PERFORMANCE ANALYSIS OF A THREE-PHASE INDUCTION MOTOR WITH A THYRODE STARTER

Rapid developmets in the semiconductor industry have made possible a revolutionary improvement in the control of three-phase induction motors. The studies reported. in this thesis involved a solid state "thyrode" starter used. with a three-phase, delta-connected induction motor. The starter was comprisedof an SCR and a diode connected in inverse parallel configuration in each of the three supply lines to the motor, The studies were directed specifically toward the determination of the dynamics of the motor associated with the starting and stopping sequences of the drive system. Particular attention was directed toward a failure-to-stop problem exhibited. by a particular industrial application of the thyrode type drive. In this thesis, the detailed operation of the thyrode controller and its associated switching circuit are explained: a dynamic model of the induction motor based on the three-axis a-b-y transformation is developed; and a digital simulation of the system including the solid state switching controller and the induction motor is described. Waveforms of the voltage, current and speed obtained from staged tests run in the laboratory and in the field on the actual motor and those obtained from tests run on the simulation are compared and analyzed, It was demonstrated that the simulation approach used adequately represented the physical system under starting and stopping conditions. These models and simulation may be used as an analytical aid for further studies of the dynamic characteristics of induction motors with solid state controllers