HVDC

1. PRESENTED BY:SHRUTI
USN:3PD21EPE06
M.TECH POWER ELECTRONICS

2. CONTENTS :
 INTRODUCTION
 WORKING OF AN INDUCTION MOTOR
 EQUIVALENT CIRCUIT OF INDUCTION MOTOR
 SCALAR CONTROL
 VECTOR CONTROL
 COMPARISION BETWEEN SCALAR AND VECTOR
CONTROL
 ADVANTAGES OF SCALAR AND VECTOR CONTROL
 DISADVANTAGES OF SCALAR AND VECTOR CONTROL

3.  Introduction:
An induction motor is an electric motor that works on the
method of electromagnetic induction.
 Electromagnetic induction leads to rotation of rotor.
 In this way electric energy is converted to mechanical energy.

4. Working of an Induction Motor :
1. The main working of the induction motor depends on
Faraday’s law of electromagnetic induction.
2. When the alternating current is provided to stating part
of the induction motor, it produces the rotating
magnetic field in the stator of the motor.
3. The speed of the rotating of the rotor is equal to the
field speed in the stator in the synchronous motor so it
called synchronous but in the case of the induction
motor, the speed of rotor rotation is less than the
revolving magnetic field.

5. 4. Like the transformer function, the field in the
stator also produced current in the rotor due to
the changing of the flux.
5. This current produces the magnetic field that
interacts with the field of the stator.

6. Equivalent circuit:
A simple per phase equivalent circuit model
of an induction motor is a very important
tool for analysis and performance prediction
at steady state condition .
figure shows the development of a per phase
transformer like equivalent circuit.

7. Stator copper loss : Pls= 3I2
sRs
Core loss :
Power across air gap :
PFW= friction and windage loss of the machine.
Since the output power is the product of developed
torque Te and speed Wm, Te can be expressed as
Rotor copper loss : Plr = 3I
2rRr
Output Power : P0=P8-Plr = 3I2
rRr
Shaft power : Psh=P0=PFW
Input power :

8. The magnitude of current Ir can be solved as
Substituting the above equation we get

9. Scalar control :
Scalar control, as the name indicates, is due to
magnitude variation of the control variables
only, and disregards the coupling effect in the
machine.
Scalar-controlled drives give somewhat inferior
performance, but they are easy to implement
Scalar-controlled drives have been widely used
in industry.
In the following sections scalar control
techniques with voltage-fed inverters are
discussed.

10. • The open loop Volts/Hz control of an
induction motor is far the most popular
method of speed control because of its
simplicity and these types of motors are
widely used in industry.
Open Loop Volts/Hz Control:
• Traditionally, induction motors have been
used with open loop 60Hz power supplies for
constant speed applications. For adjustable
speed applications, frequency control is
natural.

11. Fig:Block diagram of the open loop
Volts/Hz control for an induction motor.

12. Vector Control Of Induction Motor:
• Vector Control: The machine current and
voltage space vectors, the transformation of a
3 phase speed and time dependent system into
a two co ordinate time invariant system and
effective PWM pattern generation.

13. Scalar Control vs Vector Control:
Scalar
1. Simpler form of motor control
2. Good steady state performance
3. Poor dynamic response
4. Low performance drives
5. Higher power dissipation
Vector
1. Complex mathematicalmodel
2. Precise control of ac motors
3. Excellent dynamic response
4. High performance drives
5. Low power dissipation

14. Advantages of scalar control and vector
control:
Scalar control :
 Scalar control of AC motors is a good
alternative for applications where there is no
variable load and no good dynamics (fans,
pumps) are required.
 The scalar control does not require a rotor
position sensor, and the rotor speed can be
estimated from the frequency of the supply
voltage.

15.  high accuracy of speed control.
 soft start and smooth motor rotation in
full speed range.
 fast response to a load change.
vector control:

16. Disadvantages of scalar control and vector
control:
Scalar control:
• With scalar motor control, the stator currents
are not directly controlled.
• The scalar method is not suitable for the
control of low speed for applications
requiring high dynamics.
Vector control:
• the need to set motor parameters.
• large speed fluctuations at constant load.

17. THANK YOU