PhD projects - Institutt for elkraftteknikk - NTNU · Since the PhD projects represent the main...

PhD projects Department of Electric Power Engineering

May 2012

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Postadresse: Besøksadresse: Telefon +47 73 59 42 10 N-7491 Trondheim O. S. Bragstads pl..2E, Telefaks +47 73 59 42 79 http://www.ntnu.no/elkraft N-7034 Trondheim

An overview over PhD Projects 2012

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 41 students are registered in our PhD program. This number is now peaking after a steady growth for several years, reflecting the increased general interest in energy and electric power from renewable resources. The department has 11 professors, three associate professors, and seven adjunct professors. The number of Postdocs has increased the last few years from zero to four and three more are employed as guest researchers. 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 booked within 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, 1 May 2012 Hans Kristian Høidalen Professor

Table of contents

Name

Title p

Aanensen, Nina Sasaki Load Current Interruption in Air for 12/24 kV systems 1 Agheb, Edris Simulation and design of high frequency high power transformers 2 Aigner, Tobias System Impacts of Large Scale Wind Power 3 Bahirat, Himanshu Collection System Design for DC Series Wind Farms 4 Barrera, C. R. Alexander

Multi-Domain Optimization Model for Evaluation of Power Density and Efficiency of Wind Energy Conversion Systems

5

Farahmand, Hossein Integrated Power System Balancing in Northern Europe – Models and Case Studies

6

Garcés Ruiz, Alejandro Design, Operation and Control of series-Connected Power Converters for Offshore Wind Parks

7

Gebrekiros, Yonas T Exchange of Balancing Services 8 Gjerde, Sverre S. Integrated converter design with generator for weight reduction

of offshore wind turbines 9

Haileselassie, Temesgen Mulugeta

Control, Dynamics and Operation of Multiterminal VSC-HVDC 10

Hillberg, Emil Models and methods for risk analysis of extraordinary events 11 Holtsmark, Nathalie Wind Energy Conversion using High Frequency Transformation

and DC Collection 12

Hosseini, Seyed M. A. Power System Analyses and Transmission Planning in a Competitive Environment

13

Hølto, Jorunn Electrical treeing in syndiotactic polypropylene 14 Ishengoma, Fredrick M.

A DSP-based control for optimal operation of a stand-alone Photovoltaic Power System

15

Jaehnert, Stefan Balance Management in Multinational Power Markets 16 Jafar, Muhammad Electrical Systems for Offshore Wind Parks: From the Generator

to the Grid Connection onshore 17

Jelani, Nedeem Investigating Stability in the Future Electrical Grid Dominated by Power Electronics

18

Jensen, Joachim Dahl Impact of Short Term Effects on Long Term Hydro Scheduling 19 Jonsson, Erik Load current interruption in air 20 Kile, Håkon Evaluation, classification and grouping of operational states 21 Klæboe, Gro Stochastic short term optimization of hydro power production 22 Larsen, Camilla Thorrud

Long-Term hydropower scheduling using stochastic dual dynamic programming (SDDP)

23

Lindberg, Karen Byskov

The impact of ZEB buildings on the overall energy system 24

Nademi, Hamed Advanced Control of Power Converters 25 Nge, Chee Lim Energy Management System for PV/Battery System 27 Nguyen, Dung Van Experimental studies on streamers of electrical prebreakdown

and breakdown phenomena in long electrode gap 28

Olsen, Pål Keim Long term performance of insulation materials exposed to DC superimposed AC voltage

29

Preda, Traian Nicolae Stability requirements for distributed generators 30 Røkke, Astrid Investigation of permanent magnet synchronous machines with

fractional slot windings for use in renewable energy applications 31

Sanchez A. Santiago Identifying electrical instability in grids dominated by power electronics

32

http://129.241.31.118/telefon/FMPro?-db=telefonliste.fp5&-lay=web&-sortfield=navn&Tittel=phd&-skip=11&-Format=telefonkort.htm&-Lay=web&-max=1&-Find

http://129.241.31.118/telefon/FMPro?-db=telefonliste.fp5&-lay=web&-sortfield=navn&Tittel=phd&-skip=11&-Format=telefonkort.htm&-Lay=web&-max=1&-Find

Schimpf, Fritz New Concepts for Converters and Control of Photovoltaic Systems

33

Shailendra Kumar, Jha Interconnection and Control of Micro Grids 34 Sjolte, Jonas Skar, Christian Modelling of European energy markets for low emission

scenarios 35

Soloot, Amir Hayati Switching Transient in Offshore Wind Farms 36 Toh, Chuen Ling Advanced Monitoring and Control in Power Electronics Converter

for Future Energy Efficient Marine Power system 37

Torres Olguin, Raymundo E.

Use of HVDC multi-terminal VSC and CSC options to incorporate offshore wind or wave power to the Norwegian grid

38

Tønne, Erling Active distribution grids – concepts, architecture and functionality

39

Valavi, Mostafa Magnetic Forces and Vibrations in Wind Power Generators 40 Ve, Torbjørn Effect of Moisture on Space Charge Accumulation in Polymeric

HVDC Cable Insulation 41

Vrana, Til Kristian Development and operation of the North Sea super grid 42 Yordanov, Georgi Hristov

Performance of Different Photovoltaic Modules in Southern Norway

43

Zadeh, Mehdi K. Identification of Potential Instability in AC Distributed Multi-converter System under Non-ideal Electrical Conditions

44

Zahedi, Bijan Integrated Marine Electrical Power and Control Systems 45 Zhang, Zhaoqiang Coupled 3D models of large-diameter permanent magnet

generators and its loss calculation 46

PhD graduated from 1990

47

Nina Sasaki Aanensen Home Country: Norway

Year of Birth: 1987

Email: [email protected]

Home Page: www.ntnu.no/employees/nina.aanensen

Master Degree: MSc Applied Physics and Mathematics,

2011

University: 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 effects of different geometries, gas pressures, nozzle materials and other parameters of air insulated load break switches. Using the newly built high current / switchgear laboratory at NTNU, experiments can be performed 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 performed in order to study the gas flows in load break switch geometries. In these simulations, geometrical parameters such as nozzle length and shape can be studied, as well as the effect of different gas pressures. The simulations will give some supplemental information to the experiments.

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: Iran Year of Birth: 1984 Master Degree: Electrical Engineering University: Tehran University Graduation Year: 2009 Research Group: Electric Power Technology Supervisor: Hans Kristian Hoidalen PhD Start: 2009 Phone: +47 735 94233 Email: [email protected] Home Page: 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

mailto:[email protected]

Tobias Aigner Home Country: Germany

Year of Birth: 1979


Master Degree: Automotive Engineering, Electrical

Engineering

University: University München, University Hagen.

Graduation year: 2005. 2008

Supervisor: Terje Gjengedal

Research Group: Electric Power Systems

System Impacts of Large Scale Wind Power

The European Commission proposal for 20% renewable energy by 2020 paves the way for a massive expansion of wind energy and a new energy future for Europe. To reach the goal wind energy is a key technology and large scale integration is required both onshore and offshore. This represents heavy challenges to the power system requiring new ways of designing and operating the system. Especially large scale offshore wind power will require attention to new focus areas. The wind may be more stable offshore, but there will be less geographical smoothing effect, so wind variations will still be a key issue. Power transmission and grid connection represent other main challenges for realisation of large scale wind power, and especially for offshore wind farms. The influences and impacts of large scale wind power production on the Nordic system and on single parts of the EU have already been discussed and are well covered. According to these analyses, feed in fluctuation caused by wind speed variations, may affect the reserve requirements as well as the system reliability on a short and long term basis. Using the interconnected European grid may offer advantages in balancing the variable energy production from renewable energy and reduce reserve requirements in the different areas. The variability of wind power production as well as the zero output occurrences are reduced in a large interconnected system, due to the spatial separation between the production units, while the output predictability can be increased. The scope of this fellowship is how to handle a growing amount of wind power and how to find an efficient and secure design and assure a stable operation of the overall system. The objective is to assess the variations in wind power production on a short term basis, including gradients and smoothing effects depending on geographical separation of the wind farms and how these effects may affect the system operation (operation planning, balancing control and reserve management).

