A Study of the Research Activity in the Nordic Countries on
Large Permanent Magnet Synchronous Machines
Ø. Krøvel, R. Nilssen, A. Nysveen
Department of Electrical Power Engineering, NTNU
7491 Trondheim, Norway
Phone: +47 73594241 Fax: +47 73594279
Email: oystein.krovel@elkraft.ntnu.no
II. LARGE PERMANENT MACHINES
Abstract- This paper presents an overview of the activity on
large Permanent Magnet Synchronous Machines (PMSM) in the
Nordic countries. It is found that the Nordic countries are in the
leading end of the development of large PMSM. This is much due
long traditions of ship building, an important application for
large PMSM, and pioneer work in wind conversion. The focus
has mainly been on the radial flux permanent magnet machines,
but in the later years also attentions has been given to axial and
transverse flux permanent magnet machines.
The industry has started to use large PMSM; e.g. ABB has
their compact azipod® with radial flux machine, Siemens has a
radial flux submarine motors and Jeumont uses axial flux
generator in wind turbines. The impression is that at the time,
the large machine manufacturers in Europe have radial flux
machines in their assortment and are developing the axial flux
technology. While the smaller and more specialised companies
have already developed axial flux machines for their
applications.
T
Permanent magnets have been used for different small
applications since 19th century. In the 20th century the PMtechnology has conquered a large part of the market for small
machines; either it is DC-machines or AC machines. It is only
in the last 20 years that the quality has become so high and
price so low that the PM-technology can compete with the
field wound machines for applications with higher power
(>1MW) [4]. For small machines it is cheaper to use magnets
than wound poles, and this will be true for machines up to a
diameter of 150mm [2]. This is also true for larger machines
as long as the poles are kept small. This together with other
aspects as rotor losses, efficiency, cooling of rotor, space etc.
favours the PMSM for many applications, especially for large
multi pole machines e.g. direct driven wind generators. But
also on other applications as paper mill motors and ship
propulsion the PMSM replaces the induction and wound field
machines. A way to determine whether a machine is large,
medium or small (electrically) is to look at the power pr pole
of the machine. An example is a typical wind turbine of
3MVA and 17rpm which gives a power pr pole of 14kVA,
while a field wound machine for hydro power will have power
pr pole of 8MVA (14 poles, 112MVA). Using this approach
almost all PMSM can be considered small, electrically.
Therefore large PMSM just means that the machine is among
the largest in power and size of the PMSM. Mechanically the
dimensions can be rather large. A typical wind turbine of
3MW and 17 rpm might have a diameter of 6m, a length of
2m and weight about 80 tons. Typical power range for large
PMSM is 1MW and up to 20MW, with low speed and high
torque applications.
The upper limit for PMSM has not been reached. Some
major limitations and challenges have partly been met the
latest years. Examples of improvements which have made the
permanent magnets more interesting for large machines are
lower price, higher energy density and that the magnets have
become more resistant to demagnetization.
I. INTRODUCTION
his paper present an overview of the research activity on
large permanent magnet synchronous machines in the
Nordic countries. It is the result of the initial stages of a PhDstudy on design of large PMSM, the work was initiated at
NTNU by prof. Dr.ing Robert Nilssen to meet the growing
need for knowledge on large PMSM in Norway. The focus is
on the activities in the Nordic academic institutions. Some
examples of industrial activities on large PMSM are also
mentioned together with some academic institutions outside of
the Nordic countries. Those examples are meant to put the
Nordic effort on large PMSM in perspective to the world wide
development of large PMSM’s.
There are several areas where large PMSM can be used.
Applications described in the literature are ship propulsion,
wind turbines, paper mills and elevators, [1]-[3]. In addition
large PMSM can also be used in drilling, actuators and other
special adapted machines.
Examples of smaller machines than 1 MW, is also
presented in this paper. This is mostly due to the fact that it is
more convenient to build small machines and test the theories
concerning large machines on smaller ones (50-500kW).
Therefore also most research is done on smaller models of
large machines.
The papers [1]-[3] present an overview of large PMSM
seen from Siemens and ABB and some applications for large
PMSM. They also present some trends and visions for the
development of large PMSM in the 21st century.
III. TYPES OF PERMANENT MAGNET MACHINES
There are generally three types of PM-machines [5]. The
different types are: Radial, Axial and Transversal flux
machines. Also some types of switched reluctance machines
(SRM) use PM in their construction, but they will not be
considered here. General theory about permanent magnet
1
but it is somewhat more common to use concentrated
windings. It is also used ironless stators; this reduces iron
losses, makes it possible to cool the winding more effectively
and also eliminates the attractive forces between the magnets
in the rotor and the iron in the stator, but increases the need
for magnets, [6].
machines can be found in different textbooks, one example is
Hanselmann [6].
