Download Summary of PhD Projects 2013

Department of Electric Power Engineering, NTNU
PhD projects
Department of Electric Power Engineering
May 2013
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An overview over PhD Projects 2013
at
Department of Electric Power Engineering
Faculty of Information Technology, Mathematics and Electrical Engineering
Norwegian University of Science and Technology
This report gives an overview of current PhD research projects at the Department of
Electric Power Engineering.
Currently 36 students are registered in our PhD program. This is a drop from 41
students last year and a steady growth for several years, reflecting the increased
general interest in energy and electric power from renewable resources. The
department has 11 professors, four associate professors, and six adjunct professors.
The number of Postdocs has increased the last few years from zero to four. In addition
to the scientific and administrative staff, the department houses a mechanical
workshop and an electro technical laboratory.
The research activity at the Department is mainly covered by the following tree fields:
• Power Systems
• Electrical Power Technology
• Energy Conversion
The PhD projects presented here focus on topics from all these areas. The research
projects are both theoretical and practical and based on extensive use of our computer
and laboratory resources. The projects are also influenced by our collaboration with
industry and our neighbour institution SINTEF Energy Research AS. Since the PhD
projects represent the main part of the professors’ research, this folder also gives an
overview of the entire research activity at the Department.
The nominal duration of PhD program is three years of full-time research, of which a
half year is devoted to post graduate courses. A typical PhD project, however, lasts
for four years, where the additional year is devoted to university/educational duties.
For further information about the research projects presented, please contact the
individual researcher given by name in this folder. For more information on previous
projects, please contact the Department.
NTNU, May 2013
Hans Kristian Høidalen
Professor
Postadresse:
N-7491 Trondheim
http://www.ntnu.no/elkraft
Besøksadresse:
O. S. Bragstads pl..2E,
N-7034 Trondheim
Telefon +47 73 59 42 10
Telefaks +47 73 59 42 79
Phd summary 2013
Name
Title
Supervisor
p
Aanensen, Nina
Sasaki
Load Current Interruption in Air for 12/24 kV systems
Arne Nysveen
1
Agheb, Edris
Simulation and design of high frequency high power
transformers
Hans Kristian
Høidalen
2
Barrera C.R.
Alexander
Multi-Domain Optimization Model for Evaluation of
Power Density and Efficiency of Wind Energy Conversion
Systems
Voltage stability monitoring and control based on wide
area measurement system
Marta
Molinas
3
Olav B. Fosso
4
Gebrekiros,
Yonas T.
Exchange of Balancing Services
Gerard L.
Doorman
5
Gjerde, Sverre
S.
Integrated converter design with generator for weight
reduction of offshore wind turbines
Tore
Undeland
6
Holtsmark,
Nathalie
Offshore Wind Energy Conversion using High Frequency
Transformation and DC Collection
Marta Molinas
7
Hosseini, Seyed
M. A.
Power System Analyses and Transmission Planning in a
Competitive Environment
Olav B. Fosso
8
Jelani, Nadeem
Investigating Stability in the Future Electrical Grid
Dominated by Power Electronics
Load Current Interruption in Air
Marta Molinas
9
Magne Runde
10
Multivariable Control of Facts Using PMU Measurements
Controller Design and Coordination
Evaluation, classification and grouping of operating states
Kjetil Uhlen
11
Kjetil Uhlen
12
Olav B. Fosso
13
Larsen, Camilla
Thorrud
Stochastic bidding optimization for hydro power
producers
Long-term hydropower scheduling using stochastic dual
dynamic programming (SDDP)
Gerard L.
Doorman
14
Lindberg, Karen
Byskov
The impact of Zero Energy/Emission Buildings on the
energy system
Gerard L.
Doorman
15
Lotfi, Abbas
Transformer Modeling for Low and Mid Frequency
Transients
Advanced Control of Power Converters
Hans Kristian
Høidalen
Norum, Lars
16
Duong, Dinh
Thuc
Jonsson, Erik
Kalemba, Lester
Kile, Håkon
Klæboe, Gro
Nademi, Hamed
Olsen, Pål Keim
Long term performance of insulation materials exposed to Frank Mauseth
DC superimposed AC voltage
17
19
Preda, Traian
Nicolae
Stability requirements for distributed generators
Kjetil Uhlen
20
Røkke, Astrid
Investigation of permanent magnet synchronous
machines with fractional slot windings for use in
renewable energy applications
Identifying electrical instability in grids dominated by
power electronics
Robert Nilssen
21
Marta Molinas
22
New Concepts for Converters and Control of Photovoltaic
Systems
Development of Electricity Market Model Incorporating
Offshore Grids and Offshore Wind Farms
Power control systems and grid interface for renewable
energy production
Modeling of the European power system for low emission
scenarios
Switching Transient in Offshore Wind Farm
Lars Norum
23
Olav B. Fosso
24
Marta Molinas
25
Gerard L.
Doorman
Hans Kristian
Høidalen
26
Modelling of Void Formation and PD Activity due to Mass
Transport in Mass Impregnated HVDC Subsea Cables
Integration of offshore DC grids and onshore AC power
networks – Stability and Control
Advanced Monitoring and Control in Power Electronics
Converter for Future Energy Efficient Marine Power
System
Active distribution grids – concepts, architecture and
functionality
Magnetic Forces and Vibrations in Wind Power
Generators
Effect of Moisture on Space Charge Accumulation in
Polymeric HVDC Cable Insulation
Development and Operation of the North Sea Super Grid
Erling Ildstad
28
Kjetil Uhlen
29
Lars Norum
30
Kjell Sand
31
Arne Nysveen
32
Frank Mauseth
33
Olav B. Fosso
34
Zadeh, Mehdi
Karbalaye
Stability Analysis of AC Distributed Multi-converter
System under Non-ideal Electrical Conditions
Marta Molinas
35
Zahedi, Bijan
Integrated Marine Electrical Power and Control Systems
Lars Norum
36
Zhang,
Zhaoqiang
Coupled 3D models of permanent magnet generators
with very large diameters and with a special focus on
losses
Robert Nilssen
37
Sanchez A.,
Santiago
Fritz Schimpf
See, Phen Chiak
Sjolte Jonas
Skar, Christian
Soloot, Amir
Hayati
Støa, Bendik
Tai Su, Vin Cent
Toh, Chuen Ling
Tønne, Erling
Valavi, Mostafa
Ve, Torbjørn
Vrana, Til
Kristian
PhD graduated from 1990
27
38
Nina Sasaki Aanensen
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
2011
University:
Norway
1987
[email protected]
www.ntnu.no/employees/nina.aanensen
MSc Applied Physics and Mathematics,
NTNU
Supervisor:
Magne Runde
Research Group: Electric Power Technology
Co-Supervisor(s): Arne Nysveen
Project: “Air Insulated Switchgear Technology”
Load Current Interruption in Air for 12/24 kV systems.
The problem with using SF6 (sulphur hexafluoride) as insulating gas in high voltage
equipment is the large contribution to the greenhouse effect. Therefore, it is desirable to
replace the SF6 gas in load break switchgear with air. The challenge is to make the air
insulated switchgear in the same geometrical dimensions as the old SF6 breakers, without
compromising the current interruption capability.
The main goal of this PhD research is to be able to understand the air flow interaction with
the electric arc, and how the flow parameters influence the current breaking capability.
Different contact and nozzle geometries will therefore be investigated. Using the newly built
high current / switchgear laboratory at NTNU, experiments can be conducted with the
possibility of changing one parameter at a time. There are currently two PhD students
working on this project, myself and Erik Jonsson.
In addition to the laboratory work, some computational simulations will be conducted as a
supplement to the experimental results. Computational simulations can be a fast and
inexpensive tool in the design process of a switchgear manufacturer.
The “Air Insulated Switchgear Technology” project is financed by the Norwegian Research
Council with Tom Rune Bjørtuft from
ABB as project manager.
1
Edris Agheb
Home Country:
Year of Birth:
Iran
1984
Master Degree:
University:
Graduation Year:
Electrical Engineering
Tehran University
2009
Research Group:
Supervisor:
PhD Start:
Electric Power Technology
Hans Kristian Hoidalen
2009
Phone:
Email:
Home Page:
+47 735 97295
[email protected]
http://www.ntnu.no/ansatte/edris.agheb
Simulation and design of high frequency high power transformers
Over the last decades, the worldwide interest in renewable energy sources has risen drastically.
At this stage the generation of electrical power via wind turbines is one of the most promising
renewable sources. Primarily, in Europe the installed power has risen drastically so that wind
power is today, after hydro power, the second largest renewable energy source and is still
growing most rapidly of all the renewables with respect to the installed power rating per year.
Wind energy is typically converted to electrical energy by electrical induction machines and
AC/AC converters in combination with a power frequency (50Hz) transformer and AC/DC
rectifiers. This is a physically large and heavy construction that is challenging in a floating wind
generator structure.
The idea is further to use a high frequency transformer to feed a more traditional AC/DC converter
and insure galvanic isolation between the AC and DC side of the wind generator system. A high
frequency transformer solution seems beneficial since the required core cross section is inversely
proportional to the frequency of the applied flux. Increasing frequency can thus save weight and
cost and enable a solution where the entire energy conversion system is placed in the nacelle
close to the wind turbine. This requires fundamental research on the behaviour of the transformer
at frequencies in the range of 500 Hz to 10 kHz. Transformers at 400 Hz are used today in ships
and airplanes to save space and weight, but to go above 1 kHz requires new solutions both
regarding core material and handling of capacitive effects and core losses. Increased copper
losses at increased frequency could also pose a challenge.
