A Summary of PhD Projects 2002

Norwegian University of Science and Technology, NTNUFaculty of Information Technology, Mathematics and Electrical EngineeringDepartment of Electrical Power Engineering

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

A summary of PhD Projects 2002

at

Department of Electrical Power Engineering Faculty of Information Technology, Mathematics and Electrical Engineering

Norwegian University of Science and Technology This annual report gives an overview of current dr.ing research projects at the Department of Electrical Power Engineering. The folder contains a short status report of each project. Currently 22 students are registered in our PhD program, of which approximately 4 present their dissertation each year. The department has 10 professors, 3 associate professors and 3 assistant professors. In addition to the scientific and administrative staff, the department house a mechanical workshop and an electrotechnical laboratory employing 6 people. The following three fields mainly cover the Research activity at the department: Power Systems Electrotechnical Materials and Installations Energy Conversion The PhD projects presented here are based on topic 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 co-operating institution SINTEF Energy Research AS. Since the PhD projects represent an important part of the department research this folder also gives a description of the department and the professors’ research activity. The nominal duration of PhD program is 3 years for full-time researchers. On of these years is devoted to post graduate courses. However, a typical PhD study last for 4 years, and during the additional year the researchers are involved in university/educational duties. For further information about the research projects presented, please contact the individual student given by name in this folder. For more information on previous projects, please contact the Department. NTNU, January 15, 2003 Ivar Wangensteen Professor

Dr.ing. student: Supervisor: Title: p

Bjerkan, Eilert Høidalen, Hans Kr. High frequency modelling of Power Transformers - Condition moni-toring and fault detection

4

Botterud, Audun Wangensteen, Ivar Energy System Analysis 6

Catrinu, Maria Holen, Arne T. Multi-criteria optimization of distributed systems 8

Ericson, Torgeir Finden, Per End-user flexibility by efficient use of ICT 10

Ettestøl, Ingunn Wangensteen, Ivar

Fadum, Hege Sveaas Hans K. Høidalen EMC in railway installation. A component study of the booster trans-former in the catenary system

12

Hansen, Oddbjørn Hansen Eilif H. System solutions for electrical installations in buildings 14

Hellesø, Svein Magne

Runde, Magne Vibrations on overhead power lines 16

Ishengoma, Frederick M.

Norum, Lars Modelling, Simulation and Digital Control of Photovoltaic Power Supply

18

Korpås, Magnus Holen, Arne T. Hydrogen Energy Storage for Renewable Energy Sources 20

Kragset, Vidar Norum, Lars

Kristiansen, Tarjei Wangensteen, Ivar Risk Management in Electricity Markets 22

Lund, Richard Nilsen, Roy Multilevel Power Electronic Converters for High Power Drives 24

Maribu, Karl Magnus Wangensteen, Ivar Distributed Generation in Liberalised Electricity Markets 26

Opdal, Knut Hansen, Eilif Hugo

Pedersen, Atle Ildstad, Erling Principle of electrocoalescence in crude oil 28

Skaar, Stev E. Nilssen, Robert Optimal Design of Permanent Magnet Generators for Distributed Power Generation

30

Skjellnes, Tore Norum, Lars Digital Control of Power Electronic Inverters 32

Tomta, Gjermund Nilsen, Roy High power high voltage electronic dc-dc converter 34

Trætteberg, Sidsel Ildstad, Erling Polymer insulation of HVDC cable 36

Vogstad, Klaus-Ole Faanes, Hans H. A system dynamics analysis of the Nordic Power market 38

Øvrebø, Sigurd Nilsen, Roy Sensorless control of Permanent Magnet Synchronous Machines 40

Previous projects from 1990 42

High frequency modelling of Power Transformers- Condition monitoring and fault detection

Eilert Bjerkan

Initiation

After graduation from NTNU in 1998, I’ve beenworking with R&D at Nortroll AS in Levanger.I’ve worked for 2 years with a new generation offault-indicators for overhead lines. These indica-tors make use of complex electromagnetic-field-analysis. Thus my interest in electromagneticmodelling.

The project is funded by SEFAS/ the NorwegianResearch council.

This doctoral study started in November 2000 andis sceduled to be finished by the end of 2004.

Introduction

Detailed modelling of transformer windings hasbeen a fundamental problem for almost a century[1]. A lot of effort is put into identifying correctmodels for different phenomenas. Abbetis electro-magnetic model [2] was a definite achievement,because it provided a substitute for the difficulttheoretical calculations used earlier.

In my doctoral study I will focus on high frequencymodelling through analytical- and FEM-calcula-tions. Such models have a wida area of appliance:

- Determining impulse-overvoltages in windings,during both design-stage and when coordinatingisolation-levels. The same parameter is checkedduring factory acceptance tests.

- Understanding measurements and propagation ofsignals in windings due to partial discharges(locating partial discharges).

- Determining resonances in power networks andtransformers (related to the first point).

- Understanding frequency response measure-ments when applied in diagnosis and conditionassessment.

The last application is included in my work.

Modelling

Several methods have been proposed during theyears. The most difficult part has been the model-ling of frequency-dependent properties of the in-ductances and losses. Fergestad and Henriksen [3]made an extensive contribution regarding induct-ance calculations. And in the last years severalpublications [4] have made the accuracy of themodels better by correcting earlier assumptions re-garding both losses and inductances.

When modelling a complex structure such as atransformer, one has to make certain simplifica-tions. Typical power transformers have approxi-mately thousand turns in the HV-winding. Fornetwork invetigations the winding assembly isrepresented by equivalent elements, also calledlumped elements. An accurate calculation needsabout 200 to 400 elements [5]. Depending on the

required preci-sion, a lump el-ement canrepresent oneto twentyturns. A typi-cal model[5]has about 10terminals, 30tappings and300 internalwinding nodes.

Figure 1: A double disk model (3 x 2 turns).

In figure 1 an equivalent model of a double disk isshown. This model is often reduced to a few nodesin the final model (depending on needed accuracy)

Complete software-packages for modelling trans-formers are also developed [5],[6]. These claim tocalculate an accurate high frequency-model fromconstructional data. I will try to evaluate these pro-grams in near future.

Frequency Response Analysis (FRA)

FRA is, during the last decade, introduced as an ad-ditional diagnosis tool for power transformers. Thefrequency response is measured and comparedwith a reference-measurement from the factory,with measurements from identical transformers, acomputerized model of the transformer or else aninterphase comparison is used (not possible if del-ta/z-winding is present and cannot be opened).

Figure 2: A typical FRA-measurement setup

The reason for applying such measurements is toget an early warning of damages because of faults.A short-circuit-fault creates huge mechanical forc-es within the windings, and mechanical deforma-tions can occur. Typical deformations are buckling(radial deformation) and compression (axially de-formation). Such deformations do not always de-grade the normal operational characteristics of thetransformer, but the insulation level may be de-graded severely. And if not detected, he next faultcan be fatal.

In my work I will try to identify the characteristicsof the most common faults in the frequency re-sponse measurements through modelling (apply-ing faults to the model). I will also try to analyzethe sensitivy of FRA by taking measurements on afull scale transformer and comparing these withmodels of the same transformer. Evaluating thedifferent methods and equipment used for FRA-measurements will also be a part of my work.

The first transformer I will study, is a 20MVAtransformer manufactured in 1965. This wasscrapped due to upgrading of the voltage-level.The iron core is removed and I will try to refine themeasurements by using single windings within anearthed arrangement inside our laboratory to sim-plify comparisons between measurements andmodel.

Progression

The first 2 years, I have mainly been attendingcoarses, and studying the literature published with-in the field of high frequency modelling and FRA.I have also performed alot of FRA-measurementson different transformers. During the first semesterof 2003, I will stay at EdF’s R&D-dept. in Paris,using their FEM-software dedicated for transform-er modelling. The rest of 2003 will be used com-paring simulations and measurements (sensitivityanalysis). 2004 will mainly be spent writing mythesis.

Primary Goals

The main goals for my work is to analyze the sen-sitivity of the methods related to FRA on powertransformers through modelling and real scalemeasurements.

Advisors

The supervisor for my work is Assosiate ProfessorDr.Ing. Hans Kristian Høidalen.

References[1] Abetti, P.A., "Bibliography on the surge performance oftransformers and rotating machines", AIEE Trans., vol.77,pt.III Dec. 1958, 1958, pp.1150-68. First suppl., AIEETrans., vol.81, pt. III, Aug. 1962, pp. 213-219. Second.Suppl., IEEE Trans., vol. PAS-83, Aug. 1964, pp.855-58.[2] Abetti, P.A., "Transformer models for the determinationof transient voltages", AIEE Trans., vol.72, pt.III, June1953, pp. 468-80.[3] Fergestad, P.I., Henriksen, T., "Inductances for the calcu-lation of transient oscillations in transformer windings",IEEE Trans., 1974, PAS-93, (3), pp. 510-517[4] Wilcox, D.J, Hurley, W.G, Conion, M., "Calculation ofself and mutual impedances between sections of transformerwindings", IEE proc. Vol.136, Pt.C, No.5, september 1989[5] Glaninger; P., Willy, B., "Calculation and visualisation ofsurge voltages in transformer windings", Int.conf.on powertransformers, may 2001[6] Moreau, O, et.al.”FRA-diagnostic method..." ISH 2001

Energy System Analysis

by Audun Botterud

Introduction We experience a growth in energy demand in most parts of the world today, including Norway. At the same time, the knowledge and concern about environmental consequences of energy utili-sation are increasing. In this situation there is a need for finding better and cleaner energy supply systems for the future. Another trend in the global energy sector is the ongoing restructuring of energy markets. Consequently, competition has increased and decision-making takes place at more decentralised levels in the system than earlier. New long-term planning challenges arise for both energy companies and regulating authorities following these changing conditions. The energy industry must take investment decision in a more uncertain world. Authorities, on the other hand, need to organise the markets so that the right incentives are given to make the energy system evolve in the desired direction. In this situation new decision support tools are needed, to understand more of the dynamics behind the long-term development of the energy system (Fig. 1).

Power market

Markets forother energy

carriers

Energy andenvironmental

policy

Investments inthe energy

system

Fig. 1 Illustration of relations influencing on the long-term development of the energy system.