3

Himanshu J. Bahirat Home Country: India

Year of Birth: 1981


Visiting PhD student from Michigan Technological University,

USA

Master Degree: MS Electrical Engineering, 2009

University: Michigan Technological University, USA

Supervisor: Dr.Bruce Mork (MTU)/ Hans Kr. Hoidalen(NTNU)


Project: High Frequency Wind

Collection System Design for DC Series Wind Farms

Increasing energy demand and environmental factors are driving the need for the green energy sources. The trend, in general, with respect to wind farms is to increase the number and the size of wind farms. The wind farms are also being located offshore with the prospect of more consistent and higher energy capture. The offshore wind farms are likely to move farther off from the shores to reduce visual impacts and increase the size. But, this has implications in terms of design of the collection grid and grid interconnection. Farms of 1 GW size and at distances of about 100 km are envisaged. The project aims to explore design considerations, operation and control of DC wind farm with series connected wind turbines. The turbines are expected to produce high voltage DC and use a high frequency transformer weight reduction. Control and operation of the wind farm can be challenging and faults in DC system could be difficult to handle, given that the DC interruption devices are in state of development. Project further explores fault behavior of the series wind farms.

Collection System

Transmission (XSM) System

DC wind Turbine

+

Circuit Breaker

+ + +X X X XX X

+

Onshore Grid

DC

AC

4

Rene Alexander Barrera Cardenas Home Country: Colombia Year of Birth: 1982 Email: [email protected] Home Page: http://www.ntnu.edu/employees/rene.barrera Master Degree: MSc Electrical Engineering, 2006 University: 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 High frequency link

Efficiency and Power Density evaluation of the WECS including

parameter variation (Converter Topology, transf. material, link freq.)

PMSG

PMSG

PMSG

PMSG

GEARBOX

AC

DC

AC

DC

AC

DC

ACDC

AC

ACAC Link

3-phase or 1-phase

H.F.Transformer

Diode RectifierConverter

AC/DC Converter Module

0 0.2 0.4 0.6 0.8 1 1.2 1.475

80

85

90

95

100

Power Density [KW/dm3]

Effic

iency [%

]

B2B (FINEMET)

B2B (MAGNAPERM)

B2B(Ferrite(Ni-Zn))

MC (FINEMET)

MC (MAGNAPERM)

MC(Ferrite(Ni-Zn))

IMC (FINEMET)

IMC (MAGNAPERM)

IMC (Ferrite Ni-Zn)

B2B1p (FINEMET)

B2B1p (MAGNAPERM)

RMC (POWERLITE)

RMC(FINEMET)

RMC(MAGNAPERM)

RMC(Ferrite Mn-Zn)

RMC(Ferrite Ni-Zn)

5

Hossein Farahmand Home Country: Iran Year of Birth: 1979 Email: [email protected] Master Degree: MSc Electrical Engineering, 2005 Supervisor: Gerard L. Doorman Research Group: Electric Power Systems Co-Supervisor(s): Olav Bjarte Fosso Project: Balance Management in Multinational Power Markets Integrated Power System Balancing in Northern Europe - Models and Case Studies Maintaining a continuous balance between generation and load is crucial for the safeguarding of the power systems. In order to effectively deal with the various uncertainties that contribute to the real-time imbalance in liberalised power systems, Transmission System Operators (TSOs) procure and employ the so-called balancing services through balancing markets. In Europe, though such mechanisms are well in place at the national level, the potential of multinational balancing markets has not been fully exploited (with the exception of the Nordic system and various pilot projects). This research analyses the potential for integrating the balancing power markets in northern Europe, including the Nordic system, Germany and the Netherlands. It addresses the twin issues of the procurement and employment of cross-border balancing services by using mathematical models. The methodology developed in the research work enables the study of the benefits of integrating the northern European balancing markets, and the resulting exchange of balancing services among the Nordic countries, Germany and the Netherlands. The multinational balancing market can be adapted to capture the effect of different market integration scenarios. The presented modelling approach includes a flow-based market model, which takes into account physical power flows and loop flows, especially suitable for the European systems with highly meshed transmission grids. A four tiered sequential approach is used to organize the primary contributions of the research work, as highlighted by the four distinct publications arising out of it.

• Tier 1: An optimal methodology for reserve activation in the Nordic system is established. • Tier 2: Using the first tier as the basis, a cross-border reserves procurement algorithm is

proposed for an integrated European system. Superimposing Tier 2 on Tier 1 results in a bottom-up approach of capturing the full spectrum of reserve procurement and activation for integrated balancing markets.

• Tier 3: The profitability of balancing market integration is brought forward through both weekly and yearly analysis on the basis of mathematical models developed in Tier 1 and 2.

• Tier 4: It is shown that the flexibility concerns warranted by penetration of renewable energy resources can be well addressed by using the developed framework of cross-border balancing market integration. A case study of a future power system (in 2030) with wind energy penetration has been employed in this regard.

The results include the optimal distribution of balancing reserve capacity allocations for procurement among the constituent countries, and the optimal exchange of balancing energy that ensues upon activating these capacity reserves. An annual analysis of the post-integration scenario results demonstrates the significant cost savings that are achievable under the framework of multinational balancing markets. The results also demonstrate the potential for increased production flexibility, in light of increased wind energy penetration in the future operation of power systems through the mechanism of multinational balancing markets.

6

1

Design, Operation and Control of Series-ConnectedPower Converters for Offshore Wind Parks

PhD candidate: Alejandro Garces Ruiz ([email protected])Advisor: Marta Molinas ([email protected])

OFFSHORE wind farms deal with new challenges andrequirements from the power systems and power elec-

tronics point of view, namely:Size and weight reduction: each component placed off-

shore represents high investment and operative cost due tothe transportation of replacement parts from shore to theemplacement and the construction of supporting platforms.

Efficiency: Long distances are expected in offshore windfarms and hence, losses must be minimized in the convertersand the transmission lines. HVDC is the most suitable technol-ogy in these conditions, but the offshore grid topology and theconverters must be optimized for their particular conditions.

Reliability: Maintenance and replacement of componentsrepresent high transport costs. Accordingly, the reliability ofthe components themselves as well as the grid topology mustbe optimized.

The objective of this research is to face these three chal-lenges by using a new topology of high frequency link (HFL)and series connection of wind turbines. The project studiesnot only topologies and new modulation strategies but alsothe coordinated operation of the complete system by a nonlinear optimization model. The general approach of the projectconsist of theoretical and experimental investigation.

The proposed HFL is depicted in Fig 1. The main compo-nent of this new topology is a matrix converter which is anAC/AC converter without intermediate DC stage.

|3

Clamp

Generator

Reduced matrix converter

High frequency transformerFull-bridge (diode)

Nacelle

Fig. 1. Proposed high frequency link (HFL)

The HFLs are connected in series as shown in Fig 2.The advantages of this topology include the elimination ofthe centralized support platform and the reduction of the

HFL

HFL

HFL

Hig

hVo

ltage

Platform

Fig. 2. Series connected offshore wind farm

transmission losses. However, it carries some technologicalchallenges which need to be further studied: variation inthe wind velocity causes variations in the output power andtherefore in the output voltage. Therefore, a wide variationcapability of the output voltage is required in each turbineand an optimal power flow must be developed.