2
Rene Alexander Barrera Cardenas
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Colombia
1982
[email protected]
http://www.ntnu.edu/employees/rene.barrera
MSc Electrical Engineering, 2006
UIS - Colombia
Supervisor:
Marta Molinas
Research Group: Electric Power Systems
Co-Supervisor(s): Tor Arne Johansen
Project: NOWITECH WP4
Multi-Domain Optimization Model for Evaluation of Power Density and
Efficiency of Wind Energy Conversion Systems
The prospective development of the wind energy conversion systems (WECS) is mainly promoted by
demand for higher efficiency and power density. These requirements can be satisfied through the use or
development of new topologies, modulation strategies or new semiconductor technologies. The gain in
performance improvement is reduced over time, once the new concept or technology has been established.
After the basic concept has been adopted, a significant gain in performance can only be achieved by
allocating the optimal values of design variables during the design process. In the other hand, by detecting
the sensitivity of the system level performance on component parameters, the development of components
could be adjusted for maximal impact on the system level.
So to achieve such an optimization first a complete model of the converter circuit must be set, including
thermal and magnetic component models. This model could be based on analytical equations, on numerical
simulations or on a combination of both. Based on WECS circuit model, an optimization for multiple
objectives, efficiency and power density, will be performed. The optimization makes best use of all
degrees of freedom of a design and also allows determining the sensitivity of the system performance
based on technologies like measurement of the efficiency of the power semiconductors or properties of the
magnetic core materials. Furthermore, different topologies can be easily compared and inherent
performance limits can be identified.
This project is looking for developing a methodology of multi-domain design to optimize the power
density and efficiency of the wind energy conversion system in offshore wind farms. Analytical
approaches for designing the main functional elements of a wind energy conversion system will be
described and arranged to a linear design process in a first step. Moreover, the linking of the component
models, i.e. of the electric, magnetic and thermal design domains and an overall optimization of the
respective design variables based on the linked models will be considered and including the coupling of the
different domains.
WECS Based on medium frequency AC-link
Pareto surface: Efficiency, Power Density and Power to mass ratio
for WECS solution 10[MW] including parameter variation
(Converter Topology, number of modules, AC-link freq.)
3
Dinh Thuc Duong
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Vietnam
1979
[email protected]
www.ntnu.no/emploees/thuc.duong
MSc in Electrical Power Engineering, 2011
NTNU
Supervisor:
Prof. Kjetil Uhlen
Research Group: Electric Power Systems
Co-Supervisor(s): Prof. Olav B. Fosso
Project: STRONgrid
Voltage stability monitoring and control based on wide area
measurement system
Voltage stability remains one of the major stability issues in electrical power systems,
especially in those heavily loaded. The initiation of this phenomenon is the operating point
where the maximum power transferred from source to load is hit. Operation beyond this point
will lead to significant voltage drop while current continues increasing. Due to recent voltage
collapse incidents, more attention has been paid to this stability concern, presently focusing
on real time assessment. However, online indicators of voltage stability and mitigating
methods are still under investigation and require further work.
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This research aims at developing a methodology that is able to assess, in real time,
voltage stability of all load buses in transmission grid based on estimated Thevenin equivalent
parameters and load impedances. The approach is intended for applications to monitor, with
respect to voltage stability, not only the whole system but also part of it. Moreover, this
research also examines mitigating solutions when the system is approaching limits. To attain
the objective, the study pursues methods associated with, but not limited to, system topology
and wide area measurements of phasor measurement unit.
4
Yonas Tesfay Gebrekiros
Home Country:
Year of Birth:
Ethiopia
1983
Master Degree:
University:
Graduation year:
MSc. Electrical Engineering
Delft University of Technology
2009
Research Group:
Electric Power Systems
Supervisor:
Gerard L. Doorman
Email:
Phone:
Home Page:
[email protected]
+47 73594252
http://www.ntnu.no/ansatte/yonas.gebrekiros
Exchange of Balancing Services
In the coming few years large scale integration of wind power is expected in the European
power system. This is an appreciated progress as seen from the utilization of more renewable
energy sources (RES) in the system. This, however, makes the operational planning,
forecasting, balancing, and control of the system more challenging. This is due to the
intermittency and unpredictability of wind and other RES: subsequently increasing the
requirement of balancing reserves in the system.
The increasing integration of European electricity markets is an indication towards the long
term goal of establishing a single European electricity market. The prospect of exchange of
balancing resources will further increase market efficiency. This happens, among others, as a
result utilizing cheaper and abundant balancing resources. The thesis will focus on the
implementation of market-based exchange of balancing services (procurement of reserves,
transmission capacity allocation for reserves exchange and implementation of real-time
balancing).
5
Sverre Skalleberg Gjerde
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1984
[email protected]
http://www.ntnu.no/ansatte/sverresk
MSc Electrical Engineering, 2009
NTNU
Supervisor:
Prof. Tore Undeland
Research Group: Energy Conversion
Co-Supervisor:
Dr. Roy Nilsen
Project:
NOWITECH WP4
Integrated converter design with generator for weight reduction of
offshore wind turbines
Offshore conditions suggest that few large turbines
are more beneficial than many small. However, larger
turbines means higher current ratings, and therefore it
is necessary to perform the transformation to higher
voltage in the nacelle. But a distribution transformer
would add significantly to the top weight, and hence
increase the overall cost of the turbine
Therefore, the focus of this research project is to
Fig: Overview of the generator/converter
analyze a converter solution which may, together with
system
an Ironless Axial Flux Permanent Magnet Generator,
eliminate the need for a transformer. A modular, series connected converter consisting of N
standard 3-phase voltage source converters has been identified as a suitable topology.
Estimates indicate that an output of 100 kV DC is achievable with this integrated
generator/converter design, without compromising the generator weight.
A control system, based on standard 3-phase control schemes, has been proposed and
analyzed for the converter. The focus was to synthesize a modular and robust system which
can function with minimum communication requirements.
For improved turbine reliability, the fault tolerance in the system has been investigated.
Based on this, individual module deloading control and redundant operation control have
been proposed
A laboratory set-up with a 45 kW generator prototype and three modules has been built.
The experimental results have verified the operation- and control aspects investigated in this
project.
6
Nathalie Holtsmark
Home Country:
Year of Birth:
Norway
1986
Master Degree: Electrical Engineering
University:
NTNU
Graduation Year: 2010
Research Group: Electric power systems
Supervisor:
Marta Molinas
PhD Start:
August 2010
Phone:
Email:
Home Page:
+47 73594228
[email protected]
http://www.ntnu.no/ansatte/nathalie.holtsmark (NO)
http://www.ntnu.edu/employees/nathalie.holtsmark (EN)
Offshore Wind Energy Conversion using High Frequency Transformation and DC
Collection
All wind parks commissioned, under construction or planned as of today (2013) emulate the
onshore grid by featuring an internal AC grid with either AC or DC transmission to shore. It is
not certain however that the onshore model is still superior when moved off shore. The
alternative wind park considered in this work is the series connection of DC wind turbines with
an HVDC transmission to shore as shown below. The main motivation for this configuration is
that an expensive offshore platform with transformer, AC/DC or DC/DC converter is not required
as a DC voltage high enough for transmission is build up by the series connection of turbines.
Inside the nacelle, the conversion system is composed of a permanent magnet synchronous
generator, a three phase AC-AC converter, a high frequency three-phase transformer for
galvanic isolation and possibly voltage step up and finally a diode bridge rectifier for the AC-DC
conversion.
Three PhD students are working on this project, funded by the Norwegian Research Council
and the RENERGI Program. The scope of my PhD work is the AC-AC converter in the
conversion system of the wind turbine. The goal is to select the best converter topology in terms
of efficiency, volume, thermal performance and make simulation models to demonstrate the
operation and control of the selected converter in this wind park configuration. So far results
show that the matrix converter, a direct AC-AC converter with no intermediate DC link with
energy storage elements, performs well and a prototype is under construction for experimental
verification, see picture.
7
SeyedMohammadAliHosseini
Home Country: Iran Year of Birth: 1983 Email: [email protected] Home Page: ‐ Master Degree: MSc Electrical Engineering, 2008 University: Eastern Mediterranean University (EMU) Supervisor: Olav Bjarte Fosso Research Group: Electric Power Systems Co‐Supervisor(s): ‐ Project: KMB project PowerSystemAnalysesandTransmissionPlanninginaCompetitive
Environment
Transmission network plays a fundamental role in the deregulated power market systems. In
fact, the necessary fair environment due to compete for the participants in the power market
would be provided by a suitable and well-designed transmission network. Therefore,
transmission network expansion is definitely considered as a very significant study in the
power market, especially when it is going to be assumed as a strong, secure and a determining
basis in order to have a right scheduling.
Due to many reasons such as: the deregulating in the electricity industry, adding many
uncertainties to the power market studies and highlighting the economical issues beside them,
a need for a deep revision has been felt throughout the used and traditional algorithms in order
to be able to find an optimum solution for the transmission network expansion problems,
though a lot of extensive studies have been done in this area so far.
The main objective is to build the competence necessary to face future challenges in the
power system analysis and transmission expansion planning within the Scandinavian
countries. An important contribution of this project will be knowledge and methods used for
optimization and simulation of electric power systems.
The main goal in this activity is to define the future generation of models for transmission
planning purposes, in terms of model structure, data flow, and coupling between market
optimization and network simulation parts. In particular this project focuses on tasks related
to power market analysis and transmission expansion planning taking into accounts the
different hydro power constraints. In another word, the different methods of power flow
calculations are going to be simulated in order to have the optimum dispatch of production.
