2. ELECTRIC DRIVES
• Systems employed for motion control are
called as Drives.
• It may employ any of 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.
• Drives employing electric motors are called as
Electrical Drives.
4. POWER MODULATOR
• The power modulator regulates the output power
of the source.
• It controls the power from the source to the motor
in such a manner that motor transmits the speed
torque characteristic required by the load.
• During the transient operations like starting,
braking and speed reversing the excessive current
drawn from the source. This excessive current
drawn from the source may overload it or may cause
a voltage drop. Hence the power modulator restricts
the source and motor current.
5. POWER MODULATOR
• The power modulator converts the energy
according to the requirement of the motor e.g.
if the source is DC and an induction motor is
used then power modulator convert DC into AC.
• It also selects the mode of operation of the
motor, i.e. motoring or braking.
6. CONTROL UNIT
• The control unit controls the power
modulator which operates at small voltage and
power levels. The control unit also operates the
power modulator as desired.
• It also generates the commands for the
protection of power modulator and motor. An
input command signal which adjusts the
operating point of the drive, from an input to
the control unit.
7. SENSING UNIT
• It senses the certain drive parameter like
motor current and speed.
• It mainly required either for protection or for
closed loop operation.
8. ADVANTAGE OF ELECTRIC DRIVES
• The electrical drives are available in a wide range of
torque, speed and power.
• They are adaptable to almost any operating
conditions such as explosive and radioactive
environment, submerged in liquids, vertical mounting
and so on.
• The electrical drive does not pollute the environment.
• It can operate in all four quadrants of speed torque
plane.
• They can be started instantly and can immediately be
9. ADVANTAGE OF ELECTRIC DRIVES
They have flexible control characteristic and can be
employed to automatically control the drive.
Because of the above advantages, the mechanical
energy already available from a non-electrical prime
mover is sometimes first converted into electrical
energy by a generator and back to a mechanical
energy of an electrical motor.
Electrical link thus provides between the non-
electrical prime mover and the load impact to the
drive flexible control characteristic.
10. DISADVANTAGE OF ELECTRIC
DRIVES
• The power failure completely disabled the
whole of the system.
• The application of the drive is limited because
it cannot use in a place where the power supply
is not available.
• It can cause noise pollution.
• The initial cost of the system is high.
12. POWER MODULATORS
Power Modulators – are the devices which alter the nature or
frequency as well as changes the intensity of power to control
electrical drives. Roughly, power modulators can be classified
into three types,
1) Converters 2) Variable impedance circuits 3) Switching
circuits.
As the name suggests, converters are used to convert currents
from one type to another type. Depending on the type of
function, converters can be divided into 5 types –
1) AC to DC converters 2) AC regulators 3) Choppers or DC-DC
converters
13.
14. SOURCES
Sources may be of 1 phase and 3 phase. 50 Hz AC
supply is the most common type of electricity supplied
in India, both for domestic and commercial purpose.
Synchronous motors which are fed 50 Hz supply have
maximum speed up to 3000 rpm, and for getting
higher speeds higher frequency supply is needed.
Motors of low and medium powers are fed from 400
V supply, and higher ratings like 3.3 kV, 6.6 kV, 11 kV
etc are provided also.
15. CONTROL UNIT
Choice of control unit depends upon the type
of power modulator that is used.
These are of many types, like when
semiconductor converters are used, then the
control unit consists of firing circuits, which
employ linear devices and microprocessors.
16. CHOICE OF ELECTRICAL DRIVE
Choice of an electric drive depends on a number of factors. Some of
the important factors are
1. Steady State Operating conditions requirements: Nature of speed
torque characteristics, speed regulation, speed range, efficiency, duty
cycle, quadrants of operation, speed fluctuations if any, ratings etc
2. Transient operation requirements: Values of acceleration and
deceleration, starting, braking and reversing performance.
3. Requirements related to the source: Types of source and its
capacity, magnitude of voltage, voltage fluctuations, power factor,
harmonics and their effect on other loads, ability to accept
regenerative power
17. CHOICE OF ELECTRICAL DRIVE
4. Capital and running cost, maintenance needs life.
5. Space and weight restriction if any.
6. Environment and location.
7. Reliability.
18. REFERENCES
G. K. Dubey, “Fundamentals of Electrical Drives”, Second Edition,
Narosa Publishing House
