Change search
Refine search result
3456789 251 - 300 of 806
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 251.
    GAO, XIANG
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Remedial Action Schemes Derived from Dynamic Security Assessment2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Electric power is becoming more and more important in the modern world. Since most electric power utilizations should be supplied by the power transmission and distribution system, the security of power system is paid more and more heed to nowadays. All over the world, there are some trends to introduce the deregulated power system into the power system operation, and to increase the stability of electric power supply. As a result, making accurate predictions for the power system operating conditions is an important task for the current power system research. The research mainly interests in checking if the operating conditions are acceptable after contingencies. Dynamic Security Assessment (DSA) is proposed and studied under such context. One tool to implement the DSA is to create the Stability Indices (SI) system. The SI system is used to indicate the operating conditions for the power system. This master thesis project aims to develop the appropriate Remedial Actions Scheme (RAS) by using the SI system. The RAS is used against different instabilities. Firstly, all indices of the SI system are summarized. The summarization is based on theoretical study on to-date DSA researches. The indices of the SI system are able to predict power system operating conditions. They are also able to release the stress of DSA computing, and to reduce misclassification and failed-alarm. The SI system is computed by quantities of state variables from the components of the power system. Secondly, the functionalities of different remedial actions are clarified. Then, those remedial actions are used to develop the RAS. The RAS is developed according to the evaluation by the SI system. Using the SI system, different remedial actions are tested and evaluated. The results of evaluation are used to develop and categorize different RASs against different instabilities. After that, the RASs are analyzed, and qualities of RASs are ranked by the SI. In this way, more suitable RAS against each type of instability is developed. The results show the process of analysis is both fast and accurate. All analysis and evaluations are implemented by simulation software of PSS TMNETOMAC. The thesis has been implemented between cooperation of Royal Institute of Technology (KTH) in Sweden and Energy Sector of Siemens AG in Germany.

  • 252.
    Garzon, C. L.
    et al.
    Automatizac Avanzada, Bogota, Colombia..
    Chamorro Vera, Harold Rene
    KTH, School of Electrical Engineering (EES), Electric Power Systems. NDT Innovations Inc, Bogota, Colombia..
    Diaz, M. M.
    Sequeira, E.
    UTEP, El Paso, TX USA..
    Leottau, L.
    Univ Chile, Adv Min Technol Ctr, Dept Elect Engn, Santiago, Chile..
    Swarm Ant Algorithm Incorporation for Navigation of Resource Collecting Robots2014In: 2014 5th IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob), IEEE , 2014, p. 987-992Conference paper (Refereed)
    Abstract [en]

    Swarm robotics requires the development of new strategies and algorithm integration, which allow for the improvement of the design and the applications for harvesting or collecting resources. This paper describes the programming and design of Finite State Machines (FSM) bio-inspired algorithms for seeker and resource gathering Pherobots systems, like Anthill Known Location (AKL) aggressiveness and sense of panic. FSM designing allows for the use of control architectures for behaviour-based agents and for measuring the change in system performance. Simulations demonstrate the capability of the algorithms under different environments and scenarios.

  • 253. Gebro, P.
    et al.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hansson, O.
    National scale impact of the stockholm royal seaport project2013In: IET Conference Publications, 2013, no 615 CPConference paper (Refereed)
    Abstract [en]

    This paper investigates how results from limited pilot studies concerning Smart Grids can be extrapolated to a Swedish national scale. The paper investigates the challenges with a national scale implementation of a proposed price model for electricity that combines the cost of energy with the cost of distribution that aims to encourage end-consumer Demand Response (DR). The estimated change in the national scale load-curve that may be achieved given high customer DR participation is analysed as well. Numerous challenges of a national scale implementation are identified, mainly regarding the suggested price model's economic incentive and the Swedish apartment configuration of white goods that differs from that of the pilot studies. The estimated change in the national scale load-curve may also pose problems since the endconsumer behaviour that is desirable from a distribution grid point of view may differ from that of an optimal production capacity point of view.

  • 254. Gentile, Claudio
    et al.
    Morales-España, Germán
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
    Ramos, Andres
    Universidad Pontificia Comillas.
    A Tight MIP Formulation of the Unit Commitment Problemwith Start-up and Shut-down ConstraintsManuscript (preprint) (Other academic)
    Abstract [en]

    This paper provides the convex hull description for the following basic operating con-straints of a single thermal generation unit in Unit Commitment (UC) problems: 1)generation limits, 2) startup and shutdown capabilities, and 3) minimum up and downtimes. Although the model does not consider some crucial constraints, such as ramping,the proposed constraints can be used as the core of any UC formulation, thus tighteningthe final UC model. We provide evidence that dramatic improvements in computationaltime are obtained by solving a self-UC problem for different case studies.

  • 255.
    Geze, Arthur
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling and Simulating the French Capacity Market2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As a capacity mechanism is currently being designed in France, a new capacity market will be created. The French transmission system operator RTE needed to conduct some studies on this market behaviour and the parameter influences. This report analyses in detail the French capacity mechanism and presents a model of the capacity market in order to study it. It then introduces a simulator called CLeMix that uses this model to run Monte Carlo and Agent based simulations. Several studies concerning the actors strategies and possible use of market power are then presented and their results analysed.

  • 256.
    Ghandhari, M.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Application of control Lyapunov functions to static var compensator2002In: IEEE Conference on Control Applications - Proceedings, Glasgow, 2002, Vol. 1, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper a control strategy for Static Var Compensator (SVC) is derived. The derived control strategy is based on Control Lyapunov Functions (CLF). The input signals of the derived control strategy can be relied on local or remote information. In this paper, the remote input signals will be used. These signals can be identified by applying the Single Machine Equivalent (SIME) method.

  • 257.
    Ghandhari, M
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Andersson, G
    Noroozian, M
    Angquist, L
    Non-linear Control of Controllable Series Devices (CSD)1997In: Proc. of the 29th NAPS, Wyoming, USA, pp. 398-403, Oct. 1997, 1997, p. 398-403Conference paper (Refereed)
  • 258.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dynamic Analysis of Power Systems, Part I2006Other (Other academic)
  • 259.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dynamic Analysis of Power Systems, Part II2006Other (Other academic)
  • 260.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Stability of Power Systems, An Introduction2011Other (Other academic)
  • 261.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The impact of FACTS and HVDC Systems on Transient Stability and Power Oscillation Damping2007Other (Other academic)
  • 262.
    Giannoccaro, Dimitris
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Impact of Statcom on the Interconnection Of Offshore Wind Farms with HVDC Technology2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this study is to define the minimum size of Statcom supporting the interconnection of a large offshore wind farm with high voltage direct current line commutated converters (HVDC LCC) and high voltage direct current voltage source converter (HVDC VSC) connected to a power system.

