End Effects and Geometric Compensation in Linear Permanent Magnet Synchronous Generators with Different Topologies

Jonathan Sjölund,Mats Leijon,Sandra Eriksson,Anna E Frost

doi:10.3390/designs5040064

Abstract

Electricity production from ocean waves with different solutions is a topic of major research interest. Many of such designs are based on linear generators that inherently introduce end forces. In this paper, detent force using Maxwell Stress Tensor and induced voltage is initially investigated for two different winding patterns for a generator topology with buried magnets in a finite element software. Two ways of overcoming the end forces are further examined: the first method reduces the magnetic flux variations of the translator between stator and air. The second method aims at countering the end forces at both ends for full active stator area. A comparison is then made between buried and surface-mounted topologies for the second end effect compensation method. Both no-load and load conditions are investigated in the comparison. The end effect compensation shows promising results for both topologies. Some clear similarities of the extended stator used to counter the end forces are also apparent, where the stator extensions completely cover the outer poles of both topologies. The results also indicate a longer full active stator area for the buried topology for the same pole-pitch and stroke length, resulting in a higher average voltage for partial stator overlap.

Highlights

Linear electrical machines, though much less common than rotating electrical machines, can be utilized in several applications such as wave-powered electricity generation
The electromagnetic forces were investigated for linear machines of buried and surfacemounted topologies, and means of reducing the end forces were included in a simulated
Initial investigation of the buried topology shows attraction forces and cogging forces that increase with active stator area

Summary

Introduction

Though much less common than rotating electrical machines, can be utilized in several applications such as wave-powered electricity generation. The basic working principles for linear electrical machines and their rotating counterpart are in several aspects the same. In a linear electrical machine, there are open ends that cause an uneven flux distribution both in regards to the transition between air and stator iron and, as for a buried topology, the reduced flux for the outer poles [1]. The open ends mean that the overlap between the translator, the moving part of the linear electrical machine, and the stator can vary. The open ends lead to some special traits of the linear electrical machines, for example, that the stator experiences a varied number of poles for a partial stator overlap. As shown in [2], the flux distribution varies depending on if an even or odd number of poles are used, which means that the flux distribution will change when there is partial stator overlap

Methods

Results

Conclusion