Project objective The main focus in this project is on the dynamics of new investments in technologies on the supply and demand side within restructured electric power markets. The challenge is to detect and

model the main driving forces behind long-term changes in the power system, and how authorities via different policy measures can contribute to influence on the development. A natural point of departure is to look at the prevailing conditions within the Norwegian and Scandinavian power markets, where the process of deregulation started in the early 1990s. However, our intention is that new methodologies should be of a general nature, and therefore not limited to be applied in one specific geographic area. The results achieved in this project will hopefully contribute to a better understanding of the long-term consequences of power market restructuring. The objective is to help achieve improved long-term decision making in the electricity industry, and the results from the project should be of interest for companies in the energy industry as well as for regulating authorities. Project status I started as a doctoral student in January 2000. During the first three semesters I spent most of the time with compulsory coursework and serving as a teaching assistant for the department. In the period from Sept. 2001 to March 2003 I am at MIT Laboratory for Energy and the Environment in Cambridge (USA) as a visiting student. The first part of my research focuses on developing an investment model based on system dynamics, for long-term analysis of the power market [1]. The model simulates new investments in a set of different power generation technologies, assuming that investors base their investment decisions on expectations about future price and profitability. Plant approvals and construction lead times cause substantial delays in the system, and this is likely to trigger price and investment cycles (Fig. 2). Authority intervention, for instance in terms of CO2 taxation or investment subsidies can considerably change the simulated investment decisions. While the main focus in the model is on investments in new power supply, we also represent price feedback to the power demand.

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

[TW

h/ye

ar] a

nd [N

OK

/MW

h]

Average Price Generation Load

Fig. 2 Simulated average electricity price, generation and load in Norway, year 2000-2030 [1].

Increased uncertainty about future price and profit, following the restructuring of the power market, also makes an impact on investment decisions. In order to study decision making under uncertainty we have developed a model for optimal investments in new power generation [2]. The model is based on stochastic dynamic programming and takes into account the possibility and value of postponing an investment decision in order to wait for more information about future uncertainties. When investments are modelled in this way, i.e. as so called “real options”, it turns out that the optimal investment criteria is more restrictive than what the traditional net present value suggests. New investments in generation plants would be even further delayed if the electricity industry behaves according to this theory, and this is likely to increase the magnitude of the cyclic patterns that we see in Fig. 2. During my research visit at MIT I have also contributed to the initial phase of a new joint project between NTNU, MIT and Chalmers called TRANSES1. In this project we use trade-off analysis to assess the most important economic and environmental trade-offs for a range of future energy system alternatives [3]. A set of analytical models will be used in the assessment of the different technological alternatives. An important aspect of the TRANSES project is to establish a continuous dialogue with an external stakeholder group to make the results applicable for decision makers in the Scandinavian energy sector.

1 Alternatives For The Transition To Sustainable Energy Services In Northern Europe

Future work In the remaining work of my doctoral studies I will spend some more time on further development of the model concept for generation investments under uncertainty. I also intend to incorporate the optimal investment results from into the dynamic power market simulation model in order to study the system consequences of optimal decision making. In the TRANSES project I will help finalising a preliminary trade-off study of Scandinavia, and I plan to also add some of these results into my final thesis. Initiation and funding The project is funded by the Industry’s Innovation Fund at NTNU, and is due to be finished by August 2003. My main supervisor is Prof. Ivar Wangensteen in Dept. of Electrical Power Engineering. Prof. Marija D. Ilic and Mr. Stephen R. Connors have served as my advisors at MIT. Personal background I graduated as MSc (Siv.Ing.) from Dept. of Industrial Economics and Technology Manage-ment, NTNU, in 1997. Before starting as a doctoral student I worked for 2 years at SINTEF Energy Research with different power system models for hydro-power production planning and economic risk management. References [1] Botterud A., Korpås M., Vogstad K-O. and Wangensteen I., “A dynamic simulation model for long-term analysis of the power market”, Proceedings 14th Power Systems Computation Conference, Spain, June 2002. [2] Botterud A., Ilic M.D., Wangensteen I., “Optimization of generation investments under uncertainty in restructured power markets”, submitted to Intelligent Systems Applications to Power Systems, Greece, September 2003. [3] Botterud A. “Alternatives for sustainable energy supply in Scandinavia”, presented at the Annual Meeting of the Alliance for Global Sustainability World Student Community, Costa Rica, March 2002.

Introduction

The recent development of new energy conversiontechnologies like micro-cogeneration, gas engi-nes, solar cells and fuel cells, yields the challen-ging task to design economic and environmentaloptimal energy systems to include them.The possibility to combine several different pro-cesses and energy carriers in analyses of complexenergy systems requires a much larger flexibilitythan classical technical-economic analyses.

A multi-criteria decision formulation of an energysystem planning problem can provide a realisticanalysis of a wide range of alternatives. Generally speaking an energy system planning is anon-linear, integer, multi-objective programmingproblem that can be solved by linear program-ming, non-linear programming, dynamic pro-gramming, integer programming techniques withcertain simplifications, and different emergingtechniques such as genetic algorithms, fussy logic,neural networks or analytic hierarchy processes,etc..

Project objective

The main focus of this doctor study will be theintroduction of the concept “energy quality” in amulti-criteria decision problem formulation. Theconcept includes besides economical, technicaland environmental aspects, the end-user orientedquality aspects such as quality and reliability ofsupply.

Description

The doctoral study will be closely connected tothe SINTEF project “Analysis of Energy Trans-port Systems with Multiple Energy Carriers”which aims to develop a robust and flexible met-hodology for optimization of distributed energysystems. This methodology must be able to handlemultiple energy carriers in a geographically distri-buted network with energy transmission, conver-sion and storage technologies.As an example, the methodology can be applied tolocal system corresponding to a county/region thatuses combined heat and power supply based onbiomass and waste from forestry and farming.

Water

Wind

Biomas

Waste

District heating

Gas/oil

Hydrogen

Sun

Multi-criteria optimization of distributed energy systems

Maria CatrinuDecember 2002

The user (decision-makers) can ‘build’ a physicalmodel, with possible processes and components,which can be represented simplified as in thefigure above.This model will be internally converted by themethodology into an ‘abstract’ network modelwith branches and nodes described by specificquantitative (cost, energy efficiency and environ-mental parameters) and qualitative attributes.Multi-criteria optimization techniques will then beapplied to this ‘energy network’ to find the opti-mal system design, depending on how the user hasweighted different attributes. The results will beconverted back to the ‘physical’ system model andpresented.The project will contribute to an improved quanti-fication and survey of economic, environmentaland technical consequences of operation of energysystems with new types of energy resources.

Status

I started this PhD program at the end of February2002 and for the beginning I tried to gather infor-mation about my field of study. I was also takingpart of the courses compulsory for this PhD pro-gram, and I will continue with this for the first halfof the year 2003.

Initiation and funding

This project is funded by The Norwegian Rese-arch Council and it is due to be finished at the endof January 2006.My supervisors are: Professor Arne T. Holen,from the Electrical Power Engineering Depart-ment-NTNU, and Research Scientist Bjørn H.Bakken, from SINTEF Energy Research.

Personal background

I graduated in 1999 ‘Politehnica’ University ofBucharest -Power Engineering Department. In July 2000 I obtained a MSc diploma in EnergySystems Management, in the same university.After that I was training and working for one and ahalf years for the Romanian National Authorityfor Electricity and Heat (ANRE), Department for

Electricity Tariffs. My main tasks there, were toevaluate the technical and economic status of theregulated power producers and to issue price deci-sions. I was also involved in several rate casesadjustments for final captive consumers and I wascollaborating in issuing methodologies (secondarylegislation) for prices and tariffs calculation.

End-user flexibility by efficient use of ICT

Torgeir Ericson Introduction During the last ten years we have seen an increase in the consumption of energy and effect in Norway. At the same time there has been a decrease in investments in power production. As an example, there was an average growth in installed capacity (measured in MW) on 4,1 percent each year from 1970 to 1985. During the 1990’s this percent dropped to 0,1 each year. The power that is available during winter peak loads in the Norwegian power system is around 24 000 MW [1]. 5. February 2001 we used ca 23000 MWh/h. Because of the tighter effect situation in Norway there are a need to decrease the use of effect during peak-load hours. Two-way-communication project The project “End-user flexibility by efficient use of ICT” (Information and Communication Technology) started in 2001, with SEfAS, EBL-kompetanse, NVE and other players in the energy field as participants. The objective of the project is to increase the end-user flexibility in periods with scarcity of electrical energy and power. Two network operators will install technology for two-way communication to 10.000 end-users (mostly household customers). With this technology the operator can control loads and read the meter automatically. The electricity consumers will be given a variable tariff as an incentive to reduce the load during peak hours. Possible network tariffs that can be offered to the end-users are: - A fixed term, a term concerning network

losses and a term concerning energy consumption. The last term is only activated in periods with scarcity of energy.

- A fixed term, a term concerning network losses and a term concerning power consumption. The last term is only activated in periods with scarcity of energy

If the end-user gets variable electricity price from the power supplier, the incentive for off-peak use of electricity will increase further.

The energy use of the electricity consumers will be measured on an hourly basis. There will also be given questionnaires to a part of the end-users in the project. My project As a participant in the project described above I will have energy consumption data available for analysis. The amount of data from metering of electricity and from the questionnaires will be huge. The first part of the doctorate study will be to collect, systematize and analyse parts of this base, to illustrate relations between power/energy consumption, price signals and other parameters that can be of importance for reducing peak hour consumption.

Figure: Two-way communication system. [2] The other part of the project will be to use the analysis/results from the amount of data in some models to validate and perhaps modify the models to improve the precision in the

calculations. The models can be used further to study other parameters of interest. Sensitivity analysis, cost/benefit calculations etc. can be used to map which efforts for end-users that are most efficient, how and where the efforts should be performed, in which order the efforts should be performed and the total potential for reduced power consumption. Other actors than the end-users and the network operators can have interest in ICT at the site of the end-users. Benefits for different actors can perhaps be evaluated with use of the models. Status and further work I started in November 2001, and will finish November 2004. So far I have been taking courses and reading relevant literature. Next year I will focus on analysing the energy data from the end-users. Initiating and funding This study is initiated by EBL-Kompetanse. It is a part of the project End-user flexibility by efficient use of ICT, which will be running from 2001 to 2004. My PhD is funded partly by the Nordic Energy Researh, and partly by The Research Council of Norway. My supervisor is Professor II Per Finden. Personal background I graduated from NTNU, Dept. of Mechanical Engineering in 1999. Until November 2001 I worked for Rembra AS as an environmental and energy consultant. References [1] TR A5668 ”Prissignaler og sluttbrukerfleksibilitet i knapphetssituasjoner”, A. Hunnes, O. S. Grande, August 2002 [2] http://www.energy.sintef.no/prosjekt/ Forbrukerflex/no_index.asp

IntroductionThis doctorate study is initiated through an agre-ement between NTNU, SINTEF and The Norwe-gian National Rail Administration (JBV) on co-operation in research programs. The subject“EMC in railway systems” involves severaltechnical challenges. In order to achieve appropri-ate tools for practical cases, it is desirable todevelop and improve methods to describe and cal-culate the physical phenomena. I wish to contri-bute in this process by combining ownexperiences and earlier research work, nationallyand internationally. In my work I will pay specialattention to one particular component in thecatenary system: The booster transformer.