    The size of the Statcom is defined by using a simulation model consisting of a wind farm, HVDC LCC based transmission system, HVDC VSC based transmission system, a Statcom and the Cigr� Nordic 32 power system model. Each sub model in the simulation was validated individually. Different simulation cases were used to analyse the impact of Statcom in case of a fault. The different faults (one phase to ground, three phase to ground, line tripping and generator tripping) were applied to the power system for different connection points of the wind farm, i.e. the wind farm was connected to a strong and a weak connection point. The results showed that connecting the wind farm with transmission technology HVDC LCC to the strong point in the power system did not require any Statcom support because the system reached stability after the faults. When connecting the wind farm to the weak point there is a need of Statcom support for the transmission technology HVDC LCC otherwise the power system becomes unstable. Connecting the wind farm to a weak point by using the transmission technology HVDC VSC there was no need of Statcom.

    The graph below shows the Statcom size in the HYBRID HVDC (HVDC LCC and Statcom) depending on the rating of the offshore wind farm and the wind farm model.

  • 263.
    Gonzalez, Jose Luis
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dimoulkas, Ilias
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Amelin, Mikael
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Operation Planning of a CSP Plant in the Spanish Day-ahead Electricity Market2014Conference paper (Refereed)
    Abstract [en]

    This paper addresses the short-term operation planning of a concentrated solar power (CSP) plant equipped with a backup fuel boiler and operating in the Spanish day-ahead electricity market. The problem is formulated as a mixed-integer linear programming model. Forecasted values of electricity prices and direct sun irradiation are considered. The main concern in the problem is to set an optimal use of the backup system in order to increase power generation and maximize the profits. Interaction between the solar and fuel heated systems is considered through heat balance constraints while parameters referring to the boiler are independent from the rest of the system allowing various types of boilers to be tested. A realistic case study provides results of a CSP plant operating a) without boiler, b) with a natural gas boiler and c) with a biomass boiler. Results demonstrate the advantages of the proposed model.

  • 264.
    González del Pozo, José
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Electric Energy Storage in the Stockholm Royal Seaport2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Stockholm Royal Seaport is an urban development project for a planned expansion of housing and services that will take place in the district of Hjorthagen in Stockholm. The Stockholm Royal Seaport project aims to develop a smart grid for integration of consumers and producers into the utility electrical grid. The Stockholm Royal Seaport Smart Grid integrates new concepts such as active house, local storage, decentralised renewable production, electric vehicle charging and an electrified harbour into the grid. The aim of this master thesis is to describe and study some of the main aspects and benefits of the implementation of Electrical Energy Storage (EES) systems as one of the solutions to be included in smart grids. The study is focussed in the Stockholm Royal Seaport case. The main EES technologies currently available or under research and development are introduced, studying its specifications, costs, main applications and benefits in distribution grids. EES systems can cover a wide range of applications, but not all of them are equally valuable and not all the technologies are suitable and feasible for the same applications. The regulations that should be modified in order for a utility to get benefits of the different applications that EES offer are identified. Some regulations could prevent the distribution system operator (DSO) to own and operate the EES system and some market rules cannot be fulfilled by certain EES technologies. The main applications in island operation are also described and the benefit for consumers of avoiding outages is estimated for the Stockholm Royal Seaport case. EES systems can replace other equipment and improve operation of certain units in island mode. The benefit of improving reliability and quality of the electricity service greatly varies between different kinds of customers. In the Stockholm Royal Seaport case, residential and commerce consumers has been considered and reliability indexes from Fortum grid in Stockholm have been used.The possibility of renting  some capacity in the EES system to consumer with generation facilities to store its electricity surplus is analyzed to determine its economic benefit. This kind of agreement could be beneficial for the consumer when the prize for selling the electricity surplus is low compared with the prize for buying it according to the electricity contract. The efficiency of the EES system must be high enough and the price for using it is not too high. Finally, the major milestones and key challenges for the implementation of the EES system are introduced. Those milestones cover the selection of the applications that must be carried out and its requirements, the selection of the most suitable and feasible EES technology, the design of the modes of operation and its simulation, and obtaining the right to own and operate the EES system by the DSO.

  • 265.
    González García-Mon, José-Luis
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Short-term operation planning of a CSP plant in the Spanish day-ahead electricity market: Viability study of various backup systems2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 266.
    Grahn, Pia
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Electric Vehicle Charging Impact on Load Profile2013Licentiate thesis, monograph (Other academic)
    Abstract [en]

    One barrier to sustainable development is considered to be greenhouse gas emissions and pollution caused by transport, why climate targets are set around the globe to reduce these emissions. Electric vehicles (EVs), may be a sustainable alternative to internal combustion engine vehicles since having EVs in the car park creates an opportunity to reduce greenhouse gas emissions. This is due to the efficiency of the electric motor. For EVs with rechargeable batteries the opportunity to reduce emissions is also dependent on the generation mix in the power system. EVs with the possibility to recharge the battery from the power grid are denoted plug-in electric vehicles (PEVs) or plug-inhybrid electric vehicles (PHEVs). Hybrid electric vehicles (HEVs), without external recharging possibility, are not studied, hence the abbreviation EV further covers PHEV and PEV.

    With an electricity-driven private vehicle fleet, the power system will experience an increased amount of variable electricity consumption that is dependent on the charging patterns of EVs. Depending on the penetration level of EVs and the charging patterns, EV integration creates new quantities in the overall load profile that may increase the load peaks. The charging patterns are stochastic since they are affected by the travel behavior of the driver and the charging opportunities which imply that the EV integration also will have an effect on the load variations. Increased load variation and load peaks may create a need for upgrades in the grid infrastructure to reduce the risk for losses, overloads or damaging of components. However, with well-designed incentives to the EV users the variable electricity consumption due to electric vehicle charging (EVC) may become a flexible load that can help the power system mitigate load variations and load peaks.

    The aim with this licentiate thesis is to investigate the impact of EVC on load profiles and load variations. The thesis reviews and categorizes EVC models in previous research. The thesis furthermore develops electric vehicle charging models to estimate the charging impact based on charging patterns induced by private car travel behavior. The models mainly consider uncontrolled charging (UCC) related to stochastic individual car travel behavior and induced charging needs for PHEVs. Moreover, the thesis comments on the potential of individual charging strategies (ICS) with flexible charging and external charging strategies (ECS).

