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ANALYSIS AND DEVELOPMENT OF SENSORLESS VECTOR CONTROL OF VARIABLE FREQUENCY DRIVE USING INDUCTION MOTOR
R. S. Saluja*

The variable frequency squirrel cage induction motor drive with Field Oriented Control(FOC) or Vector Control(VC) offers a high level of dynamic performance and the closed loop control associated with this drive provides stability of the system. The vector control is also called as an independent or decoupled control where in the torque and flux current vectors are controlled in a manner similar to what is done in a fully compensated separately excited DC motor. Hence the control plant of the cage motor drive is linearized and it behaves like a fully compensated separately excited DC motor.

This thesis presents an analysis of the dynamic performance of a closed loop pulse width modulated controlled voltage source inverter (VSI) fed cage induction motor drive. The induction motor drive is modeled and simulated with a view to study its dynamic behaviour in the closed loop. The control analysis of induction motor in vector controlled mode is done using real variables (currents and voltages), which is helpful for design of field oriented control of IM drive. The dynamic response of the system for conditions such as starting, speed reversal, and load perturbation has been discussed using PI and PID speed controllers.

A model for mechanical sensorless vector control fed induction motor has also been developed, and simulated results are presented for starting, speed reversal dynamics,& load perturbation . The real time implementation of VC of IM is carried out using a DSP (digital signal processor) of Texas Instruments as TMS320LF2407 DSP. It is the real time-processing properties of such as the TMS320LF2407 DSP controller, and the accurate asynchronous motor model that facilitates the development of a reliable and robust drive with accurate and variable speed controls providing fast TMS320LF2407 DSP response time and increasing the efficiency, the cost effectiveness of the drive. Hardware implementation aspects including current & speed sensing and scaling circuits along with the interfacing of the DSP and power circuit have been discussed. Experimental results are given on the developed device.


* Mr. R.S. Saluja is presently working as Manager (R&M - Engg.) in Engineering Office Complex of NTPC at Noida. His communication address is Engineering Office Complex, NTPC, Sector-24, Noida - 201301 (U.P.).
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