Torque Ripple Investigation in Squirrel Cage Induction Machines

Abstract

Low torque ripple of electrical machines is an important requirement for many different applications. The causes of torque fluctuations in squirrel cage asynchronous induction motors might be a challenging task due to the complex phenomena raised by the whole set of rotor bars. This paper proposes an accurate analysis of the torque contributions distinguishing in time-varying, synchronous and asynchronous components. The investigation is performed by adopting a general analytical approach based on a circuital modelling technique for electromagnetic devices. The analysis aims to identify spatial harmonic interactions between stator and rotor magneto-motive forces which generate torque components. The most interesting effects obtained from the analytical investigation are compared and validated against finite element results for the most significant operating points.

Reduced-Order Model of Rotor Cage in Multiphase Induction Machines: Application on the Prediction of Torque Pulsations

“…According to the Table A 3 in Appendix C, the 10 most important space harmonics (excited by the sequence "u = 1") regarding their amplitudes in the winding function are: v = 1, 5,7,11,13,17,19,23,35,37. An interaction between two of these harmonics is considered important regarding the amplitude of torque pulsation.…”

“…As an example, a previous work has shown that the rotor bars number has to be carefully chosen to avoid important torque ripple under different supplying harmonics (sequences) [22]. Hence, it is necessary to understand deeply the interactions between time and space harmonics and their impact on torque production in multiphase induction machine [23].…”

“…Considering all the α-β rotor planes, excited by important space harmonics, is important to predict torque pulsations due to harmonic interactions. Recent work has investigated the analytical estimation of torque ripples, due to interactions between stator and rotor space harmonics, for three-phase induction machine [23].…”

An Analytical-Numerical Approach to Model and Analyse Squirrel Cage Induction Motors

“…In particular, the high frequency currents induced in the rotor cage due to the high order spatial harmonics exhibited by the stator windings represent a undesirable secondary effect which deteriorate the efficiency of the machine as they mainly flow in the upper portion of the solid bars due to skin and proximity effects, thus producing not-negligible additional Joule losses. Moreover, the presence of high-order harmonics in the magnetomotive forces (MMFs) generated by the cage and stator windings produces asynchronous, synchronous and ripple torque components [4]. To reduce such parasitic effects mainly produced by the non-ideal structure of stator windings, SCIMs are often equipped with a skewed rotor, yet at the cost of a reduction of the mean torque produced.…”

The potential of exploiting non-symmetric structures in electrical machines

“…Symmetry is widely exploited in electrical machines aiming to minimize manufacturing costs and the design process complexity [1], [2]. Therefore, most commonly, symmetrical and regular stator and rotor structures are used [3], [4]. Nevertheless, this choice comes at the cost of reducing the design degrees of freedom which would be available if asymmetrical configurations were investigated.…”