Electric railway traction and EMCAmong all the electrical installations in the rail-way infrastructure, it is the traction current thatcauses most of the electromagnetic interference.And in my perspective, main interest will be focu-sed on the traction return current circuit at AC-railway lines. More specific, it is necessary todescribe the current- and voltage distribution, andit’s influence on signalling- and communicationsystems, safety earthing and remote installations.

The EMC-concept in connection with railwayinfrastructure is covered in a large amount of lite-rature. My task in this work is to summarize theexisting material, and to contribute with analysiswithin the area of traction return current circuitwith booster transformers.

Why booster transformers?Several advantages with the use of booster trans-formers are identified: Avoid leakage of tractionreturn current to earth from the track. Makesparallel cables and other electrical equipment lessvulnerable to inductive interference. Decreases theconductive connections between the traction

return current circuit and buried metallic structu-res, because of smaller amount of leakage current.Gives better balance in the traction current circuit,especially when separate return conductors also isused. Decrease touch voltages between the trackand earth.

These advantages are only valid outside track seg-ments where trains are located. Other disadvanta-ges are: As an additional component in thecatenary system, the booster transformer causesan increase in the total impedance, and it compli-cates the co-ordination with the signalling sys-tems. Also, modelling and calculations of currentand voltage distribution becomes more complica-ted.

Figure 1: The booster transformer (Isaksen [2])

How is the coupling arrangement for the boostertransformer?Typical nominal current for the catenary system inNorway is 600 A. With a serial coupling in thecatenary and the return current circuit, the boostertransformer forces the diverted return current backto the rails (and the separate return conductor, ifinstalled). This coupling is similar to a currenttransformer, which is short circuited or has lowimpedance at the secondary. The impedance seenfrom the secondary terminals “a - 0 - b“ is deter-

EMC in railway systems. A component study of the booster transformer in the catenary system.

by Hege Sveaas Fadum

mined by the external burden; track, earth andreturn conductors. The next figure shows threedifferent systems which are used in the Norwegianinfrastructure. At the top, system “B” withoutseparate return conductors, in the middle, system“D” with return conductors and insulated joints inthe rails and at the bottom, system “C”, in whichthe insulated joints are removed and the terminal“0” is not connected to the track.

Figure 2: Coupling arrangements with booster trans-former. (Fadum [3])

Modelling: Methods and comparisonFor the component study, I wish to define the dif-ferential equations based on the models suggestedin section 4.1, and use computer tools (forinstance Matlab and Maple) to realize calculationswith different parameter values. Further, analysisof frequency and magnetic properties is of inte-rest.

For a system study, I need to summarize and com-pare calculation methods. A. Pleym [1] made agreat effort in finding calculation tools that areuseful for analysing coupling phenomena inclu-ding earth in railway systems. Is of interest tostudy this and other modelling methods, forinstance the tools used by G. Hoffmann, et.al. [4]and by Varjú, Schütte, et.al.[8]. If possible, I willmake an effort to refine the methods, in order toimplement more details about the booster transfor-mer.

Verification by measurementsIt is desirable to use measurements to verify simu-lations or calculations. Measurements can be car-

ried out both in laboratoy and on site.

Plan of progressI expect I will need at least three more years tocomplete my doctoral work. My plan of progresscan roughly be descriped like this:2001:Literature studies and tracing international

status concerning EMC and booster transfor-mers in railway systems .

2002:Developing theoretical models and performcalculations

2003:Measurements2004:Summarize results and write thesis2005:Dissertation

Bibliography

[1] Pleym, A:EMC in railway systems. Coupling from catenarysystem to nearby buried metallic structuresNTNU, March 2000 (doctorate thesis)

[2] Isaksen, A.H.:Modellering av sugetransformatoren i jernbanenskontaktledningsanleggNTNU, Dec. 2000 (Graduate thesis, in Norwegian)

[3] Fadum, H.S.:Returstrømmer og jording i NSBs baneanleggNTH, Dec. 1993 (Graduate thesis, in Norwegian)

[4] Hoffmann, G.; Kontcha, A:Boostertransformatoren auf AC-BahnenElektrische Bahnen, 7/2000 (in German)

[5] Technical Seminar by SES, Safe Engineering Serv-ices & Technologies Ltd.:Power System Grounding & ElectromagneticInterference AnalysisMontreal, Sept. 17th-21st 2001.

[6] Gustavsen, B., Semlyen, A.:Rational approximation of frequency domainresponses by vector fittingIEEE Transactions on power delivery, vol. 14 issue3, July 1999. Pages 1052-1061

[7] Annakkge, U.D., McLaren, P.G., Didrkc, E., Jayas-inghe, R.P.:A current transformer model based on the Jiles-Atherton theory of ferromagnetic hysteresis.IEEE transactions on power delivery, vol. 15 no.1,Jan. 2000

[8] Seminar by STRI:Railway power supply - new opportunities andchallengesLudvika, Sweden, 11 th Sept.2000

System solutions for electrical installations in buildings

by Oddbjørn Hansen

2002.12.20

Introduction

This project was initiated by an NTNF-programmecalled New Technology for electrical installations.I started my Dr. ing. study in September 1992 andplan to finish early in 2003.

The NTNF-programme financed the first part(1992-93) of the scholarship and the departmentfinanced the years 1994-95. My present employer,Sør-Trøndelag University College, has made itpossible to conclude my work by granting leaveof absence the autumn of 2002.

Needs analysis

In order to perform a good planning of electrotech-nical installations in buildings, one has to find theneeds of the users. In my dissertation I’m lookingat this issue on a fundamental level. I start with thepsychological and practical needs of the users andthe activity. This needs analysis leads to a func-tional description for rooms, areas and the build-ing as a whole. Table 1 shows a needs analysiscarried out for an office. This is just an example,other functions could also be taken into consider-ation especially if a higher grade of user interven-tion is wanted.

With such tables for all room categories in abuilding, or part of a building, one can choosestrategies and structures for the electrotechnicalsystems. It is of special interest to coordinate allthe systems. Installation bus technology should beconsidered to do that.

Installation bus systems

European Installation Bus (EIB) and LonWorksare used more and more in commercial buildings.

Ring

Mesh

Figure 1: Alternative structures

Both systems can perform a variety of functionslike light and heat control, fire and burglary alarmand power and energy control.

The costs of the electrotechnical installationscan be reduced when choosing to use a bus sys-tem. This is not only true for the investments, butalso for operating costs. Another important advan-tage is when a rebuilding is needed. If the systemis planned carefully, a rebuilding will only involvea reprogramming of the system without having toreplace much of the installation.

The power system structure is almost fully dis-connected from the functions when choosing a bussystem. I have taken advantage of this by suggest-ing alternative structures for the power system asshown in the next section.

Level Needs Person Activity Building, etc.

1 Safety and Orientation and General lighting

security needs attention

Emergency functions

Warning of danger Fire alarm

Protection against Burglary alarm Burglary alarm

damage Fire alarm

2 Functional needs Communication Telephone

Intercom

Computer network

Activity Working light PC

3 Environmental Climate Heating

needs Ventilation

Light control

Heat control

Transport

Table 1: Needs analysis for an office

Power system structures

The need for flexible power supply call for newstrategies and structures. Radial structures are al-most exclusively chosen today. Figure 1 shows twoalternative structures I have considered in my dis-sertation.

I have calculated load and short circuit currentsfor these alternative structures to find advantagesand disadvantages. One advantage with ring andmesh are lower voltage drops even when usingsmaller sized cables than for the corresponding ra-dial solution. The cable sizing does not need to bethe same throughout the whole ring or mesh. Thecables can be sized due to the actual load current ineach branch. This will reduce cable costs, but canbe difficult to implement with today’s protectiondevices.

Smart protection system

Ring and mesh structures will demand special pro-tection strategies. If it is a goal is to maintainpower supply to most of the installation during afault, one have to install a lot of protection devices.It can be done with todays protection devices asshown in [1], but it could be solved more elegantlywith a smart protection system.

I suggest a system which measures the currents

either in each branch or for each load. These valuesare sent to a central unit which processes the dataand checks for overload situations. If an overloadis detected or predicted, the system can disconnectloads by priority or refuse an enquiry from a loadwhich wants to connect. The protection system canbe a part of a general installation bus system or beseparate.

This system can be used in any power systemstructure, not only for ring and mesh. The systemcan also include power and energy control whichmakes it possible to reduce the energy bill. An-other advantage is that the cable sizes can be keptsmall if the loads must ask for permission. The ca-ble utilisation can be much higher compared withtraditional installations.

References

[1] Frode Larsen. Discrimination by use of nonradial distribution systems in buildings. Mas-ter’s thesis, The Norwegian University of Sci-ence and Technology, Department of Electri-cal Power Engineering, December 1997.

Overhead power lines, as any slender structure, issusceptible to vibrations when exposed to wind. Itis usual to classify the vibrations according to howthey are generated. Galloping is a low-frequencyvibration that can develop if the conductor has orgets (because of icing on the conductor) an aero-dynamically unstable shape. Aeolian vibrationsare caused by vortex shedding from the conductorgiving a oscillating lifting force on conductor.Sub-span oscillations develops when one conduc-tor is laying in the vortex wake of an upstreamconductor.

Galloping can cause conductors to clash into eachother or, in extreme conditions, to fall down if themechanical strength of the line or suspensions areexceeded. Aeolian vibrations and sub-span oscil-lations can shorten the life of the power line if thevibrations causes fatigue, or breaking of individ-ual strands.

It is common to use vibration dampers on powerlines to reduce the level of vibrations. A numberof designs for dampers have been used, but todaythe most common damper is the Stockbridge-damper were damping is a achieved by frictionbetween strands in the messenger wire betweenthe two masses.

Fig 1, Stockbridge damper

The the need for dampers are usually determinedby calculating the frequency and magnitude of

possible vibrations in a worst case scenario, usingan energy balance between wind energy feed intothe conductor and energy dissipated in internal(self-damping) and external damping.

The background for my project is a combinationof two things: the need to measures vibrations onlong fjord crossings with end-span damping, andthe development of new measurement technolo-gies based on optical fibres.

Fjord crossings (in Norway and elsewhere) tend tobe very long, up to 5000 meters, and with the rightwind conditions vibrations of the conductors canbe severe. Damping is then required, and this isfitted as end-span damping close to the suspensionpoints. It is easy to verify that the vibrations closeto the suspension points are small enough to notcause damage. It is however not that easy saysomething about the vibrations at mid span,between the dampers at each end. There have beensome observations that clearly proves that thevibrations in the mid span can be large, even if thevibrations at the ends are small. There is thereforea need to be able to measure vibrations in midspan.