8
Nadeem Jelani
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Pakistan
1981
[email protected]
www.ntnu.no/emploees/nadeem.jelani
MSc Electric Power Engineering, 2010
NTNU
Supervisor:
Prof. Marta Molinas
Research Group: Electric Power Systems
Expected Date of Graduation: October 2013
Investigating Stability in the Future Electrical Grid Dominated by Power Electronics
AC power electronics system is a relatively new development whose complex dynamics and
broadband control can cause inadvertent system interactions leading to instability. With the
proliferation of distributed energy resources, micro-and smart grids, a rapid transformation into a
large AC power electronics system is fundamentally changing the largely electromechanical
power system as we know today. Instability derived from inverter control-grid interaction, and
constant power load negative incremental impedance has been reported in the latest literature.
This research is aimed at the understanding of the fundamental mechanisms behind the
interactions, and the extent to which they can affect the stable operation of the electrical grid. A
general systematic method to deal with these new complex dynamic interactions is not known
today. Conventional techniques have shown inability to deal with the wide range of problems and
specially to capture the effect of constant power loads. In this research program, analytical linear
and non-linear methods have been employed to develop a general system-level methodology to
investigate the stability of the AC power electronics systems with focus on constant power
behavior. Constant power loads (CPLs) are important part of modern power distribution networks.
Main focus has been done on the voltage Fault Ride Through (FRT) under balanced/unbalanced
grid voltage dips using CPLs instead of employing a dedicated compensating device. This results
in an increase in the efficiency and stability of the smart electrical network. Alleviation of
harmonics and current distortions caused by the non-linear loads under non-ideal voltage
conditions has also been the focus of this research. In other words, this will mean a fundamental
step toward to a zero-outage system planning for the future development of smart grids.
Induction
Generator
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Fixed
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RP
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LP
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Non-linear Load
Power Electronics Dominated Grid with DG unit, CPLs and Non-linear Loads
Erik Jonsson
Home Country:
Year of Birth:
Sweden
1979
Master Degree:
University:
Graduation Year:
Solid State Physics
Uppsala University
2006
Research Group:
Supervisor:
PhD Start:
Electric Power Technology
Magne Runde
2008
Phone:
Email:
Home Page:
+47 45010212
[email protected]
www.ntnu.no/ansatte/erik.jonsson
Load Current Interruption in Air
Load Switches for medium voltage are old and comparably simple devices. At Universities this
has for long time, not been a prioritized research area and very little information is published
directly related to this topic. However, there is now a growing interest from industry to establish a
more fundamental understanding of the processes involved in current interruption in order to
further develop today’s products. The main focus is to make a switch compact and cheep as well
as environmental friendly. By using air as interruption media it is challenging to make it compact
and therefore it is needed to develop more precise and accurate design rules.
My research has an experimental approach where each parameter which plays a role in the
process is studied separately. If the interruption process for a specific current will succeed or not
depends on;





Cooling performance of the switch
Voltage transients after interruption
Contacts separation speed
Geometry of interruption chamber
Materials used in the product
To study these issues, very high demands is put on the laboratory circuit. The circuit has to
handle power up to 30MW as well as being able to tune the current and voltage transients
independently of each other. No such circuit existed when I started my project, not here in
Trondheim and not what we know about, anywhere else either. The last 1,5 years I have spend
my time on building this circuit. I estimate it will be finished before Easter this year.
In parallel to this activity I also run experiments on ablation materials. These plastic materials
have shown to have high rate of degassing when exposed to an electric arc. The result is that the
arc looses energy and is cooled. For example can an arc chamber made of POM compared to
PTFE, quench an arc with double as high current. We are focused on a wide range of plastics
and additives in our research and have so far got promising results for publication.
10
Lester Kalemba
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Zambia
1976
[email protected]
www.ntnu.no/emploees/kalemba
MSc Electric Power Engineering, 2011
NTNU
Supervisor:
Professor Kjetil Uhlen
Research Group: Electric Power Systems
Co-Supervisor(s): Professor Morten Hovd
Project: STRONGRID
“MULTIVARIABLE CONTROL OF FACTS USING PMU
MEASUREMENTS”
(Controller Design and Coordination)
ABSTRACT: Power Systems are today increasingly interconnected, and loadings and levels of power
exchange are equally on the rise. To ensure secure operation of these increasingly stressed systems,
the provision of adequate levels of control, such as damping for electromechanical modes of
oscillation, is necessary. The development of controllers that embrace multiple inputs for augmented
system performance is, therefore, an area of great interest. Synchrophasor technology provides the
possibility for widely dispersed signals, in a power system, to be centralized, processed and
distributed in real time. This PhD Research project will focus on the Design and Coordination of
multivariable supplementary controllers for FACTS. Special consideration will be given to the Design
and Coordination of Static Var Compensator (SVCs) multivariable controllers, since this is the most
widely used FACTS component. The project aims at exploiting the wide array of variables available
through Phasor Measurements. By using PMU measured data as remote controller inputs, MultiInput Multi-Output (MIMO) robust SVC controllers will be developed and compared in terms of
performance with other controllers. The Model Based (MB) controller design approach where
controller parameters are optimized for various system operating conditions will be used. The
analysis shall mostly be based on linear analysis techniques, where the state-space formulation for a
Linear Time Invariant system will be used. The coordination of FACTS with multivariable controllers
shall also be performed, first using linear techniques and then non-linear algorithms to
simultaneously tune a large number of controllers.
11
Håkon Kile
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1985
[email protected]
www.ntnu.edu/employees/hakon.kile
MSc Physics and Mathematics, 2010
NTNU
Supervisor:
Prof. Kjetil Uhlen
Research Group: Electric Power Systems
Co-Supervisor(s): Prof. Gerd Kjølle
Project: SAMREL WP2
Evaluation, classification and grouping of operating states
The SINTEF Energy AS project “Integration of methods and tools for security of electricity
supply analysis” has as main objective to establish a comprehensive methodology for
security of electricity supply analysis, by integration of system reliability analysis with the
power market analysis. The different parts of this security of supply analysis can be seen in
figure 1.
Figure 1: Methodology for security of supply analysis
The power market model combine generation and power market scenarios into a set of
operating states, described by generation, load and, network topology. These operating
states are transferred to the contingency analysis, where the consequences of different
contingencies are determined.
The set of operating sates is very large, and to run a full contingency analysis for a large
power network is not feasible, especially if higher order contingencies are included in the
analysis. The objective of my PhD study is to reduce the number of operating states that
needs to be analysed in the contingency analysis, while maintaining an adequate base for
the reliability analysis.
12
Gro Klæboe
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1978
[email protected]
www.ntnu.no/employees/grokl
Cand. Polit,Economics, 2005
NTNU
Supervisor:
Olav B. Fosso
Research Group: Electric Power Systems
Project: Optimal Short-Term Scheduling of Wind and Hydro
Stochastic bidding optimization for hydro power producers
In my PhD I look at models for bidding hydro power production optimally into various short-term
physical markets. The work includes:
-
Creating and evaluating probabilistic price forecasts for markets
Formulating models for optimal coordinated bidding in subsequent markets – i.e. the dayahead market and the balancing market.
Investigated possibilities and weaknesses of different decomposition techniques that can cut
calculation time but also conserve the necessary technical details
13
Camilla Thorrud Larsen
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1980
[email protected]
www.ntnu.no/emploees/camillla
Siv.ing. Industrial mathematics
NTNU
Supervisor:
Prof. Gerard L. Doorman
Electric Power Systems
Birger Mo, Sintef Energy Research
Research Group:
Co-Supervisor(s):
Long-term hydropower scheduling using stochastic dual dynamic
programming (SDDP)
The objective of long-term scheduling from a global viewpoint is to find a hydro release policy which
is coordinated with generation from other sources, to meet the electricity demand at minimum
expected costs. For a local system (in a deregulated market), the objective will usually be to find a
production schedule that maximize expected profits over the planning horizon. Long-term policies
are important for price forecasting, generation scheduling, maintenance planning, investment- and
expansion planning, as well as general power system analysis. Moreover, long-term decisions provide
targets for the seasonal and short-term scheduling which concerns detailed operation of the hydro
system.
Long-term scheduling constitutes a multi-stage stochastic problem which in principle can be solved
by stochastic dynamic programming (SDP). However, for a detailed model of a system consisting of
several reservoirs, and thus many state variables, the dimension of the problem quickly explodes and
becomes computationally intractable. One approach to the problem for which SDP can still be used is
based on reservoir aggregation and depends on heuristics for disaggregation to address the multireservoir aspect realistically. Such models are frequently used by power market participants in the
Nordic countries and the commercially available EMPS and EOPS models, developed at Sintef Energy
Research, are based on this methodology.
A different solution approach, called stochastic dual dynamic programming (SDDP), is a samplingbased approximation technique for solving multi-stage stochastic problems. This method eliminates
the need to completely discretize the state space and allows for detailed modeling of multi-reservoir
systems. SDDP relies on formal optimization, rather than heuristics and manual calibration, and is
currently the state-of-the-art procedure to solve hydro-thermal scheduling problems.
The overall objective of this project is to improve the performance of the long-term hydro-thermal
scheduling models which utilize the SDDP-methodology. Primarily, the focus will be on the local
model, i.e. for a system confined in a geographical area that can be covered by a single power
balance equation, and typically owned by a single power producer. The goal is to develop a good and
reliable model which will provide a useful tool for hydropower producers in the Nordic market. The
main focus in this work will be on how to model and represent the stochastic input parameters in a
best possible way, and which is in correspondence with the SDDP framework.
