Introduction

1. EPE10 104
ELECTRIC DRIVES
Dr. Sasidharan Sreedharan
www.sasidharan.webs.com

2. OBJECTIVE
To provide a strong background on
various methods of speed control of
different electrical machines.

3. MODULE 1
Components of electrical Drives – electric machines,
power converter, controllers - dynamics of electric drive -
torque equation - equivalent values of drive parameters-
components of load torques types of load - four
quadrant operation of a motor –– steady state stability -
load equalization – classes of motor duty- determination
of motor rating

4. MODULE 2
DC motor drives – dc motors & their performance (shunt,
series, compound, permanent magnet motor, universal
motor, dc servomotor) – braking – regenerative, dynamic
braking, plugging – Transient analysis of separately excited
motor – converter control of dc motors – analysis of
separately excited & series motor with 1-phase and 3-phase
converters – dual converter – analysis of chopper controlled
dc drives – converter ratings and closed loop control -
transfer function of self, separately excited DC motors –
linear transfer function model of power converters – sensing
and feeds back elements – current and speed loops, P, PI and
PID controllers – response comparison – simulation of
converter and chopper fed DC drive.

5. MODULE 3
Induction motor drives – stator voltage control of
induction motor – torque-slip characteristics – operation
with different types of loads – operation with
unbalanced source voltages and single phasing – analysis
of induction motor fed from non-sinusoidal voltage
supply – stator frequency control – variable frequency
operation – V/F control, controlled current and
controlled slip operation – effect of harmonics and
control of harmonics – PWM inverter drives – multi-
quadrant drives – rotor resistance control – slip torque
characteristic – torque equations, constant torque
operation – slip power recovery scheme – torque
equation – torque slip characteristics – power factor –
methods of improving .

6. MODULE 4
Synchronous motor drives – speed control of
synchronous motors – adjustable frequency operation of
synchronous motors – principles of synchronous motor
control – voltage source inverter drive with open loop
control – self controlled synchronous motor with
electronic commutation – self controlled synchronous
motor drive using load commutated thyristor inverter.

7. REFERENCES
1. R. Krishnan, Electical Motor Drives, PHI
2 GK Dubey, Fundamentals of Electrical Drives,
Narosa
3. GK Dubey, Power Semi-conductor Controlled
Drives, Prentice Hall
4. Bimal K Bose, Modern Power Electronics & AC
Drives, PHI
5. S A Nasar, Boldea, Electrical Drives, CRC press
6. M A Elsharkawi, Fundamentals of Electrical Drives,
Thomson Learning
7. W Leohnard, Control of Electric Drives, Springer
8. Murphy and Turnbill, Power Electronic Control of
AC motors, Pergamon Press
9. Vedam Subarhmanian, Electric Drives, TMH

8. Examination
Internal continuous assessment: 100 marks
Internal continuous assessment is in the form of
periodical tests, assignments, seminars or a combination
of all whichever suits best. There will be a minimum of
two tests per subject. The assessment details are to be
announced to students’ right at the beginning of the
semester by the teacher.
End semester Examination: 100 marks

9. Modern Variable Speed System
A modern variable speed system has four
components:
1. Electric Motor
2. Power Converter
- Rectifiers
- Choppers
- Inverters
3. Controllers – matching the motor and
power converter to meet the load
requirements
4. Load

10. Electric Motors
Types of electric motors presently used for
speed control applications are:
1. DC motors AC motors
Shunt Induction
Series Wound rotor
Compound synchronous
Separately excited Permanent magnet
Switched synchronous
reluctance motors Reluctance motors

11. Motor Selection
1. Cost
2. Thermal capacity
3. Efficiency
4. Torque-speed profile
5. Acceleration
6. Power density, volume of the motor
7. Ripple, cogging torque
8. Peak torque capability
9. Suitability for hazardous environment
10. Availability of spare parts