A. Radial Flux Permanent Magnet Machine
The radial flux machine (RFPM) is the classic type and
most common. It is quit similar to other AC-machines and are
also used in mostly the same areas. The rotor can have buried
or surface mounted magnets, the poles can be skewed, have
pole shoes etc. The stator is quite similar to other classical
AC-machines (induction and synchronous) both for windings
and tooth shape. It is common, but not always necessary, to
use semi closed slots. Magnetic slot wedges is also an option.
Two layer fractional windings are mostly used even though
the simplicity of concentrated windings has begun to be
appreciated.
The active materials; copper, magnets, iron, sheet metal,
converting the mechanical energy to electric or visa versa, are
placed along the air gap. For RFPM with large diameter this
means that the active material becomes a thin shell around the
air gap thus most of the volume to the machine is air or
supporting structures to transfer the torque to or fro the shaft
to the rotor rim. Since the force is acting at a large radius a
high torque is produced.
C. Transversal Flux Permanent Magnet Machine
Transversal flux machines (TFPM) is the most complex and
least equal to classic machine design. It can be single sided [8]
or double sided [9] respectively with one or two wound rings
of copper with iron cores to lead the magnetic flux around the
copper. The TFPM has a rotor with either buried or surface
mounted permanent magnets. The TFPM have a very high
force and power density and therefore the TFPM has been
considered very promising in application with high torque and
low speed. One major problem with TFPM is that to achieve
this high force density the synchronous reactance can grow
very high which in turn makes the converter expensive.
Another factor is cost due to the many parts in a TFPM. For
more detailed information, confer Hystad’s dissertation [10].
IV. THE ACADEMIC ACTIVITY ON LARGE PERMANENT
MAGNET MACHINES
Axial
Radial
La
Lr
Dg
Active
material
As mentioned before, the area where PM-machines is better
than field wound machines and induction machines is where
the power pr pole is low, in low speed, high torque
applications and in special application with special
requirements to size, weight, inertia, design, etc. This study of
research activity in the Nordic countries shows that the
applications for PM-machines are mainly wind conversion and
ship propulsion.
This chapter seeks to explain what the different universities
in the Nordic countries have done of research on large PMSM.
In addition some publication from other universities has been
mentioned.
Do
Di
Center/Shaft
Fig 1 Comparison of the diameter of active material in radial and axial
machines
B. Axial Flux Permanent Magnet Machine
Axial flux machines (AFPM) is magnetized in the axial
direction. The air gap is radial to the shaft. Therefore,
compared to RFPM, the length of AFPM (La) is equal to the
thickness of active materials in the RFPM and the thickness
(Do-Di) of the AFPM is equal to the length of RFPM (Lr), see
Fig 1. Given the same outer diameter and the same force pr
area in the air gap, the AFPM have a lower torque pr volume
of active material due to the fact that much of the force is
working on a smaller radius and thus producing less torque.
The great advantage of the AFPM contra the RFPM is the
possibility to use the volume of the machine more effectively,
the power density (W/m3) gets higher.
The AFPM usually have a disc shaped design, with large
diameter and short length, which are useful in different
applications. Several discs can be connected in series and
make a multi disc machine.
As for RFPM the rotor in an AFPM can be made with
surface mounted or buried magnets. The stator has also the
same possibilities for different design of teeth and windings,
A. Activity in the Nordic Countries
At the universities in the Nordic countries it has been
conducted research on the design of PM-machines since the
eighties. At NTNU, Ådnanes [5] submitted his thesis in 1991
on “High Efficiency, High Performance Permanent Magnet
Synchronous Machines”. This was a general study of surface
mounted PM-machines and the control of them. He has also
gathered general information about the permanent magnet,
how it works, how it is manufactured, history of PM, etc, and
made a user manual for permanent magnets. Other than
general theory about PM and design, the thesis mostly treats
the control of a PMSM.
At NTNU this thesis was followed by Hystad’s [6]
“Transverse Flux Generators in Direct Driven Wind Energy
Converters” from 2000. He examined the single and double
sided TFPM and compared them with Grauers’ [11] RFPM
for direct driven wind generator. Hystad’s work was a followup of Grauers’ work. Hystad included the converter design
into the optimizing routine and found that even though the
2
Leijon has played an important role. ABB uses this
technology in i.a. Windformer® and Powerformer®.
