PERFORMANCE INVESTIGATIONS OF VECTOR CONTROLLED INDUCTION MOTOR DRIVE

Abstract

Three phase squirrel cage induction motor has been the most widely used motor for fixed speed applications for industrial environments because of its simple and compact structure, ruggedness, reliable operation, high efficiency at low cost, and minimum maintenance. Number of attempts has been made to substitute three phase squirrel cage induction motors in variable speed applications, wherein the genuine choice has been dc motors. Some of these control methods which allow the induction motor to work in variable speed drives are voltage control. frequency control, and current control. The performance of the stated methods is excellent in the steady state operation but the performance during transient period is not satisfiictory. Therefore a technique, which merges the advantages of induction motor and dc motor and allows the induction motor to work in variable speed drives with excellent dynamic performance similar to the dc motor, is developed. This technique is known as Vector Control (VC) or Field Oriented Control (FOC). The VC technique has now become the widely accepted technique for controlling of induction motor in the industries. This technique provides two hypothetical currents in the Synchronous Rotating Reference Frame (SRRF), components of stator current vector, which are responsible for controlling flux and torque independently and hence the induction motor control - becomes analogous to the control of separately excited dc motor. In this investigation, the mathematical modeling of induction motor operating in vector control mode has been carried out. The performance of vector controlled induction motor drive (VCIMD) is recorded under different operating conditions such as starting. braking, step change in speed and subjected to different types of load in the MATLAB 8.2 plat1orii using Simulink and power system toolboxes. A comparative study is done using different speed controllers under the stated operating conditions. The comparative study is done using Proportional Integral (PT) speed controller, Fuzzy Logic (FL) speed controller and Intelligent speed controller. Normally VCIMD system feeds from converter-inverter arrangement, which suffers with the problem of harmonics in the supply current and poor power factor (PF) of the system. This investigation also deals with some techniques to improve the system power quality. The conventional three phase ac-dc converter is used with LC filter at the dc link. To improve the power quality factors of VCIMD system, the ac-dc converter is fed through phase shifting transformers to realize Multi-pulse converters and the obtained results of power quality indices shows the reduced harmonics and improved dc link voltage over the conventional ac-dc converter feeding VCIMD.