An experimental prototype was developed in order to profthe concept (see Fig 3). Numerical simulations as well asanalytical calculations have demonstrated the advantages ofthis converter and the consequences of series connection.

Fig. 3. Experimental set-up

More information about this project inhttp://www.ntnu.no/ansatte/alejan

7

Yonas Tesfay Gebrekiros

Home Country: Ethiopia Year of Birth: 1983 Master Degree: MSc. Electrical Engineering University: Delft University of Technology Graduation year: 2009


Supervisor: Gerard L. Doorman Co-Supervisor(s): Ivar Wangesteen, Kjetil Uhlen

Email: [email protected] Phone: +47 73594252 Home Page: 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.

8


http://www.ntnu.no/ansatte/yonas.gebrekiros

Sverre Skalleberg Gjerde Home Country: Norway Year of Birth: 1984 Master Degree: Electrical Engineering University: NTNU Graduation Year: 2009 Research Group: Energy Conversion Supervisor: Prof. Tore Marvin Undeland PhD Start: 2009 Phone: +47 7359 4229 Email: [email protected] Home Page: www.ntnu.no/ansatte/sverre.gjerde

Integrated converter design with generator for weight reduction of

offshore wind turbines

Recent years have shown an increasing interest in offshore wind power. This is due to better, more stable wind conditions and less environmental impact than found onshore. As a result of the offshore conditions, large turbines have been pointed out as more beneficial than many small. However, larger turbines means higher current ratings, and therefore it is crucial 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 design a converter, which together with an Ironless Axial Flux Permanent Magnet (I-AFPM) - generator, will eliminate the need for a distribution transformer. A modular converter topology, consisting of 9 standard 3-phase voltage source converters has been identified as a suitable topology. The figure shows a sketch of the proposed generator/converter system. Estimates indicate that an output of 100 kV DC is achievable, without compromising the generator weight. A modular control system, operating in master/slave configuration, has been proposed for this system, and its stability and robustness has been assessed. One of the major benefits of the proposed control is that it can reuse many of the standard components from a standard, 3-phase generator/converter control. An additional advantage of the proposed drive system is the possibility to implement redundancy. A 50 kW laboratory model of the drive will be constructed. This will both be used as proof of concept, and for verification of simulation models developed for studying the system. The project does also include studies on the challenges related to integration into a DC-distribution grid.

0

AC

DC

AC

DC

DC grid

AC

DC

AC

DC

///

///

///

///

Module 1

Module 9

+

11.1 kV

-

+

11.1 kV

-

+

11.1 kV

-

+

100 kV

-

+

11.1 kV

-

Module 8

Module 2

Vll 6.8 kV

Vll 6.8 kV

Vll 6.8 kV

Vll 6.8 kV

Fig: Overview of the

generator/converter system

9

Temesgen M. Haileselassie Home Country: Ethiopia

Year of Birth: 1982


http://www.ntnu.no/ansatte/temesgen.haileselassie

Master Degree: MSc Electrical Engineering, 2008

University: NTNU

Supervisor: Prof. Kjetil Uhlen


Co-Supervisor(s): Prof. Tore undeland

Project: Norwegian Research Council Project

Control, Dynamics and Operation of Multiterminal VSC-HVDC

In recent years there have been several activities towards developing large scale offshore wind farms

especially in Europe. This in turn has increased the need for new ways of grid integration

technologies that enable maximized utilization of the variable wind energy in economically feasible

and technically reliable ways. The use of multi-terminal VSC-HVDC grid has been suggested in the

literature as a promising candidate technology for such an application. The PhD research work deals

with proposing best methods for controlling and operating multterminal VSC-HVDC and also analysis

of the dc grid dynamics and its interaction with ac grids.

Fig: Multiterminal VSC-HVDC scenario in the North Sea

10

Emil Hillberg Home Country: Sweden

Year of Birth: 1975


Home Page: www.ntnu.edu/employees/emil.hillberg


University: KTH Royal Institute of Technology

Stockholm

Supervisor: Professor Kjetil Uhlen


Co-Supervisor: Adjunct Professor Gerd Kjølle

Project: Vulnerability and security in a changing power system

Models and methods for risk analysis of extraordinary events

Increased understanding of extraordinary events in the electrical power system is vital to develop risk analysis models and methods, and to implement appropriate remedies in order to limit the presence and consequences of such events in the future. In this thesis, extraordinary events are classified and structured. The transition from stable to unstable operation is identified as the critical point in an extraordinary event, and is defined as the undesired event. Furthermore, a methodology to analyse the risk of extraordinary events is described, and measures to mitigate and quantify the risk of extraordinary events are presented. To be able to identify undesired events, and to compute the risk indices, multi-level dynamic contingency analyses are required, with dynamic models and study tools are prerequisites. The thesis also includes models developed for performing benchmark analyses of the risk of extraordinary events.

Power flow on PTCI

N – 1 Secure operation

Actual operation

N – 1N – 2N – 3N – k

Secure operation

Actual operation

SIPS security enhancement

N – 1N – 2N – 3N – k

Secure operation

Actual operation

Power flow on PTCI Power flow on PTCI

Power flow on PTCII Power flow on PTCII Power flow on PTCII

Conceptual visualisation of the secure operating region, illustrating impact of single- and multiple-contingencies as well as System Integrity Protection Schemes (SIPS); to appear in: Hillberg, et al., System Integrity Protection Schemes – Increasing operational security and system capacity, 44th CIGRE Session, August 2012, Paris, France

11

http://www.ntnu.edu/employees/emil.hillberg

Nathalie Holtsmark

Home Country: Norway Year of Birth: 1986

Master Degree: Electrical Engineering University: NTNU Graduation Year: 2010

Research Group: Energy Conversion Supervisor: Marta Molinas PhD Start: August 2010

Phone: +47 73594228 Email: [email protected] Home Page: http://www.ntnu.no/ansatte/nathalie.holtsmark

Wind Energy Conversion using High Frequency Transformation and DC Collection

The offshore wind farms are growing in size and being placed farther away from shore. From that perspective, HVDC collection and transmission system will become more advantageous, if not the only alternative, as important losses in long AC cables are eliminated. The BARD 1 wind farm (400 MW), 100 km off the coast of Germany, is currently under construction and is the first offshore wind farm that will be connected via an HVDC transmission system.

In parallel the semiconductor industry is making ever improving progress and are now producing switching devices, the reverse blocking IGBT, that increase substantially the efficiency of matrix converter. As a consequence, the matrix converter is rising up as a strong candidate for wind energy conversion due to its many advantages: independently controllable sinusoidal input current and output voltages, potentially high reliability and small size and weight due the elimination of the DC link capacitor needed in conventional back-to-back converter. There exist many different possible matrix converter topologies: conventional matrix converter, indirect matrix converter, sparse matrix converter, reduced matrix converter, etc…

The matrix converter in combination with a high frequency transformer for galvanic isolation and an efficient AC to DC converter yields an overall energy conversion system compact enough to fit inside the nacelle of the wind turbine. In this research work the three above-mentioned technologies will be combined to conceive a state of the art wind energy conversion system that is suitable for small or large offshore wind farms that are located far from shore.

A total of three PhD students will be working on this project, funded by the Norwegian Research Council and the RENERGI Program. My specific research work will be to select and make simulation models and eventually a prototype of the optimal matrix converter topology in terms of efficiency, reliability, volume and cost as well as the AC-DC conversion system.

12


http://www.ntnu.no/ansatte/nathalie.holtsmark

SeyedMohammadAliHosseiniHome Country: Iran

Year of Birth: 1983


Home Page: www.ntnu.edu/employees/seyed.hosseini


University: Eastern Mediterranean University (EMU)

Supervisor: Olav Bjarte Fosso


Co‐Supervisor(s): ‐

Project: KMB project

PowerSystemAnalysesandTransmissionPlanninginaCompetitiveEnvironment

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.

