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  • 351.
    Huang, Yalin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Electricity Distribution Network Planning Considering Distributed Generation2014Licentiate thesis, monograph (Other academic)
    Abstract [en]

    One of EU’s actions against climate change is to meet 20% of our energy needs from renewable resources. Given that the renewable resources are becoming more economical to extract electricity from, this will result in that more and more distributed generation (DG) will be connected to power distribution. The increasing share of DG in the electricity networks implies both increased costs and benefits for distribution system operators (DSOs), customers and DG producers. How the costs and benefits will be allocated among the actors will depend on the established regulation.

    Distribution networks are traditionally not designed to accommodate generation. Hence, increasing DG penetration is causing profound changes for DSOs in planning, operation and maintenance of distribution networks. Due to the unbundling between DSOs and electricity production, DSOs can not determine either the location or the size of DG. This new power distribution environment brings new challenges for the DSOs and the electric power system regulator. The DSOs are obliged to enable connection of DG meanwhile fulfilling requirements on power quality and adequate reliability. Moreover, regulatory implications can make potential DG less attractive. Therefore regulation should be able to send out incentives for the DSOs to efficiently plan the network to accommodate the increasing levels of DG. To analyze the effects of regulatory polices on network investments, risk analysis methods for integrating the DG considering uncertainties are therefore needed.

    In this work, regulation impact on network planning methods and network tariff designs in unbundled electricity network is firstly analyzed in order to formulate a realistic long-term network planning model considering DG. Photovoltaic (PV) power and wind power plants are used to demonstrate DG. Secondly, this work develops a deterministic model for low-voltage (LV) networks mainly considering PV connections which is based on the worst-case scenario. Dimension the network using worst-case scenario is the convention in the long-term electricity distribution network planning for the reliability and security reason. This model is then further developed into a probabilistic model in order to consider the uncertainties from DG production and load. Therefore more realistic operation conditions are considered and probabilistic constrains on voltage variation can be applied. Thirdly, this work develops a distribution medium-voltage (MV) network planning model considering wind power plant connections. The model obtains the optimal network expansion and reinforcement plan of the target network considering the uncertainties from DG production and load. The model is flexible to modify the constraints. The technical constraints are respected in any scenario and violated in few scenarios are implemented into the model separately.

    In LV networks only PV connections are demonstrated and in MV networks only wind power connections are demonstrated. The planning model for LV networks is proposed as a practical guideline for PV connections. It has been shown that it is simple to be implemented and flexible to adjust the planning constraints. The proposed planning model for MV networks takes reinforcement on existing lines, new connection lines to DG, alternatives for conductor sizes and substation upgrade into account, and considers non-linear power flow constraints as an iterative linear optimization process. The planning model applies conservative limits and probabilistic limits for increasing utilization of the network, and the different results are compared in case studies. The model’s efficiency, flexibility and accuracy in long-term distribution network planning problems are shown in the case studies.

  • 352.
    Huang, Yalin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Market concepts and regulatory bottlenecks for smart distribution grids in EU countries2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    the European Union, there is a driver for a change in the electricity system. The trend is to make the system more environmental friendly and improve the markets functionality. This driver often refers to the development towards a smart grid. In order to accelerate innovation in smart grid and technology application, pilot projects need to be deployed. This master thesis has been done as a part of the Stockholm Royal Seaport urban development project that is a pilot project for smart grid on distribution grid level. The aim of this report is to apply market concept and identify regulatory bottlenecks for smart grid. This report has applied market concept and identified several bottlenecks for two aspects of smart grid. The aspects are integration of distributed energy resources in medium and low voltage level and a changing customer behavior. A changing customer behavior contains both demand response and the implementation of electric vehicles. A state ‐of‐ art review on feasible solutions that improve the competition and demand side management of electricity market in smart grid and provide incentives to implement smart grid functions has been performed. The emphasis in the market aspect is on how that new actors like aggregators will enter the market and how the dynamic price can reach consumers. The emphasis in the regulatory aspect is on how regulations promote the application of smart grid supporting technologies for both the DSO and the network users. A case study has been performed for EU countries with a deeper look at Sweden. The case study investigates how far that the current regulations have reached on the way to smart grids. A state ‐of art review on conclusion papers of pilot projects has been carried out. However, many pilot projects are still ongoing and not included in the review. The result shows there is still a lack of regulatory incentive to promote smart grid development and supporting market structures. Bottlenecks identified for smart grid services in the Swedish electricity market and regulation are related to four areas. These are the metering system, dynamic consumer price, active distributed units with the possibility to provide services to the system and incentives to the DSO to use new smart grid solutions in the work to enable fast and efficient connection of distributed generation.

  • 353.
    Huang, Yalin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Distribution network expansion planning considering distributed generation using probabilistic constraints2014Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    A novel optimization model for network expansionplanning, including distributed generation is proposed. Themodel considers the stochastic natures of distributed generationand load in the power systems. More importantly, this modeladdresses the probabilistic voltage constraints in the networkexpansion planning stage. The proposed model is employed toobtain the decisions for new wind power plant connections andreinforcements in the existing distribution network.

  • 354.
    Huang, Yalin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Regulation impact on distribution systems with distributed generation2012In: 9th International Conference on the European Energy Market, EEM 12, IEEE conference proceedings, 2012, p. 6254721-Conference paper (Refereed)
    Abstract [en]

    Distribution system operators (DSOs) are facing new challenges when more distributed generation (DG) is connected to the network. In this new operating environment the DSO has to be able to plan an efficient network topology, which consists of reinforcement and extensions. In addition, the DSO has to finance the investment from tariffs. The methods to solve network planning problems are reviewed in this paper. The studied network planning problem is the case when the DSO has no influence on the location of DG due to the unbundling between DSOs and production. Furthermore, the regulation for how the DSOs are allowed to design the tariffs in systems with DG vary between countries, a comparison of how the DSOs design their tariffs under different regulations is presented. This paper ends with a case study on methods that Swedish DSOs use to plan the networks when considering the uncertainties caused by wind power and the regulation impact on distribution network planning and network tariffs in Sweden.

  • 355.
    Huang, Yalin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hagström, E.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Martínez, Alberto Fernández
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    He, Y.
    Short-term network planning of distribution system with photovoltaic2013In: 22nd International Conference and Exhibition on Electricity Distribution, CIRED 2013, 2013, no 615 CP, p. 0989-Conference paper (Refereed)
    Abstract [en]

    The number of connections of photovoltaic (PV) to distribution network is increasing. Very few PV connection guidelines that distribution system operators (DSOs) can refer to have been found. This paper deals with network planning guidelines for distribution networks with PV. The paper aims to identify planning rules that are relatively easy to implement.

