The size of offshore wind generators is increasing, and the trend is moving towards full converter gear-less solutions with permanent magnet synchronous generators (PMSG). The nacelle weight reduction is a key design criterion for offshore wind turbines. To overcome the weight challenge, a transformer-less concept is under development. This concept employs a special PMSG with an innovative high insulation level between the groups of windings. The generator supplies nine series connected converter modules, which results in a high voltage DC output of 100 kV, reducing the total weight of the system.Conventional three phase 2-level voltage source converters, each with 11.1 kV output, are utilized in concept studies and simulations. However, other voltage source converter topologies are assumed to be more beneficial in terms of efficiency, voltage quality and reliability issues. This work compares multilevel converter topologies with regards to their suitability for the proposed concept.The result of an initial study is that the modular multilevel converter (MMC) is the most promising candidate. The MMC adds more components and complexity to an already intricate system, but gives benefits that are in line with many of the ideas behind the proposed concept. A modular structure grants the easiest expansion to a high number of levels, providing a high-quality voltage with less demand for filters to save both volume and weight. The MMC also offers redundancy possibilities for higher reliability, which is important in offshore wind power installations. PSCAD/EMTDC simulation models have been built, implementing voltage balancing and redundancy control. The simulations have also investigated the functionality of the converter in the proposed system. The results show that the MMC performs well in the full system, and is therefore considered as a viable candidate. The number of levels needed is at least five to avoid series connection of IGBTs. Further studies should find an optimal number of levels, depending on the generator specifications, the desired level of losses, voltage quality and a weighting of reliability versus complexity.

This thesis is centered around the design of a grid-connected photovoltaic (PV) roof installation at a specific location in Oslo, Norway. The motivating factor in this study has been the growth of the solar industry globally, while there has been little to none larger PV investments in Norway. The objective is to investigate how much renewable PV energy that can be produced from the designed system, with an electrical focus. Factors such as the suns position during each day of the year, the shadings on modules, the electrical effect of shading and bypass diodes, and other factors influence the production of a PV installation. Due to the complexity of power production in a PV system, the simulation software PVsyst was used as support. A 3D representation of the building and shading elements was constructed in the simulation program for shading calculation purposes. Meteorological data from local weather stations in Lier, Ås and Blindern was compared with meteorological data provided by interpolation and satellite images. The distance between modular rows was dimensioned after a shading criterion so that there would be no shading from other modular rows during spring equinox (March 21st). The modular tilt was adjusted (from the optimal tilt angle of 40 degrees) in order to reduce shading loss and improve the performance ratio of the system. The number of module and inverter types and manufacturers was limited to three different module types, and four different inverter series. The simulated production from the three best alternatives, based on performance ratio and production were compared with the energy consumption in the building. Simple economical evaluations of the three best alternatives have been performed using the simple payback method and life cycle costing. As a result of the limited area on the roof, the shading objects and the dimensioning criteria (maximize performance ratio and production of the system) it was found that the module tilt was 20 degrees. The modules in the system are directed towards geographical south, and there is a pitch distance of 2 meters between the module rows. The resulting three final alternatives were two polycrystalline alternatives and one monocrystalline alternative. The polycrystalline alternatives used the same REC modules and different inverters, one from Eltek and the other from SMA. The monocrystalline alternative was simulated with SunPower modules and SMA inverters. The installations have a simulated energy production of 22.4, 22.9 and 31.0 MWh/year, which would cover the average energy consumption of a household in Norway (20.4 MWh/year). However, the installation will only contribute to reduce the energy consumption in the six storey commercial building by approximately 1 % per year. Comparing the simulated productions and the consumption in 2011, it is found that the installation will not result in a surplus of energy which could have been injected into the grid. The installation will therefore not change the buildings customer status to a surplus customer (plusskunde). With the simplified economical evaluation it is found that the energy from the PV installation will cost more than the energy agreement of today and it is triple the yearly average market price of electricity the last three years. The polycrystalline alternative with SMA inverters was the least expensive alternative of the three and the polycrystalline alternative with highest production. The monocrystalline alternative gave best simulated production and performance ratio of the three alternatives, but was the most expensive alternative.