12. Electric Motors (contd’)
For position servo applications:
The peak torque and thermal capabilities together
with ripple and cogging torques are important
characteristics for servo application
Higher peak torques decrease the
acceleration/deceleration times
Minimum cogging and ripple torques help to
attain higher positioning repeatability and higher
thermal capability leading to a longer motor life
and a higher amount of loading

13. Power Converters
The power converters driving the motors are:
1. Controlled Rectifiers
Controlled rectifiers are fed from single and
three-phase AC main supply.
Vc: Voltage controlled
Kr: Gain (proportionality constant)

14. Power Converters (contd’)
2. Inverters – Voltage and current source
converters are fed from a DC link. The DC link is
generated with either a controlled or uncontrolled
rectifier.
Vc: controlled magnitude command
fc: frequency command

15. Power Converters (contd’)
3. Cycloconverter

16. Controllers
The controllers implement the control strategy
governing the load and motor characteristics
To match the load and motor, the input to the
power converter is controlled (manipulated) by
the controller

17. Motor Drive Schematic

18. Typical Controller Block

19. Controllers (contd’)
The inputs to the controller consists of:
1. Torque, flux, speed, and/or position commands
2. Their rate of variations to facilitate soft
start, to preserve the mechanical integrity of the load
3. The actual values of torque, flux, speed, and/or
position for feedback control.
4. Limiting values of currents, torque, acceleration,
etc.
5. Temperature feedback, instantaneous currents
and/or voltages in the motor and/or converter.

20. POWER ELECTRONICS AND DRIVES
What is Power Electronics ?
A field of Electrical Engineering that deals with the application of
power semiconductor devices for the control and conversion of
electric power
sensors
Input
Source Power Electronics Load
- AC Converters
- DC Output
- unregulated - AC
- DC
POWER ELECTRONIC
CONVERTERS – the
heart of power a power
Reference Controller electronics system

21. Modern Electrical Drive Systems
Typical Modern Electric Drive Systems
Power Electronic Converters Electric Motor
Electric Energy Electric Energy Electric Mechanical
- Unregulated - - Regulated - Energy Energy
POWER IN Power
Moto Load
Electronic r
Converters
feedback
Reference
Controller

22. Modern Electrical Drive Systems
Overview of AC and DC drives
DC drives: Electrical drives that use DC motors as the prime mover
Regular maintenance, heavy, expensive, speed limit
Easy control, decouple control of torque and flux
AC drives: Electrical drives that use AC motors as the prime mover
Less maintenance, light, less expensive, high speed
Coupling between torque and flux – variable spatial angle
between rotor and stator flux

23. Modern Electrical Drive Systems
Overview of AC and DC drives
Before semiconductor devices were introduced (<1950)
• AC motors for fixed speed applications
• DC motors for variable speed applications
After semiconductor devices were introduced (1960s)
• Variable frequency sources available – AC motors in variable
speed applications
• Coupling between flux and torque control
• Application limited to medium performance applications –
fans, blowers, compressors – scalar control
• High performance applications dominated by DC motors –
tractions, elevators, servos, etc

24. Modern Electrical Drive Systems
Overview of AC and DC drives
After vector control drives were introduced (1980s)
• AC motors used in high performance applications – elevators,
tractions, servos
• AC motors favorable than DC motors – however control is
complex hence expensive
• Cost of microprocessor/semiconductors decreasing –predicted
30 years ago AC motors would take over DC motors

25. Modern Electrical Drive Systems
Overview of AC and DC drives
Extracted from Boldea & Nasar

26. Power Electronic Converters in ED Systems
Converters for Motor Drives
(some possible configurations)
DC Drives AC Drives
AC Source DC Source AC Source DC Source
DC-AC-DC DC-DC
AC-DC AC-DC-DC AC-DC-AC AC-AC DC-AC DC-DC-AC
Const. Variable NCC FCC
DC DC

27. Conclusion
All Resource Materials(Class power points, notes, assignments etc )
will be regularly posted in the website.
Please visit regularly for updated information
www.sasisreedhar.webs.com
Sent mail in case of any clarification/doubts/suggestions
sasisreedhar@vidyaacademy.ac.in