Finland is the Nordic country which has most publications
and research on large PM-machines. Both at the universities in
Helsinki (HUT) and Lappeenranta they have had several
doctoral studies on different subject concerning large PMmachines. At HUT, Lampola [17] presented his dissertation
“Directly Driven, Low Speed Permanent Magnet Generators
for Wind Power Applications” in 2000. He looked at several
different types and variations of directly driven generators,
and found that the best type of directly driven PM-machine is
a radial machine with diamond winding and curved surface
mounted permanent magnets. He comments in his conclusion
that a solution with concentrated windings will be almost as
good as with the conventional double layer diamond winding
because of the simplicity of concentrated windings.
TFPM has extremely high torque density, the cost of the
converter due to the high reactance makes the double sided
TFPM just slightly better than Grauers’ PM-machine at power
ratings below 3 MW. The single sided TFPM was found not
to be competitive on neither cost nor force densities.
The research on large PM-machines has continued at
NTNU with radial and axial flux machines. Though few
publications, there has been done a lot of work on PMmachines for ship propulsion, thrusters and wind generators in
cooperation with the industry. Later this year an integrated
100 kW PMSM in a thruster application will be presented at
ICEM’04 in Cracow.
In Sweden the research on large PM-machines has mostly
been done at Chalmers and been connected to wind energy.
As mentioned, Grauers [11] conducted a thorough study of
radial magnetized direct driven permanent magnet machine
with surface mounted magnets. He optimized a 500 kW
generator and found that the outer diameter would only be
slightly larger than the nacelle of the an already existing wind
converter i.e. minimal changes in construction. The efficiency,
including the frequency converter, is also higher than
traditional drive trains for wind conversion. Grauers also
looked at the design of PM-machines from 30kW to 3 MW
and compared them with other generators proposed by other
authors (induction generator with gear, TFPM, RFPM, AFPM
and wound field synchronous generator). The proposed
generator from Grauers has higher efficiency and lighter
weight than the other. Only the TFPM from Weh [12] is
better, but as Hystad later showed, when including the
converter into the optimizing routine, it is only slightly better.
At KTH, Stockholm, they have developed a high speed
PM-generator for distributed generation of power together
with ABB [13]. The high speed generator operates at
30000rpm to 70000rpm with an output frequency up to
2.4kHz. It has surface mounted magnets which are covered by
a carbon-fiber bandage to retain them at the high speeds. The
generator also works as a starter for the gas turbine.
Calculations and measurements of the losses both as generator
and converter fed motor have been conducted and the
efficiency was found to be 97% for generator operation and
96% for motor operation [14]. This is clearly not a low speed
high torque application, but it proves that the permanent
magnet technology is spreading to other applications.
In Uppsala several projects concerning large PMSM is in
progress under supervision of prof. Mats Leijon. Segergren
finished his licentiate thesis on “Simulation of Direct Drive
Generator for Underwater Power Conversion” in 2003 [15].
He investigates the possibility to use cable wound generators
with large diameter in underwater power conversion (UPC).
The cable winding has several advantages in under water
applications. He concludes that a cost effective underwater
power converter is possible to realize.
Other projects at the University of Uppsala concerning
large PMSM, is Wave and Wind energy conversion [16].
Much of the research on PMSM at the University is based on
cable wound machines, which is a technology where M.