14
Karen Byskov Lindberg
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
Engineering, 2004
University:
Norway
1978
karen.lindberg @elkraft.ntnu.no
www.ntnu.no/emploees/karen.lindberg
MSc Energy and Environmental
NTNU
Supervisor:
Gerard Doorman
Research Group: Electric Power Systems
Project: Part of the two FME-centres Zero Emission Buildings (ZEB) and Centre for
Sustainable Energy Studies (CenSES), and co-funded by the Norwegian Water Resources and
Energy Directorate (NVE).
The impact of Zero Energy/Emission Buildings on the energy system
In the recast of the EU Directive on Eneryg Performance of Buildings (EPBD) it is stated that
by end of 2020 all new buildings shall be “nearly zero energy buildings”. In Norway, the
Norwegian white paper on climate efforts, ”Klimameldingen 2012”, stated that technical
regulations (TEK) for buildings will be passive standard in 2015, and zero energy standard by
2020.
A zero energy (emission) building is a building which has low energy demand, and which has
the capability of producing energy such that its net energy consumption (or net GHG
emissions) on a yearly basis is zero. The definition may also be extended to including
embodied energy (or GHG emissions) of the building, reflecting energy use (or GHG
emissions) from the construction, material use and demolition of the building.
This thesis will investigate the impact of introducing such high energy efficient and energy
generating buildings, called ZEBs, into an energy system with a high share of intermittent
renewable production. What challenges do we face when combining intermittent renewable
production with a reduced, and perhaps less fexible, demand? Especially when the need for
flexible demand is rising in order to meet the fluctuating renewable generation?
The work is divided into three main parts:
(1) Forecasting hourly demand profiles, divided on heat and electricity, for normal and
passive standard non-residential buildings in Norway (schools, offices, nursery
homes, hospitals and hotels).
(2) Optimisation of four different ZEB-type buildings in order to find their hourly net
electricity load towards the grid, based on the heat and electricity demand profiles
found in (1).
(3) Analysing the net load profiles in the power market model, EMPS. Investigating the
effects on price formation and Norway’s ability to capacity trading towards Europe.
15
Abbas Lotfi
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Supervisor:
Research Group:
Co-Supervisor:
Project:
Iran
1983
[email protected]
http://www.ntnu.edu/employees/abbas.lotfi
Electrical Engineering, 2006
University of Zanjan
Prof. Hans Kristian Høidalen
Electric Power Technology
Nicola Chiesa, PhD
NFR/SINTEF
Transformer Modeling for Low and Mid Frequency Transients
The power transformer is an important component in all power systems and its operation is crucial for
system reliability. Accordingly modeling of power transformer is very important that is widely and
continuously done by researchers and engineers to be used in different levels of power system
analysis. This PhD work is mainly aimed to discuss on Power Transformer modeling enabling
simulation of switching transients. The Developed Model is able to describe transformer response
against the phenomena including slow front switching transients, Ferro resonance, Harmonics effects,
Inrush current calculation, GIC, and etc.
The developed model has this property that to be implemented with standard circuit components
available in EMTP-like Programs. The main challenges of transformer modeling in this range of
frequencies are a) short Circuit (Series Impedance) impedance representation b) modeling of
nonlinear, hysteretic and frequency dependent Iron-Core c) zero Sequence Impedance and
Tank effect. In addition, the model should have topologically correct representation of the
mentioned quantities. The main idea is the use of duality transformation to convert the
transformer magnetic circuit into equivalent electric circuit. In this case the model is pure
electric and there are no difficulties of interfacing between magnetic side and electric side of
the electromagnetic components while implementing in circuit analysis software.
The model named Hybrid Model is developed and implemented in ATPDraw by NTNU with
collaboration with MTU in USA. This Model uses duality transformation and supposed to be
extended covering higher frequencies in the current PhD work. For this purpose frequency
dependent behavior of copper and iron losses as well as non-linearity are taken into account.
16
Hamed Nademi
Home Country:
Iran
Year of Birth:
1980
Master Degree: Electrical Engineering (Control)
Graduation year: 2008
Research group: Energy Conversion
Supervisor:
Prof. Lars Norum
PhD Start:
January 2010
Phone:
Email:
+47 73550385
[email protected]
Advanced Control of Power Converters
Introduction
Many of the world’s major existing oil and gas reservoirs located either onshore or in shallow
water offshore are in decline. With increase in the consumption of oil and natural gas, more
innovative solutions for tapping the energy resources located in more challenging locations have
to be taken up. One such step in this direction is the exploration of oil and natural gas in under
sea locations remote from the shore. This requires lot of engineering expertise because of the
extreme working conditions and the need for a fail safe operation. Making design for high
reliability and high efficiency are two important challenges.
Advanced control methods have been applied to the control of power converters in order to
minimize harmonic components, control resonances and to increase the reliability. In such
cases explicit Model Predictive Control (MPC) can be applied.
Modular Multilevel Converter (MMC) is one of the most promising power converters for future
medium/high voltage drives. In this study, various methods applied for modeling of MMC. Using
the definition of switching functions, the corresponding electric circuit is mathematically
described by a system of ordinary differential equations. In general, power converters are
nonlinear and time varying devices. It is well known that a small-signal model in the frequency
domain can be used to predict the dynamic performance and stability with less computation time
compared with time-domain simulation. It also provides more insight and understanding of the
interaction between the AC and DC sides caused by the converter.
For proper operation of MMC, continuous voltage monitoring of many floating dc capacitors is
required. This will increase the number of voltage sensors resulting in increased hardware
complexity with many modules in the converter. The objective of this work will be to develop and
implement an efficient and robust capacitor voltage observer for MMC. The observer will work
as a software sensor working in parallel with the hardware measurement part. It can be used for
condition monitoring for capacitors, for fault detection and parameter estimation.
Laboratory prototypes for relevant applications have been specified and established in
cooperation with PEC, (Power Electronic Center, Siemens). Before the final prototype for the lab
is built, it was advantageous and recommended to build a smaller prototype. This prototype can
be rated at 1kW. It has been used to verify the concepts quickly, make changes and can be a
basis for further experiments. The final set-up of the converter for a power level of 10kW is
presently working (Figs. 1 and 2). A test has been successfully carried out to verify the theory
and the basic operation of the MMC.
17
This research project is initiated and funded as part of the SIEMENS-NTNU OIL AND GAS
OFFSHORE PROJECT, which is a cooperative project between Power Electronic Center of
Siemens and NTNU.
Completion Date
The PhD project is assumed to be concluded in the early of 2014 spring semester. 24.01.2014
has been stated as ending date.
This project is supervised by Prof. Lars Norum from the Department of Electrical Power
Engineering at NTNU.
Voltage sensor
board
Gate drive
boards
Capacitors
IGBTs
Traco power
Heat Sink
Plate
Fig. 1: Picture of one cell.
Phase A, upper
and lower arms
DSP, CPLD,
buffer ckt. etc.
Phase B, upper
and lower arms
Phase C, upper
and lower arms
DC bus
Arm Inductors
Fig. 2: Overall setup.
18
Pål Keim Olsen
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1982
[email protected]
www.ntnu.no/ansatte/pal.keim.olsen
MSc Electrical Engineering, 2008
NTNU
Supervisor:
Ass. Prof. Frank Mauseth
Research Group: Electric Power Systems
Co-Supervisor:
Prof. Erling Ildstad
Project: High Voltage AC and DC Subsea Cables for Offshore Wind Farms and Transmission Grids
Long term performance of insulation materials exposed to DC
superimposed AC voltage
The background for the PhD work is the need for reliable electric transmission networks and
electric equipment in an offshore environment. The last couple of years there have been
great interest for the offshore wind energy potential. This is partly due to the promising
potential in stable, high wind speed with little turbulence, and partly due to the local public
resistance typically met by wind farm entrepreneurs onshore or near shore. However, the
offshore environment is very demanding and new ageing conditions apply to the electric
equipment. Better knowledge about the ageing mechanisms related to the offshore
environment and the differences between a HVDC and HVAC network will be important for
the design of a long term reliable system. When factors limiting cable and equipment life are
known possible methods to detect these ageing mechanisms can be developed.
HVAC subsea transmission is limited in terms of distance to shore: at about 50-70 km
distance from shore the capacitive load of the subsea cables is too high, taking too much of
the current carrying capability of the cables. It has been found that the HVDC system is
economical for distances above 70 km from shore, and there is no practical limit in the
distance from shore as for HVAC systems. The majority of cables already installed in AC and
DC systems are mass impregnated cables, but there is a drive to use dielectric extruded
cables for subsea applications.
The PhD work will focus on the electric degradation phenomena which can occur in electric
equipment in an offshore HVDC network, during steady state operation and under faults. In
particular, the effect of DC voltage with superimposed AC voltage will be studied. Simulation
of partial discharges in cavities under DC superimposed AC voltage will be carried out and
ageing under such conditions will be studied through lab experiments. The main materials to
be studied are XLPE for cables and epoxy for converter transformers, generators and
switchgear. The results from the work can be used when developing qualification tests and
design of long cables and other electric equipment used in offshore HVDC networks.
19
Traian Nicolae Preda
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Romania
1986
[email protected]
www.ntnu.no/employees/traiannp
MSc Electrical Power Engineering, 2011
POLITEHNICA University of Bucharest
Supervisor:
Kjetil Uhlen
Research Group: Electric Power Systems
Co-Supervisor(s): Dag Eirik Nordgård
Project: Optimal infrastructure for seamless integration of distributed generation – OiDG
Stability requirements for distributed generators
In Norway most of the electricity is produced in large scale hydroelectric power plants
(98.5%). But in the last years more distributed generation units (subsequently referred to as
DG), such as small scale hydropower plants and wind turbines have started to be connected
at the distribution system level. Most of these DG units are located in sites with relatively
weak grids, low local load and long distances to the transmission system.
