PERFORMANCE INVESTIGATIONS OF VECTOR CONTROLLED INDUCTION MOTOR DRIVE

Abstract

The principle of vector control of AC machine enables the dynamic control of AC motors, and induction motors in particular to a performance level comparable to that of a DC machine. Various control methods of induction motor drive like voltage control, frequency control, voltage and frequency control, current control, etc, provide steady-state performance, but their dynamic response is poor. The vector control technique, which is also known as field-oriented control (FOC), allows a squirrel-cage induction motor to be driven with high dynamic performance that is comparable to the characteristics of DC motor. The vector control technique decouples the two components of stator current: one providing the air-gap flux and the other producing the torque. It provides independent control of flux and torque, and the control characteristic is linearized. In this technique, the stator currents are converted to a fictitious synchronously rotating reference frame with the flux vector and are transformed back to the stator frame before feeding back to the machine. The two components are d-axis component, ids analogous to armature current and q-axis component, iq, analogous to the field current of a separately excited DC motor. Thus, the vector control must ensure the correct orientation of the space vectors and generate the control input signals. Therefore, with a vector control, an induction motor can operate as a separately excited DC motor. In this work, a comprehensive mathematical modeling of vector controlled induction motor drive (VCIMD) system has been carried out to investigate the performance of drive system. The dynamic response of VCIMD under various operating conditions such as starting,. speed reversal, speed re-reversal and load perturbation is simulated and examined in MATLAB 6.5 environment using simulink and power system block set toolboxes. Further, the dynamic response- of the VCIMD depends on the type of the speed controller used in the closed loop operation''he speed controllers used in this work are Proportional Integral (PI) speed controller, Fuzzy Logic (FL) speed controller, hybrid of PI and FL speed controllers and Fuzzy Pre-compensated PI (FPPI) speed controller. A comparative study of the response of VCIMD is made with different speed controllers using MATLAB-simulink software. PWM signals for a three phase Voltage Source Inverter (VSI) are generated using MATLAB Embedded Controller I-8438. iii