Examenspresentation av Tim Lindberg och Zijie Lin

Opponent: Victor Lidskog

Abstract
As electric motors are becoming more widely used within the automation industry, assessing the impact of different factors on machine efficiency is essential, both from an economic and environmental aspect. In vehicles, stator housings are fitted to stators of rotating machines using a joint fit that generates compressive stress throughout the stator, affecting magnetic properties and losses of the material. In this thesis work, a custom frame for measuring magnetic properties of electrical steel when subjected to compressive stress has been developed. The developed frame showed good accuracy when compared to standardized equipment and was successful in applying compressive stress of up to 60.6 MPa to electrical steel samples and measuring their magnetic properties. It was found that for frequencies in the range 50 - 1000 Hz and compressive stress in the range of 10.3 - 60.6 MPa, the iron losses of NO-25 1350H increased with 15% - 74.88% depending on level of magnetization. Furthermore, changes in magnetization behavior were observed.

The measured stress dependent magnetic properties were utilized to create a stator material for a Finite Element Method (FEM) 2D-design of an Interior Permanent Magnet (IPM) motor with stator housing fitted to the stator through a joint fit. Loss increase in the stator due to joint fit was found to be highest in the stator yoke and impact on machine efficiency was highest at lower machine torque. For a case with lower compressive stress of approximately 16 MPa in the yoke, efficiency of the machine at different operation points decreased with up to 0.74% and for a case with higher compressive stress of approximately 31 MPa in the stator yoke, efficiency of the machine decreased with up to 1.3%. Measuring effects of tensile stress on the material and utilizing frame measurements in a 3-dimensional model were identified as future works.

Welcome!

Tim, Zijie and Torbjörn