Welcome to the defense of the PhD Thesis entitled "\;In the Air Gap of Linear Generators for Wave Power"\;.The opponent is Prof. John Ringwood from Maynooth University.

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**ABSTRACT:**

**Frost\, A. E. 2021. In the Air Gap of Linear Generators fo
r Wave Power. Digital Comprehensive Summaries of Uppsala Dissertations f
rom the Faculty of Science and Technology 2084. 96 pp. Uppsala: Uppsala
University. ISBN 978-91-513-1322-1.**

**Wave power conversion is one t
ype of renewable electricity generation. Within wave power\, there are m
any different concepts\, whereof some utilizes linear generators for con
verting the energy in the ocean waves into electricity. A linear generat
or consists of a translator\, which is moving and have magnets of altern
ating polarity\, and a stator\, which have conductors surrounded by lami
nated steel. Between the translator and stator is an air gap\, which is
only a few millimeters wide. All linear generators for wave power\, to t
he author&rsquo\;s knowledge\, are permanent-magnet synchronous generato
rs. This thesis looks into the forces and power ﬂow in the air gap of li
near generators for wave power\, with the purpose of improving their fut
ure performance. The studies have focused on permanent magnet synchronou
s generators for wave power\, but several of the results should also be
applicable for other applications of linear electrical machines.**

**D
epending on the design of the linear generators\, the translator can mov
e so long that it only partially overlap the stator. This is common amon
g several different wave power concepts with linear generators. When the
stator is only partially overlapped by the stator it is denoted as part
ial stator overlap. It is studied how partial stator overlap affects the
generated electricity\, the absorbed energy\, and the tangential and no
rmal force in the air gap. The generated electricity and absorbed energy
of a linear generator are quadratically dependent on the partial stator
-translator overlap is shown through Faraday&rsquo\;s law and simulation
s. Experimental data showed that the absorbed energy is both linearly an
d quadratic depending on partial stator overlap\, where the linear depen
dence is at least partially due to frictional losses. Simulated results
conﬁrm that voltage is linearly dependent on partial stator overlap\, wh
ich means quadratic dependence between generated electric and partial st
ator overlap. The simulated forces showed a linear dependence.**

**Dec
ades ago\, the Poynting vector was used to derive an expression for the
power ﬂow in the air gap of rotating electrical machines. In this thesis
the equivalent expressions for both ﬂat and tubular linear electrical m
achines were derived. The analytical results were also compared with res
ults from simulations. Both the analytical expressions and simulations s
howed that tubular and ﬂat linear electrical machines have slightly diff
erent behavior.**

**Keywords:** \;Linear generator\
, Wave Power\, Poynting'\;s theorem\, Partial stator overlap\, Perman
ent-magnet synchronous generator (PMSG)\, Linear electrical machines