13

Jorunn Hølto


Master Degree: Physics University: NTNU Graduation Year: 2007

Research Group: Electric Power Technology Supervisor: Erling Ildstad PhD Start: 2008

Phone: +47 73594235 Email: [email protected] Home Page: www.elkraft.ntnu.no/~holto

Electrical Treeing in Syndiotactic Polypropylene Syndiotactic polypropylene (s-PP) is being considered as an alternative extruded high voltage cable insulation, particularly for high temperature cable applications. Cross-linked polyethylene (XLPE) is normally used, but its operation temperature is limited to 90 °C. s-PP has melting point at 130 °C and low dielectric losses. In capacitors it is common to use isotactic polypropylene (i-PP), but this material has a high elasticity modulus which would make extruded cables stiff and hard to handle. s-PP has lower elasticity modulus, reducing these problems.

Electrical tree growth is the main pre-breakdown mechanism in polymeric insulation materials. It is typically initiated at a field-enhancing void or impurity, a situation which in experiments is approximated by using a needle-plane geometry. The formation of an electrical tree is characterised by three main phases: Initation, propagation and breakdown. For the experiments moulded samples with needle-plate distance of 1.05 mm is used, applying 8-12 kV 50 Hz AC voltage. Two main types of trees are observed: Branched trees with either one or multiple branches to the ground electrode before breakdown. The latter tree type is shown in Figure 1, where the width of tree can grow to 2-3 times the needle-plane distance.

The focus of this work is to study electrical tree growth in s-PP, quantifying it in terms of tree structure, propagation rate and time to breakdown. In addition, the purpose is to examine a possible correlation between mechanical properties, morphology and electrical tree growth. For comparison samples of s-PP was made with two different cooling rates, which significantly effects the tensile strength and morphology. However no significant difference in time to breakdown was found. A quality of i-PP is included in the study, which have 50% higher tensile strength than s-PP. Generally the time to breakdown in s-PP was lower than for i-PP, and there was more variation in the results. The effect of higher and lower frequencies will further be included in the study.

Figure 1 Electric tree with multiple branches to the ground electrode, grown in s‐PP.

14

Fredrick M. Ishengoma Home Country: Tanzania, East Africa

Master Degree: MSc in Control Engineering

University: Bradford University (UK) Graduation Year: 1988

Research Group: Energy Conversion Supervisor: Prof. Lars Norum PhD Start: 2009

Phone: +47 7359 4242 Email: [email protected] Home Page: http://www.elkraft.ntnu.no/eno/staff.html

A DSP-based control for optimal operation of a stand-alone Photovoltaic

Power System Increasing demand for energy, decreasing conventional fossil-fuel energy sources, and environmental concerns are driving forces toward renewable energy sources. Photovoltaic (PV) energy is one of the most promising renewable energy source especially in developing countries where majority do not have access to electricity. Main advantages of PV energy includes reliability, low operating costs, non-polluting, modular, and availability. In stand-alone PV systems, main power sources are batteries and solar arrays. In order to reduce the cost of the energy generated, it is necessary to ensure that the system operates at Maximum Power Point (MPP) of the solar arrays. Premature failure of batteries in stand-alone power systems is normally attributed to poor charge controllers due to over-charge or over-discharge of batteries. This results in higher running costs of the system. A system to be controlled comprises of three converters. The first converter is for tracking the Maximum Power Point (MPP) of the solar panel, a second converter is for controlling charging and discharging the battery, and the third converter is for supplying the power to AC loads. Coordination of the three converters is crucial for the reliability and cost effectiveness of the system. The research focuses on development of optimal operating strategies and testing the effectiveness of the developed strategies through simulation and experimental work. Prioritizing the loads connected to the system depending on the energy available is also studied. Due to advantages offered by digital control over analog control especially in the implementation of more complex control schemes, the control is implemented using a DSP.

15

Stefan Jaehnert Home Country: Germany Year of Birth: 1981 Master Degree: Mechatronics Engineering University: TU Chemnitz Graduation Year: 2007 Research Group: Power Systems Supervisor: Gerard L. Doorman PhD Start: 2008 Phone: +47 73550401 Email: [email protected] Home Page: http://www.elkraft.ntnu.no/~Jaehnert/

Balance Management in Multinational Power Markets With begin of the 1990s privatization and deregulation became a big topic in Europe and

electricity markets started to develop. The Initialization took place in England and Wales

(1989), followed by Norway (1990) and many other countries further on. The European

directives 96/92/EC and 54/EC aim to the integration of electricity markets in the member

states. Regulation 1228/2003 furthermore explicitly includes cross-boarder issues.

The Nordic electricity market (Nord Pool) is a common market ever since, as it was first

joined by Sweden and later by Finland and Denmark. In continental Europe coupled and

common markets are developing, most notably to mention the CWE-ITVC (including Nordic

and central-western Europe), which achieves a market coupling as far as from northern

Norway down to southern France.

With a European wide need for sustainable energy resources, especially resulting in an

increasing share of wind power, a higher balancing potential in the grid is needed. Moreover

there will be new HVDC cables connecting Scandinavia to continental Europe. These

developments can provide Norway with its high share of hydro power production the

possibility to become a supplier of balancing resources to the continental thermal based

system. Considering this aim, besides having a common day-ahead market, it will also be

necessary to integrate regulating power markets. Thus the project objective is to design the

scientific foundation of a framework for efficient, market-based balancing of power systems

that can be implemented in multinational power markets.

While the project objective is formulated in a general way, the actual focus is on the exchange

between southern Norway and northern continental Europe. In order to simulate the exchange

of balancing resources and investigate a possible outcome a model for a system wide

procurement of balancing resources as well as their activation is developed. The EMPS

model, developed at SINTEF, is used as the basis, describing a common European day-ahead

market. It evinces that there is a high potential of regulating resource exchange, resulting in a

significant reduction of the costs for reserve procurement and the system balancing.

16


http://www.elkraft.ntnu.no/~Jaehnert/

Muhammad Jafar

Home Country: Pakistan Year of Birth: 1975 Email: [email protected] Home Page: www.ntnu.edu/ansatte/muhammad.jafar Master Degree: Electrical Power Engineering University: University of Engineering & Technology,

Taxila, 2008 Supervisor: Prof. Marta Molinas Research Group: Electric Power Systems Co-supervisors: Prof. Shoji Nishikata (Tokyo Denki University, Japan) Dr. Noriko Kawakami (Toshiba Mitsubishi-Electric Industrial

Systems, Japan) Electrical Systems for Offshore Wind Parks: From the Generator to the Grid Connection Onshore Renewable energy sources are being considered increasingly as the concerns over global warming, energy security, and depletion of fossil fuel reserves grow. Of these, wind energy has grown considerably over the recent past throughout the world and is considered to have significant potential to replace conventional fossil fuel based electric power generation. As land is becoming scarce for installation of wind turbines, attention is being directed towards offshore wind-power production. Various offshore wind power plants are working successfully in the world right now. Norwegian North Sea has a huge wind power potential but the larger water depths are forcing researchers to consider floating wind turbines and grid integration structures.

Together with certain other factors, the issue of grid integration of this power into the onshore grid is also very critical. The available transmission options are ac and dc. The dc transmission option is more attractive when the transmission distance is above a certain length and this break-even distance is much shorter in the case of under-ground or under-sea cable transmission. The available options in dc transmission are the more mature line-commutated converter based HVDC (LCC HVDC) and relatively new voltage-sourced converter based HVDC (VSC HVDC). VSC HVDC has many virtues but this work is focused on the use of LCC HVDC mainly because of its lower losses, higher reliability, and higher voltage & power ratings than its younger counterpart.