The purpose of the experiments conducted in this Master's thesis is to predict and explain the change in breakdown voltage when insulating barriers are introduced in a rod-plane gap arrangement. The experiments have been conducted with positive lightning impulse voltage, using the up and down method to determine the 50 % breakdown voltage. A cylindrical rod with rounded tip and radius 3.5 mm was used as the high voltage electrode above a plane grounded electrode. The polycarbonate barriers used were 1 mm thick and of different sizes (4x4 cm, 6x6 cm, 8x8 cm, 16x16 cm, 30x30 cm and 40x40 cm). They were placed at various positions in the 80 mm rod-plane gap to find the optimal combination.The results show that the breakdown voltage of the gap could be increased by the use of barriers, strongly dependent upon their size and position. The largest barrier offered the highest breakdown voltage, an increase of 98.0 % versus the barrier-less rod-plane gap. With the two largest barriers, the optimal position was found to be in the upper part of the gap, 0-10 mm from the high voltage rod tip. The four smaller barriers perform their best around 20 mm from the tip. Literature has suggested that the optimal position is in the range 12-24 mm for this gap [Lebedev et al. 2005], where the breakdown voltage can be over tripled.It has been discovered that placing the smallest barriers close to the high voltage rod tip drops the breakdown voltage to levels below that of the barrier-less gap. A suggested explanation is the strong tangential field present on the barrier surface under these conditions, quickly building up charge on the barrier and leading to breakdown. Streamer inception on the underside of the barrier has not been observed despite the high field strength directly under the rod tip. This is possibly caused by the slightly higher field on the upper side of the barrier, leading to streamer inception which weakens the field under the rod tip. As the barrier size is increased, the voltage drop in the longer streamer path is the dominating factor behind the rise in breakdown voltage. It is recommended to employ barriers of considerable cross-sectional length, preferably twice the gap distance or longer, to ensure satisfactory breakdown performance improvement. An empirical equation for predicting breakdown voltage in barrier insulated rod-plane gaps has been constructed on the basis of the conducted experiments.

This thesis is written in cooperation with Fred Olsen's Wave Energy Project Bolt2 which is a Wave Energy Converter (WEC) recently deployed outside of Falmouth Bay in the UK. After the initial phases of testing, the device is to be grid connected to the local distribution network. The purpose of this thesis is to develop a model that can serve as a useful starting point for investigating grid connection issues for Wave Energy Converters or as a part of a complete wave-to-wire modelling of a WEC. The Bolt2 project will be used as a framework for the thesis. Measurements from the testing of Bolt2 have been provided and strengthen the project by applying real life conditions to the model.The work emphasizes on the challenges of grid connecting wave energy devices as motivation for the work. As a first step, the design of the grid side converter and its control system is carried out with the main criterion being a constant DC-link voltage. In addition, the control circuit ensures no reactive power exchange at the converter output that the currents are injected at the grid frequency. The control strategy applied is based on vector control due to its well documented performance in a variety of applications.One of the main barriers for wave energy developers are the large power variations that are inherent to most WECs since the produced wave power goes through zero twice in each wave period. An effective way of reducing the power fluctuations is by disposing several point absorbers in an array configuration which is one of the advantages of Fred Olsen's Bolt2.To further smooth out the power, an Energy Storage System (ESS) is considered. After a short discussion, the energy storage device was chosen to be a supercapacitor (SC) bank. Initially, the possibility to provide a constant power to the grid was investigated but was rejected as being unrealistic for a practical case. Instead, an alternative power management strategy of the ESS was developed. It was decided to chop off only the largest power peaks and to discharge whenever any amount of energy remained in the SCs for the storage system to be completely discharged and prepared for any incoming power peak. A bi-directional DC-DC converter was used to interface the SCs with the DC-link and the described power management strategy was realized through current control of the switching devices. Two similar but separate control schemes were necessary in order to perform both buck charging and boost discharging.Finally, simulations of power data from a design sea state were performed in order to prove the validity of the developed model. The peak-to-average power ratio was demonstrated to be reduced with the integration of the energy storage system. However, the expenses of including a storage would have to be justified by reduced costs for the developer in order for the scenario to be economically viable.