As increasing share of the DG leads to changes in the conventional power system structure,
the functions of traditional centralized power plants (controlling and stabilizing the power
system during faults, damping of power oscillations) must also be performed by DG units.
Therefore, the aforementioned DG is expected to play a significant role as generation
sources in the Norwegian power system. This will make the control, operation and modelling
of the power system more complicated than before, presenting many new challenges in
terms of power system stability concerns. This PhD-work will focus on the integration of DG
units into the future power systems from the perspective of power systems stability and grid
code requirements. The work will also address issues regarding the modelling of the future
Active Distribution Grids for transmission system studies. Dynamic equivalents for Active
Distribution Grids are investigated for the use in transient stability studies of the main grid.
Transmission Power
System
Voltage [kV]
1
Internal Power System
0.8
0.6
0.4
0.2
0
0
Active Distribution
Power Systems
Boundary
Buses
DPS 1 DPS 2
DPS 3 DPS 4
External Power Systems
20
Grid code FRT voltage profile
DG connected to benchmark power system
DG connected to Ward equivalent
DG connected to Extended Ward equivalent
DG connected to Thevenin equivalent
1
2
Time [s]
3
4
5
Astrid Røkke
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1982
[email protected]
www.ntnu.no/emploees/astridr
MSc Electrical Engineering, 2007
NTNU
Supervisor:
Robert Nilssen
Research Group: Energy conversion
Co-Supervisor(s): Arne Nysveen
Project: SmartMotor
Investigation of permanent magnet synchronous machines with
fractional slot windings for use in renewable energy applications
The main purpose is to identify the best configurations of PM machines for renewable
energy converters. Special focus within renewables should be on marine current turbines.
Tidal power is an area of development, predicted to produce a significant amount of energy
within the next few decades. The market can be characterized by many different actors in
different stages of development of new tidal turbines. The aim of the project is to develop
methods and tools to optimize Permanent Magnet generators for low speed high torque
tidal applications. Advanced numerical analysis software will be used to model coupled
problems including thermal, magnetic, electric and mechanical quantities. This will form a
new basis for optimization. The analysis will take into account 3D phenomena, time
dependency and motion.
The object function should take into account the practical specifications/limitations for a set
of relevant tidal power cases. The optimization will be conceptual, meaning that choices
such as the selection of winding type and layout are a part of the synthesis. The optimization
should also handle several objectives such as efficiency, cost and lifetime (linked to
temperature).
21
Santiago Sánchez Acevedo
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Colombia
1982
[email protected]
MSc Electrical Engineering, 2008
Universidad Tecnológica de Pereira
Supervisor:
Marta Molinas
Research Group: Electric Power Systems
Co-Supervisor(s): Tor Arne Johansen
Project:
Identifying electrical instability in grids dominated by power
electronics
The main purpose of the research is to identify the phenomena that affect the stability of a
micro-grid fed by multiple renewable energy sources and non renewable energy sources
with power electronics systems. The future distribution systems will be affected by the
bidirectional current flow due to the distributed generation growth. Hence, the classical
stability tools and classical system dynamic assumptions are not sufficient to design the new
grids dominated by power electronics. The grids will present AC, DC or hybrid AC-DC
behavior in multiple nodes.
The stability analysis can be realized in the different domains (i.e. time/frequency). Where a
criteria is used to identify the instability occurrence.
As final objective the project will establish a guideline for the design of a micro-grid that
ensures a safe operation region.
22
FritzSchimpf
Home Country: Germany Year of Birth: 1977 Email: [email protected] Home Page: www.ntnu.no/emploees/schimpf Master Degree: Diploma Electric Power Engineering, 2004 University: TU ‐ Berlin Supervisor: Lars Norum Research Group: Energy Conversion (ENO) Co‐Supervisor(s): Marta Molinas Project is financed by the Norwegian Research Council and the Centre for Renewable Energy (SFFE) NewConceptsforConvertersandControlofPhotovoltaicSystems
Photovoltaic systems for electricity production have become a popular source of clean,
renewable energy. The number of PV-installations is quickly growing and PV delivers a
considerable percentage of the energy production in some countries already. Converters are a
central part of all PV-systems and they are produced by industry in all power ratings.
Still, a lot of optimization and adjustment to new technological needs can be done on the
converters. Some working areas are: Reduction of the specific price per kW, increase of
reliability and lifetime, safety improvements and additional functions like interfaces to energy
storage elements or backup-functionality.
An important part of the project is the increase of reliability and lifetime of single-phase
inverters by reduction of the DC-link capacitance. When this capacitance is small enough, the
very reliable film-capacitors can be used instead of their electrolytic counterparts with limited
lifetime. For this aim an additional converter stage is introduced, which decouples the
capacitors from the DC-link.
The same concept of parallel decoupling can also be used for longer term energy storage in a
battery. The result could be a “smart” PV-system which can deliver power on demand and
more independent from the current irradiance condition.
In the latest state of the project, a two-stage, single-phase converter was considered and the
additional decoupling stage could be replaced by a very fast current control of the DC/DC and
the DC/AC-stage. This allows use of film capacitors and still achieves high efficiency.
23
Phen Chiak See
Home country: Malaysia
Year of birth: 1983
Email: [email protected]
Home page:
Master Degree: ME. Mechanical Engineering, 2008
University: University of Technology, Malaysia
Supervisor: Olav Bjarte Fosso
Research group: Electric Power Systems
Co-supervisor(s): Marta Molinas
Project: NOWITECH WP4
Development of Electricity Market Model Incorporating Offshore Grids
and Offshore Wind Farms
Integrated electricity market is a key factor for the successful implementation of
single European electricity market. It allows bid made in the wholesale electricity market of interconnected countries to be assessed by their counterparts. This
significantly enhances the competition and the security of supply in the region.
Nevertheless, it requires good liquidity of physical flow of electricity power as
well as the availability of synchronized (trade-friendly) financial rules.
Although the creation of synchronized financial rules is possible between the participating countries, the development of the integrated electricity market is often
limited by the existence of transmission constraints. Often, efficient congestion
management is a challenge faced by stakeholders in deregulated electricity market. In this regard, we study the electricity market by taking into account the
inter-connection of countries that implement different market rules. Also, we
investigate how offshore wind farms and offshore grids help in lightening the
transmission congestion issues that hinders the liquidity in power flow.
We construct a computer program for simulating the integration of crosscontinental electricity market in the North Sea countries. The program is called
Power System Economics and Electricity Market (PSEEM), which partly embraces codes and concepts previously developed by Olav Fosso. It is intended for
demonstrating the interactions between electricity markets that implement different pricing rules, and how this influences the global benefit (price convergence, intuitiveness of flow, etc.) in the connected countries.
The PhD work is expected to complete by July 31, 2015. We thank NOWITECH
and NTNU for all supports given in this research.
24
Jonas Sjolte
Home Country:
Year of Birth:
Norway
1980
Master Degree: Electrical Engineering
University:
NTNU
Graduation Year: 2007
Research Group: Energy Conversion
Supervisor:
Marta Molinas
PhD Start:
2011
Phone:
Email:
Home Page:
+47 97 688 440
[email protected]
www.ntnu.no/ansatte/jonassjo
Power control systems and grid interface for renewable energy production
Grid connection of Wave Energy Converters (WECs) poses great challenges due to the high
power fluctuations that are produced from these devices. For a cost effective grid conversion
system, these fluctuations must be managed, either by energy storage or by natural
smoothing through interconnection of devices over a large area. Moreover, interconnections
between different energy sources like wave and wind farms may influence the power quality.
The research project is performed in close collaboration with Fred. Olsen Renewables and is
funded by the NFR "Næringsphd" program. The work is based on Fred. Olsen's WEC
concept and aims to describe the best configuration and required power system for a grid
connected farm consisting of the Fred. Olsen system "Lifesaver". Advanced simulations of
the hydrodynamical and electrical properties are performed to estimate annual produced
energy.
25
Christian Skar
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1985
[email protected]
www.ntnu.no/employees/christian.skar
MSc Applied Mathematics, 2010
NTNU
Supervisor:
Gerard Doorman
Research Group: Electric Power Systems
Co-Supervisor(s): Asgeir Tomasgard (IØT)
Project:
LinkS
Modeling of the European power system for low emission scenarios
Research objectives: Develop a model for calculating optimal long-term expansion of the
European power system taking into account climate mitigation strategies given by the Global
Climate Assessment Model (GCAM). The capacity expansion model will provide results such
as country-wise investments in production capacity, investments in transmission capacity
between countries and a resulting production mix for aggregate technologies. These results
will be used to suggest optimal ways of implementing GCAM strategies along with related
costs. In addition we aim at identifying possible problematic features in GCAM scenarios, for
instance scenarios where high RES penetration result in much unserved demand. This can
then be used to adjust assumptions in GCAM simulations.