Fig 2 The different rotor topologies evaluated by Rosu [18]. a) Surface
mounted magnets without pole shoes, b) is with pole shoes, c) radially
inserted magnets d) tangentially inserted magnets
Rosu [18] finished his licentiate thesis, “Large OutputPower, Low-Speed Permanent Magnet Synchronous Motor
Designs for Ship Propulsion Drives” in 2001. It consists of
five publications, which deals with different aspects of PMmachines, ranging from general design, demagnetization of
magnets and magnetic field distribution in the air gap. Rosu is
focusing on the electromagnetic construction of the rotor. He
proposes several different solutions; surface mounted PM with
or without pole shoes and buried PM both tangentially or
radially inserted (Fig 2). Both the surface mounted solutions
are better than the buried magnets concerning torque pr
volume. The buried PM solutions suffer from high portions of
leakage flux. The solution without pole shoes uses the least
magnet volume, but the pole shoe solution is more favourable
when demagnetization, harmonics and resistive losses in
3
AFPM with different dimensions and pole numbers. The
results of his calculation tool agree well with measurements
done on an actual machine. Several different arrangements of
the PM were calculated and tested to find the different torque
patterns and minimize the torque ripple. He found that
combination of magnet shape and asymmetric distribution of
the magnets or in the teeth would minimize the ripple in the
torque most. He would not conclude that a specific magnet
shape is superior
Aalborg University has in cooperation with Risø National
Laboratory made a survey of generator and power electronics
for wind turbines [22]. The survey presents the different
machines, with or without gear, used as generators in wind
turbines to day, and lists pros and contras and the challenges
for the different types. For all the PM machines they find that
the curie temperature (maximum temperature before
demagnetization) might be to low at fault situations (250°C),
and the voltage at runaway speed can cause problems. For
AFPM the axial force in the air gap is mentioned as a
challenge in the construction. The TFPM consists of many
different parts which will cause increased fabrication cost. It
also has a relative high reactance, which increases the cost of
the converter and may cause an insufficient short circuit
current to trigger the protection. The authors conclude that a
wind turbine or a park of wind turbines has to be looked as an
integrated system, where stability, efficiency, cost etc. has to
be taken into account.
magnets are concerned.
Negrea has together with Rosu, looked at the temperature
rise in a PMSM due to losses in the machine [19]. They have
looked at the sensitivity of the temperature distribution due to
losses in different part of the machine. They studied two
different rotor topologies with surface mounted magnets, one
with pole shoes and one without, and found that the one with
pole shoes gave the lowest losses in the magnets and therefore
also the lowest temperature in the magnets. But both
topologies had temperatures in the magnets below the critical
value for the chosen magnets. As expected they found that the
temperature rise in all part of the machine was most sensitive
to changes in the copper losses.
B. Research on large PMSM in other countries
It is obvious that is not only in the Nordic countries it has
been conducted research on large PMSM. As chapter V shows
institutions in France, Germany and England have all
developed large PMSM. Also in Asia and the USA there has
been development of the technology. Here follows some
examples of activity in the academic circles on large PMSM
outside the Nordic countries.
Spooner has proposed a highly modular design for a PMSM
as wind generator [23]. He uses ferrite magnets blocks in the
rotor. In the stator he uses E-cores with a single rectangular
coil. These elements are fastened to the framework by bolts.
This gives a modularity which enables the machine
manufacturer to produce machines with very different pole
numbers with a minimum of different parts in stock. Repairs
can also be done on site by replacing the damaged unit only.
But the many modules also lead to higher assembly cost (as
for TFPM). Spooner claims the machine has low reactance
and high efficiency.
In Delft, Nederland, Dubois, Polinder and Ferreira has
made a comparison of different generator topologies for direct
driven wind turbines [24]. They look at the torque density and
the cost/torque. They conclude that the TFPM and the AFPM
are the topologies which would be most interesting to look at
for wind turbine generators. Dubois et al presented a
prototype TFPM with toothed rotor at ICEM 2002 [25]. They
developed a lumped magnetic circuit for the machine to
optimize the cost/torque of the machine. Based on the
Fig 3 Different topologies for paper mills, a) induction motor with gear, b)
PMSM [20], [2].
At the Lappeenranta University of Technology Heikkilä
[20] presented a dissertation with the topic “Permanent
magnet synchronous motor for industrial inverter application”
in 2000. It contains a good literature study and a brief history
of permanent magnet machines. The dissertation is based on
the calculation and testing of a 45kW 600 rpm PMSM with
buried V-magnets. The results are used to calculate machines
with higher power (>1MW) and lower speed. The conclusion
of the thesis is that a medium speed (600 rpm) PMSM may
replace inverter fed induction machines with gear in industrial
applications (Fig 3).
There has also been a study on torque vibration in axial
machines at Lappeenranta University of Technology.
Kurronen [21] presented his dissertation on “Torque Vibration
Model of Axial Flux Surface Mounted Permanent Magnet
Synchronous Machine”. He has developed analytic methods
for calculating the torque of a machine based on electrical and
magnetic loading. Instead of using time-consuming 3D-FEM
tools he instead used analytic models which can be used on
4
module is kept low and gives better hydrodynamics for the
azipod unit.
optimization a machine with 68 kg/phase active material, a
nominal torque of 1000Nm/phase and a speed of 100rpm were
built. The tests revealed that the model agreed with the built
machine.
V. INDUSTRIAL APPLICATIONS
Several manufacturers of electrical machines have in resent
years developed large PMSM. The use of the large PMSM has
focused on ship propulsion, wind turbines, medium speed
drives, e.g. paper machines, and special applications such as
elevators.