På grunn av den økende alderen på mye av distribusjonsnettet og den økte ressursbruken dette medfører, har nettselskap satt fokus på hvordan vedlikehold og reinvestering kan planlegges og utføres på en best mulig måte. HelgelandsKraft(HK) er et nettselskap med ansvar for mye distribusjonsnett. For å planlegge vedlikeholdet har HK laget en database, Prelib, der tilstanden til komponenter registreres etter tilstandsbefaringer omtrent hvert tiende år. Tidligere resultat fra tilstandsbefaringer lagres også, og dette gir muligheten til å undersøke utviklingen av tilstanden. Bakgrunnsdata som grunnforhold og korrosivitet er også registrert i databasen. Bakgrunnen for oppgaven var å undersøke hvordan tilstandsdataene i Prelib kan brukes i planleggingen av vedlikehold og reinvestering og på den måten være et ledd i overgangen fra en tidsstyrt til en risikobasert vedlikeholdsstrategi. Oppgavens mål var å foreslå en prosedyre for hvordan planleggingen kan utføres med de ressursene, både økonomisk og tidsmessig, som er tilgjengelige.HelgelandsKraft ble besøkt ved flere anledninger. Oppholdet ga innsikt i hvordan bedriften jobber med planlegging av vedlikehold og hvordan de har brukt Prelib. Det ble dannet et godt grunnlag for oppgaven gjennom innføring i dagens situasjon i nettet og hvordan tilstanden til komponenter bestemmes.Oppgaven har gått gjennom teori knyttet til tilstandsbasert og risikobasert vedlikehold. Teorien ga eksempel på hvordan man kan bruke risiko i planleggingen av vedlikehold av kraftnett. Den ga også en innføring i hvordan informasjon om teknisk tilstand kan brukes til å estimere sannsynlighet for svikt og tilhørende risiko. Dette ble brukt i analysen av casene og i prosedyren som ble satt opp på bakgrunn av disse. Siden arbeidet som allerede var gjort i HK stemte godt overens med teorien, kunne mye av teorien brukes i praksis. Gjennom analysen av tre konkrete case, har det blitt foreslått en prosedyre for å analysere vedlikeholds- og reinvesteringsbehovet i en nettdel. Prosedyren tar utgangspunkt i tilstandsdata som er registrert i Prelib. Først ble informasjonen brukt til å danne seg et bilde av tilstanden på nettdelen. Videre ble den brukt til å beregne økonomisk risiko for ulike tiltak i nettet. Risikoen ble satt inn i lønnsomhetsberegninger av alternative handlingsplaner. Det ble undersøkt hvordan endringer i sannsynlighet for svikt, tiltakets kostnad og tidspunkt for iverksetting av tiltak påvirker lønnsomheten til et alternativ. Med å gjennomføre tilsvarende analyse, vil bedriften ha et bedre beslutningsgrunnlag i vedlikeholdsarbeidet. Selv om prosedyren har en enkel framgangsmåte og ikke er spesielt tidkrevende, vil den kreve mer tid til å planlegge vedlikeholdet enn det som er tilfelle i dag. Før prosedyren kan implementeres i bedriften, er det nødvendig å enten etablere levetidskurver for komponentene i nettet eller å estimere sannsynligheten for svikt for komponenter i gitte tilstander.