Figure 1 shows some sample results from the capacity expansion model when run for the
GCAM 450 ppm stabilization scenario.
a) Installed generation capacity 2050
b) Investments in transmission system by 2050
Figure 1: Expansion model results for the 450 ppm scenario defined for GCAM
26
AmirHayatiSoloot
Home Country: Iran Year of Birth: 1984 Email: [email protected] Home Page: www.ntnu.no/emploees/amir.h.soloot Master Degree: Electric Power Engineering, 2009 University: Iran Uni. of Sci. and Tech. (IUST) Supervisor: Hans Kristian Høidalen Research Group: Electric Power Technology Co‐Supervisor(s): Bjørn Gustavsen Project: NOWITECH WP4 SwitchingTransientinOffshoreWindFarm
In order to connect the offshore wind turbines, large undersea cable connections
are required. Since each wind turbine has a
step-up transformer, a row of Offshore Wind
Farm (OWF) composed of cable-transformer
sections which are linked in series. Wind
Turbine Transformers (WTTs) can be
exposed to dielectric failures, internal
insulation damage as well as external one
due to switching overvoltages
The aims of this PhD study are:
1- Study and simulation of switching
transient phenomena in a row of OWF.
The focus is on the potential of
resonance
overvoltage
on
WTT
terminals within energization for various
OWF configurations. The effect of
protective devices such as surge
arresters and RC filters are also
investigated.
2- Development of the High Frequency
(HF) modelling of WTTs with available
winding designs based on RLC latter
model and the analysis of resonance
overvoltages along transformer winding.
A 500 kVA transformer equipped with
layer, disc and pancake windings and
voltage taps along the windings is
designed and manufactured to validate
the HF model of WTT with experiments.
27
Bendik Støa
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1987
[email protected]
www.ntnu.no/employees/bendik.stoa
MSc Industrial Mathematics, 2012
NTNU
Supervisor:
Erling Ildstad
Research Group: Electric Power Technology
Co-Supervisor(s): Magne Runde
Project: Load cycling and radial mass flow in mass impregnated HVDC subsea cables
Modelling of Void Formation and PD Activity due to Mass Transport in
Mass Impregnated HVDC Subsea Cables
Mass impregnated HVDC cables have been, and still remains, the state-of-the-art technology
for transmission of large amounts of energy over long sea crossings. During a certain part of
the type tests for such cables, in the cooling phase of the load cycling procedure, a reduction
of dielectric strength of up to 50% has been reported. It is suggested that breakdowns under
these conditions is caused by discharges in gas-filled cavities that has formed and grown in
the insulation.
The insulation consists of around 200 layers of paper tapes that are wound around the
conductor, with small butt gap channels between them. After being applied and dried, the
papers are impregnated with a high-viscosity mineral-oil based compound. Then a lead
sheath is extruded onto the insulation, and it is cooled down to room temperature. During
this process the oil will contract so that it is not able to fill all the available space, and
cavities are formed. Loading the cable will in turn expand the oil, leading to radial flow of oil
when all the cavities are filled.
The goal of the PhD project is to develop
a mathematical model describing radial
flow in mass impregnated HVDC cable
insulation. The model will, together with
experimental investigations on full-scale
cable samples, be used to increase our
understanding
of
the
processes
governing the dielectric strength of such
insulation. Hopefully, the work will
contribute to better exploitation of
existing cables, and assist in the design of
new projects.
28
My Name: Vin Cent Tai (Su)
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Malaysia
1983
[email protected]
www.ntnu.no/emploees/vinct
MSc Aerospace Engineering, 2009
Brunel University
Supervisor:
Kjetil Uhlen
Research Group: Electric Power Systems
Co-Supervisor(s): Marta Molinas
Project: OffshoreDC WP5
Integration of offshore DC grids and onshore AC power networks – Stability
and Control
Offshore wind power has become one of the major focuses of many researchers and energy
companies worldwide in tapping the energy from the renewable source. There has been a
lot of research on the voltage-source based high-voltage direct current (VSC-HVDC)
technology in recent years. This technology has proven to be the best solution for long
distance power transmissions. It enables the wind energy generated offshore to be
transmitted to the onshore power networks effectively. However, the integration of larger
and larger amount of wind power has posed a challenge for power system planning and
operation. For instance, the injection of large amount of offshore wind power tends to
increase the rate of the frequency change in the mainland system, which makes the system
unstable.
Many research have studied the VSC-HVDC technology in terms of its impact on the stability
of AC power systems, little has been done in the way of multi-terminal VSC-HVDC (MT-VSCHVDC). As the power system grows larger and larger, the problem of stability is becoming
more and more important. In view of this, the research work therefore is intended to
increase the understanding of the static and dynamic behaviours of the multi-area power
network interconnected by MT-VSC-HVDC systems. As different configuration can result in
different requirements for system control, protection, and management, detailed analysis
on different system configurations will also be carried out. Various offshore HVDC grid
topologies (meshed and radial) will be investigated, together with various faults scenarios
and their impacts on both the off-shore and on-shore AC grids. Control strategies that would
improve the grids' stability and mitigate faults will also be proposed.
29
Chuen Ling Toh
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Malaysia
1979
[email protected]
www.ntnu.no/ansatte/chuen.toh
MSc Electrical Engineering, 2005
Universiti Teknologi Malaysia
Supervisor:
Lars E. Norum
Research Group: Energy Conversion
Project: Integration of electrical power, propulsion and control in future energy efficient
marine power system (Advanced control of PE converter)
Advanced Monitoring and Control in Power Electronics Converter for
Future Energy Efficient Marine Power System
A simple and fast internal communication system is highly demanded for future
complex Power Electronics (PE) converters such as multilevel converters. To increase the
reliability, more data/information will be required for local/internal monitoring and control.
Therefore, a high speed control network is essential for the future PE converter system.
It is believed that Modular Multilevel Converter (MMC) will be a better choice of
multilevel converters in future, mainly of its modular and simple power cells (Power
Electronics Building Block, PEBB) concept. In order to obtain a very high quality sinusoidal
voltage and current waveforms at the output, more PEBBs can be added equivalently on the
upper and lower arms of each phase. However, this may increase the complexity of the
MMC if the conventional control topology (star network) is adopted. A simpler wiring system
(ring communication network) is highly demanded to significantly reduce the number of
wires, installation cost and noise interference.
This research will mainly design and implement high speed reliable control
architecture to meet the future complex PE converter with PEBB. A power converter
prototype will be developed at the end of the research for marine/subsea application. The
proposed control architecture will be designed in a user-friendly and standard form. It is
expected that the proposed control architecture is fully decoupled between software and
hardware with minimum engineering effort.
30
Erling Tønne
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Norway
1965
[email protected]
MSc Electric Power Engineering, 1991
NTNU
Supervisor:
Kjell Sand
Research Group: Electric Power Systems
Co-Supervisor(s): Jan A Foosnæs
Project:
Active distribution grids – concepts, architecture and functionality
Active distribution grids – concepts, architecture and functionality
The electric power system is undergoing a profound change driven by a number of needs.
There’s the need for environmental compliance and energy conservation. We need better
grid reliability while dealing with an ageing infrastructure. We need improved operational
efficiencies and customer service. The changes that are happening are particularly significant
for the electricity distribution grid, where “blind” and manual operations, along with the
electromechanical components, will need to be transformed into a “smart grid.” This
transformation will be necessary to meet environmental targets, to accommodate a greater
emphasis on demand response, and to support distributed generation, electric vehicles and
storage capabilities.
These needs and changes present the power industry with the biggest challenge it has ever
faced. On one hand, the transition to a smart grid has to be evolutionary to keep the lights
on; on the other hand, the issues surrounding the smart grid are significant enough to
demand major changes in power systems operating philosophy.
The Norwegian distribution networks have been developed over many years and have a
relatively small amount of active elements, such as generators and demand side
management. They are instead dominated by passive elements, principally uncontrolled
loads. The focus on integration of renewable energy sources into the electricity system leads
to a significant growth in the amount of distributed generation (DG) in the system. The loads
will become more dynamic and controllable due to more active response from customers
and the expected large introduction of electronic control and regulation systems. At the
same time the introduction of advanced metering systems (AMS, smart meters) will provide
the network owner with a lot more data.
The objective of my PhD-work is to find, test out and adapt methods for power system
planning for the next generation active distribution grid. I am focusing on methods using
scenarios and use-cases.
31
Mostafa Valavi
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Iran
1985
[email protected]
www.ntnu.no/emploees/mostafa.valavi
MSc Electrical Engineering, 2010
University of Tehran
Supervisor:
Prof. Arne Nysveen
Research Group: Electric Power Technology
Co-Supervisor(s): Prof. Robert Nilssen
Project: NOWITECH WP2
Magnetic Forces and Vibrations in Wind Power Generators
In direct-driven permanent magnet (PM) generator systems, gearbox is eliminated and
maintenance works can be reduced substantially. This is a clear advantage particularly in
offshore wind farms. In direct driven PM generators, the nominal speed is very low, leading
to very high number of poles and very large diameter. In this application, utilizing
concentrated windings and using fractional slot PM machines can be very advantageous. In
this type of machines, it is possible to keep the number of slots relatively low. PM machines
with concentrated windings have several significant advantages over the machines with
distributed windings, such as high efficiency, low cogging torque, short end-windings and
manufacturing advantages. However, the vibration level in machines with non-overlapping
concentrated windings can be significantly higher than conventional machines. It is mainly
due to presence of low order harmonics in the radial magnetic forces. In addition, machines
with high number of poles have a large diameter and short stator length and therefore
moderate mechanical stiffness. Due to the mentioned facts, it is important to investigate
magnetic forces and vibration in direct-driven PM generators.
In this project, the first step is to calculate and harmonic analysis of magnetic flux density
in the airgap of the machine using finite element method. Radial and tangential magnetic
forces can be computed using Maxwell’s stress tensor. Radial magnetic forces are the main
cause of the magnetic vibration in electrical machines. Influence of some design parameters
and working conditions on distribution of forces is investigated. A structural finite element
analysis is then performed to predict the vibration spectrum. Vibration measurement has
been done on a 50kW low speed PM generator in Wind Lab at the Department of Electrical
Power Engineering. Investigation of forces and vibrations in radial flux machines, first part of
the project, is finished and the second part with focus on multiple airgap machines has been
just started.