  • 356.
    Ibrahim, Hany
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Evaluation methods for market models used in smart grids2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 357.
    Ibrahim, Hany
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Skillbäck, Mikael
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hansson, O.
    Evaluation methods for market models used in smart grids2013In: 22nd International Conference and Exhibition on Electricity Distribution, CIRED 2013, 2013, no 615 CP, p. 0937-Conference paper (Refereed)
    Abstract [en]

    This paper investigates how demand response pilot projects for the residential sector can be evaluated. A simplified framework for how demand response pilot projects carried out for the residential sector can be designed has been developed. A review of 135 international pilot projects has been made. Interesting findings were that bill savings is the most common reason for participating and that customers tend to respond to blocks of prices instead of sudden increases in a certain hour. Also, customers tend to reduce their use of electricity when peak to off-peak price ratio is above three. Another finding concerning evaluation methods for DR smart grid projects is that a control group should be used to ensure the validity of a pilot project. The control group should be monitored simultaneously as the treatment group. This can facilitate determination of the true cause and effect relationship between variables and indicators.

  • 358.
    Iehl, Jeremy
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Some suggested solutions to problems encountered on the extra-high voltage network of Brittany2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 359.
    Jakobsson Ueda, Mari
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Representativa testnät försvenska eldistributionsnät2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This project was started within the Market-Design programme of Elforsk, with the aim of developing representative test systems of Swedish distribution networks. Using such test systems as a basis for reliability and customer interruption cost calculations makes it feasible to analyse the network tariff regulation of Swedish power  istribution companies. In particular, it enables studies of the incentives for companies to invest in system reliability. Until now, the available test systems are either not representative of Swedish conditions, or too small in scale and limited in function.

    Within this project we have created two test systems. In order to represent the diversity of actual Swedish distribution networks, we have created one test system for urban environments and another for rural environments. The test systems contain information about structure, customer composition, load data, component failure statistics and cost of power interruptions. To enable reliability and customer interruption cost calculations, the test systems have been implemented in Matlab. In this project power distribution company representatives and responsible authorities have been valuable as primary information sources.

    The resemblance of actual systems to the test systems has been confirmed for several individual aspects, including their overall performance. Reliability in terms of frequency and duration of power interruptions is consistent with data found in annual reports submitted to the Swedish Energy Markets Inspectorate.

    Improvements of the test systems can be made through in-depth studies of both the total system-load distribution among the different customer categories, and the cost incurred by customers from power interruptions. Data for failure statistics and time-dependent load-profiles will be more accurate in the near future, and can be used for updating the test systems.

  • 360.
    Jakobsson Ueda, Mari
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Svenska Kraftnät, Sweden .
    Engblom, Oskar
    Fortum Distribution AB, Sweden.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Representative test systems for Swedish distribution networks2009In: Proceedings of CIRED2009, 2009, p. 837-837Conference paper (Refereed)
    Abstract [en]

    This paper describes two electrical distribution systems, Swedish Urban Reliability Test System (SURTS) and Swedish Rural Reliability Test System (SRRTS), which are representative of actual Swedish distribution networks. These test systems aim to serve as a basis for reliability and cost analyses of Swedish distribution networks and for studies of regulation policies. The project was conducted within a research programme of Elforsk, a Swedish industry research association. The challenge has been to make the test systems representative in terms of load, component and customer data as well as network topology. To ensure the similarity of the test systems to actual networks, industry representatives of major Swedish power distribution companies have been an integral part of the development process. This paper shows the result of a validation of the test systems against data compiled by the Swedish Energy Markets Inspectorate. The validation was performed for the reliability indices SAIDI and SAIFI. It was confirmed that the developed test systems are good representatives of actual distribution networks, and thus suitable for further research of distribution networks and for studies of regulation policies.

  • 361.
    Janssen, Tanguy
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Cost control of the access fee to the transmission grid for the distribution network operator2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the French liberalised electricity market, the Distribution Network Operators (DNOs) and the Transmission Network Operator (TNO) are both financed by an access fee paid by any client connected to their network. Within this frame, any DNO’s is a client of the TNO as a user of the transmission grid. It is regulated by the French Government, following the recommendation of the national energy regulation committee (CRE).

    The access fee to the transmission network is a major expenditure for ERDF, the national DNO. It is also a rather new matter of concern since the electrical system was previously vertically integrated. One aim of this master thesis is to feed the evolutions of ERDF’s cost control strategy. In order to emphasize the academic interest, this report takes the point of view of a DNO looking for the best behaviour in response to the regulatory frame, based on ERDF’s example.

    In addition to that, it provides an introduction to this specific piece of regulation and it should bring new elements toward a better understanding of the access fee behaviour. The regulation, decided for at least the four years following the master thesis, is taken as an assumption in this study.

    This present report is solely the result of the author’s personal interpretation, including when referring to ERDF’s strategy. The reflections, perspectives and propositions do not commit thencompany.

  • 362. Jauch, C.
    et al.
    Matevosyan, Julija
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ackermann, T.
    Bolik, S.
    International Comparison of Requirements for Connection of Wind Turbines to Power Systems2005In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 8, no 3, p. 295-306Article in journal (Refereed)
    Abstract [en]

    Power production from wind turbines has increased considerably during the lost decade. Therefore today's wind turbines, which are typically set up in wind farms, have a significant influence on the operation of power systems. The efficient and secure operation of power systems is supported by grid codes, which are sets of requirements for all network users (suppliers, customers, etc.). In Europe, several transmission network operators have introduced special grid connection requirements for wind farms. These requirements are mainly based on existing grid codes, initially written for conventional power plants usually equipped with synchronous generators. This article presents a comparison of grid connection requirements for wind farms issued, or proposed as a draft, by transmission network operators in Denmark, Sweden, Germany, Scotland and Ireland.

  • 363.
    Jia, Jundi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Transmission Expansion Planning in Large Power SystemsUsing Power System Equivalencing Techniques2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With an increasing demand for electric power, new transmission lines should be constructed with a rational plan in the long run to guarantee a reliable and economic operation. The transmission expansion planning (TEP) is a mixed integer non-linear programming (MINLP) optimization problem in nature, which requires tremendous computational efforts especially when it comes to a large-scale power system. Although a diversity of simplifications and computational techniques has been applied to TEP, it is still challenging to derive an optimal plan within little simulation time. Since equivalencing technique is able to reduce the size of a large-scale power system and help achieve remarkable computational performance, it is possibly effective and efficient to handle the intrinsic complexity of TEP problem.

     

    In this thesis, based on a detailed literature review, a mixed integer linear programming (MILP) approach in DC model is firstly formulated for a dynamic TEP problem considering N – 1 security criterion. Then, two traditional power flow based equivalencing techniques that are appropriate for simplifying TEP, REI and WARD, with necessary modifications, are respectively implemented in the initial TEP problem. The proposed algorithms are simulated on IEEE 24-bus reliability test system (RTS) to compare optimal plans between the original and equivalent system. Further assumptions and adjustments are searched and tested to get more accurate optimal plans.