New developments in the field of fiber optics havegiven a possible solution to this problem. Byexposing a doped optical fiber to ultraviolet lightis it possible to create areas in the fiber where theindex of refraction is different from unexposedareas. With this method is it possible to make grat-ings, named Bragg gratings, in the fiber that worksas filters to laser light, in the sense that somewavelengths are reflected, while other wave-lengths are transmitted. The wavelengths that arereflected are determined by the grating spacing,and this spacing changes with the strain in thefiber. This effect is it possible to use as a straingauge to measure strain, by finding the wave-

Vibrations on overhead power lines.

Svein Magne Hellesø

length for maximum reflection from the Bragggrating.

Fig 2, Bragg grating

The aim of my work is to develop a system thatcan measure vibrations in the mid-span of a longfjord crossing using the strain-sensitive Bragg-grating. To do this is there necessary to establish arelation between the amplitude of the vibration ofthe conductor and the resulting strain in the indi-vidual strands of the conductor. For a solid con-ductor will this be a fairly trivial relation, if oneassumes sinusoidal movement, with a relationbetween the curvature of the conductor and theresulting strain on the surface of the conductor.For a multi-strand, multi-layer conductor used inoverhead lines, this relation becomes much morecomplex, due to the fact that the strands and thelayers can slide in relation to each other. A rela-tion between amplitude of vibration and strain willnow also require knowledge of how the slidingwill influence the strain in the strands.

A part of my work will consist of developing afinite element model of a conductor, and use thismodel to find the strain in the strands of a conduc-tor when it moves and sliding occurs. I will alsomeasure the same strains on an experimentalindoor line to verify the model. Some of the workwill also involve field testing of the method on afull scale fjord crossing in Norway.

During the last year I conducted an experimentwith large dynamic deflections on a test span out-side Trondheim. The experiment consisted ofapplying a known load at a point of the line, andsuddenly releasing this load. The movement of theline was recorded using digital video cameras, andthe response from fiber Bragg gratings mountedon the line was also recorded.

A comparison of measured and simulatedresponse of the line is shown on Fig 3. The simu-lations were done using the finite element codeUsfos.

Fig 3, Comparison of measurements and simu-lations of vertical displacement of line.

A full scale installation on a span with a length of3 km across the Glomfjord, operating at 420 kV,was put into operation in the autumn of 2002, andis currently operating as planned. This span has ahistory of vibration damage, and the current vibra-tion monitoring is done for verification ofextended damping installed.

One reason for this span being particularly sensi-tive to vibrations is due to the high tension of theline, operating at almost 50% of the breakingstrength of the line. Increased tension reduces theself-damping of the line, increasing the need forexternal damping to control vibrations.

My work will take place from january 2001 todecember 2004, and is financed partly by NorgesForskningsråd (75%) and Institutt for Elkraftte-knikk at NTNU (25%).

Bragg grating

Reflected Transmitted lightlight

Incominglight

Bragg wavelength

Optical fiber

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The potential threat of global climate change,increasing energy demand and diminishing non-renewable energy has resulted into the world touse renewable energy as alternative source ofenergy.

Photovoltaic solar power (PV) is one of the mostpromising renewable energy sources in the world.Among of its advantages are: reliability, lowoperating costs, non-polluting, modular, andavailability. Two main obstacles for using solarenergy are the high initial capital costs and thevery low PV cell conversion efficiency.

However, study shows that significant costreductions is increasing year to year for PVmodules and the auxiliary components known asBalance-Of-System (BOS). Cost reductions forPV modules are attributed to decrease inmanufacturing costs and improvement in moduleefficiency. BOS costs are also decreasing due toadvanced technology in power semiconductorsand experience of system designers. This trendmakes the PV technology become attractive forresidential and industrial applications [1].

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In a stand-alone PV system, the PV arrays con-tribute to nearly 60% of the total cost, with thebattery storage the second major contributor at30% [2]. To reduce the cost of the PV system, thedesigned system must be efficient. This can beachieved by (1) minimising losses in the converterswitching elements, (2) best utilization of energyfrom the PV string using Maximum Power PointTracker (MPPT), and (3) designing efficient bat-tery charging algorithms to prevent damage tobatteries due to overcharging and deep discharge.

The main objective of this research is to addressthe above three optimization factors. Due to theadvantages offered by digital control over analogcontrol especially in performing complex

algorithms and the flexibility of post-developmentmodification where control algorithms may bemodified, control algorithms for MPPT andbattery charging are done digitally. TexasInstruments microcontroller TMS320F2140 isused because of the features supported,experience already gained in using it, and toolswhich are already developed by the institute forthis DSP (PECCTerm, PECCRos, and loggingfunction).

The control system consists of PV array, step-down (buck) DC-DC converter, lead-acid battery,the load and the control unit (DSP) as shown infigure 1.

The power levels for a stand-alone PV systemsgoes up to 3kW. Since it is very expensive interms of equipment, space and risk (damageduring experiments) required to develop a systemfor such high power in a laboratory, the prototypeto be developed will be for low-power around100W converter charging a battery of 12V.

Once a low-power system works, it is just a matterof small modifications (number of solar arrays,number of battery banks, circuit elements, andvariables values in the algorithms) for large scaleimplementation.

Figure 1:PV digital controlled system with batterystorage

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MATLAB/Simulink has been used for modellingand simulation of the system with the aid ofPower System Blockset and s-functions. Maxi-mum Power Point (MPP) of the solar array is theoptimal operation point for the efficient use of thesolar array. But as the atmospheric conditions(temperature and solar irradiance) changes, theMPP changes too as shown in figure 2. So, MPPTalgorithm has been incorporated in the design totrack MPP. MPPT can reduce the PV generationcosts by about 30%.

Figure 2: Variation of MPP with temperature andirradiance.

To provide maximum battery capacity andprolonged battery life, a four state chargingalgorithm with temperature compensation whichis recommended by battery manufacturers hasbeen used. These states are: trickle charge, bulkcharge, over-charge and float charge.

After finishing modelling and simulation of thesystem, the current stage of research is animplementation of a model into a hardware.Algorithms developed in Matlab/Simulink will betransformed into C and assembly language for themicrocontroller. A complete PV system (solararray, converter, battery, load and DSP) will betested.

It is anticipated that this research will form a goodfoundation for advanced research in PV systems

including incorporating an inverter in a system topower ac loads; optimum load management (loadpriorities); controlling hybrid systems of wind-solar-generator, etc.

References

[1] C. Hua, J.R. Lin, "DSP based controllerapplication in battery storage of Photo-voltaic System", Proceedings of the IEEEIECON 22nd International conference onIndustrial Electronics, Control, and Instru-mentation, 1996, Vol. 3, pp 1705-1710.

[2] J.H.R. Enslin, "Maximum power pointtracking: A cost saving necessity in SolarEnergy Systems", IECON’90, 16th AnnualConference of IEEE Industrial ElectronicsSociety, Vol. 2, pp 1073 -1077.

[3] K.H. Hussein, I. Muta, T. Hoshino, M.Osakada, "Maximum photovoltaic powertracking: an algorithm for rapidly changingatmospheric conditions", IEE proceedingsof Generation, Transmission, and Distribu-tion, Vol. 142, No. 1, Jan. 1995.

[4] F.M. Ishengoma, L. Norum, “Speed control-led DC drive using TMS320F240”. NTNUInternal report, Nov. 2000.

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Start of work: September 1998Finishing date: 2003Supervisor: Lars NorumSponsor: Royal Norwegian Ministry of Educa-

tion, Research and Church Affairs andUniversity of Dar es Salaam -Tanzania.

0 5 10 15 200

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25

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Voltage [V]

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er[W

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1.0kW/m2, 600C

0.8kW/m2, 400C

1.0kW/m2, 250C

0.5kW/m2, 250C

Introduction

One of the most difficult challenges in the field ofwind energy and other renewable energy sourcesis the fluctuating power output. Regulation of con-ventional power plants is absolutely essential tobalance the loads. For that reason several sourceshave claimed that the installed wind power shouldnot exceed 20% of the total installed capacity inan electricity network. In addition locations withhigh wind potential are often found in rural areaswith weak distribution lines. Development ofwind power plants in such areas could requireextensive grid expansions, which results in lowutilization of the grid capacity due to the lowcapacity factor of wind power plants. Grid expan-sions may also lead to unwanted interference withthe local environment.

By using a locally sited energy storage for powersmoothing conventional generators could berelieved from some of their power smoothingfunctions. As a result, this would increase thepotential wind power penetration in electricitynetworks. In rural areas with weak grid connec-tion, a properly dimensioned energy storage couldalso be an alternative to grid expansions. Themanagement of daily and weekly wind variationsrequires both high energy capacity and powercapacity of the storage devices, especially forwind power plants consisting of generators in theMW range. Technologies like conventional batter-ies, flywheels and superconductive magneticenergy storage have the disadvantage that theenergy capacity is related to the power capacity.Moreover, the usage of pumped hydro and com-pressed air storage is limited to certain sites. Onthe contrary, fuel cell systems with hydrogen stor-age are modular devices with separated power andenergy capacity, and are promising alternatives forlarge-scale energy storage. Hydrogen-oxygen sys-

tems are the most commonly known, but there arealso other favourable hydrogen-based systemssuch as hydrogen-bromide and hydrogen-chlorideregenerative fuel cells which use one and the sameelectrochemical cell for charging and discharging.A different regenerative fuel cell technologyknown as Regenesys, which is commerciallyavailable today, is based on a polysulphide/bro-mide redox-couple.

Using hydrogen as a storage medium for intermit-tent energy sources is a very interesting alternativein the long run, especially because of the possibil-ities of using hydrogen as a fuel in the transportsector. The hydrogen storage system can in thiscase simultaneously be used for power smoothingand provide clean fuel for vehicles. In order tooptimize the usage of the hydrogen storage sys-tem, it is necessary to develop a control strategythat takes into account

- the stochastic properties of the energy resource

- electricity price variations

- the value of providing firm power to the grid

- the demand for hydrogen fuel.

Figure 1 shows a wind power plant with hydrogenstorage system. A schematic illustration of anelectrolyser and a fuel cell Polymer ExchangeMembrane (PEM) technology is given in figure 2.

Hydrogen Energy Storage for Renewable Energy Sources

Magnus Korpås17.12.2002

Progression

In june 2001, I participated at the IASTED Power& Energy Systems Conference, Rhodes, Greecewith the paper “Hydrogen Energy Storage forGrid-connected Wind Power Plants”. In thispaper, local hydrogen energy storage is proposedas an alternative to grid reinforcements in ruralareas with high wind power potential and weakdistribution lines. Present and future productioncost estimates of electricity are calculated for dif-ferent wind-storage systems assuming optimaloperation in a competitive power market. It isshown that hydrogen energy storage couldbecome an economically feasible alternative togrid expansions if cost and performance goals ofhydrogen technology are obtained. The controlla-ble power from the wind-storage system must thenbe valued 2-3 times higher than fluctuating powerin the market.

