DEVELOPMENT AND STUDY OF THE CHARACTERISTICS AND STABILITY OF A MICROPROCESSOR BASED FEEDBACK CONTROL SYSTEM FOR A THREE PHASE INDUCTION MOTOR

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. 382875 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.