    Three key factors are identified when considering the impact of EVC on load profiles and load variations. The key factors are: The charging moment, the charging need and the charging location. It is concluded that the level of details concerning the approach to model these key factors in EVC models will impact the estimations of the load profiles. This means that models taking into account a higher level of mobility details will be able to create a more realistic estimation of a future UCC behavior, enabling for more accurate estimates of the impact on load profiles and the potential of ICS and ECS.

  • 267.
    Grahn, Pia
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Electric Vehicle Charging Modeling2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    With an electrified passenger transportation fleet, carbon dioxide emissions could be reduced significantly depending on the electric power production mix. Increased electric power consumption due to electric vehicle charging demands of electric vehicle fleets may be met by increased amount of renewable power production in the electrical systems. With electric vehicle fleets in the transportation system there is a need for establishing an electric vehicle charging infrastructure that distributes this power to the electric vehicles. Depending on the amount of electric vehicles in the system and the charging patterns, electric vehicle integration creates new quantities in the overall load profile that may increase the load peaks. The electric vehicle charging patterns are stochastic since they are affected by the travel behavior of the driver and the charging opportunities which implies that an electric vehicle introduction also will affect load variations. Increased load variation and load peaks may create a need for upgrades in the grid infrastructure to reduce losses, risks for overloads or damaging of components. However, with well-designed incentives for electric vehicle users and electric vehicle charging, the electric vehicles may be used as flexible loads that can help mitigate load variations and load peaks in the power system.

    The aim with this doctoral thesis is to investigate and quantify the impact of electric vehicle charging on load profiles and load variations. Three key factors are identified when considering the impact of electric vehicle charging on load profiles and load variations. The key factors are: The charging moment, the charging need and the charging location. One of the conclusions in this thesis is that the level of details and the approach to model these key factors impact the estimations of the load profiles. The models that take into account a high level of mobility details will be able to create a realistic estimation of a future uncontrolled charging behavior, enabling for more accurate estimates of the impact on load profiles and the potential of individual charging strategies and external charging strategies. The thesis reviews and categorizes electric vehicle charging models in previous research, and furthermore, introduces new electric vehicle charging models to estimate the charging impact based on charging patterns induced by passenger car travel behavior. The models mainly consider EVC related to individual car travel behavior and induced charging needs for plug-in-hybrid electric vehicles. Moreover, the thesis comments on dynamic electric vehicle charging along electrified roads and also on individual charging strategies.

  • 268.
    Grahn, Pia
    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.
    PHEV Utilization Model Considering Type-of-Trip and Recharging Flexibility2014In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 5, no 1, p. 139-148Article in journal (Refereed)
    Abstract [en]

    Electric vehicles (EVs) may soon enter the vehicle market in large numbers and change the overall fuel usage within the passenger transport sector. With increased variable consumption from EVs together with anticipated increased production from variable sources, due to renewable wind and solar power, also the balancing of the electric power system incur increased attention. This emphasizes the importance of developing models to estimate and investigate the stochasticity of personal car travel behavior and induced EV charging load. Several studies have been made in order to model the stochasticity of passenger car travel behavior but none have captured the charging behavior dependence of the type-of-trip conducted. This paper proposes a new model for plug-in-hybrid electric vehicle (PHEV) utilization and recharging price sensitivity, to determine charging load profiles based on driving patterns due to the type-of-trip and corresponding charging need. This approach makes it possible to relate the type-of-trip with the consumption level, the parking location, and the charging opportunity. The proposed model is applied in a case study using Swedish car travel data. The results show the charging load impact and variation due to the stochastic PHEV type-of-trip mobility, allowing quantification of the PHEV charging impact on the system.

  • 269.
    Grahn, Pia
    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.
    Plug-in-vehicle mobility and charging flexibility Markov model based on driving behavior2012In: 9th International Conference on the European Energy Market, EEM 12, IEEE , 2012Conference paper (Refereed)
    Abstract [en]

    Climate targets around the globe are enforcing new strategies for reducing climate impacts, which encourage automobile and electricity companies to consider an electrified vehicle market. Furthermore, the variable electricity production in the electric power system is increasing, with higher levels of wind and solar power. Due to the increased variability in the system, the need to meet fluctuations with flexible consumption is intensified. Electric vehicles with rechargeable batteries seem to become an increasingly common feature in the car fleet. Plugin vehicles (PIVs), may therefore become valuable as flexible consumers. If so, flexible PIV owners could, if they are flexible enough, increase the value of owning an electric vehicle. This paper introduces a new PIV Mobility and Charging Flexibility Markov Model, based on driving behavior for private cars. By using the new model, it is possible to simulate the potential flexibility in a future system with many PIVs. The results from a case study indicate a potential need for usage of the batteries as flexible loads to reduce the grid power fluctuations and load peaks.

  • 270.
    Grahn, Pia
    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.
    Static and Dynamic Electric Vehicle Charging Impact on Load Profile with Electrified RoadsManuscript (preprint) (Other academic)
  • 271.
    Grahn, Pia
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Munkhammar, Joakim
    Widén, Joakim
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    PHEV Home-Charging Model Based on Residential Activity Patterns2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 3, p. 2507-2515Article in journal (Refereed)
    Abstract [en]

    Plug-in hybrid electric vehicles (PHEVs) have received an increased interest lately since they provide an opportunity to reduce greenhouse gas emissions. Based on the PHEV introduction level in the car park, the charging behaviors in an area will induce changes in the load profiles of the power system. Hence, it becomes important to investigate what impact a given PHEV introduction level has on load profiles due to expected charging behavior of residents.

  • 272.
    Grahn, Pia
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A method for evaluating the impact of electric vehicle charging on transformer hotspot temperature2011In: 2011 2nd IEEE PES International Conference and Exhibition on Innovative Smart Grid Technologies (ISGT Europe), 2011Conference paper (Refereed)
    Abstract [en]

    The expected increasing market share of electric vehicles is a response to the combination of new technological developments, governmental financial control, and an attitude shift of residents to a more environmentally friendly lifestyle. The expected capacity required for charging, imposes changes in the load to the already existing components in the electric power grid. In order to continue managing these existing assets efficiently during this load change, it is important to evaluate the impact imposed by the battery charging.