32
Torbjørn Andersen Ve
Home Country:
Year of Birth:
Email:
Home Page:
University:
Norway
1983
[email protected]
www.ntnu.no/ansatte/torbjorn.ve
NTNU
Supervisor:
Frank Mauseth
Research Group: Electric Power Technology
Co-supervisor:
Erling Ildstad
Project:
High Voltage AC and DC Subsea Cables for
Offshore Wind Farms and Transmission Grids
Effect of Moisture on Space Charge Accumulation in Polymeric HVDC
Cable Insulation
The use of extruded insulation in HVDC cables has been limited, due to accumulated space
charge causing large field enhancements during polarity reversals. However, as voltage
source converters, not requiring polarity reversals to change the power flow, have become
viable replacements to the traditional current source converters, polymeric HVDC cable
insulation has become relevant.
Submarine power cables are often equipped with a metal or polymeric water blocking
sheath. Metal sheaths are excellent water barriers, preventing water from entering the
underlying polymeric semiconductors and insulation. However, in cases where the metal is
cracked or where a polymeric water barrier is used, water will be absorbed by the insulation
system.
The presence of space charge in the insulation will cause a distortion in the local electric
field. The amount and placement of the charge will depend on several factors such as
temperature, impurities, additives, etc. In particular the conductivity of the insulation is
critical, as gradients in the conductivity-permittivity ratio directly lead to space charge buildup. For instance temperature gradients, which will occur in a cable in service, will cause a
conductivity gradient. Also, as water is a polar molecule, and also dissociable into ions, it is
expected that the presence of absorbed water will affect charge accumulation and
transport.
This project investigates the effect of water on space charge accumulation and conductivity.
Experiments measuring the charge distribution and conducted current in samples with
varying water content and at different temperatures will be performed, which will give
information on the mechanisms involved. The results can then be used to determine if
preventing water intrusion into HVDC cables is a concern.
33
Til Kristian Vrana
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Germany
1982
[email protected]
www.ntnu.no/employees/til.kristian.vrana
Electrical Engineering, 2008
RWTH-Aachen University
Supervisor:
Olav Bjarte Fosso
Research Group: Electric Power Systems
Development and Operation of the North Sea Super Grid
Due to the current focus on offshore renewable energy installations there will be a need for
connecting these installations to the onshore grids. Electric supply of oil installations from
onshore is also focused due to the environmental perspective. The paneuropean electricity
market highly demands stronger interconnections for efficient balancing of regional
fluctuations due to the increasing share of volatile electric power sources in Europe. The
North Sea Super Grid (NSSG) will evolve in the future to address these issues.
With the distances involved to these candidate installations, HVDC (High Voltage Direct
Current) will be of major importance. The wind farms which are now under construction are
realised with internal AC grids. The NSSG will therefore consist of both AC and DC, AC within
the offshore nodes and DC for the branches.
With the large future plans for offshore renewable installations it is of crucial importance to
minimize the worst case amount of disconnected power. A meshed grid has therefore
advantages regarding reliability, but there are still many challenges regarding meshed DC
grids.
The offshore DC network has to be controlled in a coordinated way to asure smooth
cooperation with the existing AC onshore grid. Reliability, technical performance, robustness
and flexibility will be of major importance. The focus of this research work is on DC voltage
control in DC grids.
34
Mehdi Karbalaye Zadeh
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Iran
1982
[email protected]
http://www.ntnu.edu/employees/mehdi.zadeh
MSc, Electrical Engineering, 2010
University of Tehran
Supervisor:
Marta Molinas
Research Group: Electric Power Systems
Co-Supervisor(s): Kjetil Uhlen
Project: Smart Grid
Stability Analysis of AC Distributed Multi-converter System under
Non-ideal Electrical Conditions
System stability is the most important pre-requisite when designing electrical grids integrated
with a large number of power electronics converters. Due to their non-linear and complex
characteristics, modeling and stability analysis of such systems are multifaceted and
cumbersome. After a thorough investigation of the state of the theoretical art on modeling and
stability, this research focuses on the development of a stability analysis tool that can
accurately capture the potential phenomena linked to the interaction between converterembedded control algorithm and the characteristics of the electrical grid. This interaction will
be investigated under non-ideal regimes in which power electronics converters will most
likely operate in the electrical grids of the future. Performance of the grid under such
influences will be investigated during normal and emergency conditions to assess to what
extent they can lead to instability of the system and consequent system outage.
Keep in mind the characteristics of power electronics dominated system, the stability analysis
will be approached by the nonlinear system dynamics. Bifurcation theory will be used in
order to identify oscillatory modes of the state variables. In this context, the non-linear impact
of the control architecture on the stability of three phase PWM converters will be simulated
through bifurcation indicators and analyzed based on nonlinear criteria. The ultimate goal will
be to develop a stability analysis tool that can be used for defining design specifications for
individual converters that can ensure the stability of the system.
200
Voltage
100
0
-100
-200
40
20
3
2
0
-20
1
-40
0
35
Bijan Zahedi
Home Country:
Year of Birth:
Email:
Home Page:
Master Degree:
University:
Iran
1981
[email protected]
www.ntnu.no/emploees/bijan.zahedi
MSc Electrical Engineering, 2006
University of Tehran
Supervisor:
Lars Einar Norum
Research Group: Energy Conversion
Project: a KMB Project with DNV titled “Integrated Marine Electrical Power and Control
Systems”
Integrated Marine Electrical Power and Control Systems
Environmental concerns and rising cost of oil have intensified the need for low emitting and fuel efficient
vehicles. The shift to electric propulsion from conventional mechanical propulsion in marine vessels aligns with
this need. Reduced fuel consumption, possibility of utilizing light high speed diesel engines, less propulsion
noise and less space consuming are some of the advantages of electric propulsion in marine vessels.
Electric propulsion has also facilitated a hybrid utilization of energy sources and storages. Operation in allelectric mode is a main advantage of hybrid ships, which makes it possible to have zero emission sailing when
ship is approaching or leaving harbor. In this mode the speed is low and energy storage can take over to supply
propulsion motors. This can affect the local air quality which is becoming a major concern at harbors and
nearby cities. As indicated in the figure the impact of shipping on local air quality is significant.
The operation of energy storage in hybrid propulsion is not limited to all-electric mode. During the normal
operation it can also be utilized effectively so that ICEs operate at their optimal efficiency work point. This is
normally done by charging the storage when load is below the optimal value and discharging it when load is
beyond optimal.
The focus of this research is on design a new control system for hybrid electric ships based on power
electronics giving the advantages of zero emission operation and optimal efficiency. The important point is to
adopt an effective strategy for power and energy management, in such a way that the ship runs at an overall
optimum operating point. Proper hybrid topology, appropriate modelling of the power system, stability
control, and reliability are other major concerns. Finally, an experimental system is to be implemented to
validate the methodology by practical results.
36
Zhaoqiang Zhang
Home Country: China
Year of Birth:
1981
Master Degree: Electrical Engineering University:
Shanghai Jiaotong University
Graduation Year: 2007
Research Group:
Supervisor:
PhD Start:
Energy Conversion
Robert Nilssen
2010
Phone:
Email:
Home Page:
+47 7359 4271
[email protected]
www.ntnu.no/ansatte/zhaoqiang.zhang
Coupled 3D models of permanent magnet generators with very large
diameters and with a special focus on losses
The mass of generator generally consists of two parts: the active part which directly
produces the torque, and the inactive part which holds the active material in position and
keeps the air-gap clearance. Normally the larger the rating of the generator, the heavier
and bigger the machine is. However, as the power rating grows, the mass of the active part
and inactive part increases differently. For example, inactive mass in a 1.5 MW machine
accounts for only 20%, but more than 70% in a 10 MW machine. The huge mass of
inactive material makes the high-power wind generator heavier and expensive, and brings
problem for operation and maintenance.
Because of the non-magnetic material in the stator, ironless permanent magnet generators
have negligible normal force between the rotor and the stator and the requirement to the
strength of the supporting structure is low. Therefore, the total generator weight can be low.
This is attractive in offshore direct drive energy conversion systems where lightweight
design is preferred.
The objective of this research is to systematically investigate different concepts of ironless
permanent magnet generators. A design strategy is developed and codes for finite
element analysis are embedded to ensure the simulation accuracy. A genetic algorithm is
employed to find the optimum designs in terms of lowest active mass, lowest cost of active
mass and highest efficiency. The influence of machine type and diameter to the machine
performances is presented and discussed. Furthermore, the lab test of an ironless axialflux permanent magnet generator confirms the effectiveness of this design strategy, and
the comparison to the parametric study is conducted to demonstrate the excellent
performance of the genetic algorithm used.
The next step of this research is to investigate the feasibility and performance of employing
high performance computing technology to assist the multi-physics analysis of electrical
machines. At the moment, an open-source coded has been installed the supercomputer
with the help of HPC center, NTNU.