     

    The results show that both modified equivalencing techniques can significantly decrease the simulation time. Regarding IEEE 24-bus RTS, the proposed algorithm for modified REI method can achieve relatively precise optimal plan with few errors while modified WARD method is not as good as modified REI method. Therefore, the modified REI method has a potential to be implemented in TEP problem to reduce the complexity and computational effort for large power system without jeopardizing accuracy. Further studies are needed to tune the modified REI method and revise the obtained optimal plan.

  • 364.
    Jiangnan, Xi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Frequency Stability Analysis of the Nordic Power Systemwith New Hydropower Governor Settings2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Nordic power system is under continuous development. New productionsources and loads are installed at a high rate and old ones are taken out of operation.This development gradually alters the power system dynamics. The NordicTransmission System Operators (TSOs) have observed that the frequency qualityis gradually decreasing and recognized a number of reasons for this. Theautomatic frequency containment reserve (FCR-N) is in place to keep the electricfrequency within the interval 50 +/- 0.1 Hz during normal operation. Thisfunction is mainly provided by a number of hydropower plants where the turbinegovernor is set to control the discharge in proportion to the measured frequencydeviation. In later years it has been shown that the disturbance damping is verylow in an interval around 1/60 Hz and it is believed that proper tuning of theturbine governors that provide FCR-N can help mitigating this problem. Newregulator settings have been suggested in a recent study performed at Vattenfalland Uppsala University to improve the performance of the FCR-N, yet keepingthe system robust and the wear on participating units at a minimum. It is nowdesired to investigate the possible eects of new governor settings on the overallpower system stability.

    This thesis work consists of three main parts. First of all, a reduced Nordicpower system model is constructed in Simpow and validated with PMU datafrom the TSO. Secondly, the frequency responses with the newly suggestedgovernor settings have been investigated when introducing a disturbance into thesystem. Thirdly, the eects of the new governor settings on electro-mechanicaloscillations are investigated. In a word, the overall performance for new governorsettings are tested in a large scale power system model in this thesis work.

  • 365. Johansson, Emil
    et al.
    Persson, Jonas
    Lindkvist, Lars
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Location of Eigenvalues Influenced by Different Models of Synchronous Machines2002In: Proceedings of the 6th IASTED International Multi-Conference on Power and Energy Systems, Marina del Rey, Los Angeles, USA, 2002Conference paper (Refereed)
    Abstract [en]

    This paper provides understanding in how different synchronous machine models influence locations of its eigenvalues in the complex plane. Four different synchronous machine models are presented. By simulating and linearizing them in a small network the paper shows how each expansion of them influence the number of eigenvalues and their locations. It is shown how the damping constant D for low-order models can be set to obtain the same damping as for high-order models. The paper also shows how the eigenvalues of the synchronous machine are affected when the output signal from a turbine model is defined as either mechanical power or mechanical torque.

  • 366. Jonas, Persson
    et al.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Validity of a Linear Model of a Thyristor-Controlled Series Capacitor for Dynamic Simulations2002In: 14th Power Systems Computation Conference 2002, Sevilla Spain, 2002Conference paper (Refereed)
  • 367.
    Jonsdottir, Gudrun Margret
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Almas, Muhammad Shoaib
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Palsson, Magni
    Landsnet, Reykjavik.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, Norway.
    RT-SIL Performance Analysis of Synchrophasor-and-Active Load-Based Power System Damping Controllers2015In: 2015 IEEE Power & Energy Society General Meeting, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    The Icelandic power network has transmission constraintsthat often lead to inter-area oscillations. Although conventionalstabilization methods have been applied successfully inthe past, there is potential to exploit large industrial loads toenhance system stability during stringent operation conditions.This paper analyzes the performance of two damping controllers.The controllers can use both synchrophasor signals and localmeasurements as their inputs. Damping is achieved by loadmodulation generated by a phasor-based oscillation signal. Real-Time Software-in-the-Loop testing is performed using Opal-RT’s eMEGAsim Real-Time Simulator to derive hardware andcomputational requirements of a hardware prototype that willbe implemented in the future.

  • 368.
    Jonsson, Sara
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Neplan-baserad utvärdering av reläskydd vid installation av vindkraftpark i norra Norrland2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 369.
    Jose, Della
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Comparison of a three phase single stage PV system in PSCAD and PowerFactory2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The main objective of the project is to develop a Photovoltaic (PV) system using three phase Pulse Width Modulation (PWM) converter as the interfacing component in Power factory. Already existing model in Power factory tool uses static generator as the interfacing converter. Moreover the control technique implemented within the PV model is very basic. Aworking model is already available in PSCAD simulation tool using PWM converter but it is a very detailed one in terms of modeling which results in longer simulation time. Through this project a new PV model is developed in Power factory, an improved version of existing PSCAD and Power factory models. Then a comparison study is carried out between the PSCAD and the new Power factory model in order to validate the created model’s functionality. Several case studies with the DC and AC side disturbances are performed to analyze the behavior of two models. The new PV model is found to function very similar to that of the existing PSCAD model, thus proving its credibility. Further improvements and additional functions are also included in the new Power factory model which makes it a better choice to carry out grid studies than the existing model in PSCAD.

  • 370.
    Jäderström, Anna
    KTH, School of Electrical Engineering (EES), Electric Power Systems. KTH, Superseded Departments, Electric Power Systems.
    Coordinated regulation of wind power and hydro power with separate ownership2004Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    bad format, retyped

    Both wind power and hydro power must be built in immediate proximity to the source. Almost all hydro power is concentrated in the north of Sweden, since the largest rivers can be found here. The northern parts of Sweden also have good wind conditions and are therefore interesting for wind power projects. The transmission system in such areas may not have the sufficient capacity for additional power production, which calls for some kind of coordinated regulation between the hydro power producer and the wind power producer, in order to not produce more than can be transferred. A strategy for how to coordinate both power productions will avoid an expensive reinforcement of the net. In this thesis different strategies for coordinated regulation are studied and simulated using a linear programming model (LP). The major planning objective is to keep production goals and physically constraints of the power system. A model including objective function and constraints are presented for each strategy. Computational results are reported showing that both sides benefit from the coordination strategies and a better utilization of the transmission net. 

