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Lecture 22-01-14
Electronic Speed Control Method
for DC Motors
Engr. Zahoor Ahmed Maharvi
Introduction
• Solid state circuits using semiconductor
diodes and thyristors have become very
popular for controlling the speed of d.c.
motors.
• Solid state circuits are progressively
replacing the traditional electric power
control circuits based on thyratrons,
ignitrons, mercury arc rectifiers, magnetic
amplifiers and motor-generator sets etc.
Engr. Zahoor Ahmed Maharvi
Merits of Electronic Control
Circuits
•
1.
2.
3.
4.
5.
As compared to the electric power control
circuits, the electronic control methods have
Higher accuracy
Greater reliability
Quick response
Higher efficiency as there are no I2R losses
and moving parts.
Full 4-quadrant speed control is possible to
meet precise high speed standards.
Engr. Zahoor Ahmed Maharvi
Electronic Speed Control Methods
•
All electronic control circuits control the
motor speed by adjusting either
1. the voltage applied to the motor
armature
2. the field current, or
3. both
Engr. Zahoor Ahmed Maharvi
D.C. Motors Power Supply
• D.C. motors can be run from d.c. supply if
available or from a.c. supply after it has
been converted into d.c. supply with the
help of rectifiers which can be either halfwave or full-wave and either controlled
(by varying the conduction angles of the
thyristors used) or uncontrolled.
Engr. Zahoor Ahmed Maharvi
Motor Speed Control using
Thyristor Controlled Rectifier
• The average output voltage of a thyristorcontrolled rectifier can be changed by
changing its conduction angle and
hence the armature voltage of the d.c.
motor can be adjusted to control its
speed.
Engr. Zahoor Ahmed Maharvi
Motor Speed Control using
Thyristor Chopper Circuit
• When run on a d.c. supply, the armature d.c.
voltage can be changed with the help of a
thyristor chopper circuit which can be made to
interrupt d.c. supply at different rates to give
different average values of the d.c. voltage.
• If d.c. supply is not available, it can be obtained
from the available a.c. supply with the help of
uncontrolled rectifiers (using only diodes and
not thyristors). The d.c voltages so obtained
can be then chopped with the help of a thyristor
chopper circuit.
Engr. Zahoor Ahmed Maharvi
Uncontrolled Rectifiers
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Controlled Rectifiers
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Controlled Rectifiers (contd..)
Engr. Zahoor Ahmed Maharvi
Thyristor Choppers
Engr. Zahoor Ahmed Maharvi
Thyristor Choppers (Contd..)
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Thyristor Speed Control of a
Separately Excited D.C. Motor
Engr. Zahoor Ahmed Maharvi
Thyristor Speed Control of a D.C.
Series Motor
Engr. Zahoor Ahmed Maharvi
Full-Wave Speed Control of a
Shunt Motor
Engr. Zahoor Ahmed Maharvi
Thyristor Speed Control of a
Shunt Motor
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Thyristor Speed Control of a D.C.
Series Motor
Engr. Zahoor Ahmed Maharvi
?
Reference
Chapter # 30
Electrical Technology
By B.L.Theraja
Engr. Zahoor Ahmed Maharvi