TeoriI denne oppgaven er plusskunder sin påvirkning på ulike spenningsparametre i lavspenningsnettet forklart. Parametrene tar utgangspunkt i kravene stilt i ”Forskrift om Leveringskvalitet i kraftsystemet”. Videre er det redegjort for teorien for disse parametrene. For harmoniske spenninger og langvarige spenningsendringer er det i tillegg vist, med eksempler, hvordan beregninger av deres verdi gjøres. SolcelleanleggTeknologien for et nettilknyttet solcelleanlegg blir beskrevet med virkemåte og oppkobling. Et eksempel på et fullstendig solcelleanlegg er vist, der alle komponentene i forslaget deretter forklart. Det er blitt fokusert på vekselretteren og hvordan valget av denne vil være viktig for i hvilken grad en plusskundes solcelleanlegg påvirker spenningsparametere i distribusjonsnettet.SimuleringerDet er blitt gjort lastflytsimuleringer i simuleringsprogrammet SIMPOW for produksjon fra ingen, en eller flere plusskunder i lavspenningsnettet. Det benyttes to ulike eksempelnett; et sterkt og et svakt nett. Det er blitt simulert for ulike lastforhold og plasseringer av plusskunden i distribusjonsnettet. Endringer i spenningsforhold er blitt studert og deretter kommentert. En plusskunde gir størst endring i spenningsverdiene i de ulike tilknytningspunktene til sluttbrukerene i nettet dersom han/hun er plassert ytterst i et svakt nett og har en lav effektfaktor. Krav gitt plusskunderTre viktige dokumenter for plusskunder er nevnt. De er NVEs ”Vedtak av 16. mars 2010”, ”FIKS” og ”ENTSO-E Draft Requirements for Grid Connection Applicable to all Generators”. Forslag til krav som skal stilles en sluttbruker som ønsker å bli plusskunde og en grov oversikt over prosessen en sluttbruker med solcelleanlegg må gjennom for å bli en plusskunde er gitt. Det forklares at bidraget fra et solcelleanlegg til kortslutningsstrømmen kan forventes å være lik merkeverdien. Overstrømsvern kan derfor ikke benyttes, og vekselretteren må frakoble anlegget når den oppdager avbrudd i distribusjonsnettet. Det er forklart hvorfor harmoniske strømmer fra et solcelleanlegg kan være sterkt avhengig av graden av harmoniske spenninger i distribusjonsnettet med plusskunden frakoblet. Bruk av filtre vil forandre effektfaktoren til vekselretteren og vil kunne danne resonansekrets i nettet. Oppgaven viser at plasseringen, valget av vekselretteren og samlet merkeeffekt for solcellepanelene vil gi det aktuelle nettselskapet innsikt til i hvilken grad tilknytningen av solcelleanlegget vil påvirke tekniske forhold i distribusjonsnettet. Størrelsen på merkeytelsen til solcelleanlegget i forhold til kortslutningsytelsen i det aktuelle tilknytningspunktet vil angi om lastflytberegninger skal gjøres.Selv om en ny plusskunde alene ikke skal trenge å føre til betydelige nettanalyser, er det viktig å tenke fremtidsrettet for å være forberedt på konsekvensene et økende antall plusskunder i lavspenningsnettet vil kunne ha. Kravene det aktuelle nettselskapet stiller til plusskundene burde være like for to plusskunder med like parametre. Nettselskapet må også kunne utnytte det store spillerommet ordningen til NVE tillater av tilpassede krav i særskilte saker.