  • 273.
    Grahn, Pia
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Static and Dynamic Vehicle-to-Grid Potential with Electrified Roads2013In: 2013 IEEE Innovative Smart Grid Technologies - Asia, 2013Conference paper (Refereed)
    Abstract [en]

    A large scale introduction of electric vehicles (EVs) enables for interesting opportunities such as meeting the need for power balancing in the electric system. With increased introduction of variable and renewable electricity production resources such as wind power and solar power, the need for power balancing also increases. If EV batteries can be used as individual and flexible storages performing vehicle-to-grid (V2G) services with or without the possibility to inject power to the grid, this increased need for power balancing could be met. This paper investigates the potential for individual and flexible EV batteries to be used for V2G services by introducing a new model. With the model it is possible to estimate the potential for V2G power consumption and power injection with a well-developed charging infrastructure including dynamic EVC at electrified roads (ERs) and static EVC at parking sites. The model includes models for time-dependent V2G potential, dynamic EVC at ERs, static EVC at parking sites, vehicle mobility and vehicle driving power demand. A case study shows the resulting V2G potential for power consumption and power injection under different conditions with a charging infrastructure including both dynamic and static EVC infrastructure.

  • 274.
    Grahn, Pia
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The customer perspective of the electric vehicles role on the electricity market2011In: 2011 8th International Conference on the European Energy Market (EEM), Piscataway: IEEE , 2011, p. 141-148Conference paper (Refereed)
    Abstract [en]

    Recent studies have investigated the impact and effects of using batteries in connected electric vehicles as ancillary services to the electricity grid. A common assumption made is that all parked cars are connected to the grid and available for recharging or discharging. However, the level of flexibility of people’s behavior is important and will affect the potential of using car batteries for regulation power. How customers will react if they are expected to recharge or discharge whenever the electric system need it, will depend on incentives and peoples willingness to adapt. This paper reviews existing research regarding electric vehicles and their interaction with the electric power system and investigate conditions for a potential use of the batteries as regulation power. The customer perspective of the electric vehicle’s role on the electricity market is analyzed considering participation in the control power market.

  • 275.
    Grahn, Pia
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Widén, Joakim
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Impact of Electric Vehicle Charging Strategies on Load Profiles With a Multinomial Logit ModelManuscript (preprint) (Other academic)
  • 276.
    Guha Thakurta, Priyanko
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    An Approach for Optimal Placement of SVC to Minimize Load Curtailment2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Modern electric power system is very complex and undergoes unforeseen rapid changes in terms of demand/generation patterns and trading activities that hinder the system security. For example, a steep rise in load or a certain critical line/equipment outage can cause line overload or undesirable voltage profile and such events can push the system towards instability and possibly even a black out. In order to cope with such situations, it is common practice to purchase the rights of asking for a reduction of load from certain customers. However, it is not an ideal situation from reliability perspective, financial as well as having critical load in the power system. Load curtailment is the collection of control strategies employed to reduce the electric power loading in the system and main aim is to push the disturbed system towards a new equilibrium state. Load curtailment may be required even when voltages at some buses are out of their safe operating limits, to prevent a possible voltage collapse.

    Flexible AC Transmission Systems (FACTS) controllers could be a suitable alternative to provide reactive power support at the load centres locally and hence keep the voltages within their safe operating limits. Due to high costs of FACTS devices, their proper location in the system must be ascertained.

    To deal with the above problem a new methodology has been proposed, in this thesis, in terms of sensitivity factors for the optimal location of Static Var Compensator (SVC) to minimize the system load curtailment requirements for maintaining the system security. In this work, SVC has been considered for the study to minimize the load curtailment. The effectiveness of the proposed method has been tested on IEEE 14-bus and practical 75-bus Indian systems. Optimal placement have been obtained for the base case loading and to verify its locations, an Optimal Power Flow (OPF) problem has been formulated with an objective to minimize the load curtailment and satisfying all operating constraints along with optimal settings of SVC which is used at suggested places from developed methodology. Moreover, the effects of SVC on load curtailment reduction, which are located at base case loading, have also been investigated for different operating conditions e.g., increased load or having different contractual obligation in the system.

  • 277.
    Guironnet, Adrien
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Computations on the Frenchtransmission grid in order to improvethe voltage security assessment2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As the electric consumption increases and the investments are hard to make, electricitynetworks are operated closer to their limits. In such conditions, a generator or a transmissionline outage can have tremendous impact, leaving a great number of people without electricity. Itis therefore a matter of prime importance to ensure power system security and in particularvoltage stability. Static criteria used in on-line simulations as well as protection and defensedevices such as load-shedding devices play a critical role for voltage stability and are thus crucialfor the network security. The core of this project is to determine efficient tools to detectundesirable conditions in operational context and to determine a pertinent activation level foran automatic load-shedding device used for the system protection against voltage instability.In the first part of this report, theoretical background regarding voltage stability ispresented, followed by the software and methodologies used during the Master’s thesis work.The second part of this report focuses on case studies conducted for the French powersystem. From an initial objective of updating static criteria, the results have actually led to thewithdrawal of these criteria and a switch to dynamic simulations for the North-East and Eastareas, as well as to the improvement of Astre software database. Simulations on the moststressed conditions from last winter allowed the updating of the activation level for theautomatic load-shedding device. These changes have been validated and will be applied forvoltage security assessment of the French network in the future.

  • 278.
    Guldner, Sophie
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Natural Gas Netback value for the electricity Generation2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The netback value is a price mechanism approach for determining prices in long‐term contracts. This method consists in ensuring that gas remains competitive with competing fuels by setting the border in each long ‐term sale contract below the weighted‐average price of the cheapest alternative fuels across all sectors, including industry, residential tertiary, transportation and electricity generation. This price mechanism is used in Continental Europe because the gas does not have captive uses and it can be replaced by other energy in all sectors such as the coal in the electricity generation sector. This price is then indexed under long ‐term contracts to the main competing fuel. This pattern of indexation allows avoiding volatility and the use of market power but some actors really want to change this method of indexation. Indeed, the power sector represents the main source of incremental demand growth for gas in the recent years and therefore, indexation to coal is conceivable. Moreover, the economic crisis contributes to lower the gas market price, opening a gap between the spot and the long ‐term contract prices. The spot price and the long ‐term price are currently at nearly the same level but during the winter, the long ‐term contract price should be normally lower. More and more Combine Cycle Gas and Turbines (CCGT) are built in Europe and the investors would like to include the gas value of the electricity generation in the calculation of the weighted Netback value. Some key factors such as the construction of the coal plant cost, the fuel cost and the CO2 cost have a significant impact on this Netback value for electricity generation. The CO2 Capture and Storage (CCS) is also a promising technology regarding the share of fossil fuel in the energy mix. However, the netback value found with the CCS coal plants must be viewed with some caution regarding the uncertainties around the capture costs, the transport costs, the distribution of storage sites and the learning rate.