A. Wind turbines
For wind turbines and generators there are several
manufacturers of PMSM generators. ABB has their
Windformer® system with the cable wound high voltage
generator [3]. Siemens has delivered a 3.3MVA RFPM to
Scandwinds prototype test site at Hundhamarfjellet, Norway.
Jeumont, Leitner Lifts, Mitsubishi, MTorres, Permapower,
Zephyros and WinWinD are all companies which delivers
wind turbines with PMSM [2], [26]-[32]. Jeumont has an
AFPM generator of 750kW and are planning to deliver up to
2MW wind turbines. Permapower has a 1.2MW generator
with external rotor. Zephyros uses a high voltage (4kV), 2MW
generator from ABB. WinWinD uses a planetary one stage
gear and a PM generator from ABB. They offer wind turbines
from 1 to 3MW.
Fig 5 A Compact azipod® propulsion unit from ABB [34]
Siemens/Shottel has developed the SSP which also is a
podded propulsion, but with twin propellers and a power
range of 5MW to 20MW [35]. They also make PMSM for
submarines [36].
Rolls Royce is developing a 180rpm, 20MW TFPM for
propulsion of small warships. A 2MW demonstrator to
demonstrate the technology ahead of the full scale TFPM has
been built [37].
Kaman [38] has together with the US Navy developed a
3000 Hp (2.25MW) motor for ship propulsion. They have also
developed a podded propulsion of 1000Hp (750kW) and
850rpm. They also have developed a motors and generators
for other applications such as drilling. Kaman uses AFPM.
C. Paper machines
ABB has developed a medium speed PMSM for direct
drive for paper mills. It replaces inverter fed induction motors
with gear. (Fig 3) This reduces maintenance and increases the
efficiency of the system. The first drives were installed in a
paper machine in Finland in 1999. It is clear that other
industries which use medium speed drives can benefit from
the technology [34].
D. Elevators
Jokinen [2] mentions Kone [33] and their AFPM machine
for elevators as a interesting case of new PMSM. By
developing a direct driven, low speed AFPM which can be
placed inside the elevator shaft, Kone has eliminated the need
for a machine room. Further Kone uses some sort of rope
system and pulleys that have also eliminated the need for
counterweights.
Fig 4 The tower head of a Zephyros wind turbine
B. Ship propulsion
Several companies have developed PMSM for ship
propulsion [2]. ABB has already delivered several azipods to
different types of ships. They use PMSM in the power range
from 400kW to 5MW and its typical used in e.g. offshore
support vessels, floating oilrigs, cable layers and ferries.
The PMSM is placed inside the submerged unit (Fig 5) and
directly coupled to the propeller, and it is only the power
cables which goes true the hull. By fitting the stator to the
outer shell of the azipod, effective cooling of the stator is
achieved. By using the PMSM, the diameter of the motor
VI. SUMMARY
This paper has focused on the Nordic activity on large
PMSM. It is found that in the last 15 years universities in the
Nordic countries has researched on all the three types of large
PMSM and that the Nordic countries are in the leading end of
5
the development. Most of the research has been focused on
applications for wind conversion and ship propulsion. The
focus has been on RFPM, but also AFPM and TFPM has been
investigated. It seems that the RFPM is the safe and cheap
way to make a PMSM. AFPM can compete, but has a slightly
higher cost and therefore is of interest for special applications
which can allow large diameters, but must have short
machines. The TFPM has supreme capabilities on torque pr
volume, but the cost of the converter is high. Therefore it is
most relevant for special applications where cost is secondary.
Also the industry reflects the same attitude to the different
PMSM. RFPM is the safe and cheapest way and therefore
used by the established industry in the large production lines.
The relative new technology of AFPM is embraced by the
smaller companies and those with special needs. But both
ABB and GE have started to develop AFPM for wind
turbines. Rolls Royce has focused on the potential of the
TFPM and is developing TFPM for ship propulsion.
[12] Weh, H., Hoffmann, H., Landrath, J., Mosebach, H., Poscadel, J,.
Directly-driven permanent-magnet excited synchronous generator for
variable speed operation. Eurpean Wind Energy Conference
(EWEC’94) Thessalonika, Greece, 10-14 October 1994 Proceedings vol.
I, p. 542-546
[13] Aglén, O., A high-speed generator for microturbines, Proc. of ICEET01,
University of Dar es Salaam, 2001.
