Stator Current Spectral Content of Inverter-Fed Cage Rotor Induction Motor

Gojko Joksimovic,Andraz Rihar,Peter Zajec,Vanja Ambrozic,Alberto Tessarolo

doi:10.1109/access.2022.3154481

Gojko Joksimovic, Andraz Rihar + Show 3 more

Open Access

https://doi.org/10.1109/access.2022.3154481

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Abstract

The paper analyzes the influence of the number of rotor bars on the stator current spectral content in a three-phase cage induction motor fed by a pulse-width modulated (PWM) inverter. It is shown that each of the higher-order time harmonics in the supply voltage produces space harmonics in a rotating magnetic flux density wave, which results in induced rotor slot harmonics (RSHs) in the stator current spectrum. The conditions for the existence of these space harmonics are identical to those applying to a mains-fed motor. In other words, the number of rotor bars of a mains-fed motor yielding an RSH-free stator current spectrum produces the same stator current spectrum even in case the motor is inverter-fed. Additionally, to minimize the adverse effects of RSHs in the stator current spectrum, one must consider not only the number of rotor bars, but also its relationship with the frequency modulation ratio of the PWM inverter. Analytical predictions are presented to illustrate these results supported both by numerical simulations of the induction motor modelled through the winding function theory and experimentally taking the case a two-pole cage induction machine as a case study.

Highlights

After more than a century since their invention, induction motors still play a paramount importance in industry and vehicle traction applications over a huge variety of ratings, thanks for their cheapness, ruggedness and reliability [1], [2], [3]
A detailed dynamic mathematical model of the selected induction motor was prepared, implementing the winding function theory. It uses the parameterized winding function (PWF) model, in which the number of rotor bars and its skewing angle appear as free parameters, [7], [8], [18], [19]
It further shows that the conditions for rotor slot harmonics (RSHs) in the stator current spectrum of an inverter-fed cage induction motor are identical to the case of mains-fed motors

Summary

Introduction

After more than a century since their invention, induction motors still play a paramount importance in industry and vehicle traction applications over a huge variety of ratings, thanks for their cheapness, ruggedness and reliability [1], [2], [3]. More and more efforts are being placed on the attempt to improve the performance of induction motors under various respects, such as increasing their efficiency to meet present energy saving standards and targets [5] as well as reducing noise and vibrations [6]. These targets apply to traditional mainsfed motor but are even more relevant to inverter-fed motors, which account for the vast majority today thanks to their capability of operating at variable speed. The main problem being considered is how some key design choices such as the selection of the number of stator slots and rotor bars, for VOLUME XX, 2017

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