  • 371. Jäderström, Anna
    et al.
    Matevosyan, Julija
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Coordinated regulation of wind power and hydro power with separate ownership2005In: Proceedings Hydropower'05, 2005Conference paper (Other academic)
  • 372.
    Kaisinger, Reinhard
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    ELECTRICAL MODELING OF A THERMAL POWER STATION2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Physical systems are becoming more heterogeneous. Different engineering domainsare interacting more and more. Therefore, it is desirable to have modeling tools that allow multi-domain modeling. In thermal power plants, three engineering domains are of particular relevance: a) thermodynamics, b) mechanics and c) electrical engineering. The interaction of these three domains, among a few others, allows the generation of power, power control and power conversion. The goals of this project are: a) to derive a model of a thermal power station and its responses to frequency deviations (primary control), and, b) to document how frequency control is carried out in Denmark and Germany. A model of a thermal power plant has been derived in Dymola, a multi-domain modeling and simulation software tool. Fundamental components of thermal power plants, such as generator, steam turbine and turbine governor, are united in one overall model. Hence, the derived model integrates aspects of three engineering domains and captures respective phenomena relevant for frequency control. Recorded data from Block 1 of Amagerværket in Copenhagen, Denmark, is used to verify the model. Simulation results show that the model responds appropriately to frequency deviations and changes in power set point. Model simplifications are presented and motivated, and, for further model enhancements, possible future work is given. Environmental concerns enhance the integration of renewable energy sources, such as wind and solar power, into electricity production. Wind and solar power can cause fluctuations in power generation which must be compensated by controllable generating units. Due to the large and steadily increasing share of renewable electricity generation in Denmark and Germany, frequency control is documented in these two countries. Frequency control follows different strategies in the ENTSO-ERG Continental Europe (former UCTE) and Nordic (former NORDEL) systems 1 . Load-frequency control is used in the ENTSO-E RG Continental Europe system as a centrally controlled frequency restoring action. In the future, the market for balancing reserves can be expected to be intensified.

  • 373. Kargarian, A.
    et al.
    Falahati, B.
    Fu, Y.
    Baradar, Mohamadreza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Multiobjective optimal power flow algorithm to enhance multi-microgrids performance incorporating IPFC2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, p. 6345605-Conference paper (Refereed)
    Abstract [en]

    The idea of connecting some adjacent microgrids and making a multi-microgrid (MMG) have recently attracted attention among power system researchers. It helps better operate, control and manage the power system. This paper presents a multiobjective optimal power flow (MOPF) algorithm for improving the performance of MMGs incorporating interline power flow controller (IPFC). The proposed MOPF simultaneously minimizes MMG operating cost and total energy loss, as well as voltage profile deviation of all buses in the system. The proposed multiobjective nonlinear constraint optimization problem is formulated considering the control variables of IPFC. Also, the proposed algorithm guarantees that the final system operating point has a suitable security margin from the voltage instability point. A typical MMG system is used to demonstrate the effectiveness and proficiency of the algorithm.

  • 374.
    Karlsson, Klas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Load flow control and optimization using phase shifting equipment in combination with Banverkets rotating converters2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of the thesis was to further investigate the possibility to complement the rotary converters with a phase shifting device as a continuation of the work done in the master thesis; Load flow control and optimization of Banverkets 132 kV 16 2/3 Hz high voltage grid. With this modification, rotating converters can be used almost as flexible as static converters.

    The earlier thesis has come to the conclusion that the best way of compensating the phase displacement is with a series inductance. In this thesis the possibility to use capacitors instead of or in combination with inductors was investigated.

    To investigate this three different models were built: One for the railway between H�ggvik (Stockholm) and Boden; the same model that was used in the earlier thesis; it was used to confirm the results, one for the railway between Boden and Haparanda and one model that was the same as for the Haparanda track but half the distance. The models were built in the simulation program SIMPOW.

    The results from the simulations performed for the railway between Boden and H�ggvik confirmed the results from the earlier thesis, with a series inductance as phase shifter.

    For the railway between Boden and Haparanda one phase shifting device consisting of reactors and one consisting of a combination of reactors and capacitors were dimensioned. The railway with half the length compared to the Haparanda track was used to see if the length of the track in a low impedance transmission system has a large influence of the size of the reactances needed. From the simulation the conclusion can be drawn that the track length does not have a large influence when suitable reactances are chosen. It is the size of the load and the phase angle that matter when choosing reactances.

    For the Haparanda track it is possible to save power. With a phase shifter that consists of reactors that is placed in the converter station in Kalix, power savings of 340 MWh/year were achieved. With a combination of reactors and capacitors with the capacitors in the converter station in Boden and reactors in the converter station in Kalix power savings of 750 MWh/year were achieved.

  • 375.
    Karnama, Ahmad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Analysis of Integration of Plug-in Hybrid Electric Vehicles in the Distribution Grid2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The new generation of cars are so-called Plug-in Hybrid Electric Vehicles (PHEVs) which has the grid connection capability. By the introduction of these vehicles, the grid issues will be connected to the private car transportation sector for the first time. The cars from the gird perspective can be considered as a regular load with certain power factor. The effects of this type of new load in distribution grid are studied in this thesis.

    By modelling the cars as regular load, the effects of the cars in three distinct areas in Stockholm are investigated. The car number in each area is estimated based on the population and commercial density of electricity consumption in the three areas. Afterward, the average electricity consumption by the cars in one day is distributed among 24 hours of the day with peak load in the studied year. This distribution is done by two regulated and unregulated methods.

    The regulated method is based on the desired pattern of electricity consumption of PHEVs by vehicle owners. On the other hand, the regulated pattern is designed based on encouragement of the car owners to consume electricity for charging their car batteries at low-power hours of day (usually midnight hours).

    The power system from high voltage lines in Sweden down to 11 kV substations in

    Stockholm simulated in PSS/E software has been used in this study. The automation program (written in Python) is run in order to get the output report (voltage variation and losses) of the load flow calculations for different hours of day by adding the required power for PHEVs both by regulated and unregulated patterns.

    The results show the possibility of introducing growing number of cars till year 2050 in each area with existing grid infrastructures. Moreover, the number of cars, yearly and daily electric consumption for PHEVs in pure electric mode are shown in this project and the effects of regulated electricity consumption are investigated.

    It is concluded that since the car number is estimated based on the population, the areas with higher residential characteristics are more problematic for integration of

    PHEVs from capacity point of view. Moreover, by regulating the charging pattern of

    PHEVs, the higher number of PHEVs can be integrated to the grid with the existing infrastructures. In addition, the losses have been decreased in regulated pattern in comparison with unregulated pattern with the same power consumption. The voltage in different substations is within the standard boundaries by adding 100 percent of PHEVs load for both regulated and unregulated patterns in all three areas.