[14] Aglén, O., Back-toback test of a high-speed generator, 2003 IEEE
International Electric Machines and Drives Conference, June 1-4, 2003,
Madison, Wisconsin, USA.
[15] Segergren, E., Simulation of Direct Drive Generator for Underwater
Power Conversion, Licentiate Thesis, University of Uppsala, dept. of
engineering physics. 2003
[16] http://www.el.angstrom.uu.se/
[17] Lampola,P. Directly Driven, Low-Speed Permanent-Magnet Generators
for Wind Power Applications. Acta Polytechnica Scandinavica,
Electrical Engineering Series No 101, Finnish Academies of
Technology, Espoo 2000. 62 p + 84 appendices
[18] Rosu, M. Large output-power, low-speed permanent magnet
synchronous motor designs for ship propulsion drive. Licentiate Thesis,
Helsinki University of Technology, Laboratory of Electromechanics,
Report 64, Espoo 2001, 77 p. ISBN 951-22-5430-1, ISSN 1456-6001.
[19] Negrea, M., Rosu, M., Thermal Analysis of a large Permanent
Synchronous Motor for Different Permanent Magnet Rotor
Configurations. Proceedings of the International Electric Machines and
Drives Conference, Cambridge, Massachusetts, USA, 17–20 June 2001,
pp. 777–781.
[20] Heikkilä, T., Permanent Magnet Synchronous Motor for Industrial
Inverter Applications – Analysis and Design, Dr.thesis, Lappeenranta
University of Technology, 2002, ISBN 951-764-699-2, ISSN 1456-4491
[21] Kurronen, P., Torque Vibration Model of Axial-Flux Surface-Mounted
Permanent Magnet Synchronous Machine, Dr.thesis, Lappeenranta
University of Technology, 2003, ISBN 951-764-773-5, ISSN 1456-4991
[22] Hansen, L. H., Helle, L., Blaabjerg, F., Ritchie, E., Munk-Nielsen, S.,
Bindner, H., Sørensen, P., Bak-Jensen, B., Conceptual Survey of
Generator and Power Electronics for Wind Turbines, Risø National
Laboratory, Roskilde, Denmark, 2001. ISBN 87-550-2743-1, ISBN 87550-2745-8 (Internet), ISSN 0106-2840
[23] Spooner, E., Williamson, A.C., Catto, G., Modular design of
permanent-magnet generators for wind turbines, Electric Power
Applications, IEE Proceedings- , Volume: 143 , Issue: 5 , Sept. 1996
Pages:388 – 395
[24] Dubois M, Polinder, H., Ferreira, J. A., Comparison of generator
topologies for direct-drive wind turbines. NorPIE/2000 workshop
proceedings. 2000 IEEE Nordic Workshop on Power and Industrial
Electronics (Aalborg, June 13-16, 2000), Aalborg University, Aalborg,
2000, p. 22-26. ISBN: 87-89179-29-3, cat. c, Projectcode: ET00-13
[25] Dubois M, Polinder, H., Ferreira, J. A., Prototype of a new tranverseflux permanent magnet (TFPM) machine with toothed rotor, 2002, 15th
International Conference on Electrical Machines. (pp. 1-6).
[26] http://www.jeumont-framatone.com/english/homepage.asp
or www.framatone.com
[27] http://www.leitner-lifts.com/
[28] http://www.mhi.co.jp/power/e_power/product/
[29] http://www.mtorres.com/ingles/ee/index.asp
[30] http://www.permapower.de
[31] http://www.winwind.fi/english
[32] http://www.zephyros.com
[33] http://www.kone.com/en/main
[34] http://www.abb.com
[35] http://www.industry.siemens.com/broschueren/downloads/marine/S
SP_V51001.pdf
[36] http://www.industry.siemens.com/marine/en/index.htm
[37] Husband, S. M., Hodge, C. G., The Rolls Royce Transverse Flux Motor
Development, 2003 IEEE International Electric Machines and Drives
Conference, June 1-4, 2003, Madison, Wisconsin, USA. pp. 1435-1440
[38] http://www.kamanaero.com/electromagnetics
VII. ACKNOWLEDGMENT
This PhD-study is financed by strategic resources from
NTNU, Norway and is a part of the project Energy Efficient
All Electric Ship (AE3S). AE3S is a project with participants
from NTNU (dept. of electric power engineering and dept. of
marine technology), ABB, AkerKvaerner, Brunvoll,
MARINTEK and NorPropeller. They are hereby
acknowledged.
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