A rapid development of offshore wind power is planned in GB as a part to fulfil the EU2020 targets. 25 GW wind power capacity has been awarded to developers in nine different offshore zones outside the coast of UK. VSC-HVDC transmission is expected to be a both technical and economical favourable solution for transmitting the power into the main grid. This study investigates if such a transmission solution could comply with the regulatory framework in UK. Vattenfall and Scottish Energy Renewable will be part of this development and have been awarded the rights to develop 7200 MW of wind capacity outside the cost of East Anglia as a part of the offshore expansion plans in UK. The zone is broken down to several projects. The first project is called East Anglia ONE and this project is used as a reference case in this study. The GB Grid Code has been broken down into four areas, voltage and frequency variations; fault ride through requirements, active power control and reactive power control. Load flow calculations and dynamic simulations are designed to investigate compliance of each area. Further, simulations to investigate the interaction between the wind turbines and the offshore converter stations where done. A model representing East Anglia ONE was built in PSS/E and used to investigate grid codes compliance by load flow calculations and dynamic simulations. Data from earlier studies at Vattenfall was used to get a good representation of the wind park. A model representing a HVDC-transmission solution was provided by ABB. The results from load flow calculations and simulations show that a HVDC-solution can comply with the investigated parts of the grid codes. The limiting factor seems to be the capability to inject enough reactive power to the gird at small voltage dips during normal operation. This capability can, however, be enhanced with the right tap-changer settings at the onshore converter transformer.

The EU has concluded that it needs a fully functioning and integrated internal electricity market to face the challenges of integrating renewable energy sources into the electricity grid. The European Commission has created guidelines for what the legislation is supposed to contain to create such a market. The so called grid codes are today around ten codes which successively are being implemented in national legislation for all member states. They regard connection-, marketand operation of the electricity grid and consists of several legal requirements for all member states. This study is divided in three parts. In the first part challenges with more renewable energy sources are described and the technical strategies that are suitable to solve those challenges. The second part describes an analysis of the connection- and operational codes on behalf of Ellevio, a distribution system operator in Sweden. They are interested in how the new legislation will affect their work and which new costs that will appear. The third part contains an overall study about the German electricity system since they have a lot of renewable energy sources in their production. The purpose was to see how they have handled challenges within their grid and their view on the new legislation. The overall result in this study was that the grid codes will change the role for Ellevio, which in the following years will have to handle higher information flow between grid users and Svenska kraftnät, which is the transmission system operator in Sweden. An another result was that the technical strategies are included in the legal requirements of the codes and that the legal requirements have been influenced to a great extent by the current German legislation.

Many AC grids suffer from decreased frequency stability due to less system inertia. This has increased the risk of large-scale blackouts. This thesis and its papers address the frequency stability problem from a hydropower perspective. Grid frequency stability assessments often require accurate system inertia estimates. One approach is to estimate the inertia of all individual power plants and sum up the results. We implemented three inertia estimation methods on a Kaplan unit and compared their results. The generator contributed with 92-96% of the unit inertia, which verified the results from previous studies. However, the three methods estimated slightly different values for the unit inertia, which raises the question of when to use which method. Hydropower often deliver frequency control, yet we found no studies which validate Kaplan turbine models for large grid frequency disturbances on strong grids. Therefore, we performed frequency control tests on a Kaplan unit, implemented three hydropower models, and compared the simulation results to the measurement data. The models overestimated the change in output power and energy delivered within the first few seconds after a large change in frequency. Thus, it is important to have sufficient stability margin when using these types of hydropower models to assess the grid frequency stability. The Nordic transmission system operators are updating their frequency control requirements. We used measurement data and simulation models to assess whether improved runner blade angle control could help a Kaplan unit fulfill the coming requirements. The results showed that improved runner control does not improve the performance sufficiently for requirements fulfillment. The requirements are based on an assumption on minimum system inertia and became easier to fulfill if they were implemented with more system inertia. Thus, more inertia could allow more participants to deliver frequency control in the Nordic grid.

Long term supporting schemes for photovoltaic (PV) system installation have led to accommodating large numbers of PV systems within load pockets in distribution grids. High penetrations of PV systems can cause new technical challenges, such as voltage rise due to reverse power flow during light load and high PV generation conditions. Therefore, new strategies are required to address the associated challenges. Moreover, due to these changes in distribution grids, a different response behavior of the distribution grid on the transmission side can be expected. Hence, a new equivalent model of distribution grids with high penetration of PV systems is needed to be addressed for future power system studies. The thesis contributions lie in three parts. The first part of the thesis copes with the PV modelling. A non-proprietary PV model of a three-phase, single stage PV system is developed in PSCAD/EMTDC and PowerFactory. Three different reactive power regulation strategies are incorporated into the models and their behavior are investigated in both simulation platforms using a distribution system with PV systems. In the second part of the thesis, the voltage rise problem is remedied by use of reactive power. On the other hand, considering large numbers of PV systems in grids, unnecessary reactive power consumption by PV systems first increases total line losses, and second it may also jeopardize the stability of the network in the case of contingencies in conventional power plants, which supply reactive power. Thus, this thesis investigates and develops the novel schemes to reduce reactive power flows while still keeping voltage within designated limits via three different approaches: decentralized voltage control to the pre-defined set-points developing a coordinated active power dependent (APD) voltage regulation Q(P)using local signals developing a multi-objective coordinated droop-based voltage (DBV) regulation Q(V) using local signals   In the third part of the thesis, furthermore, a gray-box load modeling is used to develop a new static equivalent model of a complex distribution grid with large numbers of PV systems embedded with voltage support schemes. In the proposed model, variations of voltage at the connection point simulate variations of the model’s active and reactive power. This model can simply be integrated intoload-flow programs and replace the complex distribution grid, while still keepingthe overall accuracy high. The thesis results, in conclusion, demonstrate: i) using rms-based simulations in PowerFactory can provide us with quite similar results using the time domain instantaneous values in PSCAD platform; ii) decentralized voltage control to specific set-points through the PV systems in the distribution grid is fundamentally impossible dueto the high level voltage control interaction and directionality among the PV systems; iii) the proposed APD method can regulate the voltage under the steady-state voltagelimit and consume less total reactive power in contrast to the standard characteristicCosφ(P)proposed by German Grid Codes; iv) the proposed optimized DBV method can directly address voltage and successfully regulate it to the upper steady-state voltage limit by causing minimum reactive power consumption as well as line losses; v) it is beneficial to address PV systems as a separate entity in the equivalencing of distribution grids with high density of PV systems. / <p>The Doctoral Degrees issued upon completion of the programme are issued by Comillas Pontifical University, Delft University of Technology and KTH Royal Institute of Technology. The invested degrees are official in Spain, the Netherlands and Sweden, respectively. QC 20141028</p>

