Additional asynchronous and pulsating torque analysis of 3-phase induction machine

Abstract

This document contains possibilities of additional asynchronous torque development due to the high harmonics and their general derivation. Also, there is calculated a pulsating torque of 3-phase induction machine with power 1.1kW from electromagnetic field and example of additional asynchronous torque calculation. Whole analysis is done by finite element method in ANSYS. The torque is calculated via a circular path integral of the Maxwell stress tensor. The Maxwell stress tensor provides a convenient way of computing forces acting on bodies by evaluating a surface integral.Index Terms -AC machines, electromagnetic analysis, magnetic fields, magnetic forces, pulse analysis, torque. I. INTRODUCTIONENERALLY, the magnetic field is possible to resolve to the high harmonic series incurred from concentrated winding in the slots, air-gap inequality due to the slotting. Each of these fields could generate additional torque on the rotor at variable speed at start up. A well known method to reduce the harmonic content in the line current when operating a grid-commutated inverter is to use a twelve-pulse convertor and a three-winding transformer. This method could be modified and applied in convertor applications with induction machine [1]. When supplied from conventional three phase inverters, three phase squirrel cage induction motors exhibit harmonic pulsating components of torque. These torque pulsations attain objectionable values during low frequency and in many cases dictate the satisfactory lower limit of speed range. In applications requiring uniform speed of rotation these pulsating torques need to be minimized. The results of minimizing the sixth harmonic pulsating torque component in an inverter induction motor drive system using a modified version of Rosenbrock's hillclimb technique are presented in [2]. The pulsating torque of an induction motor caused by Steinmetz connection which has been used for a three-phase motor operating on a singlephase supply is examined in [3]. The starting procedure of induction motor, with estimation of change of inductive reactance of equivalent circuit, is examined in [4]. Induction machines when fed by sinusoidal currents show distortions in This work has been prepared under the support provided by research projects: CZ.1.07/2.3.00/09.0162 -Knowledge