In june 2002, I presented the paper “Operation andSizing of Energy Storage for Wind Power Plantsin a Market System” at the Power Systems Com-putation Conference in Seville, Spain. A dynamicprogramming algorithm is employed to determinethe optimal energy exchange with the market for aspecified scheduling period, taking in accounttransmission constraints. During operation, theenergy storage is used to smooth variations inwind power production in order to follow thescheduling plan. The method is suitable for anytype of energy storage and is also useful for otherintermittent energy resources than wind. An appli-cation of the method to a case study is also pre-sented, where the impact of energy storage sizingand wind forecasting accuracy on system opera-tion and economics are emphasized. Recently, I have written an extended summarytitled “Optimal Operation Strategy of HydrogenStorage for Energy Sources with StochasticInput”. The summary is submitted for review forthe IEEE Power Tech Conference in Bologna2003. In this work, the operation strategydescribed in the previos paper has been improvedby empolying a stochastic dynamic programmingalgorithm.

Initiation and funding

This doctoral study started in November 1999 andis scheduled to be finished by the end of 2003.The programme is funded by Statkraft and theNorwegian Research Council and my supervisoris prof. Arne T. Holen. Since knowledge of elec-trochemical energy technology is required, a co-operation with the Department of Materials Tech-nology and Electrochemistry is established. Myown background is from Department of Physics atNTNU, and I graduated in December 1998.

Figure 1. Wind turbine with a local hydrogenstorage.

~- -

~

Electrolyser

Hydrogentank

Fuel cell

AC 22 kV

AC 66 kV

AC 22 kV

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H2+½O2 H2O+power

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power+H2O H2+½O2

Figure 2. Proton exchange membrane (PEM)electrolyser and fuel cell.

Risk Management in Electricity Markets

by Tarjei Kristiansen November 2002

Personal background I graduated from the University of Oslo, Department of Physics in July 1995, with an MSc in theoretical nuclear physics. Afterward, I served my compulsory military service at the Norwegian Defence Research Establishment (FFI) as a research assistant. I worked with programming and system development of computer code used in the monitoring of radioactive contamination by the Norwegian Defence. I also worked for six months as a researcher with theoretical models for contamination of radioactivity. I have one year’s experience as a high school science teacher. In January 1999, I began work toward a doctoral degree at NTNU. My research is risk management in electricity markets, emphasising how risks associated with transmission congestion can be hedged. I plan to finish my dissertation in 2003. Initiation and funding This work is financed by The Research Council of Norway and is a part of the Strategic Institute Program (SIP). My supervisors are Professor Ivar Wangensteen at the Department of Electrical Power Engineering and senior researcher Birger Mo at Sintef Energy Research. Study and objectives My study first focused on hydropower scheduling and risk management. In 2000 I switched to the field of risk management associated with transmission congestion. The subject interests me because such risks can be managed by transmission congestion contracts (TCCs) [1].

The payoff from the contract is given in the following formula: TCC = (λj -λi) Pij ≤ ≥ 0 (1) where λj is the spot price of location j, λi is the spot price of location i and Pij is the directed quantity specified in the TCC for the path from i to j. When there is congestion, the prices at the locations will differ and a player injecting power at location i and withdrawing at location j, will receive a positive payoff equal to the fee paid for congestion. In this way it hedges against the congestion fee. In the context of the Nordic market, the situation is illustrated in Figure 1. If there is congestion in the Nordic power system the Area Prices will differ from the System Price, with prices lower in the surplus area and higher in the deficit area. To hedge the Area/System Price differential the player can buy a Contract for Difference, with payoff equal to the price differential. In 2002/2003 I received an appointment as a Doctoral Fellow at the JFK School of Government at Harvard University under Professor William Hogan, a leading expert on electricity economics and the architect of TCCs. My research is now concentrated on the following topics: • congestion risks and financial products

for hedging against these in the Nordic area and the USA

• evaluation of transmission rights and techniques for risk management.

I have written a paper describing how the Nordic contracts for hedging transmission congestion were priced at Nord Pool. Currently I am researching and writing four papers.

Results I have completed my coursework, and been a research assistant in the courses, Energy Planning and Power Markets, at NTNU. I have also taken voluntary courses in economics and finance. During the academic year 2001-02 I worked for Norsk Hydro ASA as a generation planner in its Department of Electricity Portfolio Management and Trading. This gave me a better understanding of how the power market works, and I implemented a model for integrated risk management there. To date I have presented seven papers at international conferences. Another one has been accepted for publication in the journal “Modelling, Identification and Control.” I have also been asked to become a referee for a journal.

References [1] W. W. Hogan, “Contract Networks for Electric Power Transmission,” Journal of Regulatory Economics, 4:211-242, 1992.

Demand

Supply Area Price Sweden

Demand

Supply

Area Price Norway

Demand

SupplySystem Price

• Transmission constraints between Sweden and Norway • Assume electricity flow from Sweden to Norway

Area Price Norway > System Price > Area Price Sweden

Figure 1. Transmission congestion in the Nordic region.

Multilevel Power Electronic Converters for High Power Drives

Richard Lund (richardl@elkraft.ntnu.no)

Initiation I graduated from the Dept. of Elec. Power Engineering, NTNU in March 1999, I attended the Electric Energy Conversion Group as a research assistant in April 1999, and started on my Ph.D. degree in January 2000. My Ph.D. project was initiated by my advisor prof. Roy Nilsen, and is financed by the Dept. of Elec.Power Eng., NTNU. The plan is to finish my work in Dec. 2003. Introduction Multilevel Power Electronic Converters (MLPCs) have become attractive the resent years in high voltage and high power applications such as adjustable speed drives and electric utility applications. The development of MLPCs began in the early eighties when Nabae et al. [1] presented a neutral-point clamped (NPC) PWM Inverter in 1980. Since then a variety of topologies have been presented. The general structure of the MLI is to synthesise a sinusoidal voltage out of several levels of volt-ages. The MLI can therefore be described as a voltage synthesiser. For a three phase Voltage Source Inverter (VSI), often named 2-level inverter, the maximum voltage level output is determined by the voltage blocking capability of each device. By using a multilevel structure, the stress on each device can be reduced proportional to the number of levels, and the inverter can handle higher voltages. This means that an expensive and bulky step up transformer can be avoided in the application. Another advantage of a multilevel outputwaveform is that several voltage levels leads to a better and more sinusoidal voltage waveform, thus a lower Total Harmonic Distortion (THD) is obtained. With several levels in the outputwaveform the switching dv/dt stresses are

reduced, and hence the lifetime of motor and cables are increased. The different MLPC topologies can be divided into the following categories (Figure1):

Diode Clamped Converters Flying Capacitor Converters Series Connected Single Phase H-Bridge

Converters Configurations with Multiple Three-Phase

Converters

a)

b)

c) d) Figure 1: One phase leg of different inverter topologies: a) 3-level Diode Clamped (NPC), b) 4-level Flying Capacitor, c) 5-level Series Connected H-bridge, d) 2-level.

There also exist a variety of topologies based on the inverters in Figure 1. Topology b) in Figure 1 needs separate isolated dc supplies for each dc-bus, thus a complicated transformer/rectifier system is needed. The Diode Clamped Inverter can be supplied through a single dc-source, which is favourable in most applications. The problem of this topology is the balancing of the capacitors in the dc-link.

Figure 2: Typical output waveform for 2-, 3-, 4- and 5-level motor drives. From left: voltage, current and harmonics.

In Figure 2, a comparison of the output waveform is shown. It can be seen that the distortion is far lower for the MLPCs. In Figure 3, a plot of the output voltage THD is given.

Figure 3: THD as a function of modulation index. In the extrapolation of converters to higher power level, the fundamental question of increasing the converter current rating (devices in parallel) or the converter voltage rating (devices in series) always has to be answered. The conduction losses in converters always favour the increased voltage model. All these factors contribute to the necessity for multilevel converter topologies. In Figure 4 results from a analytical calculation are shown for a drive application at 1 MW at full speed, 2500 V DC-bus, 1 KHz switching freq., constant load torque and IGBTs from EUPEC.

The results show that for this application, the total losses are reduced by up to 50 % using a multilevel topology [3].

Figure 4: Normalized total losses for 1 MW drive. Status of work Analytical expressions for switching- and conduction losses for MLPCs are developed. Harmonic analysis of the output waveforms has also been done. Laboratory prototypes have been built and control strategies for these are under development. Primary Goals The main goals for my work are to analyse the different topologies presented in the literature and optimise the most interesting topologies with respect to losses and harmonics. Another topic is the dc-bus balancing problems in Diode Clamped Multilevel topologies. The theory will be supported by converter prototypes in the lab. References [1] A.Nabae, I.Takahashi, H.Akagi: "A Neutral-point Clamped PWM Inverter", IEEE-IAS’80 Conference Proceedings pp. 761-766, 1980. [2] B.K.Bose (editor): "Power Electronics and Variable Frequency Drives, Technology and Applications", IEEE Press 1996. [3] R.Lund et.al: "Analytical Power Loss Expressions for Diode Clamped Converters", PEMC 2002.

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Distributed generation is generating plant servinga customer on-site or providing support to a distri-bution network, connected to the grid at distribu-tion-level voltages [1]. In the definitions, upperlimits on the plant size ranges from 1.5 to 100MW [2]. Electricity from distributed generationcan both be used for on-site purposes and be soldto the distribution network.

The last decade the power system has undergonelarge changes. Electricity markets have been liber-alised and there has been an increased focus onemissions and sustainability in the sector.

Traditionally most power generation has origi-nated from large central power plants. However,in the future this might change because of the newrequirements to power generation. The EuropeanRenewable Energy Study found that around 60%of the renewable energy potential that could beutilized within 2010 could be described as distrib-uted. Some studies indicate that within 2010 asmuch as 30% of the new generation capacity canbe distributed [2].

To be implemented in liberalised power marketsdistributed generation will have to be economi-cally competitive. Today most options are tooexpensive but this might change due to many fac-tors such as mass production, technology learningcurves, increased electricity price, increased envi-ronmental taxes, changes in the grid taxation andby government incentives.