The major obstacle to the application of this technology for integration of deep-sea offshore wind power is the large size of the ac/dc conversion terminal. This becomes more complicated when considering floating grid-integration structures. The main reasons for large converter terminal size are the fundamental-frequency reactive power- and harmonic compensation equipment. These are necessary because of the inherent reactive power and lower-order harmonic in such a terminal.

This project has suggested a series transformer-less reactive / harmonic compensation topology which caters to both the compensation demands with a minimum amount of power electronic switches and small capacitors. Simulation and experimental results have been obtained which show the adequateness of the topology in controlling the parameters that require large compensation equipment. This would lead to a compact conversion terminal lowering the cost of not only the electrical equipment but also that of grid-integration support platform. Smaller terminal size also points to the fact that this will make the transmission system more reliable than before therefore leading to lower down-time as well as lower maintenance costs.

17

Nadeem Jelani Home Country: Pakistan

Year of Birth: 1981


Home Page: www.ntnu.no/emploees/nadeem.jelani

Master Degree: MSc Electric Power Engineering, 2010

University: NTNU

Supervisor: Prof. Marta Molinas


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 will be used to develop a general system-level methodology and tool to investigate the stability of the AC power electronics systems with focus on constant power behavior. Understanding these phenomena will allow diagnosing system condition by the developed techniques, preventing grid emergency and system outage. In other words, this will mean a fundamental step towards a zero-outage system planning for the future development of smart grids. Alleviation of harmonics and current distortions caused by the non-linear load present at the distribution level by constant power loads is also the focus of this research. Another wide area open for this research is the use of constant power loads for unbalance voltage compensation to increase the working life of the generation systems within the smart grid. This will results in an increase in the efficiency and stability of the smart electrical grid.

System

=

Grid

GeneratorL

RP

L

LP

R

C

FixedCapacitor

=

RP

LP

R

C

Lg

Line to ground fault

PCC

CPL1 CPL2

L

STATCOM

RP

LP

Distribution

A

Induction

Rl,d

c

Ll,d

c

Non-linear Load

Power Electronics Dominated Grid with DG unit, CPLs and Non-linear Loads 18

Joachim Dahl Jensen


Master Degree: Industriell økonomi og teknologiledelse

University: NTNU Graduation Year: 2002

Supervisor: Gerard Doorman PhD Start: 2009

Phone: +47 73597367 Email: [email protected]

Impact of Short Term Effects on Long Term Hydro Scheduling

The project objective is to consider what adaptations are necessary to

prepare mid‐ and long‐term hydro power scheduling tools for a power

system with increased production volatility combined with an increased level

of restrictions on production.

Increased production volatility is likely to be caused by an increasing amount

of non‐regulated renewable power production and/or increased exchange

capacity with European power systems.

An increased level of restrictions is caused by local environmental concerns,

e.g. as prescribed by the EU Water Framework directive.

19

Erik Jonsson

Home Country: Sweden Year of Birth: 1979

Master Degree: Solid State Physics University: Uppsala University Graduation Year: 2006

Research Group: Electric Power Technology Supervisor: Magne Runde PhD Start: 2008

Phone: +47 45010212 Email: [email protected] Home Page: 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.

20

Håkon Kile Home Country: Norway

Year of Birth: 1985


Home Page: www.ntnu.edu/employees/hakon.kile

Master Degree: MSc Physics and Mathematics, 2010

University: NTNU

Supervisor: Prof. Kjetil Uhlen


Co-Supervisor(s): Prof. Gerd Kjølle

Project: SAMREL WP2

Evaluation, classification and grouping of operational 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 operational states, described by generation, load and, network topology. These operational states are transferred to the contingency analysis, where the consequences of different contingencies are determined. The set of operational 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 operational states that needs to be analysed in the contingency analysis, while maintaining an adequate base for the reliability analysis.

21

Gro Klæboe Home Country: Norway Year of Birth: 1978 Master Degree: Economics University: NTNU Graduation Year: 2005 Research Group: Power Systems Supervisor: Olav Bjarte Fosso PhD Start: 2009 Phone: +47 7359 7367 Email: [email protected] Home Page: http://www.ntnu.no/ansatte/gro.kleboe

Stochastic short term optimization of hydro power production Stochastic optimization tools for hydro power production has been subject to research and put to industry use among Nordic hydro power producers since the 70’s. The deregulation of the power market in the 90’s created increased need for short term optimization tools. This led to the development of the deterministic optimization tool SHOP (by Sintef Energy research) and the implementation of this tool in industry. The increased integration of intermittent new renewable power sources in the power system and the increased transfer capacity and trade across national borders imposes new challenges to short term scheduling: More volatile prices and increased activity in intraday, balancing and capacity markets. Stochastic optimization models creates more robust strategies given uncertain scheduling conditions and are therefore preferred in this setting. My research focuses on price uncertainty and bidding strategies in the day-ahead spot market, intraday market and markets for ancillary services. Research topics include: - Probabilistic forecasts for price - Decomposition methods - Quantification of the gains of stochastic methods versus deterministic - Bidding strategies for multiple markets with similar or related products, but different time horizon

22

http://www.ntnu.no/ansatte/gro.kleboe

Camilla Thorrud Larsen Home Country: Norway

Year of Birth: 1980


Home Page: www.ntnu.no/emploees/camillla

Master Degree: Siv.ing. Industrial mathematics

University: NTNU

Supervisor: Prof. Gerard L. Doorman


Co-Supervisor(s): Birger Mo, Sintef Energy Research

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 multi-reservoir 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 sampling-based 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.

23

Karen Byskov Lindberg Home Country: Norway

Year of Birth: 1978

Email: [email protected], or [email protected]

Home Page: www.ntnu.no/employees/karen.lindberg

Master Degree: MSc Energy and Environmental Engineering, 2005

University: NTNU

Supervisor: Gerard Doorman


Co-Supervisor(s): Asgeir Tomasgard (IOT) and Igor Sartori (SINTEF Byggforsk)

Project: Part of the two FME-centres Zero Emission Buildings (ZEB) and Centre for

Sustainable Energy Studies (CenSES)

The impact of ZEB buildings on the overall energy system

The thesis will investigate the impact of zero emission buildings (ZEB) on the overall energy system through smart grid and demand side management (DSM). A zero emission building is one that has zero net carbon emission over its entire lifetime, including building & construction, operation and demolishing. In this thesis it is possible that the simplified definition, zero energy building, will be applied. The thesis is divided into three main parts:

(1) Investigating hourly load profiles for existing non-residential buildings. A regression analysis on up to 200-300 buildings will be performed to identify explanatory variables and their level of significance. E.g. building category, outdoor temperature, size (square metres), and existence of cooling or IT-servers.

(2) DSM and smart grid makes it possible for the consumer to optimize its own electricity load from the grid. Part (2) will consist of estimating hourly load profiles for ZEB buildings, both non-residential and residential. Either an optimization model or a prediction model based on the information on load profiles for existing buildings in Norway from part (1), combined with knowledge on European ZEB-buildings will be conducted. The optimization model will seek to optimize energy performance to least cost principle, according to various capital investment systems (storage, mini wind turbine and/or heat pumps) and fixed power prices. Alternatively, a prediction model is to be developed dependent on e.g. outdoor temperature and power market prices.

(3) The third part of the thesis will consist of analyzing the ZEB load profiles found in part (2) with an energy system model and a power market model. Analysis with the energy system model, the Norwegian TIMES-model, we seek to find impact on future production capital investments and transmission capital investments. Analysis with the power market model, the Nordic EMPS-model, we seek to find the impact on price formation in the power market.

The thesis will be performed on data for Norwegian conditions.