  • 376.
    Karnama, Ahmad
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, V.
    Scenario-based investigation of the effects of plug-in hybrid electric vehicles (PHEVs) in 11 kV substations in Stockholm2010In: 2010 7th International Conference on the European Energy Market, EEM 2010, 2010, p. 5558782-Conference paper (Refereed)
    Abstract [en]

    Plug-in Hybrid Electric Vehicles (PHEVs) with larger battery size in comparison with Hybrid Electric Vehicles (HEVs) are designed to run alternatively on electric mode by means of grid electricity. They are mainly introduced in order to decrease the emissions and reduce the fossil fuel dependency in the transportation sector. These vehicles are considered as a new type of additional load for the power system which are introduced while smart grid concept is being developed rapidly. The effects of different number of conventional vehicles changed to PHEVs on the 11 kV substations in Stockholm are investigated in this paper. This is done by planning scenarios for penetration of the PHEVs in the city. The output results of the scenario are implemented in the simulated power system in PSS/E by using the Python as the automation tool. The results showed that the existing grid infrastructures in 11kV substations in Stockholm can handle 100 percent of the existing conventional cars converted to PHEVs in case regulated charging pattern is implemented. However, more residential areas are subject to more problems from grid infrastructures capacity perspective in case one-phase charging facility is the only available one. In addition, by the same amount of energy consumption, the losses are lower (by 0.48 percent) if the energy consumption for the PHEVs is regulated.

  • 377. Keane, A.
    et al.
    Milligan, M.
    Dent, C. J.
    Hasche, B.
    D'Annunzio, C.
    Dragoon, K.
    Holttinen, H.
    Samaan, N.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    O'Malley, M.
    Capacity value of wind power2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 2, p. 564-572Article in journal (Refereed)
    Abstract [en]

    Power systems are planned such that they have adequate generation capacity to meet the load, according to a defined reliability target. The increase in the penetration of wind generation in recent years has led to a number of challenges for the planning and operation of power systems. A key metric for generation system adequacy is the capacity value of generation. The capacity value of a generator is the contribution that a given generator makes to generation system adequacy. The variable and stochastic nature of wind sets it apart from conventional energy sources. As a result, the modeling of wind generation in the same manner as conventional generation for capacity value calculations is inappropriate. In this paper a preferred method for calculation of the capacity value of wind is described and a discussion of the pertinent issues surrounding it is given. Approximate methods for the calculation are also described with their limitations highlighted. The outcome of recent wind capacity value analyses in Europe and North America, along with some new analysis, are highlighted with a discussion of relevant issues also given.

  • 378.
    Kerouanton, Sylvain
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Substation consumption forecast in the French power system2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This paper presents the methods and the results obtained during the project conducted by

    Sylvain Kerouanton for the French transmission system operator RTE. The objective of the

    project is to define methods to estimate the electric consumption of the substations of the

    high voltage network. The developed methods are based on the analysis of the past

    consumption of the substations to predict the load repartition of area consumption forecast

    over the substations of this area. This project does not deal with the consumption forecast

    but only with the repartition of it. Methods are presented in this report; the first one, the two

    floors method, classifies the substations with respect to their active power consumption in

    order to ease the repartition. The great issue of this method is the load transfers: the load of

    one substation that is transiently transferred to another substation. The second one aims to

    adapt the reactive power of substations from the variation of the active power. The third

    method finds a historical network situation which is as close as possible from the one that

    must be estimated. A study case on one of the seven regions of France defined by RTE is

    presented. The conclusion of the study case is that the two floors method can be used to

    clean up the load transfers of a well-chosen reference situation. This gives the best

    consumption repartition.

  • 379.
    Khan, Naveed Ahmad
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. HVDC ABB AB, Dept Syst Studies, Ludvika, Sweden.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Stattnet SF, Oslo, Norway.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Haider, Arif
    KTH, School of Electrical Engineering (EES), Electric Power Systems. HVDC ABB AB, Dept Syst Studies, Ludvika, Sweden.
    Hybrid Nearest Level and open loop control of Modular Multilevel Converters with N+1 and 2N+1 levels2014In: Power Electronics and Applications (EPE'14-ECCE Europe), 2014 16th European Conference on, IEEE conference proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    In this paper a Nearest Level Control with open loop approach for modular multilevel converter (MMC) is proposed. By using open loop approach it is possible to suppress circulating currents without using feedback controllers. Moreover, with this method, both N+1 and 2N+1 levels (N=number of sub-modules) can be obtained at the output voltage. In addition, the voltage quality is improved and the total harmonic distortion is reduced at higher and lower modulation indices by increasing the number of levels up to 2N+1. Simulation results of 3-phase MMC are presented for both 2N+1 and N+1 levels together with the description of proposed Nearest Level Control scheme.

  • 380.
    Kiener, Elsa
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Analysis of Balancing Markets2006Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    During the 20th century, most countries had their electricity production, transport and distribution organised as vertically integrated monopoly. Since the 90s more and more countries, especially in Europe, have replaced their state monopoly by an open market to manage their electrical power system. In order to settle a deregulated market of electricity, countries must adopt new methods and rules for trading electricity, planning production and managing the balance between electricity production and consumption of national power systems. In this context new tools are needed, such as software tools and information systems.

    This master thesis is part of an R&D project, aiming at developing software tools for the implementation of electricity markets, especially the mechanisms of bidding to buy and sell electricity on the Balancing Market. The new software developed by this R&D project is a generic software, based on a flexible model, and it should be adapted to different systems of electricity markets.

    The present master thesis report explains the principles and processes of electricity markets, focusing on the auction mechanisms for the purchase of electricity in real time: the Balancing Market. The report exposes different methods to regulate the stability of electricity network in different European countries (Regulation Services to maintain the balance between electricity production and consumption), and analyses different systems of Balancing Market in various countries; more specifically, it inludes syntheses of the balancing market systems in Romania, Hungary, Germany, France and the Nordic countries. From the confrontation of those systems, the basis for a new flexible model has been developed.

    This report aims to be useful for people who have to work on a project related to electricity market (especially this R&D project) and need to acquire the required knowledge about markets of electricity, regulation services and balancing markets (especially the market systems of Romania, Hungary, Germany, France and the Nordic countries).

  • 381.
    Kilander, Erik
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Förstudie av kraftöverförning vindkraftspark2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 382. Kilter, Jako
    et al.
    Almas, Muhammad Shoaib
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Palu, Ivo
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett.
    Experiences with dynamic PMU compliance testing using standard relay testing equipment2015In: Innovative Smart Grid Technologies Conference (ISGT), 2015 IEEE Power & Energy Society, IEEE conference proceedings, 2015, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of dynamic compliancetesting of phasor measurement units (PMUs) from threedifferent vendors in a laboratory environment. Testing is performedby providing three phase voltage and current injectionsto the VT and CT inputs of the PMUs through Freja-300stand-alone protection relay test set. Testing is performedaccording to the standard “IEEE C37.242-2013 - IEEE Guidefor Synchronization, Calibration, Testing, and Installation ofPhasor Measurement Units (PMUs) for Power System Protectionand Control”. The paper discusses the test setup, testingprocess, calculation of performance evaluation parametersand overall test results of this project.

