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Minimization of a SynRel’s oscillating torque by calculation of the appropriate skew angle

Javier Martinez (Electric Drives and Machines Institute, Graz University of Technology , Graz, Austria)
Klaus Krischan (Electric Drives and Machines Institute, Graz University of Technology , Graz, Austria)
Annette Muetze (Electric Drives and Machines Institute, Graz University of Technology , Graz, Austria)

Abstract

Purpose

Synchronous Reluctance (SynRel) motors are known to suffer from excessive torque ripples. The classical way to avoid this drawback of the motor is skewing the slots. This paper aims to provide an analytic estimation of the best skew angle to minimize the ripples in such SynRel motors with tooth windings. The approach used in this paper consists of the minimization of the spectral components of the magnetic energy that cause these oscillation torques. The method was validated by means of a multi-slice finite element model (FEM).

Design/methodology/approach

An analytic model, based on permeance theory, is derived to analyse the electromagnetic phenomena taking place inside of the motor. This model allows the identification of the causes underlying the torque ripple production. Based on this understanding, the most suitable skew angle can be determined. The analytic method, together with the best skew angle, is validated by means of an FEM of a SynRel machine.

Findings

A method to determine the optimum skew angle for a SynRel machine is presented. It depends on the wave-number of the magnetic waves producing the torque ripple. It is twice the one typically chosen for induction machines.

Practical/implications

The proposed approach allows improving on the design methodology for the production of smoothly running SynRel machines.

Originality/value

The methodology utilized in this paper is based on the relationship between the mechanical torque and the magnetic energy stored in the motor (virtual work law). From this, the best skew angle to eliminate the magnetic energy causing torque ripple can be determined. It, therefore, proposes an effective alternative to the common use of inductance models to determine such angles.

Keywords

Acknowledgements

This work has been carried out within the framework of ECO-COOL, a research project funded by FFG (Austrian Research Promotion Agency).

Citation

Martinez, J., Krischan, K. and Muetze, A. (2017), "Minimization of a SynRel’s oscillating torque by calculation of the appropriate skew angle", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 36 No. 3, pp. 824-835. https://doi.org/10.1108/COMPEL-09-2016-0403

Publisher

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Emerald Publishing Limited

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