Energies 2011, 4, 2166-2179; doi:10.3390/en4122166
OPEN ACCESS

energies
ISSN 1996-1073 www.mdpi.com/journal/energies Article

A Novel Cogging Torque Simulation Method for
Permanent-Magnet Synchronous Machines
Chun-Yu Hsiao *, Sheng-Nian Yeh and Jonq-Chin Hwang
Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei
10607, Taiwan; E-Mails: snyeh@mail.ntust.edu.tw (S.-N.Y.); jchwang@ee.ntust.edu.tw (J.-C.H.)
* Author to whom correspondence should be addressed; E-Mail: D9607101@mail.ntust.edu.tw;
Tel.: +886-921135781; Fax: +886-2-27376699.
Received: 16 September 2011; in revised form: 22 November 2011 / Accepted: 30 November 2011 /
Published: 6 December 2011

Abstract: Cogging torque exists between rotor mounted permanent magnets and stator teeth due to magnetic attraction and this is an undesired phenomenon which produces output ripple, vibration and noise in machines. The purpose of this paper is to study the existence and effects of cogging torque, and to present a novel, rapid, half magnet pole pair technique for forecasting and evaluating cogging torque. The technique uses the finite element method as well as Matlab research and development oriented software tools to reduce numerous computing jobs and simulation time. An example of a rotor-skewed structure used to reduce cogging torque of permanent magnet synchronous machines is evaluated and compared with a conventional analysis method for the same motor to verify the effectiveness of the proposed approach. The novel method is proved valuable and suitable for large-capacity machine design.
Keywords: cogging torque; permanent magnet; finite element method; half magnet pole pair

1. Introduction
Permanent magnet synchronous machines (PMSMs) are less noisy, highly efficient and have long life spans. Differences in permeability between the permanent magnet and the rotor