Abstract:
A microprocessor based three phase induction motor speed
control system is designed and developed. The rated value of
the motor is 1390 revolution per minute(rpm) 50 Hz. But by the
use of present control system the motor speed can be varied
from 500 rpm to 2000 rpm at the rated torque.
A six step three phase inverter is designed to drive the
motor. To avoid commutation failure in a wide frequency range
n-channel MOS FET is used place of SCR. One way digital delay
circuit is designed to avoid high voltage dc short circuit
situation due to the FET's turn off delay.
A computer interface card is designed to read the speed
of the motor and to write (set) the required voltage level
either in digitat to analogue(D/A) converter or in
Demultiplexer to set the appropriate voltage which drive the
VCO for generating required motor driving frequency. This
frequency is then fed in logic circuit to generate device
triggering pulses for three phase inverter. A number of
programs in C++ is written to perform the activities between
the computer and the interfacing card. In the screen of the
computer we can see several aspects of the running motor such
as speed, slip, torque and deviation of all these values from
the rated values.
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A mechanical section is developed to apply some load to
the motor. Several characteristics of the motor is observed in
different loaded condition and presented in a graphical form.
This experimental graphs are compared with the theoretical
ones.
And last the performance of the present work is evaluated
and proposal is made for further development of the present
motor control system.