  • 383.
    Kirik, Mehmet
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    VSC-HVDC for Long-Term Voltage Stability Improvementrol2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis an investigation of voltage stability improvement for power systems with VSCHVDC has been demonstrated. This investigation has been made by controlling active power flow through VSC-HVDC. The present work is demonstrated by comparing the VSC-HVDC to decrease and increase of active power transmission through VSC-HVDC, where VSCHVDC is one such device that can be used to quickly supply reactive power if the voltage goes below a certain level.

  • 384.
    Kiviluoma, Juha
    et al.
    Smart Energy and System Integration.
    Holttinen, Hannele
    Smart Energy and System Integration.
    David Edward, Weir
    Scharff, Richard
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Menemenlis, Nickie
    Institut de recherche d'Hydro-Québec.
    Nicolaos, Cutululis
    Department of Wind Energy.
    Danti Lopez, Irene
    University College Dublin, Electricity Research Centre.
    Lannoye, Eamonn
    Electric Power Research Institute.
    Estanqueiro, Ana
    Universidad de Castilla-La-Mancha, Intituto de Investigación en Energías Renovables.
    Zhang, Qin
    State Grid Corporation of China.
    Bai, Jianhua
    State Grid Energy Research Institute.
    Wan, Yih-Huei
    National Renewable Energy Laboratory,Transmission and Grid Integration Group.
    Michael, Milligan
    National Renewable Energy Laboratory, Transmission and Grid Integration Group.
    Variability in Large-Scale Wind Power Generation2016In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 19, no 9, p. 1649-1665Article in journal (Refereed)
    Abstract [en]

    The article demonstrates the characteristics of wind power variability and net load variability in multiple power systems based on real data from multiple years. Demonstrated characteristics include probability distribution for different ramp durations, seasonal and diurnal variability, and low net load events. In some characteristics the power systems are different, but in others they are significantly similar. Somewhat surprisingly there seems to be no straightforward correlation between wind power penetration level and variability. As long as there are several wind power plants with enough geographical spread, most of the smoothing impact is captured. Wind power variability is mainly explained by the extent of geographical spread, but also higher capacity factor causes higher variability. It was also shown how wind power ramps are auto correlated and dependent on the operating output level. In most cases wind power did not have strong diurnal or seasonal variations in the variability. However, there can be exceptions depending on the latitude and on the local characteristics of the wind resource.

  • 385.
    Kiviluoma, Juha
    et al.
    VTT Technical Research Centre of Finland.
    Holttinen, Hannele
    VTT Technical Research Centre of Finland.
    Scharff, Richard
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    David Edward, Weir
    Norwegian Water Resources and Energy Directorate.
    Nicolaos, Cutululis
    Denmark Technical University.
    Marisciel, Litong-Palima
    Denmark Technical University.
    Michael, Milligan
    National Renewable Energy Laboratory.
    Index for wind power variability2014In: Proceedings of 13th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power (WIW 2014), 2014Conference paper (Refereed)
    Abstract [en]

    Variability of large scale wind power generation isdependent on several factors: characteristics of installed windpower plants, size of the area where the plants are installed,geographic dispersion within that area and its weatherregime(s). Variability can be described by ramps in powergeneration, i.e. changes from time period to time period. Givenenough data points, it can be described with a probabilitydensity function. This approach focuses on two dimensions ofvariability: duration of the ramp and probability distribution.This paper proposes an index based on these two dimensionsto enable comparisons and characterizations of variabilityunder different conditions. The index is tested with real, largescale wind power generation data from several countries.Considerations while forming an index are discussed, as wellas the main results regarding what the drivers of variabilityexperienced for different data.

  • 386. Koliou, Elta
    et al.
    Bartusch, C.
    Picciariello, Angela
    Eklund, Tobias
    KTH, School of Electrical Engineering (EES).
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hakvoort, R. A.
    Quantifying distribution-system operators' economic incentives to promote residential demand response2015In: Utilities Policy, ISSN 0957-1787, E-ISSN 1878-4356, Vol. 35, p. 28-40Article in journal (Refereed)
    Abstract [en]

    Demand response (DR) from end-users is widely investigated as a power-system flexibility resource in a European smart-grid environment. Limited knowledge exists on the added value such flexibility can bring to actors in the electricity value chain. This work investigates the economic effect of consumption flexibility under current regulatory remuneration on distribution-system operators with a Swedish case study. Results indicate DR leads to savings for the distribution-system operator, which might be used towards smart-grid investments. Peak demand is and will continue to be a main driver for grid costs and therefore should be a focal point in tariff design.

  • 387.
    Kotb, Omar
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    Sood, Vijay K.
    A study on the control of a hybrid MTDC system supplying a passive network2014In: POWERCON 2014 - 2014 International Conference on Power System Technology: Towards Green, Efficient and Smart Power System, Proceedings, 2014, p. 2427-2432Conference paper (Refereed)
    Abstract [en]

    A hybrid Multi-Terminal DC (MTDC) system can combine the benefits of both Line Commutated Converter (LCC) and Voltage Source Converter (VSC) technologies in the form of reduced losses and flexibility to connect to weak and passive grids. In this paper, an analysis of control strategies used in a hybrid MTDC system is presented. A case study of a four terminal hybrid MTDC system supplying a passive AC network was considered for simulation study. A control scheme based on voltage margin was developed to cope with the condition of main DC voltage controlling station tripping. Two various control scenarios for controlling the VSCs connected to the passive network were presented and compared. The system performance was studied through EMTP-RV simulations under different disturbances. The results show the ability of selected converter control modes and proposed control schemes to operate the hybrid MTDC system under different disturbance conditions.

  • 388.
    Kuehn, Walter
    et al.
    FH FFM Frankfurt University of Applied Sciences.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fischer, W.
    PSI AG.
    HVDC System Stability – Analysis, Monitoring and Control in Wide Area Power Systems2014In: CIGRÉ Belgium Conference 2014: INNOVATION FOR SECURE AND EFFICIENT TRANSMISSION GRIDS, CIGRE (International Council on Large Electric Systems), 2014Conference paper (Refereed)
    Abstract [en]

    To a great extent future electric power systems will use HVDC technologies, based on either current sourced or voltage sourced converters (CSC, resp. VSC). Both technologies have their merits and range of applications being connected to technical capabilities, costs and operational properties and performance. Voltage stability is an important issue in classical CSC-based HVDC systems, while voltage stability and angle stability (both transmission angle and rotor angle) are of concern in VSC-HVDC systems. The systems are vulnerable against static instability when the AC connection point at either transmission end becomes weak in a very slow and unobserved manner. These systems may also be subject to transient instability at sudden major changes of grid structure and power flow. The present work intends to provide pertinent information for the development of diagnostic tools for stability assessment and of stabilizing controls relating to HVDC systems.