Det har i denne oppgaven blitt vist at inntektsgrunnlaget for plusskunder iNorge er forholdsvis lavt. Dette til tross for at Norges Vassdrags- og Energidirektorat(NVE) har foretatt flere dispensasjoner, samt kommet med forslag tiltariffering for å gjøre plusskundeordningen mer lønnsom og attraktiv. Blantbarrierene for plusskunder kan det nevnes; få leverandører av aktuell produksjonsteknologi,forholdsvis liten erfaring om plusshus blant norske byggefirmaog den mest dominerende barrieren, den økonomiske. Produksjonsteknologienesom er mest aktuelle for plusskunder, vind- og solkraft, har foreløpig forhøy kostnad per kWh til at ordningen er lønnsom.Det har i oppgaven blitt vist til studier utført av SINTEF og NVE somkonkluderer med en kostnad per kWh for kraftproduksjon fra solceller påmellom 3,33 NOK og 5 NOK. To småskala vindturbiner, i utgangspunktetgodt egnet til bygningsmontering grunnet rotordiameter under 2 meter,viste seg i et pilotprosjekt i Nederland å ha en produksjonskostnad på 22,91NOK/kWh og 14,48 NOK/kWh. Den største turbinen, med en rotordiameterpå 5 meter, kom best ut i testen med en produksjonskostnad på 2,03NOK/kWh. Et liknende prosjekt i Storbritannia konkluderte med at i 16av 26 testtilfeller var den målte ytelsen på bygningsmonterte vindturbiner40% lavere enn det som var oppgitt fra produsent. Dette avviket skyldes ihovedsak at virkningsgraden synker drastisk i urbane områder som følge avustabile vindforhold forårsaket av bygninger.NVEs forelåtte tariffering av plusskunder medfører at inntekter og besparelsertil en plusskunde i BKKs nett er estimert til å utgjøre 3352 NOKårlig. Med en oppgitt investeringskostnad på 200 000 NOK er det blitt vistat innvesteringen, gitt en forventet levetid på anlegget på 25 år, ikke vil blilønnsom med dagens kraftpriser og tariffsystem.I oppgaven har det blitt vist til tariffsystemene ”Erneuerbare-Energien Gesetz”(EEG) og ”Feed in Tariff Scheme” (FITs), henholdsvis i Tyskland ogStorbritannia. Det tyske tariffsystemet har bidratt sterkt til at Tyskland vedslutten av 2011 hadde 25 GW installert effekt fra solceller. I Storbritanniakan en plusskunde med et solcelleanlegg på 2,9 kWp forvente inntekter ogbesparelser opp mot 11 000 NOK årlig. I løpet av anleggets levetid kan detteutgjøre opp mot 280 000 NOK. Denne summen står i sterk kontrast til hva en norsk plusskunde per i dag kan forvente, som i løpet av levetiden til anleggeter estimert til å utgjøre om lag 87 000 NOK.Det har også i oppgaven blitt trukket frem at distribuert fornybar kraftproduksjonkan gi utfordringer knyttet til leveringskvalitet, spenningsstabilitetog personsikkerhet. Blant annet er vekselrettere, som er nødvendig for å omformelikespenning til vekselspenning, en kilde til harmoniske i kraftnettet.Et høyt innslag av vekselrettere i kraftnettet innebærer at anleggene for eksempelmå installerer filtre for å unngå at harmoniske sprer seg ut i nettet.Uønsket øydrift av distribuert kraftproduksjon kan i tillegg være en fare fornettselskapets ansatte ved vedlikehold i kraftnettet. Dette stiller også kravtil anleggets evne til å detektere øydrift og koble ut plusskunden. Det internasjonaleenergibyrået (IEA) har i en rapport konkludert med at risiko forpersonskade som følge av øydrift av solcelleanlegg hos plusskunde er 10^-9 årlig.Det har blitt diskutert at varierende innstråling på solcelleanlegg og ustabilevindforhold byr på utfordringer med spenningsregulering. Det har blitt trukketfrem at transient skydekke kan gi ramper i kraftproduksjonen opp mot15% i sekundet. Grunnet det høye innslaget av kraftproduksjon fra solcellerhar tyske myndigheter innført et nytt regulativ for vekselrettere. Regulativetsetter blant annet krav til en vekselretters effektfaktor, samt at en vekselretterskal ha støtte for frekvensbasert effektreduksjon ved frekvenser over 50,2 Hz.Det har blitt vist at et kundedisplay i kombinasjon med avanserte måle- ogstyringssystem (AMS) kan være en sentral kilde til informasjon for plusskunden.Displayet kan presentere forbruk og produksjonsdata i tillegg tilinformasjon om feilsituasjoner i kraftnettet eller plusskundens produksjonsanlegg.Det har i oppgaven blitt presentert et system for hjemmeautomasjon ikombinasjon med et kundedisplay levert av selskapet Control41. Dette systemetstøtter individuell laststyring i husholdningen og innebærer at plusskundensenergiforbruk i større grad kan tilpasses tidspunkt for kraftproduksjon.Eksempelvis kan en vaskemaskin settes til å starte på tidspunkter der plusskundenproduserer egen kraft. Dette innebærer at det aktuelle apparatetdrives med særdeles kortreist og klimavennlig kraft.