  • 279.
    Guler, Hazal
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Tedgren, Camilla
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Establishing the Optimal Tariff in Rural Electricity Distribution Networksy.2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Access to electricity is a key factor of improving the living standard in a country, as it enhances the quality of services such as education, health care and productivity. The rural population of Uganda is however only supplied with electricity to a degree less than three percent. There are large financial issues in extending the national electricity grid why small stand alone systems are sometimes a more valuable option. Even then, there are large investment costs that need to be covered by the sale of electricity. Due to the limited buying power of rural consumers, the end-user tariff setting becomes of great significance of the financial outlook. If the tariff is set too high, the consumption will most likely be lower than what it could be, resulting in a loss of revenue as well as inhibiting the improvement of living standards for the consumers. On the other hand, if the tariff is set too low, it could lead to excessive consumption, resulting in power failures.

    In view of the above, the main aim of this study has been to investigate the consequences of different tariffs in an isolated rural power system. This was done by studying the electricity consumption in two already electrified rural networks in order to find information on demand behavior and load profiles. Interviews with electricity consumers were conducted to investigate how their demand would change if tariffs were altered.

    Demand as a function of price was shown by linear curves indicating the price sensitivity and demand factor, the latter being the theoretical maximum demand when price is zero. These parameters were modelled in Monte Carlo simulations with the aim to predict the demand behavior of a site that is not yet electrified and find the tariff that should be applied to this site. The simulations were based on two potential economic objectives of how to operate the system; by altruistic or profit maximising means.

    Depending on whether the system is altruistic or profit maximizing, the optimum point of tariff differs. In the altruistic case, this tariff should be set where the costs are covered by the revenues. The profit maximizing system instead requests the tariff where profit is as high as possible. Furthermore, two different structures of tariff setting were tested for the system; a structure with time-of-use levels where the tariff should be higher during the peak demand hours of the day, and a flat rate structure where the tariff is constant throughout the day.

    The field study showed that, on average, the price sensitivity factor of domestic consumers were slightly higher than of the commercial consumers. The results also showed that the majority of the commercial consumers reside in the same building as their business. Furthermore, rural consumers exhibit low awareness of their consumption patterns and the price of electricity. Extensive information from the distribution companies to the customers is therefore essential to maintain a sustainable electricity consumption, as it enables consumers to make rational decisions about their electricity consumption and opt for more efficient alternatives.

    A financial analysis for the specific case study was also conducted from simulations. The analysis found for an altruistic system a tariff slighly lower tariff than the tariff applied in the national grid today. However, the system will require an additional financing to cover the payments before the year when revenues exceed expenses, but can be paid back within eight years. The tariffs found by simulating with a profit maximizing system operator are more than twice as high as the current tariff applied in the national grid today. On the other hand, the system requires a very small additional loan or subsidy compared to the altruistic simulations and has a pay-off time within six years.

  • 280.
    Gunnar, Anders
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Towards robust traffic engineering in IP networks2007Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    To deliver a reliable communication service it is essential for the network operator to manage how traffic flows in the network. The paths taken by the traffic is controlled by the routing function. Traditional ways of tuning routing in IP networks are designed to be simple to manage and are not designed to adapt to the traffic situation in the network. This can lead to congestion in parts of the network while other parts of the network are far from fully utilized. In this thesis we explore issues related to optimization of the routing function to balance load in the network.

    We investigate methods for efficient derivation of the traffic situation using link count measurements. The advantage of using link counts is that they are easily obtained and yield a very limited amount of data. We evaluate and show that estimation based on link counts give the operator a fast and accurate description of the traffic demands. For the evaluation we have access to a unique data set of complete traffic demands from an operational IP backbone.

    Furthermore, we evaluate performance of search heuristics to set weights in link-state routing protocols. For the evaluation we have access to complete traffic data from a Tier-1 IP network. Our findings confirm previous studies that use partial traffic data or synthetic traffic data. We find that optimization using estimated traffic demands has little significance to the performance of the load balancing.

    Finally, we device an algorithm that finds a routing setting that is robust to shifts in traffic patterns due to changes in the interdomain routing. A set of worst case scenarios caused by the interdomain routing changes is identified and used to solve a robust routing problem. The evaluation indicates that performance of the robust routing is close to optimal for a wide variety of traffic scenarios.

    The main contribution of this thesis is that we demonstrate that it is possible to estimate the traffic matrix with good accuracy and to develop methods that optimize the routing settings to give strong and robust network performance. Only minor changes might be necessary in order to implement our algorithms in existing networks.

  • 281.
    Guymard, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling of Technical Losses in theSenegalese Transmission andDistribution Grids and Determination ofNon-technical Losses2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Electricity is a sector in crisis in Senegal. The main part of production and all the activities oftransmission and distribution of electricity are managed by the Senegalese National Society ofElectricity called SENELEC which is encountering enormous difficulties. One of the mostimportant problems is the fact that 21% of the produced energy is lost without being sold.This figure is enormous but quite typical with regards to African countries.Moreover, the distribution of these losses is insufficiently known. Only the production andtransmission losses can be determined from frequent and accurate measurements. Thedistribution losses represent the rest and constitute more than 80% of the losses. However, thedistribution between technical and non-technical losses (essentially due to fraud) is unknownin the distribution grid. In addition, the distribution of distribution technical losses betweenthe 30 kV, 6.6 kV and 400V grids is unknown. The goal of this Master’s Thesis is to estimatethese unknown losses. Moreover, some recommendations are suggested to reducetransmission and distribution losses.Regarding the transmission grid, Senelec does not take transmission losses into account in itsdispatching decisions, which increases transmission losses. After a Matlab modeling of thetransmission grid, a basic optimal dispatching program was developed to include losses and toprove that it would be better to consider losses in the dispatching decision.The study of the distribution grid constitutes the main part of this Master’s Thesis. Thedistribution grid can be divided in a medium-voltage grid (30 kV and 6.6 kV) and a lowvoltagegrid (400V). Losses in medium-voltage grid are estimated by the modeling of a partof this grid by using the software PSAF. Losses in low-voltage grid cannot be estimated thisway because of the lack of knowledge regarding the structure of this grid; thus, these lossesare estimated using a semi-empirical formula. Finally, non-technical distribution losses arededuced by calculating the difference between the total losses and the technical losses.The results show that the main part of the losses in Senegal are non-technical losses, whichrepresent 2/3 of the total losses and 40 billion of FCFA (61 million €), which is twice as highas what the company believed. High priority must be given to reduce them by an ambitiousplan against fraud. Technical losses even if they are smaller are not negligible and can also bereduced with some well-focused actions.