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There are many different technologies that can beused on a local level. Examples are:

• Gas turbines that can use oil, petrol, diesel oil,natural gas, hydrogen and biogas

• Reciprocating engines that can use oil, petrol,diesel oil, natural gas, bio wastes and biogas

• Fuel cells that use hydrogen

• Photovoltaic systems

• Small-scale hydropower

• Wind turbines

Distributed generation has economically advan-tages over power from the grid because on-siteproduction avoids transmission losses and distri-bution costs and because power production fromcombustion generates heat that can be used by thecustomer. In addition inexpensive fuels such aslandfill gas can easy be used locally. Despite this, most of the technologies listed abovehave to high current costs to be profitable in theNorwegian market. Therefore technologicaldevelopment and government support are neces-sary for them to be implemented on a large scale.However, if the electricity price rises to 100 øre/kWh some of the technologies can be profitable.For the combustion technologies this requires uti-lization of heat, and wind power and small-scalehydropower requires sites with particularly goodconditions [3].

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Karl Magnus Maribu18/12 2002

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The objective for the work is to develop modelsand methodologies to analyse distributed genera-tion in the power system. The model will be usedto analyse whether increased investments in dis-tributed generation are a sensible path to a sustain-able, efficient and secure energy system. Differenttechnologies have different properties, and theproperties and external effects of the technologieswill be compared with the alternative of increasedcentral generation and transmission capacity.

An important part of the work will be to analysedifferent political strategies that stimulates invest-ments in efficient and environmental friendly dis-tributed technologies that gain society.

The plan is to analyse electricity and heat produc-tion with the same model. Combined heat andpower plants (CHP) are promising, and have ahigh energy-efficiency.

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My PhD studies began in September 2002 and areplanned finished during the spring 2006. The PhDis a part of a project on SINTEF Energy Researchon distributed generation. The Research Councilof Norway finances the work and my supervisor isIvar Wangensteen.

This first year most of the time will be spent onfinishing the exams and doing literature studies inthe area of distributed generation. Gradually morework will be spent on modelling and case studies.

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I graduated from the physics department at NTNUJuly 2002. In addition I have an intermediate sub-ject in political science also from NTNU. On mydiploma thesis I worked with system dynamicmodelling of the Nordic power system, and analy-sed different paths to a sustainable energy future.

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[1] IEA (2002 ) ��������������� ����������� ����������������� ������ IEA/OECD Paris.

[2] Ackermann (1999) �������������������� ������� ������� ��� ���������������� Work-ing Paper. Stockholm.

[3] Grinden, B., Morch, A., Brandås, M., Stang, J.,Berner, M., (2002). ��� � �� ����������� ������������� ! "������� ������������ SINTEF TRA5712.

IntroductionExternal electric fields have been applied extensi-vely to break water in oil emulsions. Historically,the electric treatment has been established sincethe beginning of the 20th century. The electro-static treaters use the electric field to enhance coa-lescence of water droplets in crude oil and thenreduce the settling time. Although the exact wayin which this occurs is not yet clearly understood.Water-in-oil type emulsions are readily formed inthe production of crude oil. This is causing pro-blems at different stages of the production.Corrosion of pipes, pumps and other processingequipment and the complications due to increasedemulsion viscosity are consequences of presenceof water. There are number of commercial reasons forremoving the emulsified water from the crude oil.The cost of transporting water in pipeline or tan-ker and the extra processing equipment requiredto produce quality crude oil add to the productioncost. The slow rate at which liquids may be naturallyseparated in many water-in-oil type dispersionshas important commercial consequences.Currently there are several available methodssuch as chemical demulsification, gravity or cen-trifugal settling, filtration, heat treatment mem-brane separation and electrostatic demulsification.Each of these methods has its own advantages anddisadvantages. The conventional electroseparators are huge, aslarge residence time are required for the electro-coalescense regions and settling zones to separatethe enlarged water droplet from the crude oil.however this could cause complications for off-shore as platforms structures usually has limitedspace. Optimisation of the coalescense processwould be able to reduce the residence time of thedroplets in a given physical system, and therebyincreasing the volumetric throughput and enab-ling the utilisation of more compact and conse-cuently cheaper units.

ObjectivesThe main aim of this work is to study and charc-terize the forces on the droplets in an emulsionstressed wtih an electric field.

Forces on a droplet in an electric fieldTo describe the electric forces on a droplet it ishelpfull to compare the responses of charged andof neutral matter in both uniform and nonuni-formfields. In a uniform field (fig 1a) a chargedroplet is pulled along the field lines towards theelectrode carrying the charge of the opposite tothat on a droplet. There will act a coulomb forceon the object written as:

In the same field a neutral droplet will be polari-zed. There will be induced a negative charge onthe side nearer the positive electrode and positive

charge on the side nearer the negative electrode,as shown in fig 1a. Since the field is equal on bothside of the matter in an uniform field, there willnot be any net translation force on it. The matter

Principle of electrocoalescence in crude oil

Atle Pedersen

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eq. 1FE qE=

Fig.1 Different respons on neutral matter in uni-form and nonuniform field

will not move to any of the electrodes. In fig. 1b a nonuniform field is applied, there is adifferent behaviour of the charged and unchargedobjects. The charged behaves much as before,being pulled along the field line. It is still attrac-ted toward the electrode with opposite polarity.The neutral matter will in this case get an transla-tion force on it. Since the matter is neutral the twocharges due to polarisation will be equal. But thefield operating on the two sides on the matter isunequal. This gives a net force towards the regionof stronger field. Under the assumption that theneutral matter can be considered as a dipole theforce can be written as below.

Fig 1b also show that the force on the neutral mat-ter is in the same direction no matter which elec-trode is charged positive and which is negative.Therefore will the object in an AC field move inone direction towards the region of stronger field

Drag forces. When a droplet is moving in a fluid a drag forcewill act on the droplet. This is a sum of the fricti-on drag and the pressure drag. In a stagnant fluidthe force can be quantified by the drag coefficientthrough the equation

where ρc is the density of the continuous phase,CD is the drag coefficient, A is the representativearea of the droplet and v is the velocity of the dro-plet.

Forces in an emulsionAn aqueous droplet will distort the field due to thedifference of the permittivity of the water and theoil. This will result in a nonuniform field aroundthe droplets. In principle the forces between twodroplets will be as described above. But in anemulsion there is mutual polarisation of the dro-plets by any neighbouring droplets. Therefore willthe assumption of regarding the droplets as dipolenot be applicable. To allow for mutual polarisati-on the forces must be simulated numerically. Thiscan be done with Finite element method (FEM)or boundary element method (BEM).

Experimental method. The velocity of the drops is measured with a highspeed video camera with a microscope lens. Theoptical bench used in the measurements is shownin figure 2. From eq 3 the drag forces can be esti-mated and the electric forces can be derived fromnewtons 2. law. The forces measured with the camera will be com-pared with the forces simulated numerically.

Further workFurther experiments will be designed in order tomeasured the forces between the droplets in anemulsion. Numerically, Boundary ElementMethod, simulations will be performed on compa-rable distributions of droplets to investigate theforces between droplets in an emulsion

AdvisorsProf Erling Ildstad is the main advisor in thiswork. Prof Arne Nysveen is co-advisor.

Digitalt Camera Long Distance Microscope Test Cell

Background Light

Test object

Laptop

Electrodes

Translation stages

Strobe Light

Figure 2. Optical bench be used for investigation of droplets and emulsions

eq. 2FE µ∇E=

eq. 3FD12---ρcCDAv2

=

Initiation and fundingI graduated from NTNU, Department of ElectricalPower Engineering in December 2000. After gra-duation I have been working as a scientific rese-arch assistant with the Energy Conversion Groupat the same department. I started my studiestowards a Ph. D. in September 2002. The thesis isplanned to be finnished during the fall 2005.

The Ph. D. work is a part of the project Technolo-gies for Reliable Distributed Generation of Elec-trical Power from Renewable Energy Sources,funded by the Research Council of Norway andwith Power-One as industrial partner.

Professor Robert Nilssen is my supervisor.

Main objectivesThe main goal for the project is to develop energyefficient components and enviromental friendlysolutions that enables different distributed rene-wable energy sources to work as stand alone elec-trical power supplies or to be optimally integratedwithin the future electric power infrastructure.Having a transfere of this knowledge to industryor eventually establish new industry and toimprove scientific knowledge and develope a sci-entific competent staff in the field of renewableenergy systems.

BackgroundElectric power systems include power generation,distribution and control, and consumption of elec-tric power. The electric utility industry has histo-rically utilised a centralised, hierarchical structurewhere electricity is generated in large powerplants and then distributed through an extensivetransmission and distribution network to thepoints of demand.

The Energy Conversion Group at Department ofPower Engineering at NTNU also has a definedRenewable Sources of Energy strategy. Todevelope cost-optimal power electronics and elec-trical machines which enable best utilization ofthe energy sources with respect to energy-effici-ency and environmental issues.

GoalThe goal for my thesis is to develope a computertool for calculation and optimization of a genera-tor/starting motor to be integrated in several typesof distributed power systems using reciprocatingengines. With use of compact winding, integrationof permanent magnets and using the generator as astarting motor with minimum energy consump-tion. Optimization will focus on minimal materialcost and maximum efficency, combined with afocus on the cost of the power electronic converterand control of the generator.

StatusI started my studies in September 2002, my mainfocus this fall has been to follow compulsorycourses.

Future workSpring 2003 will be used to finish the compulsorycourses.

I will also start the work of building a computeri-zed calculation program of a synchronous perma-nent magnet machine. The programming languagechosen is C++. The program is planned to be usedup against a optimization routine. For the thesis Iplan on using genetic optimization, which is anexciting and powerful optimization technique.The challenge in using this technique lies in get-ting a good mathematical description of the mac-hine analysed.

Optimial Design of Permanent Magnet Generators for Distributed Power Generation

Stev E. SkaarDecember 2002

Background

I graduated from NTNU, Department of Enginee-ring Cybernetics in December 1997.

The research started January 1999, and is schedu-led to be completed by summer 2003. I have wor-ked 18 months on another project in this period aswell.

The PhD work is connected to a research programfunded by the Research Council of Norway.

Prof. Lars Norum is my supervisor.

Introduction

The goal of my PhD is to develop a new genera-tion of flexible digital control systems. It includesspecification, calculations, simulations, circuitdesign and experiments on a prototype invertersystem based on the Texas TMS320F281x DSPseries.

A inverter consists of a pulse width modulator anda filter. The pulse width modulator gives an outputvoltage which is then filtered by the filter to give asmooth sinusoidal output voltage. A simple sche-matic is shown below:

The filter has as little resistance as possible toavoid power losses. This means that the filter hasa very strong resonance which must be attenuatedby the regulator controlling the pulse width modu-lator.

The pulse width modulator introduces an nonli-near phenomenon called deadband. This is causedby non-ideal switches, as they require a certaintime between one switch is switched off andanother is switched on. The deadband gives a dis-turbance in the output voltage of the pulse widthmodulator which is dependent of the current. Asmost regulator design tools expects linear systemsthis introduces problems in the design phase, lead-ing to more conservative designs than necessary.By modelling this phenomenon and measuring thecurrent, its impact on the output voltage can bereduced by adding a correction factor to the regu-lator output.