24



http://www.ntnu.no/employees/karen.lindberg

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: +47 7359 4271 Email: [email protected]

Home Page: www.ntnu.no/ansatte/hamed.nademi

Advanced Control of Power Converters Introduction Modular Multilevel Converter (MMC) is one of the most promising power converters for future high voltage drives. During the first two years, 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. Such a model is advantageous in many cases because it requires 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. The computation and study of Fourier series is known as harmonic analysis. In addition, in the next step a generalized small signal ac equivalent model is derived. For subsea applications both ruggedness and low losses are of vital importance. Making design for high reliability and high efficiency are two important challenges. Advanced and fault tolerant control methods will be applied to the control of power converters in order to minimize harmonic components, control resonances and to increase the reliability. Evaluation and power circuit topologies for fail tolerant and fail safe operation will be investigated and suitable controller architecture will be suggested. Laboratory prototypes for relevant applications have been specified and established in cooperation with PEC, (Power Electronic Center, Siemens). Before the final prototype at 10kW for the lab is built, it is advantageous and recommended to build a smaller prototype. This prototype can be rated at 500W. It can be used to verify the concepts quickly, make changes and can be a basis for further experiments. For building the smaller prototype, the following circuit will be followed (Fig.1). It consists of 3 cells in each arm. Each cell is fabricated on a PCB. The arm inductances are used to limit the circulating current. The resistances along with a bypass switch are used for initial charging of the capacitors. The load is a passive R-L load. Two pictures from the setup (Fig. 2 and Fig. 3) are included below to give an idea of the dimensions of the setup.

25


http://www.ntnu.no/ansatte

Fig. 1: Schematic of small laboratory prototype.

This PhD 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.

Fig. 2: A picture of the converter showing the different parts.

Fig. 3: Overall setup.

26

Chee Lim Nge Email: nge (at) elkraft.ntnu.no

Master Degree: Master of Engineering (Electical), 2005

University: Universiti Teknologi Malaysia

Home Country: Malaysia

Supervisors: Ole-Morten Midtgård and Lars Norum

Energy Management System for PV/Battery System

Energy storage unit such as battery array and pumped-storage hydroelectric power plant can be used to balance intermittent PV generation. It stores excess PV power when solar irradiance is abundance or the load consumption is low. On the other hand, it discharges when the demand rises or when PV ceases generation. The problem of scheduling PV system with energy storage is similar to the optimization problems found in the traditional power generation systems. A special-case energy management system (EMS) is proposed for battery-link topology suitable for roof-top PV installations with local consumption. Figure 1 shows the topology where the battery provides the alternative path for power that flows from PV to the ac output. The local EMS controls the ratio of power that flows into the battery and that feeds into the AC side. This in turn, controls the output power making the PV system a dispatchable power source.

PV

Boost Converter1

Vpv Vb

Battery

Pf

Pb

Pp Full-bridge

Inverter Vdcl Vg

Boost Converter2

Vb Vdcl

Local demand

Pd

Pac

Grid

PV/Batt EMS

Figure 1: Grid-connected PV inverter with storage battery

The proposed EMS is a development of solutions to the dispatching problem of maximizing the revenue over the period. When there is no limitation on the supply and storage capacity, the economic dispatch can be carried out with only the present conditions. As we consider PV/battery system where there are limitations to the available PV power generation and battery capacity, each economic dispatch calculation must account for what happened before and what will happen in the future.

27

Dung Van Nguyen

Home Country: Vietnam Year of Birth: 1976

Master Degree: Electrical Materials University: Gyeongsang National University Graduation Year: 2005

Research Group: Electric power technology Supervisor: Hans Kristian Høidalen PhD Start: 2010

Phone: +47 735 94442 Email: [email protected] Home Page: www.ntnu.no/ansatte/

Experimental studies on streamers of electrical prebreakdown and breakdown phenomena in long electrode gap Today most of the dimensioning rules for transformer dielectric insulation are empirical and based on long experience and less on basic scientific understanding. However, most of the present understanding related to prebreakdown and breakdown phenomena in insulating dielectric liquids are of qualitative nature. In other words, the basic phenomena leading to electrical breakdown is presently very well documented but not yet fully understood.

In addition, the branching mechanism of streamer has still been unknown as well as the nature of streamer in fast event, the exact electric field at the head of streamer, and streamer mechanism for fast mode have been other unanswered questions. Therefore, the investigation streamer in each compositions of transformer oil in long gap and then compares among them in order to get more understanding is very essential.

This research will focus on examining streamer initiation and propagation in slow modes and fast modes for dm gap as well as electric field calculation at the head of streamer and electric field distribution in inter-electrode gap space are also studied. In addition, the effect of additives on streamer, the mechanism of enhancing or reducing of streamer branches, and the development of streamer mechanism are other topics of research.

Figure 1. Experiment setup.

Figure 2. streamer images.

28

Pål Keim Olsen Home Country: Norway

Year of Birth: 1982


Home Page: www.ntnu.no/ansatte/pal.keim.olsen


University: NTNU

Supervisor: Ass. Prof. Frank Mauseth


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.

29

Traian Nicolae Preda Home Country: Romania

Year of Birth: 1986


Home Page: www.ntnu.no/employees/traiannp

Master Degree: MSc Electrical Power Engineering, 2011

University: POLITEHNICA University of Bucharest

Supervisor: Kjetil Uhlen


Co-Supervisor: 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 (DG) units, mostly small scale hydropower plants, but also wind turbines have been 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 an increasing share of the DG leads to changes in the conventional power system structure and generation technologies, the functions of traditional centralized power plants (controlling and stabilizing the power system during a fault-ride through, damping the power oscillations) must also be performed by DG units. This will make the control and operation 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 power systems from the perspective of power systems stability and grid code requirements. The work addresses important parts of the Active Distribution Grids challenge providing updated knowledge and practical guidelines regarding the proper integration of DG under aforementioned technical challenges.

Smart Transmission

Grid

Active

Distribution

Grids

Hydro Power

Thermal Power Wind Power

StorageSmall scale wind power

Small scale hydro power

PV panels

Households

Industry and commercial load

30

Astrid Røkke Home Country: Norway Year of Birth: 1982 Email: [email protected] Home Page: Master Degree: MSc Electrical Engineering, 2007 University: NTNU

Supervisor: Robert Nilssen Research Group: Energy conversion Co-Supervisor(s): Project: Small Hydro

Investigation of permanent magnet synchronous machines with fractional slot windings for use in renewable energy applications

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. An investigation of the importance of speed range, power, weight, vibrations, cogging, cost, converter-cable configurations, voltage range is needed to establish the complete object function. The optimization will be conceptual, meaning that choices such as the selection of winding type and layout is a part of the synthesis. The optimization should also handle several objectives such as efficiency, cost and lifetime (linked to temperature). Of particular interest are the different stator configurations shown below.

(a) Single-layer winding: coils on each second tooth, equal width of teeth.

(b) Single-layer winding: coils on each second tooth, unequal width of teeth.

(c) Double-layer winding: coil on each tooth, equal width of teeth.

Fig.1. Fractional slot windings types.

31

Santiago Sánchez Acevedo Home Country: Colombia

Year of Birth: 1982


Home Page:


University: Universidad Tecnológica de Pereira

Supervisor: Marta Molinas


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.

32

FritzSchimpfHome Country: Germany

Year of Birth: 1977


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.

33

Shailendra Kumar Jha Home Country: Nepal

Year of Birth: 1976


Home Page: www.ku.edu.np/ee

Master Degree: MSc Renewable Energy Engineering, 2006

University: Tribhuvan University

Supervisor: Kjetil Uhlen


Co-Supervisor(s): Petter Stoa

Project: EnPe - exchange student from Kathmandu University (Jan 2012-Dec 2012)

Interconnection and Control of Micro Grids

The social reforms have a direct impact on the growing energy demand and consequently the

installation of distributed generators(DG) like micro hydro, wind turbines and solar

photovoltaic systems are increasing for rural communities. For the need of reliable and secure

power the need of interconnections of the smaller DGs is becoming necessary. As per the

technical and economical viability microgrids are to be formed interconnecting two or more

DGs. To make the system more reliable two or more microgrids can be interconnected or a

microgrid can be interconnected to the distribution system of the main grid nearby.