    The proposed approach is to implement online stability assessment (OSA) based on

    1. Synchrophasors obtained from WAMS for measurement based assessment,

    2. Off-line predictive static and dynamic stability computations from D-2 to near real-time considering uncertainties and the inclusion of detailed HVDC dynamics

    3. Online static and dynamic stability computations utilizing continuous power flow (CPF) and fast dynamic simulations using detailed HVDC models

    This article proposes developments in necessary concepts and methodologies to support different tasks in point 3 above, focusing on angle and voltage stability where VSC-HVDCs are considered. Such methods can enhance operator tools such as those currently being developed in different European projects ([1], [2]). This paper deals primarily with the computation of the voltage sensitivity factor (VSF) of VSC-HVDC systems and the impact of converter controls and controls limitation on VSF curves and stability margins. Sensitivity curves holding for normal undisturbed operation and for credible (n-1)-contingencies are calculated and from these curves thresholds are determined. The study shows the effect of VSC current limitation on the stability margin. The limitation can be imposed either on the reactive current or on the real current. In both cases the limitation reduces the stability margin.

    Transient simulations on the PSCAD/EMTDC simulator are performed with static voltage sources feeding the HVDC converter converters. Comparison of the power dependent voltage and angle curves obtained from these simulations with the static curves obtained from load-flow computations show differences due to control lags. This, however, does not impair the validity of the static curves for normal power ramps and their applicability for undisturbed operation.

    By replacing the static voltage sources with rotating synchronous generators it can be shown that suddenly occurring negative steady state margins must not necessarily lead to instability. Immediate DC power reduction can prevent instability. Required are a sufficiently fast response and an adaptive reduction value. It needs to be further investigated whether and how pre-calculated VSF curves from contingency computations can be used for this task.

  • 389.
    Latorre, Hector
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling and Control of VSC-HVDC Transmissions2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Presently power systems are being operated under high stress level conditions unforeseen at the moment they were designed. These operating conditions have negatively impacted reliability, controllability and security margins.

    FACTS devices and HVDC transmissions have emerged as solutions to help power systems to increase the stability margins. VSC-HVDC transmissions are of particular interest since the principal characteristic of this type of transmission is its ability to independently control active power and reactive power.

    This thesis presents various control strategies to improve damping of electromechanical oscillations, and also enhance transient and voltage stability by using VSC-HVDC transmissions. These control strategies are based of different theory frames, namely, modal analysis, nonlinear control (Lyapunov theory) and model predictive control. In the derivation of the control strategies two models of VSC-HVDC transmissions were also derived. They are Injection Model and Simple Model. Simulations done in the HVDC Light Open Model showed the validity of the derived models of VSC-HVDC transmissions and the effectiveness of the control strategies.

    Furthermore the thesis presents an analysis of local and remote information used as inputs signals in the control strategies. It also describes an approach to relate modal analysis and the SIME method. This approach allowed the application of SIME method with a reduced number of generators, which were selected based on modal analysis.

    As a general conclusion it was shown that VSC-HVDC transmissions with an appropriate input signal and control strategy was an effective means to improve the system stability.

     

  • 390.
    Latorre, Hector F.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A Multichoice Control Strategy for a VSC-HVdc2008Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Utilization of power electronics based controllable systems (or devices) in transmission systems has opened new opportunities for the power industry to optimize utilization of the existing transmission systems, and at the same time to keep high system reliability and security.

    As a member of these controllable systems, Voltage Source Converters-based High Voltage direct current (VSC-HVdc) systems have the ability to rapidly control the transmitted active power, and also to independently exchange reactive power with transmissions systems. Therefore, VSC-HVdcs with a suitable control scheme can offer an alternative means to enhance transient stability, to improve power oscillations damping, and to provide voltage support. An interesting application of this system is the analysis of a power system when a VSC-HVdc is connected in parallel with ac transmission lines.

    This thesis presents the derivation of control strategies to damp power oscillations, to enhance the transient stability and to provide voltage support for a VSC-HVdc. The thesis also formulates a multichoice control strategy and its application when the VSC-HVdc is connected in a synchronous system.

    The control strategy for enhancing transient stability is based on the theory of Control Lyapunov Function. The control strategy for increasing the damping is based on Linear Analysis. A very effective well known way to increase damping in the system is modulating the active power through the HVdc. However, besides the control of active power, the thesis explores an alternative way to mitigate power oscillations by controlling the reactive power. This condition might be very useful when the dc link in the VSC-HVdc system is out of service, but the converter stations are in operating conditions.

    A simple model of VSC-HVdc is considered in order to test the control strategy. The model represents the VSC-HVdc as an element in the power system that provides adequate interaction with other systems elements. The model is intended for analysis of power flows and electromechanical transients. It is then sufficient to consider the power frequency components of voltages and currents represented by phasors that vary with time during transients. The model is valid for symmetrical conditions, i.e. positive sequence phasors are used for the representation of the electrical state.

  • 391.
    Latorre, Hector F.
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari Alavijh, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Improvement of Voltage Stability by Using VSC-HVdc2009In: T& D ASIA: 2009 TRANSMISSION & DISTRIBUTION CONFERENCE & EXPOSITION: ASIA AND PACIFIC, NEW YORK: IEEE , 2009, p. 275-278Conference paper (Refereed)
    Abstract [en]

    This paper analyzes and compares the stability of a power system when either a new ac transmission line or a dc link based on VSCs is connected in the grid. The location of the new transmission line is determined by the restrictions in the transfer of power. From the controllability point of view, this is not the most suitable location for a VSC-HVdc to provide damping. However the voltage support capability of the VSC-HVdc can be exploited to keep the system from losing synchronism due to voltage collapse.

  • 392.
    Latorre, Hector F.
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Use of Local and Remote Information in POD Control of a VSC-HVdc2009In: 2009 IEEE BUCHAREST POWERTECH / [ed] Toma L; Otomega B, NEW YORK: IEEE , 2009, p. 793-798Conference paper (Refereed)
    Abstract [en]

    VSC-HVdcs have shown to be effective means to increase margins of stability in transmission systems. An appropriate control strategy and a correct selection of input signals allow VSC-HVdcs to enhance transient stability, damp power oscillations and provide voltage support in a significant way. In this paper the use of local and remote information in control strategies for POD in the control of a VSC-HVdc are studied. Two main control strategies are considered one of them based on linear control and the other one based on nonlinear control. As local signals current through transmission lines and frequency at connecting nodes of the VSC-HVdc are used. Rotor angles and speed of the generators are used as remote signals.

