DOUBLY FED INDUCTION MOTOR USING SCR INVERTER

Abstract

Direct current drive schemes have been employed in the past for industrial applications where closely controlled torque-speed characteristics were necessary. Alternating current drive schemes, which otter the advantages of simplicity of operation and maintenance have not been able to give similar torque-speed characteristics without the use of auxiliary commutator machines. Attempts to employ the induction motor as a variable speed drive using static devices as control elements have met with some success. This thesis presents an analysis of the characteristics of a three phase induction motor drive where the stator and the rotor are both fed with energy, the stator from the supply mains and the rotor through a bridge connected silicon controlled inverter. The necessary analysis of the inverter operation, the torque calculations with the inverter in the rotor circuit and the design of a suitable control circuit tor the control of the drive scheme are presented. This thesis also outlines the tests which were performed in the laboratory to check the accuracy of the analysis of the inversion process and the motor torque calculations. The results of this preliminary study are encouraging and indicate that this scheme otters possibilities for dynamic braking of hoisting and traction type loads. A number of aspects which require further investigation are outlined.