  • 282.
    Guyot, Emilie Solange Lucienne
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Study on the development of the public Study on the development of the public transmission network around Goéland until 20302008Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The project was performed in RTE (“Réseau de Transport d’Electricité”), the French Transmission System Operator (TSO) within the Network Optimisation and Development Service (SDOP) that has to plan and direct the development of the regional transmission network (225 and 63 kV). The goal was to carry out a study on the development of the power transmission network until 2030 in a context of increasing demand, in order to match power need in the future. Thus, it consists into the determination of the different constraints (transmission capacity constraints, short-circuit current limitations, voltage stability constraints, environmental constraints…) that might appear in the area of study in the medium-term (2020) and longterm (2030). These constraints were analyzed with the determination of the causes and the calculation of the seriousness (for example power cut and not distributed energy) of the aforementioned constraints. The next step consists in the analysis of several technical and economical solutions to satisfy these constraints. Then, the study results in an investment plan from 2007 to 2030 including the solutions, their costs and their years of investment. Finally, this work was presented, explained and approved by the regional management of RTE.

    This master thesis report is divided into four parts: a brief presentation of RTE is given, then the context of study and a prediction of the long-term behaviour of the electrical market are presented, followed by the technical issues and the general tools of the study and finally the consistent results related to the study are explained.

    A chart of confidentiality was signed not to transmit the results outside of the company. This report is based on an existing grid, even though the names of the substations have been changed for the sake ofconfidentiality.

  • 283.
    Gómez, Francisco José
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, Oslo.
    Olsen, Svein
    Statnett SF, Oslo.
    A Modelica-based execution and simulation engine for automated power system model validation2014In: Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), 2014 IEEE PES, 2014, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Power systems model information exchange and the simulation of user defined models is a challenge for Transmission System Operators (TSOs) due to the use of different simulation software with specific data format and models strongly coupled to the simulation software's numerical routines. The use of Open Source software for simulation and modelling can help to decouple power system models from simulation tools. This work describes the design of a software tool following the Free/Libre Open Source Software philosophy to simulate equation-based models and implement a standard data format for model information exchange.

  • 284.
    Gómez, Francisco José
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, Oslo.
    Olsen, Svein
    Statnett SF, Oslo.
    Binding CIM and Modelica for Consistent Power System Dynamic Model Exchange and Simulation2015Conference paper (Refereed)
    Abstract [en]

    The Common Information Model (CIM) is considered the most prominent data model for power systems information exchange between Transmission System Operators (TSO), facilitating coordination of TSO for steady-state operation. However, information exchange should also consider power systems dynamic models required to perform dynamic simulations so to coordinate TSOs operations under emergency conditions. This work describes the design and implementation of a mapping between CIM and Modelica. The Modelica models provide a strict mathematical representation of power system dynamic models using a standardized modeling language. The proposed solution combines both modeling languages, thus providing a CIM-compliant unambiguous power system model exchange and simulation solution considering both steady-state and dynamic models.

  • 285.
    Hallia, Sofi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Strategi för utvecklande av reglerbudata2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This Master Thesis discusses the development of bids for regulation power with consideration of change of discharge. The study was initiated by Vattenfall PD and is a limited part of a substantial development project at the same division. The background of the project is the new demands from SvK, which among other things includes more detailed regulation bids. As from the 1st of November 2008, the regulation bids are supposed to be calculated regarding each specific regulation object, something that is defined by SvK. These new demands changes Vattenfall�s conditions and will increase the need for detailed knowledge about available regulation power and costs for regulation.

    In this study a strategy for regulation bids was developed. Proper quantities for bids have been defined and costs for regulation power have been calculated. The pricebids are calculated with regard to change of efficiency as a function of the discharge and the water value. The strategy has been developed with consideration to hydrological couplings, physical and technical parameters and market constrains. In order to provide background information for the reader, the first chapters of the report describes the Nordic power market, production planning of hydropower plants and regulation power.

    A case study has been performed with the purpose to understand how the new demands and the strategy developed in this report might influence the regulation bids. The results from the study indicates the developed strategy increases the quantity of regulation power thought the market and will lead to more competitive bids since they will be more detailed and have more advantageous pricebids.

  • 286.
    Hamberg Magnusson, Joel
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Elproduktion i Vindkraftverk2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 287.
    Hamon, Camille
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Doubly-fed Induction Generator Modeling and Control in DigSilent Power Factory2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    International agreements have set high demands on the share of renewable energy in the total energy mix. From the different renewable sources, significant investments are made in wind power. More and more wind turbines are being built and their number is due to rise dramatically. There are many different generator technologies, but this paper focuses on the doubly-fed induction generator (DFIG).

    DFIGs are generators which are connected to the grid on both stator and rotor sides. The machine is controlled via converters connected between the rotor and the grid. The size of these converters determines the speed range of the DFIG.

    Wind farm connections to the grid must satisfy grid requirements set by transmission system operators. This means that the study of their dynamic responses to disturbances has become a critical issue, and is becoming increasingly important for induction generators, due to their growing size and number.

    Several computer programs exist to carry out dynamical simulations and this work will focus on one of them, namely Power Factory from DigSilent. It offers a large choice of builtin components. These components can be controlled through input signals. It is therefore possible for the user to design control strategies.

    Power Factory has two models of DFIG. A new model has also been developed, based upon a controllable voltage source. These three models are compared, in terms of dynamical behavior and simulation time. One is then used to study the effect of introducing a certain signal to the control strategy.

  • 288.
    Hamon, Camille
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On Frequency Control Schemes in Power Systems with Large Amounts of Wind Power2012Licentiate thesis, monograph (Other academic)
    Abstract [en]

    In recent years, large investments have been made in wind power, and this trend is expected to continue in the coming decades. Integrating more wind power in the production mix offers great opportunities for the society, such as reducing greenhouse gas emissions and the dependence on foreign fuel. Large wind power penetration does, however, require changes in the way power systems are planned and operated.

    The power transfers across the electrical grid are determined by the load and the production. A secure operation of power systems requires that these power transfers stay within certain limits. Frequency control schemes are crucial for ensuring the balance between the electric demand and the production. They enable system operators to re-dispatch the production (for example via the activation of balancing bids) during real-time operations to follow the load variations. With wind power, these frequency control schemes must not only meet the variations of the load but also those of the wind.

    An optimal use of the frequency control reserves would allow system operators to operate the system in the most cost effective and secure manner, that is, using the cheapest available resources while taking into account the stability limits of the system and the uncertainty. With no wind power, the load is the main source of uncertainty, and it can be forecasted accurately. This enables system operators to dispatch the generation in the most cost-effective way to meet the load while keeping the system within its stability limits. Adding wind power to power systems, on the other hand, introduces a new source of uncertainty on the production side, which is more difficult to forecast. The tools used today for computing the stability limits and operating the system do not consider the whole range of possible future load and wind power production levels, but only pick a few likely values in this range.

