Time Domain Modeling and Digital Simulation of Variable-Frequency AC Motor Speed Control Using PLL Technique

A time domain model of the system has been developed and simulated on a digital computer. Starting transients as well as the steady-state speed control performance of the system have been studied. In order to improve the starting performance significantly, a modification has been incorporated in the control scheme for the starting period only. This modification avoids traditional osciflatory behavior of the induction motor and reduces undesired high current peaks (with high starting torque). To verify the validity of the time domain model and simulation method used, the computed results were compared with those obtained by the frequency domain method and found much closer to the reported test results. For efficient computation, the voltage equations for stator and rotor circuits of the motor were developed separately to avoid inversion of a time dependent matrix in every step of integration.