37
Dr. ingeniørs/PhD graduated at Department of Electric Power Engineering, NTNU,
from 1990
Year
2013
Name
Torres Olguin, Raymundo Grid Integration of Offshore Wind Farms using Hybrid HVDC
Transmission Control and Operational Characteristics
Wei, Yingkang
2012
2011
2010
2009
Title
Propagation of Electromagnetic Signal along a Metal Well in an
Inhomogenous Medium
Yordanov, Georgi Hristov Characterization and Analysis of Photovoltaic Modules and the Solar
Resource Based on In-Situ Measurements in Southern Norway
Abuishmais, Ibrahim
SiC Power Diodes and Juction Feild-Effect Transistors
Zhang, Shujun
Percussive Drilling Application of Translation Motion Permanent
Magnet Machine
Ruiz, Alejandro Garces
Design, Operation and Control of Series-connected Power Converters
for Offshore Wind Parks
Jaehnert, Stefan
Integration of Regulating Power Markets in Northern Europe Offshore
Wind
Tesfahunegn, Samson G.
Fuel Cell Assisted Photo Voltaic Power Systems
Farahmand, Hossein
Integrated Power System Balancing in Northern Europe
Models and Case Studies
Suul, Jon Are
Control of Grid Integrated Voltage Source Converters under Unbalanced
Conditions – Development of an On-line Frequency-adaptive Virtual
Flux-based Approach
Marvik, Jorun Irene
Fault localization in medium voltage distribution networks with distributed generation
Krøvel, Øystein
Design of Large Permanent Magnetized Synchronous
Electric Machines – Low Speed, High Torque Machines – Generator for
Direct Driven Wind Turbine –
Motor for Rim Driven Thruster
Chen, Anyuan
Investigation of PM machines for downwhole applications
Chiesa, Nicola
Power Transformer Modeling for Inrush Current Calculation
Danielsen, Steinar
Electric Traction Power System Stability
Low-frequency interaction between advanced rail vehicles and a rotary
frequency converter
Nordgård, Dag Eirik
Risk Analysis for Decision Suppurt in Electricity Distribution System
Asset Management
Greiner, Christopher
Johan
Sizing and Operation of Wind-Hydrogen Energy Systems
Eek, Jarle
Power System Integration and Control of Variable Speed Wind
Turbines
Kulka, Arkadiusz
Sensorless Digital Control of Grid Connected Three Phase Converters
for Renewable sources
Guidi, Giuseppe
Energy Management Systems on Board of Electric Vehicles, Based on
Power Electronics
2008
2007
2006
2005
2004
2003
2002
Pedersen, Per Atle
Forces Acting on Water Droplets in Electrically Energized Oil Emulsions; Observations and Modelling of Droplet Movement Leading to
Electrocoalenscence
Østrem, Trond
Reliable Electric Power Conversion for Connecting Renewables to the
Distribution Network
Skjellnes, Tore
Digital Control of Grid Connected Converters for Distributed Power
Generation
Næss, Bjarne Idsøe
Operation of Wind Turbines with Doubly Fed Induction Generators
During and After Line Voltage Distortions
Belsnes, Michael Martin
Optimal Utilization of the Norwegian Hydropower System
Helseth, Arild
Modelling Reliability of Supply and Infrastructural Dependency in
Energy Distribution systems
Di Marzio, Giuseppe
Secure Operation of Regional Electricity Grids in Presence of Wind
Power Generation
Gullvik, William
Modeling, Analysis and Control of Active Front End (AFE) Converter
Andreassen, Pål
Digital Control of a Zero Voltage Switching Inverter for distributed
Generation of Electrical Energy
Hoff, Erik
Stjernholm
Status and Trends in Variable Speed Wind Generation Topologies
Løken, Espen
Multi-Criteria Planning of Local Energy Systems with Multiple Energy
Carriers
Ericson, Torgeir
Short-term electricity demant response
Mauseth, Frank
Charge accumulation in rod-plane air gap with covered rod
Maribu, Karl
Magnus
Modeling the Economics and Market Adoption of
Distributed Power Generation
Catrinu, Maria
Decision-Aid for Planning Local Energy Systems.
Application of Multi-Criteria Decision Analysis
Hellesø, Svein Magne
Dynamic analysis and monitoring of power transmission cables using
fibre optic sensors
Lund, Richard
Multilevel Power Electronic Converters for Electrical Motor Drives
Bjerkan, Eilert
High Frequency Modeling of Power Transformers Stresses and Diagnostics
Vogstad, Klaus-Ole
A system dynamics analysis of the Nordic electricity Market: The transition from fossil fuelled toward a renewable supply within a liberalised
electricity market
Øvrebø, Sigurd
Sensorless control of Pemanent Magnet Synchronous Machines
Kristiansen, Tarjei
Risk Management in Electricity Markets Emphasizing Transmission
Congestion
Korpås, Magnus
Distributed Energy Systems with Wind Power and Energy Storage
Botterud, Audun
Long Term Planning in Restructured Power Systems: Dynamic Modelling of Investments in New Power Generation under Uncertainty
Ettestøl, Ingunn
Analysis and modelling of the dynamics of aggregate energy demand
Kolstad, Helge
Control of an Adjustable Speed Hydro Utilizing Field Programmable
Devices
2001
2000
1999
1998
1997
1996
1995
Norheim, Ian
Suggested Methods for Preventing Core Saturation Instability in
HVDC Transmission Systems
Warland, Leif
A Voltage Instability Predictor using Local Area Measurements. VIP++
Ruppert, Christopher
Thermal Fatigue in Stationary Aluminium Contacts
Larsen, Tellef Juell
Daily Scheduling of Thermal Power Production in a Deregulated Electricity Market
Kleveland, Frode
Optimum Utilization of Power Semiconductors in High-power Highfrequency Resonant Converters for Induction Heating
Myhre, Jørgen Chr.
Electrical Power Supply to Offshore Oil Installations by High Voltage
Direct Current Transmission
Oldervoll, Frøydis
Electrical and thermal ageing of extruded low density polyethylene
insulation under HVDC conditions
Doorman, Gerard
Peaking capacity in Restructured Power Systems
Hystad, Jan
Transverse Flux Generators in Direct-driven Wind Energy converters
Pleym, Anngjerd
EMC in Railway Systems. Coupling from Catenary System to Nearby
Buried Metallic Structures.
Gjerde, Oddbjørn
Systemanalyser av skipselektriske anlegg
Evenset, Gunnar
Cavitation as a Precursor to Breakdown of Mass-Impregnated HVDC
Cables
Hvidsten, Sverre
Nonlinear Dielectric Response of Water Treed XLPE Cable Insulation
Pálsson, Magni Tor
Converter control design for Battery Energy Storage systems applied in
autonomous wind/diesel systems
Warland, Geir
Flexible transfer limits in an open power market.
Congestion versus risk of interruption.
Hans Kristian Høidalen
Lightning-induced overvoltages in low-voltage
systems.
Selvik, Eirik
Information models as basis for computer-aided tools.
Huse, Einar Ståle
Power generation scheduling
A free market based procedure with reserve constraints included.
Bjørn Harald Bakken
Technical and economic aspects of operation of thermal and hydro
power systems.
Ole-Morten Midtgård
Construction and assessment of hierarchal edge elements for threedimensjonal computations of eddy currents.
Qing Yu
Investigation of dynamic control of a unified power flow controller by
using vector control strategy.
Gerd Hovin Kjølle
Power supply interruption costs: Models and methods incorporating
time dependent patterns.
Tom Fagernes Nestli
Modelling and Identification of Induction Machines
Bjørn Sanden
XLPE cable insulation subjected to HVDC stress.
Space charge, conduction and breakdown strenth
Gisle Johannes Torvetjønn
Switchmode Powersupplies
Optimum topologies and magnetic components
Lars Arne Aga
A Laboratory Platform for Theoretical and Experimental Research on
Rotor Flux Oriented Control of Motor Drives.
1994
1993
1992
1991
1990
Knut Styve Hornnes
A Model for Coordinated Utilization of Production and Transmission
Facilities in a Power System Dominated by Hydropower
Rolf Ove Råd
Converter Fed Sub Sea Motor Drives
Snorre Frydenlund
A study of voltage stresses in ARC furnace transformers due to switching operations
Anne Cathrine Gjærde
Multifactor Ageing of Epoxy - The Combined Effect of Temperature
and Partial Discharge
Arne Nysveen
A Hybrid Fe-Be Method for Time Domain Analysis of Magnetic Fields
Involving Moving Geometry
Feng Xu
Power System Security Assessment. Identification of Critical Contingencies and Outage Distance by a Zone Filter
Bjørn Alfred Gustavsen
A study of overvoltages in high voltage cables with emphasis on sheath
overvoltages.
Svein Thore Hagen
AC breakdown strength of xlpe cable insulation
Olve Mo
Time Domain Simulation and Modelling of
Power Electronics Circuit.
Development of a Simulation Tool
Terje Rønningen
Internal faults in oil-filled distribution transformers.
Fault mechanisms and choice of protection.
Gorm Sande
Computation of Induced Currents inTthree Dmensions
Per Hveem
Computer Aided Learning, Simulations, and Electrical Motor Drives.
Ståle Johansen
Energy resource planning a conceptual study of a multiobjective problem.
Astrid Petterteig
Development and Control of a Resonant DC-link Converter for Multiple Motor Drives
Bendik Storesund
Resonant overvoltage transients in power systems
Jonny Nersveen
Kvalitetskriterier og helhetlig planlegging av innendørs belysningsanlegg.
Torbjørn Strømsvik
Kraftelektronikk som kilde til forstyrrelser i fordelingsnettet.
Alf Kåre Ådnanes
High Efficiency, High Performance Permanent Magnet Synchronous
Motor Drives
Eilif Hugo Hansen
Bruk av kunstig lys og lysmanipulering for styrt produksjon av laksefisk.
Guijun Yao
Modelling, Dynamic Analysis and Digital Control of PWM Power
Converters