This research work aims at analyzing the interconnection issues with micro grids. It mainly

focuses on stability analysis, control and protection of micro grids in interconnected as well as

islanded mode. The research work is carried out on micro grid models similar to the real rural

electrification scenario in Nepal.The study will also present a strategic plan for the proper

implementaion of the microgrids in interconnected as well as islanded mode.

34

http://www.ku.edu.np/ee

Christian Skar


Master Degree: Applied Mathematics (Statistics) University: NTNU Graduation Year: 2010

Research Group: Power Systems Supervisor: Gerard Doorman PhD Start: 2010

Phone: +47 99017521 Email: [email protected] Home Page: www.ntnu.no/ansatte/christian.skar

Modelling of European energy markets for low emission scenarios This research work is part of a multi-disciplinary project called LinkS. The LinkS project combines global top-down climate related research and bottom-up regional energy system design. The main objective is to develop an integrated decision support framework for more sustainable energy infrastructures.

The LinkS project’s starting point is a set of emission mitigation scenarios which are studied using a global energy-economy-climate model called GCAM.1 This model calculates supply, demand and prices for energy and agricultural products and the emission of 16 climate gases and the effects of these emissions on the climate system.

One issue with the GCAM model is that the results are on a highly aggregate level (the world is, at the moment, modeled as fourteen regions) and it does not model any infrastructure within each region. To see how the GCAM projections play out in detail, demand and price forecasts from GCAM will be used as input for SINTEF’s EMPS2 model. The particular strength of the EMPS model in this setting is that it incorporates the stochastic nature of power generation from renewable energy sources.

Mitigating climate gas emissions will inevitably increase the share of power production from renewable sources which will require transmissions of large amounts of power and gas across Europe. By using the EMPS model it will be possible to verify the feasibility of the GCAM results, provide adjustments for the projections and unveil where investments in transmission systems will be necessary along the projections.

1 GCAM - The Global Climate Assessment Model 2 EMPS - European Multi-area Power market Simulator

35

Amir Hayati Soloot

Home Country: Iran Year of Birth: 1984

Master Degree: Electric Power Engineering University: Iran Uni. of Sci. and Tech. (IUST) Graduation Year: 2009

Research Group: Electric Power Technology Supervisor: Hans Kristian Høidalen

Co-supervisor: Bjørn Gustavsen

Project: NOWITECH WP4 PhD Start: 2009

Phone: +47 7359 4233 Email: [email protected] Home Page: www.ntnu.edu/employees/amir.h.soloot

Switching Transient in Offshore Wind Farm

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 applied to validate the HF model of WTT with experiments.

36


http://www.ntnu.edu/employees/amir.h.soloot

Chuen Ling Toh Home Country: Malaysia

Year of Birth: 1979


Home Page: www.ntnu.no/ansatte/chuen.toh


University: Universiti Teknologi Malaysia

Supervisor: Lars E. Norum

Research Group: Energy Conversion

Co-Supervisor(s): --

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 for 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.

37

My Name Raymundo E. Torres-Olguin Home Country: Mexico

Year of Birth: 1981


Home Page: http://www.ntnu.no/ansatte/raymundo.torres

Master Degree: MSc in Applied Science 2006

University: Instituto Potosino de Investigacion

Cientifica y Tecgnolgica (IPICyT)

Supervisor: Tore Undeland

Research Group: Energy Conversion Group

Co-Supervisor(s): Marta Molinas

Project:

Use of HVDC multi-terminal VSC and CSC options to incorporate offshore

wind or wave power to the Norwegian grid

One of the main challenges for the integration of offshore wind farms is the transmission of this large amount of energy over long distances. High-voltage direct current (HVDC) appears to be the most viable option. HVDC transmission based on the line-commutated converter (LCC) is the most established and widespread technology around the world. However, HVDC based on the voltage source converter (VSC) has emerged as the best option to integrate offshore wind farms. This work investigates the feasibility of using a conventional LCC-HVDC transmission in combination with a VSC to integrate offshore wind farms. Such integration results in a hybrid HVDC connection, i.e. the connection of a VSC with an LCC through a DC cable. The operational features of various hybrid topologies have been investigated using PSCAD/EMTDC. The simulations include an aggregate model to emulate the wind farm. The corresponding control strategies are tested under various conditions including wind speed variations and AC faults. The Figure shows an example of the hybrid HVDC solution.

38

http://www.ntnu.no/ansatte/raymundo.torres

Erling Tønne Home Country: Norway

Year of Birth: 1965


Home Page: Under construction

Master Degree: Electric Power Engineering, 1991

University: NTNU

Supervisor: Kjell Sand


Co-Supervisor(s): Jan A Foosnæs

Project:

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 overall objective of the PhD-work is to find, test out and adapt methods regarding transformation of today’s passive distribution network into the future active network focusing on concepts, architecture and functionality. Methods for planning and estimation of loads and production will be especially addressed in my PhD-work.

39


Mostafa Valavi Home Country: Iran Year of Birth: 1985 Master Degree: Electrical Power Engineering University: University of Tehran Graduation Year: 2010 Research Group: Electric Power Technology Supervisor: Arne Nysveen PhD Start: December 2010 Phone: +47 73594442 Email: [email protected] Home Page: www.ntnu.no/ansatte/mostafa.valavi

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 should be investigated. A structural finite element analysis is then needed to predict the vibration spectrum. A 50kW low speed PM generator is available for vibration measurements in Wind Lab at the Department of Electrical Power Engineering. Currently, the focus of this research work is on radial flux machines but it is planned to investigate the magnetic forces in axial flux generators, as well as machines with multiple airgaps.

40


Torbjørn Andersen Ve


Master Degree: Physics University: Norwegian University of Technology and Science Graduation Year: 2008

Research Group: Electric Power Technology Supervisor: Frank Mauseth Co-supervisor: Erling Ildstad

PhD Start: 2010

Phone: +47 7359 7280 Email: [email protected] Home Page: www.ntnu.no/ansatte/torbjorn.ve

Effect of Moisture on Space Charge Accumulation in Polymeric HVDC Cable Insulation The use of polymeric insulation materials for submarine HVDC cable systems has been introduced quite recently, with the first cable installed in 1999. Previously, oil-filled and mass-impregnated cables were the only practical alternatives, but the low production and maintenance costs of polymeric cables and the development of specialized HVDC polymers, extruded HVDC cables have become viable.

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 migrate into the insulation system. The amount of water absorbed and the rate of absorption depends on the type of polymers, both in the insulation and the sheath, and the temperature of the system.

In a polymeric DC cable, space charge, i.e. net positive or negative charge distributed in a region of space, will accumulate. Space charge accumulation occurs when there is an imbalance between injected and transported charge in an area, causing a buildup of excess charge. The presence of space charge in the insulation will cause a distortion in the local electric field. At HVDC cable service conditions, which include temperature gradients and polarity reversals, this field distortion may cause the local electrical field to exceed the breakdown strength of the insulation, leading to insulation breakdown. While the occurrence of space charge in polymeric insulation is a well-known phenomenon, very little has been done to examine the effect absorbed water may have on charge accumulation and transport.

The goal of this PhD project is to investigate the effect of moisture on space charge accumulation. Both the space charge distribution and the conductivity in polymeric materials with varying water content will be of interest. The results of the research will give an indication on how critical the prevention of water intrusion into polymeric HVDC cables is, and possibly yield design criteria on water barriers for such cables.

