Examenspresentation av Victor Lidskog

Conducted with Volvo Cars supervised by Sima Soltanipour

Opponent: Tim Lindberg & Zijie Lin

Abstract
As more car manufactures are moving to a fully electric fleet of cars , and electrical
machines are a majority of the global electricity demand, the design of highly efficient electrical machines is a very important task. To achieve accurate simulation results when designing the electrical machines, one important aspect is to consider the effect of cutting the lamination steel used in the stator and rotor.

In this thesis work, an Epstein frame and a Single Strip Tester are used to measure the cut effects on the electrical steel, under both sinusoidal and non-sinusoidal flux distribution, specifically using a laser cut technique. Both degradation in magnetic properties and iron losses were measured and analyzed. A test sequence was designed to measure multiple different fundamental frequencies, as well as different flux density levels. The measured result was analyzed and discussed extensively, together with the complications of comparing sinusoidal with non-sinusoidal flux distribution.

The non-sinusoidal flux was created with a Pulse Width Modulation (PWM), and the effect of changing amplitude modulation index, as well as changing of frequency modulation index, was measured and analyzed. The degradation of magnetic properties had an exponential shape, with the highest degradation closest to the cut edge. While the degradation of the iron losses had more of a linear increase, with the highest around the cut edge. The degradation amplitude depended both on the flux density level as well as the fundamental frequency, with higher degradation at lower frequencies and lower degradation around saturation levels in the electrical steel.

With the measured result, a model was derived for implementing the degradation in an FEM simulation model of a Permanent Magnet Synchronous Machine (PMSM). A FEM simulation was performed at several frequencies, for one load point, at half rated current. The degradation with non-sinusoidal flux is a very complex subject and needs to be investigated further. The degradation depends on several factors such as fundamental frequency, frequency modulation index, amplitude modulation index, flux density level, distance from cut edge, and more. Leading to a high number of degrees of freedom, and thereby the complexity. The simulation results led to a decrease of torque and an increase of iron losses for the degradation model compared to a non-degraded model. This led to an efficiency of the machine lowered by between 0.5 to 2%

Welcome!

Victor, Sima and Torbjörn