A Comparative Study of the Variable-Speed Induction Motor Drive Stability Investigations

Abstract

The objective of this research is to develop a dynamic mathematical model of the rectifier-inverter induction motor drive system from first principles using the MATLAB program. Two MATLAB friendly-user interfaces were developed that allow assessment of system stability for Light load - low frequency operation. The MATLAB programs developed can be used to study system stability for zero-input response as well as the complete system response. The linearized drive model was obtained by applying Small-Displacement Theory to the static drive system. System equations were derived, and a linear algebraic model was used to describe the system in steady state conditions. The dynamics of the system are presented in matrix form relating small changes in the terminal voltage and load torque to perturbations in currents and mechanical speed of the motor. The dynamic equations are incorporated in the two MATLAB programs. Two user-friendly interfaces were designed to facilitate investigating the effect of different system parameters on system stability. The results are displayed as contours of instability regions that change as machine or filter parameters change. It is worth mentioning that a similar work has been done by T.A Lipo and P.C Kruse in 1968 and 1969. However, due to limited computing facilities at that time, the approach and computer simulation used were more complicated. In order to compare the results, the same parameters used in their studies have been used in this project. The results reached were similar to their conclusion in all cases of study.