  • 393.
    Latorre, Hector Fabio
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Application of Control Lyapunov Functions to voltage source converters-based high voltage direct current for improving transient stability2007In: 2007 IEEE LAUSANNE POWERTECH, VOLS 1-5, NEW YORK: IEEE , 2007, p. 244-249Conference paper (Refereed)
    Abstract [en]

    VSC-HVdc has become an important member in the field of power electronics with application in transmission systems thanks to its capability of fast response operation and independent control of active and reactive power. An appropriate control strategy and a correct selection of input signals allow the VSC-HVdc to enhance transient stability, damp power oscillations and provide voltage support in power systems in a significant way. This paper presents, as part of a development of a Multichoice Control for a VSC-HVdc, the derivation of a control strategy for transient stability, based on Control Lyapunov Function. The VSC-HVdc is represented by a general model, referred to as Injection Model which represents the VSC-HVdc as an element in the power system that provides adequate interaction with other system elements.

  • 394.
    Latorre, Hector Fabio
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Multichoice control strategy for VSC-HVdc2007In: 2007 IREP SYMPOSIUM- BULK POWER SYSTEM DYNAMICS AND CONTROL: VII REVITALIZING OPERATIONAL RELIABLITY, NEW YORK: IEEE , 2007, p. 38-44Conference paper (Refereed)
    Abstract [en]

    Multichoice Control Strategy -MCS- consists in the selection of the correct input signals that will allow the VSC-HVdc to enhance the transient stability of the system, increase the level of damping, provide voltage support at specific nodes or change the power flow in the system, as it is required by the system when disturbances occur or ordered by the operator. This paper gives a description of the MCS and presents the procedure followed in the calculation of POD signals and a comparison of those signals with the signal derived from Lyapunov theory (Control Lyapunov Function -CLF-). All the signals were used in both small and large disturbances. The formulation of the MCS is based on a synchronous connection of the VSC-HVdc.

  • 395.
    Latorre, Hector
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Improvement of Power System Stability by Using a VSC-HVdc2011In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 33, no 2, p. 332-339Article in journal (Refereed)
    Abstract [en]

    The capabilities of a VSC-HVdc to improve the stability in power systems are analyzed in this paper. The analysis considers a power system which has the need for increasing the transmission capacity. Two options are analyzed: connection of a new ac transmission line or connection of a VSC-HVdc link. Different disturbances are applied in the system in order to analyze the dynamic response of the system. Supplementary control is included in the control of the VSC-HVdc. The control strategies in the supplementary control are based on nonlinear and linear theory. Furthermore, remote and local information are used as input signals in the control strategies. Simulation results clearly showed the benefits of VSC-HVdc in the improvement of power system stability.

  • 396.
    Latorre, Hector
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Active and reactive power control of a VSC-HVdc2008In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 78, no 10, p. 1756-1763Article in journal (Refereed)
    Abstract [en]

    Voltage source converter-based HVdc(VSC-HVdc) systems have the ability to rapidly control the transmitted active power, and also to independently exchange reactive power with transmissions systems. Due to these characteristics, VSC-HVdcs with a suitable control scheme can offer an alternative means to enhance transient stability, to improve power oscillations damping, and to provide voltage support. In this paper, a VSC-HVdc is represented by a simple model, referred to as the injection model. Based on this model, an energy function is developed for a multi-machine power system including VSC-HVdcs. Furthermore, based on Lyapunov theory (control Lyapunov function) and small signal analysis (modal analysis), various control strategies for transient stability and damping of low-frequency power oscillations are derived.

  • 397.
    Latorre, Hector
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Control of a VSC-HVDC operating in Parallel with AC Transmission Lines2006In: 2006 IEEE/PES TRANSMISSION & DISTRIBUTION CONFERENCE & EXPOSITION, 2006, p. 917-921Conference paper (Refereed)
    Abstract [en]

    As part of an analysis of a VSC-HVDC operating in parallel with AC transmission lines, this paper presents an adaptive control of VSC-HVDC that allows the device: to provide voltage support by means of reactive control at both ends; to damp power oscillations and improve transient stability by controlling either active or reactive power; and to control the power flow through the HVDC link. Simulations showed that the control operated correctly and that the VSC-HVDC significantly contributed to voltage stability, damping of power oscillations and improving of transient stability.

  • 398. Laury, John
    et al.
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    OPF for an HVDC Feeder Solution for Railway Power Supply Systems2012Conference paper (Refereed)
  • 399.
    Laury, John
    et al.
    KTH, School of Electrical Engineering (EES).
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    OPF for an HVDC feeder solution for railway power supply systems2014In: WIT Transactions on the Built Environment, ISSN 1746-4498, E-ISSN 1743-3509, Vol. 135, p. 803-812Article in journal (Refereed)
    Abstract [en]

    With increasing railway traffic, the demand for electrical power increases. However, railway power systems are often weak causing high transmission losses and large voltage drops. One possible method for strengthening the railway power supply system is to implement a High Voltage Direct Current (HVDC) feeder in parallel to the Overhead Contact Line (OCL). The HVDC feeder is connected to the OCL by converters. This paper describes different properties and characteristics of such an HVDC feeder solution. An AC/DC unified Optimal Power Flow (OPF) model and unit commitment is used to obtain proper control of the converters. The non-linear load flow and converter loss equations, and the binary variables for the unit commitment, lead to an optimization problem of Mixed Integer Non- Linear Programming (MINLP) type. The optimization problem is formulated in the software GAMS, and is solved by the solver BONMIN. In each case, the objective has been to minimize the total active power losses.

  • 400.
    Lavenius, Jan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    An Algorithm for Finding Minimal Load Interruption Costs2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis presents an algorithm for finding the minimal interruptioncost associated with the loads.Electric power systems are necessary to transfer electric energy fromproducers to consumers. The power system may lose stability as thesenonlinear systems are subject to contingencies. The loss of stabilitymay result in large costs for the society, by the loss of productivityand worsening standard of living. If the likelihood of instability is low,then it may be that it is not economically motivated to allocate costlyresources necessary to prevent this from happening. For some casesload shedding is the alternative with best economical performance, torestore the stability and ensure that delivery of power is not interrupted.With increasing amounts of renewables in a power system, the planningand scheduling of the electric power production will get more difficultto forecast and control. Therefore the system operators will needto be able to handle more diverse situations than before. Thus thereis a need to find computationally efficient methods to predict systemstability and the minimal load shedding needed.This report uses second-order approximations to the stability boundariesof the system, developed and calculated by Magnus Perninge andCamille Hamon to determine how much and where the load sheddingshould be done to shed the minimal amount of load that restores thestability of the system.Two cases, the IEEE 9-bus system and the IEEE 39-bus system,illustrates the proposed method and compares three different methodsused to determine the load shedding. The results show that the approximationscan be used to minimize the load shedding, and that theamount of load shed is significantly reduced. Time-domain simulationsof the system were necessary to ensure the stability of the system anddetermine of much margin that is needed to the approximations.The methods and approximations used in this report could in thefuture be applied to real power systems, a possible application is tocalculate the severity of contingencies and use the information to minimizethe total costs of the system when considering operation andinvestments. Another possible application is to design automatic loadshedding controllers using wide-area monitoring to increase the systemreliability.

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