    In this work, we propose a new approach which accounts for the whole uncertainty in the load and wind power, and gives the optimal re-dispatch which ensures a given level of system security given this uncertainty. The approach is a so-called Stochastic Optimal Power Flow (S-OPF) formulation, developed in the scope of this project for the optimal activation of balancing bids. It is a nonlinear optimization problem with one probabilitistic constraint ensuring a certain level of system security -- computed as the probability that the system stays within its stability limits -- and whose objective function is the minimization of the generation re-dispatch. Compared to what is done today, the S-OPF formulation enables system operators to consider the uncertainty when making decisions.

    An approximation of the proposed S-OPF formulation is developed to render the problem tractable. In particular, the stability boundary, defined as the set of stability limits, is approximated by second-order approximations. The accuracy of these second-order approximations are analyzed in the IEEE 9 bus system by computing the distance between the actual boundary and its approximation. The S-OPF problem is then solved in the IEEE 39 bus system using the approximated stability boundaries. Monte Carlo simulations are run in order to assess the accuracy of the approximation and check whether the optimal solution of the approximation does ensure the specified level of system security.

  • 289.
    Hamon, Camille
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Probabilistic security management for power system operations with large amounts of wind power2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Power systems are critical infrastructures for the society. They are therefore planned and operated to provide a reliable eletricity delivery. The set of tools and methods to do so are gathered under security management and are designed to ensure that all operating constraints are fulfilled at all times.

    During the past decade, raising awareness about issues such as climate change, depletion of fossil fuels and energy security has triggered large investments in wind power. The limited predictability of wind power, in the form of forecast errors, pose a number of challenges for integrating wind power in power systems. This limited predictability increases the uncertainty already existing in power systems in the form of random occurrences of contingencies and load forecast errors. It is widely acknowledged that this added uncertainty due to wind power and other variable renewable energy sources will require new tools for security management as the penetration levels of these energy sources become significant.

    In this thesis, a set of tools for security management under uncertainty is developed. The key novelty in the proposed tools is that they build upon probabilistic descriptions, in terms of distribution functions, of the uncertainty. By considering the distribution functions of the uncertainty, the proposed tools can consider all possible future operating conditions captured in the probabilistic forecasts, as well as the likeliness of these operating conditions. By contrast, today's tools are based on the deterministic N-1 criterion that only considers one future operating condition and disregards its likelihood.

    Given a list of contingencies selected by the system operator and probabilitistic forecasts for the load and wind power, an operating risk is defined in this thesis as the sum of the probabilities of the pre- and post-contingency violations of the operating constraints, weighted by the probability of occurrence of the contingencies.

    For security assessment, this thesis proposes efficient Monte-Carlo methods to estimate the operating risk. Importance sampling is used to substantially reduce the computational time. In addition, sample-free analytical approximations are developed to quickly estimate the operating risk. For security enhancement, the analytical approximations are further embedded in an optimization problem that aims at obtaining the cheapest generation re-dispatch that ensures that the operating risk remains below a certain threshold. The proposed tools build upon approximations, developed in this thesis, of the stable feasible domain where all operating constraints are fulfilled.

  • 290.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Elkington, Katherine
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Doubly-fed Induction Generator Modeling and Control in DigSilent PowerFactory2010In: 2010 International Conference on Power System Technology: Technological Innovations Making Power Grid Smarter, POWERCON2010, IEEE , 2010, p. 1-7Conference paper (Refereed)
    Abstract [en]

    Several computer programs exist to carry out dynamicsimulations and this study will focus on one of them,namely DigDilent PowerFactory. It offers two built-in modelsof doubly-fed induction generator. A new model has also beendeveloped, based upon a controllable voltage source. Thesethree models are compared, in terms of dynamic behavior andsimulation time. One of them is then used to study the impact ofan input control signal based on the single machine equivalentmethod. This signal provides power oscillation damping.

  • 291.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A computational framework for risk-based power system operations under uncertainty. Part II: Case studies2015In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 119, p. 66-75Article in journal (Refereed)
    Abstract [en]

    With larger penetrations of wind power, the uncertainty increases in power systems operations. The wind power forecast errors must be accounted for by adapting existing operating tools or designing new ones. A switch from the deterministic framework used today to a probabilistic one has been advocated. This two-part paper presents a framework for risk-based operations of power systems. This framework builds on the operating risk defined as the probability of the system to be outside the stable operation domain, given probabilistic forecasts for the uncertainty, load and wind power generation levels. This operating risk can be seen as a probabilistic formulation of the N - 1 criterion. In Part I, the definition of the operating risk and a method to estimate it were presented. A new way of modeling the uncertain wind power injections was presented. In Part II of the paper, the method's accuracy and computational requirements are assessed for both models. It is shown that the new model for wind power introduced in Part I significantly decreases the computation time of the method, which allows for the use of later and more accurate forecasts. The method developed in this paper is able to tackle the two challenges associated with risk-based real-time operations: accurately estimating very low operating risks and doing so in a very limited amount of time.

  • 292.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A computational framework for risk-based power systems operations under uncertainty. Part I: Theory2015In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 119, p. 45-53Article in journal (Refereed)
    Abstract [en]

    With larger penetrations of wind power, the uncertainty increases in power systems operations. The wind power forecast errors must be accounted for by adapting existing operating tools or designing new ones. A switch from the deterministic framework used today to a probabilistic one has been advocated. This two-part paper presents a framework for risk-based operations of power systems. This framework builds on the operating risk defined as the probability of the system to be outside the stable operation domain, given probabilistic forecasts for the uncertainty (load and wind power generation levels) and outage rates of chosen elements of the system (generators and transmission lines). This operating risk can be seen as a probabilistic formulation of the N - 1 criterion. The stable operation domain is defined by voltage-stability limits, small-signal stability limits, thermal stability limits and other operating limits. In Part I of the paper, a previous method for estimating the operating risk is extended by using a new model for the joint distribution of the uncertainty. This new model allows for a decrease in computation time of the method, which allows for the use of later and more up-to-date forecasts. In Part II, the accuracy and the computation requirements of the method using this new model will be analyzed and compared to the previously used model for the uncertainty. The method developed in this paper is able to tackle the two challenges associated with risk-based real-time operations: accurately estimating very low operating risks and doing so in a very limited amount of time.