Several inverters may be connected in parallel inorder to increase total capacity or reliability(redundant systems):

If one inverter fails the others can still maintainthe voltage on the safe bus. The reliabilty of theparalleled inverters will be even higher if theinverters are able to work as autonomous unitswithout communication, see e.g. [1]. One of theregulators developed has this capability. By usingthe regulator to shape the apparent impedance ofthe inverter, it is possible to let several inverterssupply power to the same net without any commu-nication other than the net voltage. A paper descri-bing this regulator was presented at the norpieconference in Stockholm, September 2002.

Digital Control of Power Electronic Inverters

Tore Skjellnes14.01.2002

Status

Obligatory courses are all done, and simulationmodels have been developed. A new generation ofthe PeccRos software system used for communi-cation between the DSP controller and a PC sys-tem has been created.

Hardware for experimental verification for threephase inverters is still missing, but some experi-ments have been conducted on one phase inver-ters. The work has been delayed by the lack ofhardware.

References

[1] M. C. Chandorkar, D. M. Divan, Y. Hu, and B.Banerjee, “Novel architectures and control for dis-tributed systems,” in Proc. IEEE APEC'94, 1994,pp. 683-689 vol. 2.

InitiationI graduated from Department of Power Engineer-ing at NTNU December 1999. In January 2000 Istarted as a scientific assistant and continued on aPhD from September 2000. The project is sched-uled finished in December 2003. The project isinitiated by my advisor Prof. Roy Nilsen and isfounded by NFR and ABB Corporate Research.

BackgroundABB in Norway has world responsibility withinABB of offshore and subsea installations. Theelectric power in these installations is increasing.Use of controllable switches as high voltageIGBT’s can open up for more competitive andcompact components and systems. ABB want tobuild up competence about these new high voltageIGBT's design, control and practical use. It is nowavailable samples of power electronic componentsfor 4.5 to 6 kV. It is important to study how thesecomponents can be controlled and how new topol-ogies can be used to reduce the losses in thesecomponents.

The projectThe primary goal in my PhD study is to develop atopology and the power electronic components tomake a high power, high voltage electronic dc-dcconverter with galvanic separation. It means useof high voltage IGBT and high frequency trans-formers in the MW area.

I am going to study, analyse and develop topolo-gies for the power circuit for the converter. I willalso study and test new high voltage IGBTswitches and design of high frequency transform-ers.

A prototype of the converter will finally be madeand tested. The results from the measurement willbe compared to the theoretical analysis. Cost and

power factor is important criteria's that must bemaintained in the design.

Some parts of the work will be published in inter-national conferences and in scientific magazines.The goal is to publish at least two articles.

StatusI have chosen to use a Dual Active Bridge topol-ogy as the figure below shows.

Figure 1: DAB converter

This topology gives galvanic separation betweeninput and output. It is also possible to run the con-verter as a resonant converter. This can reduce thestress on the switches and give lower losses in theconverter.

Modern IGBT switches has a blocking voltage upto 6kV. The input voltage on the converter is in therange of 30kV. This implies serial connection ofIGBT’s to be able to block the voltage.

Power supply to the gate driver for these serialconnected IGBT’s are difficult. The supply volt-age of a gate driver is in the order of 15 - 30Vdc.

Transformatorn:1

D1A+T1A+ D1B+T1B+

D1A-T1A- D1B-T1B-

D2A+T2A+ D2B+T2B+

D2A-T2A- D2B-T2B-

L

IL

A

B

C

D

High power high voltage electronic dc-dc converter

Gjermund Tomta13.12 2002

Some of the IGBT switches may be at a potentiallevel 20 to 30kV. This level is also jumping. To liftthis voltage from ground level up to a potentiallevel of 30kV require bulky transformers althoughthe power transfer may be small.

To solve this problem I have made a self suppliedgate driver. It extracts the energy from the turn offsnubber over the switch and converts it to a properDC voltage for the gate driver. Figure 2 belowshow one of the series connected IGBT’s and itsgate drive and power supply.

Figure 2: Self supplied gate driver

This power supply is tested and functions well.The power supply is independent of the number ofswitches series connected. Figure 3 below showsthe scheme of the power circuit.

Figure 3: Circuit scheme of power supply

This solution does not avoid galvanic separationfor the gate driver power supply completely, butthe transformer is reduced to the same voltage asthe switch is rated for. A regenerative solution ofthe power supply is also made but not tested yet.This passes the surplus energy of the from the turnoff snubber back to the dc-grid.

Further workThe remaining work is to find the appropriatedesign of the transformer between the two bridgesin the Dual Active Bridge.

The control system of the Dual Active Bridgetopology must be designed.

A study the type of IGBT best fitted in a seriesconnection and a study switching of series con-nected IGBT’s is also planned.

This is scheduled for spring 2003. During autumnbuilding of converter and testing will be done.

References

[1] K. Vangen, T. Melaa, S. Bergsmark R. Nilsen,“Efficient high-frequency soft-switched powerconverter with signal processor control”INTELEC’91

[2] P. R. Palmer, A. N. Githiari “The series con-nection of IGBT’s with active voltage sharing”IEEE Transactions on power electronics vol.12no.4 july 1997

[3] R. Roesner, J. Holtz, R. Kennel “Self poweringdriver circuit for series connected power semicon-ductors” EPE 2001

CS

Dsw

TswB2

DS

Gatedrive

Powersupply

switching signalby fibre optic

+

-

+-

R0 1.2k

Rc 7.5

VoltageregulatorVout=15V

Cs 0.1u

D0

Rg 100k

Zg=10V

Rs 10k

Lc 1.5m

Cc 470u Zc=22VDs

Dsw

Tcharge

Tsw

Dc

C

E

+

-

Vout=15v

+

IntroductionThis dr.ing study is a part of the project“Polymerisolasjon for neste generasjon HVDCkabel.” The initiation is made by Nexans NorwayAS which is also responsible for the financestogether with Norsk Forskningsråd and Statnett.My work started in August 2001 and is due to befinished in 2005.Superviser will be Erling Ildstad and RolfHegerberg.

BackgroundDuring the last 50 years HVDC distribution hasbecome more common, especially use of subseacables. For long distance bulk distribution HVDCis often the only available technology. Since the1950’s the insulation of the cables has been massimpregnated paper, which has shown good quali-ties with few problems. Still investigations havebeen done on another type of insulation, polymermaterials. These are already widely used in ACcables, but with HVDC electric charge builds upin the insulation and may cause breakdown of thecable. Also, the conductivity of this insulation arestrongly dependent of temperature and field gradi-ent.

A and B are material constants and these varywidely for different materials as well as with theadditives added. When the properties of the poly-mer insulations are investigated properly the resultwill be cables with a technical, economical andenvironmental advantage to the mass cable.Projects in the close future may be the connectionfrom an oil-platform in the North Sea to the distri-bution system on the mainland.

WorkThis work will be conserned with the conductivityin Crosslinked polyethylene (PEX.) Investigationswith constant field and varying temperature orvice verca will be accomplished

The measurements will be done with PEX insula-tion material. Rogowski shaped objects are made,and electrodes of aluminium is used for currentmearsurements while semiconductors are used forthe space charge measurements.

The conductivity of a object is measured by a cur-rent measurement. It is often assumed that thefield through an object is uniform given by E=U/d. This will not be the case with a polymer as thefield is given from the space charge in the object,and the space charge is influenced by the tempera-ture and the amount of time the object has beenstressed. To investigate this, space charge measur-ments are done using the pulsed elctro-acousticmethode (PEA.) The objects are charged by avoltage and a temperature gradient, and this givesa variation of the field through the object. Thebuild up of space charge in a 1 mm object during24 hours is shown in figure 1.Comparing these measurements with the conduc-tivity measurement should give an understandingof how temperature and field influence the con-ductivity of the HVDC insulation.

σ A ϕkT------

B E( )sinh( )1 E

--------------------------------exp=

Polymer insulation of HVDC cable (preliminary title)

written by Sidsel Trætteberg

1.5x101

1.0

0.5

0.0

-0.5

-1.0

nC/m

m3

2.01.51.00.50.0

mm

12/12/02 10:42

Fig.1 Build up of space charge during 24 hours.The red curve is taken at t=0.

A long-term system dynamic analysis of the Nordic power marketThere are several models for analysis of the Nor-dic power market, the ones used in Norway is theEMPS model, and SSB’s Nordmod-T. The EMPSmodel focuses on production scheduling of hydro-power, and is a tool for analysis of productionscheduling and prices. Nordmod-T on the otherhand, is a model for long-term analysis of the pow-er market, where investment decisions are endog-enously included. However, the model does notinclude hydropower scheduling, which is an im-portant feature of the Nordic power market. Wehave constructed a system dynamics model withthe ambition of including both long-term mecha-nisms such as investment decisions, technologicalprogress and resource availability, and short-termmechanisms such as production scheduling andprice formation. The work was initiated by Botter-ud et al. (2000, 2002) through the first version ofKraftsim, and we have continued developing the

system dynamic model later on (Vogstad et al.,2002). Figure 1 shows the main feedback relation-ships that are important for the long-term develop-ment of the Nordic power market. Though themodel is not finished yet and has to be modified,some interesting results are already apparent. Fig-ure 2 shows the simulation runs for a reference

run, with 100 NOK/MWh subsidies for renewa-bles (as will be the assumed average for the Nordiccountries when the Swedish green certificate mar-ket is introduced in 2003). The thick lines showsthe system response when 3200 MW of conven-tional gas power is introduced from 2005 on. Theresults show that gas power might substitute somecoal power in the short run, but this substitution ef-fect is very short and limited due to the low opera-tional costs of the existing coal power plants inoperation. In the long-run, gas power also substi-tute investments in renewables by suppressingelectricity prices which reduce the expected profit-ability of wind power and biomass and stimulatedemand growth In total, new gas power in the Nor-dic market increase the CO2-emission in the Nor-dic countries.

Figure 1 Main feedback loops of the electricity supply side

Price of electricity

Capacity factor

operational costs

Electricitygeneration

Capacity

Expected profitabilityof new capacity

Investment &operational costs

Technologicalprogress

Resourceavailability

+

-

-

+

+

-

-

+

B1 - Unitcommitment

B2 - Capacityacquisition

R1 - Learningcurve

B3 - Resourcedepletion

-

+

-

+

B4- erosion ofCF

Demand

Fractional growthrate

Price elasticity ofdemand

-+

-

+

B0 - Demandbalance

+

Figure 2 Simulation results. Thin lines show reference run scenario: The nordic power system with 100 NOK/MWh subsidies for renewables. Bold lines show what happens when 3200 MW of gas power is introduced in 2005.

