DESIGN OPTIMIZATION OF INVERTER FED INDUCTION MOTOR

Abstract

Optimal design of a three-phase squirrel cage induction motor excited from a volatge source inverter is carried out here. Initially, motor is designed by conventional design procedure for 50-Hz sinusoidal supply. Then, entire performance including total losses of the motor fed from square wave voltage waveforms is determined. Flow charts have been developed for determination of performance and total losses with constant .v/Hz mode of operation. Computer programs based on these flow-charts have been developed in FORTRAN language to calculate performance and losses of three different ratings of motor with constant full load torque over a frequency range from 10-Hz to 75-Hz. Finally, a flow chart for minimisation of the losses of the inverter-fed induction motor has been developed using the Univariate type of method. The quantities which are considered as variables are specific electric loading-ac, specific magnetic loading-Bay, Ratio of core-Length to pole-pitch-Rlp, ratio of slot-depth to slot-width of stator-Ax, and stator winding current density-cs. A program develped on the basis of this flow chart, has been used to obtain suitable values of the design variables so that the total losses of the motor are minimised. Performance of the optimised motor is compared with normal designed motor over the entire frequency range. In chapter I, general discussion and literature review on the topic is presented. In chapter II, performance of VSI-fed I.M. with constant V/Hz'mode of operation Is studied. Also, special features required for the design of Induction motor for non-sinusoidal supply are discussed) calculation of components of total losses is carried out in detail. The minimisation of losses of VSI-fed Induction motor is considered in chapter III. The performance of the motor for the optmised parameters is compared with the normal design and results have been discussed, Finally, conclusions as well as scope for further work is indicated..