41

Til Kristian Vrana

Home Country: Germany Year of Birth: 1982

Master Degree: Electrical Engineering University: RWTH Aachen University Graduation Year: 2008

Research Group: Power Systems Supervisor: Olav Bjarte Fosso PhD Start: 2009

Phone: +47 7359 6476 Email: [email protected] Home Page: www.ntnu.no/ansatte/til.kristian.vrana

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 and could be seen as a hybrid (AC+DC) grid, but the share of those technologies is not known yet.

The focus of this research work is on how to design such an offshore network which must be operated in parallel with the existing AC onshore grid. Reliability, technical performance, robustness and flexibility will be of major importance. Other issues to consider are the protection and sectioning of the system in case of component fault. With the large future plans for offshore renewable installations it is of crucial importance to minimize the worst case amount of disconnected power. The results could be partly also relevant for a possible redesign of the Krigers Flak wind park connection and the Desertec project.

42

Georgi Hristov Yordanov Home Country: Bulgaria

Year of Birth: 1974


Home Page: N/A

Master Degree: MSc Physics, 1999

University: The Sofia University “St. Kliment Ohridski”

Supervisor: Prof. Ole-Morten Midtgård (UiA)

Research Group: Photovoltaics

Co-Supervisor(s): Prof. Lars Einar Norum (NTNU)

Project: “End Use of Photovoltaic Technology in Norway”

Performance of Different Photovoltaic Modules in Southern Norway

The joint project “End Use of Photovoltaic Technology in Norway” co-funded by Elkem Solar AS, the University of Agder (UiA), and the Research Council of Norway has as main objective to test the hypothesis that PV generation of electricity is a viable alternative also in Norway. The objective of my PhD study is to build, run and analyze data from field test setups with various PV modules. Fig. 1 shows the two installations located in southern Norway.

Figure 1: Outdoor testing of PV modules in Grimstad and in Kristiansand.

At present, the commercial PV modules are rated in terms of power at standard testing conditions (STC). The latter are optimized for industrial indoor measurements, and do not represent well the typical outdoor operating conditions. Consequently, the efficiency of a PV module in a real power system is usually well below the ‘paid-for’ label efficiency. Prediction of the energy yield of a PV system involves models of device performance under various solar irradiances and device temperatures as well as statistics of meteorological data. Scientific discussion towards energy rating standardization has been going for some time. The study is focused on 1st generation crystalline-silicon PV technology. Several cell structures and different types of Si feedstock are tested. In addition, the local solar resource is recorded with high temporal resolution which may benefit designers of inverters for PV.

43

Mehdi Karbalaye Zadeh Home Country: Iran

Year of Birth: 1982


Home Page: www.ntnu.no/emploees/


University: University of Tehran

Supervisor: Marta Molinas


Co-Supervisor(s):

Project: Smart Grid

Identification of Potential Instability in 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 switching converters. Due to their non-linear and time varying characteristics, modelling and stability analysis of such systems are complex and cumbersome. After a thorough investigation of the state of the theoretical art on modelling and stability, this research will be focused on the development of a stability analysis tool that can accurately capture the potential phenomena linked to the interaction between converter-embedded control algorithm and the characteristics of the electrical grid. This interaction will be investigated under non-sinusoidal/unbalanced 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. 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.

44

Bijan Zahedi Home Country: Iran

Year of Birth: 1981


Home Page: www.ntnu.no/emploees/bijan.zahedi


University: University of Tehran

Supervisor: Lars Einar Norum


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 all-

electric 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.

45

Zhaoqiang Zhang

Home Country: China

Year of Birth: 1981


Home Page: www.ntnu.no/ansatte/zhaoqiang.zhang

Master Degree: Electrical Engineering

University: Shanghai Jiaotong University

Supervisor: Robert Nilssen


Co-Supervisor: Arne Nysveen

Project: NOWITECH WP2

Coupled 3D models of large-diameter permanent magnet generators

and its loss calculation

Offshore application demands the generator reliable, cost-effective and high-efficiency. Traditionally geared drive train has problem to meet this requirements when it comes to high power turbine (>5MW). Ironless large-diameter permanent magnet generator is the focus in this research because of the advantages of modularity, high efficiency and high torque density. The objectives of this research are

Investigate the state of art in generator technology for offshore wind power plant

Develop the machine design tools based on the best-available commercial FEM software

Investigate the optimum machine type for the offshore application

Develop the loss calculation method based on the best-available commercial FEM software

Investigate the machine loss in ironless permanent magnet machine

46


Dr. ingeniørs/PhD graduated at Department of Electric Power Engineering, NTNU, from 1990

Year Name Title

2012 Suul, Jon Are Control of Grid Integrated Voltage Source Converters under Unbal-anced Conditions – Development of an On-line Frequency-adaptive Vir-tual Flux-based Approach

2011 Marvik, Jorun Irene Fault localization in medium voltage distribution networks with distrib-uted generation

Krøvel, Øystein Design of Large Permanent Magnetized SynchronousElectric 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

2010 Chiesa, Nicola Power Transformer Modeling for Inrush Current Calculation

Danielsen, Steinar Electric Traction Power System StabilityLow-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

2009 Eek, Jarle Power System Integration and Control of Variable Speed Wind Tur-bines

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 Pedersen, Per Atle Forces Acting on Water Droplets in Electrically Energized Oil Emul-sions; 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

47

2007 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

2006 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

2005 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 tran-sition from fossil fuelled toward a renewable supply within a liberalised electricity market

2004 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

2003 Botterud, Audun Long Term Planning in Restructured Power Systems: Dynamic Model-ling of Investments in New Power Generation under Uncertainty

Ettestøl, Ingunn Analysis and modelling of the dynamics of aggregate energy demand

2002 Kolstad, Helge Control of an Adjustable Speed Hydro Utilizing Field Programmable Devices

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

2001 Larsen, Tellef Juell Daily Scheduling of Thermal Power Production in a Deregulated Elec-tricity Market

Kleveland, Frode Optimum Utilization of Power Semiconductors in High-power High-frequency Resonant Converters for Induction Heating

Myhre, Jørgen Chr. Electrical Power Supply to Offshore Oil Installations by High Voltage Direct Current Transmission

Year Name Title

48

2000 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.

1999 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.

1998 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 schedulingA free market based procedure with reserve constraints included.

1997 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 three-dimensjonal computations of eddy currents.

Qing Yu Investigation of dynamic control of a unified power flow controller by using vector control strategy.

1996 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 Tor-vetjønn

Switchmode PowersuppliesOptimum topologies and magnetic components

1995 Lars Arne Aga A Laboratory Platform for Theoretical and Experimental Research on Rotor Flux Oriented Control of Motor Drives.

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

Year Name Title

49

1994 Snorre Frydenlund A study of voltage stresses in ARC furnace transformers due to switch-ing 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 Contin-gencies and Outage Distance by a Zone Filter

1993 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 ofPower 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

1992 Per Hveem Computer Aided Learning, Simulations, and Electrical Motor Drives.

Ståle Johansen Energy resource planning a conceptual study of a multiobjective prob-lem.

Astrid Petterteig Development and Control of a Resonant DC-link Converter for Multi-ple Motor Drives

Bendik Storesund Resonant overvoltage transients in power systems

1991 Jonny Nersveen Kvalitetskriterier og helhetlig planlegging av innendørs belysningsan-legg.

Torbjørn Strømsvik Kraftelektronikk som kilde til forstyrrelser i fordelingsnettet.

Alf Kåre Ådnanes High Efficiency, High Performance Permanent Magnet Synchronous Motor Drives

1990 Eilif Hugo Hansen Bruk av kunstig lys og lysmanipulering for styrt produksjon av lakse-fisk.

Guijun Yao Modelling, Dynamic Analysis and Digital Control of PWM Power Converters

Year Name Title

50

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