A system dynamics analysis of the Nordic power marketPhD abstract

Klaus-Ole VogstadMSc. Mech.engineering, NTNU

SEFAS/Sem Sælandsvei 11/7465 Trondheim/NorwayAt NTNU: Phone: +47 73 59 76 44 Fax: +47 59 72 50 mobile: 928 510 67

e-mail: klausv@stud.ntnu.nohttp://www.stud.ntnu.no/~klausv

2

Production scheduling with wind powerThe large increase of wind power in the Nordicelectricity supply provides interesting opportuni-ties for regulating power. Short-term, hourly fluc-tuations can be handled through the market forregulating power, whereas seasonal and yearlyvariations in hydro are handled through schedulingtools such as EOPS and EMPS1. The complemen-tary characteristics of hydro inflow and wind pow-er shown in figure 3 can be utilised to improve themanagement of the water reservoirs. The in-creased flexibility in reservoir management is re-flected in the added profits of buying/selling in themarket, and simulation runs (using EMPS) showthat the value could be as much as 9% higher thanthe area spot price. These results are still uncer-

tain, and currently, a simplified EOPS model fordetailed analysis is being built. The simplifiedEOPS model serves the purpose of studying thechange in optimal hydro scheduling from the wa-ter value calculation for various constraints on in-flow, wind energy, reservoir size and access tomarket. In addition, the simplified model will alsobe used in the system dynamic model to representproduction scheduling with hydropower. In partic-ular, new investments and changes in technologymix will also change the qualitative shape of opti-mal reservoir curves, and some of these concernswill be addressed.Collaboration with the SINTEF-project “New re-newable energy production in Norway” was con-ducted during 1999-2000, and the work is reportedin four conference publications and a final SIN-TEF report:“Integrasjon av vindkraft i det norskekraftsystemet”. (Vogstad, 2001)

The work was financed by The Research Councilof Norway (NFR), under the “EFFEKT” pro-gramme. The PhD work started in Sept. 98’, andwill be completed during March 03.

Publications (also available at homepage)Vogstad, K-O, Belsnes, M. M., Tande, J.O.G., Hornnes,K.S., Warland, G. (2001): Integrasjon av vindkraft i det nor-ske kraftsystemet. Sintef TR A5447 EBL-K 32-2001

Vogstad, K-O. (2000a) Utilising the complementary chara-teristics of wind power and hydropower through coordinat-ed hydro production scheduling using the EMPS model.Proceedings, Nordic Wind Power Conference, March 2000,Trondheim, Norway.

Vogstad K-O, Holttinen H, Botterud A. and Tande J.O.G.(2000b) : System benefits of coordinating wind power andhydro power in a deregulated market. Published in proceed-ings "Wind power for the 21st Century" 23-25. Sept 2000, inKassel, Germany

Tande J.O.G., Vogstad, K. (1999) Operational implicationsof wind power in a hydro based power system. ProceedingsEuropean Wind Energy Conference, 1.-5.3.1999, Nice,France

Holttinen, H., Vogstad, K-O., Botterud, A., Hirvonen, R.(2001) : Effects Of Large Scale Wind Production On TheNordic Electricity Market. Ewec‘2001, Copenhagen, Den-mark, 2-6 July, 2001.

Botterud, A., Korpås, M., Vogstad, K-O (2000): En langsik-tig systemdynamisk kraftmarkedsmodell. Proceedings, NEFtechnical meeting. pp157-165 , Trondheim, Norway.

Botterud, A., Korpås, M., Vogstad, KO., Wangensten, I.,(2002): A Dynamic Simulation model for Long-term Analy-sis of the Power Market. Paper accepted for the Power Sys-tems Computation Conference, 25th -28th June 2002,Sevilla, Spain.

Vogstad, K-O., Botterud, A., Maribu, KM., Grenaa, S.,(2002): The transition from a fossil fuelled towards a renew-able power supply in a deregulated electricity market. Paperaccepted for the System Dynamics Conference 28th -1st Au-gust, 2002, Palermo, Italy.1. EOPS: Efi’s One-area Power Market Simulator; EMPS: Efi’s

Multi-area Power Market Simulator

Figure 3 The complementary properties of wind and hydro inflow

5 10 15 20 25 30 35 40 45 50

1

2

3

4

5

6

Week no.

No

rma

lise

d w

ee

kly

da

ta [

%]

Hydro inflow MidtnorgeHydro inflow Norway Demand Norway Demand Midtnorge Wind Energy

Figure 4 Water values from SDP computation

05

10

5

10

0

50

100

150

200

250

period [months]reservoir [MWh]

Wat

er v

alue

[N

OK

/MW

h]

Sensorless control of Permanent Magnet Synchronous Machines

Sigurd Øvrebø

Initiation The work is supported by the Norwegian University of Science and Technology. Industrial partner for the project is Smart Motor. The study was started in January 2000, and the thesis is due by January 2004. Introduction The development of electric machine drives must meet new challenges as the cost of electronic equipment rapidly decreases. Electric machines are becoming a part of most people’s lives as their arena continues to expand through household equipment, office equipment and even in new car designs. The enormous expansion of the application arena for electric machines gives new criteria for integration and reliability of the drive systems. High performance drives have earlier been dependent on sensors for flux and position measurement. The reliability of these systems depends on cabling, connectors and the sensors located at the motor location. Great advantages can be obtained if flux and position estimates can be obtained without the sensors located at the motor. During the last decade a lot of research has been done to make a high performance drive system without a position sensor. Most of the research use saliency’s in the electric machines as the input to the position estimators. This saliency’s can be apparent in the machines for different reasons. With interior permanent magnet the magnetic properties in the rotor are inherently different in the d-q axis. This is due to the different magnetic permeability of iron and magnet.

Machines with surface mounted magnets have no saliency if there is no saturation in the machine. When the permanent magnets are introduced in the machine there will be some parts of the stator that goes into saturation. This results in a position dependent variation in the machine inductance. Several different methods are used to extract the variations in the current resulting from the position dependent inductance. Common for all methods is that one need to use an additional signal to get the position information from the measured currents. Different machines have different behavior of the position dependent inductance. The inductance in the machine is frequency and load dependent. To precisely describe the saliency position one has to understand totally the electromagnetic behavior of the machine. Also one have to describe the different test signal flux pats in the machine. Two different methods are tested on booth surface mounted and buried magnet machines. The first method [1] is developed in University of Wisconsin, Madison, USA. This method use a balanced three phase high frequency test signal.

Current

Regulator

PWM - Voltage

Source Inverter

( PWM-VSI)

AC Machinewith Saliency

HPF

+

–

++

θr, ωr

scV

sfI

sfV

sVαβ

sIαβ

s_ cIαβ

Figure 1 Balanced three phase voltage superimposed

The high frequency component of the current is filtered out and fed trough an observer.

Kp

Ki1s +

+

sin(2θ – ωct)^cos(2θ – ωct)

+

–

Heterodyning Process

ε

Controller

^

s_ cIα

s_ cIβ

θ

ω

1s

1J

dKJ

+

+

1s

e mT Physical Model

LPF

Figure 2 Position observer The second method was developed by M. Shrodl at “Technischen Universitat”, Wien. This technique use the same physical phenomena as the first method but the test signal is different. The derivation of the position estimate is also different. Shrodl use the step response in the current to estimate the inductance. Three voltage vector directions are used to describe the position dependent part of the inductance. By summing the three derivatives from the currents in a space phasor manner the result is a space phasor describing the double rotor position. Figure 3 show the phasor relationships.

d

q

u2β

uβ

u

sdid βτ

e 2k2

µ−

e0kµ

γ

stator s,A(U ) Figure 3 Phasor diagram

Primary Goals Develop a high performance drive system for PMSM. Compare different excitation methods and their electromagnetic response in the machines. Status of Work A new test setup is complete. Big improvements are expected due to higher ADC resolution and more computational power. Booth sensorless schemes are implemented but nut fully tested in the lab. FEM work is started to verify the phenomenas that cause saliency in the machines. Advisors My advisor is Prof. Roy Nilsen. References [1] P.L.Jansen, R.D.Lorenz: “Transducerless position andvelocity estimation in induction and salient AC machines ” IEEE Transactions on industry applications Mar/Apr 1995, pp2 40-247 [2] M. Shrødl: “Sensorless control of A.C machines” PhD. Thesis, Wien 1992

Dr. ingeniørs from Department of Electrical Power Engineering from 1990:

Year Name Title

2002

Kolstad, Helge Control of an Adjustable Speed Hydro Utilizing Field Pro-grammable Devices

Norheim, Ian Suggested Methods for Preventing Core Saturation Insta-bility in HVDC Transmission Systems

Warland, Leif A Voltage Instability Predictor using Local Area Measure-ments. VIP++

Ruppert, Christopher Thermal Fatigue in Stationary Aluminium Contacts

2001

Larsen, Tellef Juell Daily Scheduling of Thermal Power Production in a Dereg-ulated Electricity 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

Oldervoll, Frøydis Electrical and thermal ageing of extruded low density poly-ethylene insulation under HVDC conditions

2000

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-Impreg-nated HVDC Cables

Hvidsten, Sverre Nonlinear Dielectric Response of Water Treed XLPE Cable Insulation

Pálsson, Magni Tor Coberter 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 Høi-dalen

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 control-ler by using vector control strategy.

1996 Gerd Hovin Kjølle Power supply interruption costs: Models and methods incorpo-rating 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 Trans-mission Facilities in a Power System Dominated by Hydropower

Rolf Ove Råd Converter Fed Sub Sea Motor Drives

1994 Snorre Frydenlund A study of voltage stresses in ARC furnace transformers due to switching operations

Anne Cathrine Gjærde Multifactor Ageing of Epoxy - The Combined Effect of Temper-ature and Partial Discharge

Arne Nysveen A Hybrid Fe-Be Method for Time Domain Analysis of Magnetic Fields Involving Moving Geometry

Feng Xu Power System Security Assessment. Identification of Critical Contingencies and Outage Distance by a Zone Filter

1993 Bjørn Alfred Gus-tavsen

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

Year Name Title

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

Ståle Johansen Energy resource planning a conceptual study of a multiobjective problem.

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

Bendik Storesund Resonant overvoltage transients in power systems

1991 Jonny Nersveen Kvalitetskriterier og helhetlig planlegging av innendørs belysn-ingsanlegg.

Torbjørn Strømsvik Kraftelektronikk som kilde til forstyrrelser i fordelingsnettet.

Alf Kåre Ådnanes High Efficiency, High Performance Permanent Magnet Synchro-nous Motor Drives

1990 Eilif Hugo Hansen Bruk av kunstig lys og lysmanipulering for styrt produksjon av laksefisk.

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

Year Name Title