The current model for electricity generation is based on power plants connected to the transmission network. This provides electricity to the distribution network and after that to the consumers. To ensure the security of the electrical network and prevent a blackout, the performance of every electricity generation unit connected to the network is quantified in grid codes. In the case of the French transmission system, the requirements regarding the performance are written in a document produced by the French Transmission System Operator (TSO). Various events with various configurations of connection to the network have to be simulated and the corresponding performance has to be evaluated. The aim of these simulations is to determine the stability of the generators and key elements, including the response time on the active power after events such as a short circuit.Taking into account the amount of generators connected to the transmission network, the need for optimization appears and is the purpose of this Master Thesis. To perform those simulations in an efficient way on all the generators owned by the main French electricity producer, EDF, this Master Thesis contributes with a tool called AuDySim coded with the softwares MATLAB and EUROSTAG. The implemented tool allows the user to configure an electricity generation unit before realizing all the simulations specified by the TSO and produces a report containing the results by means of curves and data. The simulations and the production of the report are achieved automatically to create a gain of time and resources.In order to validate the performance of the tool, two case studies are performed on different types of power plants. The two case studies analyzed present a hydraulic and a nuclear power plant. In the results the performance of each type of power plant is assessed focusing on the rotor angle stability of the machine and key elements, such as the voltage and the active power. These results lead to the conclusion that AuDySim fulfills its mission, by achieving automatically an analysis of the performance of an electrical generation unit and producing it in a report. / Den nuvarande elproduktionsmodellen baseras på kraftverk som är direktkopplade till stamnätet. Stamnätet i sin tur matar distributionsnätet som därefter levererar el till slutkonsumenterna. För att säkerställa stamnätets integritet samt säkerhet och undvika strömavbrott kvantifieras prestandan hos varje generator som är ansluten till det med hjälp av nätkoder. När det gäller det franska stamnätet skrivs prestandakraven i ett dokument som utfärdas av den franska transmissionssystemoperatören (TSO). Olika händelser med olika anslutningskonfigurationer måste simuleras där dess prestanda ska utvärderats. Syftet med dessa simuleringar är att identifiera stabiliteten vid varje elproduktionsenhet med bl. a. dess reaktionstid för den aktiva effekten efter kortslutningar.Med tanke på antalet generatorer som är anslutna till stamnätet framträder ett behov för överföringsoptimering vilket är syftet med detta examensarbete. För att utföra dessa simuleringar på ett effektivt sätt på alla generatorer som ägs av den ledande franska elproducenten, EDF, bidrar denna avhandling med ett verktyg som heter AuDySim kodat i mjukvarorna MATLAB och EUROSTAG. Verktyget gör det möjligt för användaren att konfigurera en elproduktionsenhet innan man utför alla simuleringar som specificeras av TSO:n och samtidigt producerar en rapport som innehåller grafisk- och data resultat. Både simuleringar och rapporten produceras automatiskt för att optimera en bearbetningstid och resursanvändning.För att validera verktygets prestanda utförs två fallstudier på olika typer av kraftverk. De två fallstudierna fokuserar på ett hydraulisk- respektive ett kärnkraftverk. I resultaten utvärderas prestanda för varje typ av kraftverk, med fokus på maskinens rotorvinkelstabilitet och andra viktiga faktorer, såsom spänning och aktiv effekt. Resultat leder till slutsatsen att AuDySim uppfyller sitt uppdrag genom att automatiskt analysera prestanda hos en elektrisk generationsenhet och presentera analysen i en rapport.

In order to reduce emissions and achieve sustainable energy systems, renewable energy is increasingly being integrated into the power grid. However, the integration of renewable energy into the grid poses several challenges, including maintaining a stable power supply under changing and unpredictable conditions. Low Voltage Ride Through (LVRT) assesses a generator's ability to maintain stable voltage during grid voltage drops, which is crucial for renewables due to their low inertia and vulnerability to voltage disruptions caused by changes in wind or sunlight. LVRT requirements are defined by regional grid codes and regulations, which vary in their diversity. A study was conducted using Matlab Simulink to model and simulate the LVRT phenomenon on Siemens Energy's medium gas turbine generator. The entire power system generation system was simulated to observe the system's response and the generator's behavior during LVRT events. A previous gas turbine power plant project in Romania, delivered by Siemens Energy in Finspång, was simulated for analysis and compared against the grid code requirements. The findings indicated that the Siemens Energy gas turbine model SGT-750 satisfies the Romanian LVRT grid code requirements.