUCTION MOTOR MODELLING
The induction motor has two models for it’s analysis.
1.Steady state model
2.Dynamic model
The steady state model shows the information about the
power flow from the supply mains to the shaft in steady
state condition.
The steady state model is used to know the parameters of
the motor like motor current, motor torque etc. in steady
state.
The steady state model does not give the information about
the transient currents and voltages produced during sudden
load changing on the shaft of the motor.
12. In order to analyze transient behaviour we are going for
designing of the dynamic model.
In an adjustable speed drive the machine constitutes an
element in the feedback loop. and therefore the transient
behaviour of the motor has to be taken into consideration.
Besides, High performance drive control such as vector or
field oriented control is based on the dynamic d-q model of
the machine.
The dynamic model of the induction motor can be formed by
transforming the three phase stationary reference frame
(As-Bs-Cs) variables into two phase stationary reference
frame (d^s-q^s) variables and then transform these
variables to synchronously rotating reference frame
(d^e-q^e), and vice versa.
13. The dynamic model equations are used to find
out the equation of the torque in terms of the
motor parameters such as motor flux linkages
and motor currents. which will be controlled
from the control circuit to achieve required
torque.
14. Different speed control techniques
1.Pole changing technique.
2.Variable voltage technique.
3.Variable frequency technique.
4.V/f technique
15. Pole changing technique
1.In pole changing technique the different speeds can be
achieved by changing the no.of poles on the stator of the
motor.
2.But the disadvantages of this method are
a).Motor has to be designed specially
b). We can obtain only intermittent speeds.
Variable voltage technique
1.The speed of the motor can be controlled by varying the
stator voltage of the motor. we can achieve this method by
using transformers(Eg; Auto transformer & tap changing
transformer) and AC voltage controller.
16. The disadvantage of this method is reduced maximum
torque at low voltages.
Variable frequency Technique
In this method the speed of the induction motor can be
changed by changing the supply frequency which can be
achieved by VSI,CSI & Cyclo converter.
By changing the frequency of the motor the synchronous
speed of the motor will going to be changed. Then
automatically the rotor speed will be controlled.
The disadvantage of this method is that the operating point
of the flux of the motor is going to be changed which will
results some drawbacks such as reduction in the torque
handling capability when the operating point falls bellow the
normal location of the point & motor goes into saturation
and draws more current when the operating point goes to
saturation.
17. V/f control
This method of control can be achieved by using VSI ,Cyclo
converter to control the V & f of the motor.
In the induction motor the induced emf in the stator
Will be directly proportional to the stator flux and
frequency.
E ∞ Φf
By maintaining the ratio of V/f as constant the flux in the
stator is made constant and we can achieve the different
speeds below the rated speed with out changing the
operating point of the stator flux.
For above rated speeds the voltage made as constant and
frequency will be changed.
This method can be achieved by using a Voltage source
Inverter
18. Voltage source inverter(VSI)
DC to AC converter is called as inverter.
The function of the inverter is to change a dc input voltage
to a symmetric ac output voltage of desired frequency and
magnitude.
A variable output voltage can be obtained by varying the
input dc voltage and maintaining the gain of the inverter
constant.
If the dc input voltage is fixed and is not controllable, a
variable output voltage can be obtained by varying the gain
of the inverter, which is normally accomplished by PWM
control with in the inverter.
The output voltage of an ideal inverter should be sinusoidal,
however the waveforms of practical inverters are non
sinusoidal and contain certain harmonics.
19. An inverter is called a voltage fed inverter or Voltage source
inverter if the input voltage remains constant.
Applications of VSI
1.AC motor drives
2.AC Uninterruptible power supplies.(UPS)
3.Induction heating.
4.Active harmonic filters.
20. Different PWM techniques
Single pulse width modulation.
Multiple pulse width modulation.
Trapezoidal pulse width modulation.
Sine triangle PWM technique.
Space vector PWM technique.