  • 293.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A Stochastic Optimal Power Flow Problem With Stability Constraints-Part I: Approximating the Stability Boundary2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 2, p. 1839-1848Article in journal (Refereed)
    Abstract [en]

    Stochastic optimal power flow can provide the system operator with adequate strategies for controlling the power flow to maintain secure operation under stochastic parameter variations. One limitation of stochastic optimal power flow has been that only line flows have been used as security constraints. In many systems voltage stability and small-signal stability also play an important role in constraining the operation. In this paper we aim to extend the stochastic optimal power flow problem to include constraints for voltage stability as well as small-signal stability. This is done by approximating the voltage stability and small-signal stability constraint boundaries with second-order approximations in parameter space. Then we refine methods from mathematical finance to be able to estimate the probability of violating the constraints. In this first part of the paper, we derive second-order approximations of stability boundaries in parameter space. In the second part, the approximations will be used to solve a stochastic optimal power flow problem.

  • 294.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    An Importance Sampling Technique for Probabilistic Security Assessment In Power Systems with Large Amounts of Wind Power2016In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 131, p. 11-18Article in journal (Refereed)
    Abstract [en]

    Larger amounts of variable renewable energy sources bring about larger amounts of uncertainty in the form of forecast errors. When taking operational and planning decisions under uncertainty, a trade-off between risk and costs must be made. Today's deterministic operational tools, such as N-1-based methods, cannot directly account for the underlying risk due to uncertainties. Instead, several definitions of operating risks, which are probabilistic indicators, have been proposed in the literature. Estimating these risks require estimating very low probabilities of violations of operating constraints. Crude Monte-Carlo simulations are very computationally demanding for estimating very low probabilities. In this paper, an importance sampling technique from mathematical finance is adapted to estimate very low operating risks in power systems given probabilistic forecasts for the wind power and the load. Case studies in the IEEE 39 and 118 bus systems show a decrease in computational demand of two to three orders of magnitude.

  • 295.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Applying stochastic optimal power flow to power systems with large amounts of wind power and detailed stability limits2013In: Bulk Power System Dynamics and Control - IX Optimization, Security and Control of the Emerging Power Grid (IREP), 2013 IREP Symposium, 2013Conference paper (Refereed)
    Abstract [en]

    Increasing wind power penetration levels bring about new challenges for power systems operation and planning, because wind power forecast errors increase the uncertainty faced by the different actors. One specific problem is generation re-dispatch during the operation period, a problem in which the system operator seeks the cheapest way of re-dispatching generators while maintaining an acceptable level of system security. Stochastic optimal power flows are re-dispatch algorithms which account for the uncertainty in the optimization problem itself. In this article, an existing stochastic optimal power flow (SOPF) formulation is extended to include the case of non-Gaussian distributed forecast errors. This is an important case when considering wind power, since it has been shown that wind power forecast errors are in general not normally distributed. Approximations are necessary for solving this SOPF formulation. The method is illustrated in a small power system in which the accuracy of these approximations is also assessed for different probability distributions of the load and wind power.

  • 296.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Closure of 'applying stochastic optimal power flow to power systems with large amounts of wind power and detailed stability limits'2013In: Proceedings of IREP Symposium: Bulk Power System Dynamics and Control - IX Optimization, Security and Control of the Emerging Power Grid, IREP 2013, 2013Conference paper (Refereed)
    Abstract [en]

    We thank the authors of the discussion in [1] for raising the issue of cascading events and correlated blackouts. Our method in [2] was designed as a stochastic version of the security-constrained optimal power flow (SCOPF), in which the system should be operated to remain stable in some sense (deterministic or stochastic) after any single pre-selected contingency occurs.

  • 297.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Lund University.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Efficient importance sampling technique for estimating operating risks in power systems with large amounts of wind power2014In: Proceedings of the 13th International Workshop on Large-scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power Plants / [ed] Uta Betancourt, Thomas Ackermann, Energynautics GmbH, 2014Conference paper (Refereed)
    Abstract [en]

    Uncertainties faced by operators of power systems are expected to increase with increasing amounts of wind power. This paper presents a method to design efficient importance sampling estimators to estimate the operating risk by Monte-Carlo simulations given the joint probability distribution describing the wind power and load forecasts. The operating risk is defined as the probability of violating stability and / or operating constraints. The method relies on an exisiting framework for rare-event simulations but takes into account the peculiarities of power systems. In case studies, it is shown that the number of Monte-Carlo runs needed to achieve a certain accuracy on the estimator can be reduced by up to three orders of magnitude.

  • 298.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Stochastic Optimal Power Flow Problem with Stability Constraints2013In: 2013 IEEE Power and Energy Society General Meeting (PES), IEEE , 2013Conference paper (Refereed)
  • 299.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Perninge, Magnus
    Department of Automatic Control, Lund University, Sweden .
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The value of using chance-constrained optimal power flows for generation re-dispatch under uncertainty with detailed security constraints2013In: 2013 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC), IEEE Computer Society, 2013, p. 6837148-Conference paper (Refereed)
    Abstract [en]

    The uncertainty faced in the operation of power systems increases as larger amounts of intermittent sources, such as wind and solar power, are being installed. Traditionally, an optimal generation re-dispatch is obtained by solving security-constrained optimal power flows (SCOPF). The resulting system operation is then optimal for given values of the uncertain parameters. New methods have been developed to consider the uncertainty directly in the generation re-dispatch optimization problem. Chance-constrained optimal power flows (CCOPF) are such methods. In this paper, SCOPF and CCOPF are compared and the benefits of using CCOPF for power systems operation under uncertainty are discussed. The discussion is illustrated by a case study in the IEEE 39 bus system, in which the generation re-dispatch obtained by CCOPF is shown to always be cheaper than that obtained by SCOPF.

  • 300.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Amelin, Mikael
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Two partitioning methods for multi-area studies in large power systems2015In: International Transactions on Electrical Energy Systems, E-ISSN 2050-7038, Vol. 25, no 4, p. 648-660Article in journal (Refereed)
    Abstract [en]

    Multi-area studies are an important tool for today's and future power systems. In this paper, a two-step algorithm for creating multi-area models is presented that, first, identifies areas, and, second, computes reduced models of these areas. For the first step, two new methods to identify areas in power systems have been developed. The first method is based upon spectral partitioning, whereas the second one is formulated as a linear optimization problem. The methods are compared in terms of computation time on the IEEE 118 bus system, and the first method clearly stands out in this comparison. The first method is then applied to the IEEE 300 bus system and to a model of the Polish power system with 2746 buses to study how it scales in large power systems. Even in the latter case, it runs in less than 30s. For the second step, existing equivalencing methods can be used. As an example, radial, equivalent, and independent equivalents are used to model the areas identified by the partitioning methods. The partitioning and equivalencing methods have been tested on the IEEE 118 bus system by running 1000 regular and optimal power flows. Comparisons with the original IEEE 118 bus system in terms of flows, costs and losses are carried out.

3456789 251 - 300 of 806
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf