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1. Subject Name: Electric Drives
Subject Code: KEE 075
Unit 1 :
Introduction and Block Diagram
Representation of Electric Drives
Dr. Sarika Kalra
EN Department
AKGEC, Ghaziabad

2. Content
• Electric Drives
Block Diagram
Power Modulator
Sources
Control unit
Choice of electric Drives
Classification of Electric Drives

3. Electrical Drives
• Motion control is required in large number of
industrial and domestic application. E.g. transportation
systems, rolling mills paper mills, textile mills,
machine tools fans, pumps robots washing machines
etc.
• Systems employed for motion control are called drives
and they may employ any of the prime- movers such
as, diesel or petrol engines, gas or steam turbines,
steam engines, hydraulic motors and electric motors
for supplying mechanical energy for motion control.

4. Features of Electric Drive System
• They have flexible control characteristics. The steady-
state and Dynamics characteristics of electrical Drives
can be shaped to satisfied load requirements.
• They are available in wide range of torque, speed and
power.
• Electric motors have higher efficiency, low No load
losses and considerable short time overloading
capacity.
• Can operate in all four quadrant of speed-torque plane.

5. Part of Electric Drive System

6. Power Modulator
A power modulator performs one or more of the following four
functions:
i. Modulates flow of power from source to the motor in such a
manner that motor is imparted the speed torque characteristic
required by the load.
ii. During transient operations, such as starting braking and
speed reversal, it restricts source and motor currents within
permissible values; excessive current drawn from source
may overload it or it may cause a dip in voltage.
iii. Converts electrical energy of the source in the form suitable
to the motor, e.g. if the source is DC and an induction motor
is to be employs, then the power modulator is required to
convert dc into variable frequency AC.
iv. Selects the mode of operation of the motor, i.e. motoring or
braking.

7. Classification of Power Modulators
a) Converters
b) Variable impedances
c) Switching circuits

8. Converters
• Need of converter arises when the nature of available
power is different than required by the motor.
• The power sources are of two basic types:
i. Fixed voltage and fixed frequency AC
ii. Fixed voltage DC
• For DC motor control variable DC is required and
for AC motor control variable AC is required.

9. AC to DC Converters

10. AC Voltage Controllers or AC Regulators

11. Choppers or DC to DC Converters

12. Inverters or DC to AC Converters

13. Cyclo-converters

14. Sources
• In India 1- phase and 3- phase 50 Hz ac supplies are
readily available in most locations.
• Very low power drives are powered from single phase
supply.
• High power load is powered from three phase ac
supply.
• But in traction drives, drive powers are high and they
are fed by single phase supply because of the
economy.
• So, most of the drives are powered from ac source
either directly or through some converters.

15. Control Unit
• Controls for power modulator are provided in the
control unit.
• Nature of control unit for a particular drive depends
upon the type of power modulator employed in that
particular drive.
• e.g. when semiconductor converters are used, the
control unit consists of firing circuits.
• When control of switching circuits are employed, the
function of control unit will be to provide sequencing
and interlocking.

16. Choice of Electric Drives
 Steady state operation requirements: Nature of speed
torque characteristics, speed regulation, speed range,
efficiency, duty cycle, quadrants of operation, speed
fluctuations etc.
 Transient operation requirements: acceleration and
deceleration, starting, braking and reversing
performance.
 Requirements related to the source: type of source and
its capacity, voltage magnitude, voltage fluctuations,
power factor harmonics and their effect on other
loads, ability to accept the regenerated power.

17. • Capital and running costs maintenance needs,
life of drive etc.
• Space and weight restrictions if any.
• Environment and location.
• Reliability.

18. Classification of Electric Drive Systems
• Number of machines and interrelations
• Means of control
• Classification of methods of speed control
• Mode of operation
• Dynamic and transients

19. Number of Machines and
Interrelations
• Individual electric drive
• Group electric drive
• Multi-motor electric drive
Individual Drive
• In the Individual Drive system, each machine tool has its
own electric motor which drives the machine through
belt, chain, gearing or by direct coupling. The system is
also called as a self-contained drive.
• Each individual machine is driven by a separate motor.
The motor also imparts motion to various other parts of
the machine.

20. • Example: Single spindle drilling machine and lathes.
• In a lathe, the motor rotates the spindle, moves the
feed and also with the help of gears, transmits motion
to lubricating and cooling pumps.

21. Group Drive
• The drive consists of a single motor, which drives one or
more line shafts supported on bearings. The line shafts
may be fitted with either pulleys and belts or gears. It is
also sometimes called the shaft drive. These drives are
seldom used because of their low efficiency. But they are
economically attractive.
• The Group Drive system uses a high powered motor
which drives an overhead shaft called the main shaft.

22. • The main shaft runs across the workshop from one
end to other ends. The main shaft sometimes
drives another shaft called counter shaft. Finally,
the countershaft drives the group of machines
through belting and pulleys.

23. Multi-motor drive:
• In this drive system, there are several drives, each of
which serves to actuate one of the working parts of the
drive mechanism. There applications are found in
complicated metal cutting machine tools, paper making
machines, rolling mills etc.
• The drives of crane can also be considered as an
example of multi motor drive system This type of
multi-motor incorporates three drives: first for vertical
movement, second for side movement, and third for
forward movement. Each of these drives function
separately and the operator of the crane co-ordinates
their function.

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