Because of ocean waves' high energy density and substantial, global technical potential wave energy might become a significant contributor to supply the world's increasing energy demand. The nature of ocean waves is strongly irregular and the power generation from a Wave Energy Converter will have large fluctuations what is a challenge for the electrical system. In the history of wave energy research the focus has been on controlling devices for increasing the absorbed power based on results from mechanical and hydrodynamic mathematical analysis. However, recent work shows that the peak of produced power increases compared to the average absorbed power when traditional control strategies like passive loading and optimal control are applied. The rating and the energy storage requirements of the electrical system will then be increased and the gain due to the increased power production might be lost.In recent work a control strategy that optimizes the torque of the generator with respect to a power saturation level is presented. The work in this report focuses on a practical implementation of this strategy. Further, modifications to meet the torque and speed limitations of the system are made. A control algorithm is presented that utilizes the overrated speed region of the generator to maximize the power production with regards to the power and torque ratings. Simulations for irregular waves and control parameters chosen according to passive loading are then executed and the control algorithm is realized by use of field oriented control of the induction generator. The average absorbed power is changed only to moderate extends compared to the unconstrained case. At the same time the peak to average ratio and the maximum torque is considerably reduced. However, the strategy's reduced torque capability results in a higher maximum speed and pull out speed can be reached. Consequently there will be a trade off between investment costs, produced power and operation range of the system. Therefore the system should be optimized with respect to torque and power limitations, costs, produced power and pullout speed.

When a wind park is sited offshore, compact, lightweight and reliable components are important requirements. In this Master's thesis a wind energy conversion system has been proposed, where the objective is to meet the requirements of an offshore environment. The system consists of a permanent magnet generator, a reduced matrix converter, a high frequency transformer and a full-bridge converter. It is the reduced matrix converter which is the main focus of the thesis. The reduced matrix converter (RMC) provides direct AC-AC conversion without the need of a bulky DC link capacitor, it is thus a compact solution. It is built with six bi-directional switches. Each switch consists of two reverse blocking IGBTs in antiparallel. The reverse blocking IGBT is different from the conventional IGBT because it blocks voltage of both polarities.Due to the direct AC-AC conversion of the RMC it is necessary to implement a special protection scheme for the circuit. The scheme provides reliable operation of the RMC so the switches are not damaged. This is achieved by the introduction of a clamp circuit. The clamp circuit has been studied during normal operation and the operation during faults has been described. The entire WECS has been implemented in the simulation program PSIM to simulate behavior of the clamp circuit during normal operation and to calculate switching and clamp circuit losses. Both losses are related to the RMC, and are important for the study of the overall energy efficiency of the converter. Total losses have been compared for two different modulation techniques, these are carrier based modulation and space vector modulation. The simulation results indicated that space vector modulation is the most energy efficient solution for the system.

Electricity generation, along with motor vehicles, is one of the biggest sources of pollution for the planet. Renewable energies are not able to replace massively polluting power plants but they can at least alleviate for it. Biomass and hydro power are the main source of renewable energy but wind power is developing to high extent, increasing by 30% its installed capacity every year in the world. Norway is increasing its wind power production since every hydro power areas are already used. The shallow Norwegian waters along with the increase of energy demand leads to offshore wind project.The aim of this thesis is to study the integration of large scale offshore wind farms into the grid. The biggest offshore wind farm is currently installed in the United Kingdom (Thanet) and its capacity is 300 MW. The wind farm studied here has a capacity of 1000 MW. HVAC and HVDC transmission are investigated in order to connect the wind farm to Norway. Case faults are performed in order to study the system stability. The connection points are located in the most populated areas of Norway, where there is a real need for new power plants: Sørlandet and Vestlandet.Statnett is the Norwegian transmission system operator and thus the focus was made on the connection with power flow and stability analysis and not on the full description of the wind farm. For simulations, Statnett is mainly using PSS®E (Power System Simulator) from Siemens but as much of the help was providing by SINTEF, the largest independent research organisation in Scandinavia, it was more convenient to use their tool: SIMPOW from STRI AB.