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  • 451.
    Matevosyan, Julija
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wind Power in Areas with Limited Transmission Capacity2005In: Wind power in power systems / [ed] Ackermann, Thomas, Chichester, West Sussex, England: John Wiley & Sons, Ltd , 2005, p. 433-459Chapter in book (Other academic)
  • 452.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ackermann, Thomas
    Bolik, Sigrid M.
    Technical Regulations for the Interconnection of Wind Farms to the Power System2005In: Wind power in power systems / [ed] Ackermann, Thomas, John Wiley & Sons, Ltd , 2005, p. 115-142Chapter in book (Other academic)
  • 453.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Olsson, Magnus
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hydropower planning coordinated with wind power in areas with congestion problems for trading on the spot and the regulating market2009In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 79, no 1, p. 39-48Article in journal (Refereed)
    Abstract [en]

    In this paper a day-ahead planning algorithm for a multi-reservoir hydropower system coordinated with wind power is developed. Coordination applies to real situations, where wind power and hydropower are owned by different utilities, sharing the same transmission lines, though hydropower has priority for transmission capacity. Coordination is thus necessary to minimize wind energy curtailments during congestion situations. The planning algorithm accounts for the uncertainty of wind power forecasts and power market price uncertainty. Planning for the spot market and the regulating market is considered in the algorithm. The planning algorithm is applied to a case study and the results are summarized in the paper.

  • 454.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Minimization of imbalance cost trading wind power on the short term power market2005In: 2005 IEEE Russia Power Tech, PowerTech, 2005Conference paper (Other academic)
    Abstract [en]

    Present power markets are designed for trading conventional generation. For wind generation to participate in short-term energy market lengthy (up to 36 hours) wind power production forecasts are required. Although wind speed forecasting techniques are constantly improving, wind speed forecasts are never perfect and resulting wind power forecast errors imply imbalance costs for wind farm owners. This paper presents a method for minimization of imbalance costs. Stochastic programming is used to generate optimal wind power production bids for short term power market. Wind power forecast error is represented as stochastic parameter. The imbalance costs resulting from this strategy are then compared to the case when wind power production bids on short term power market are based only on wind speed forecast.

  • 455.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Minimization of Imbalance Cost Trading Wind Power on the Short-Term Power Market2006In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 21, no 3, p. 1396-1404Article in journal (Refereed)
    Abstract [en]

    Present power markets are designed for trading conventional generation. For wind generation to participate in a short-term energy market, lengthy wind power production forecasts are required. Although wind speed forecasting techniques are constantly improving, wind speed forecasts are never perfect, and resulting wind power forecast errors imply imbalance costs for wind farm owners. In this paper, a new method for minimization of imbalance costs is. developed. Stochastic programming is used to generate optimal wind power production bids for a short-term power market. A Wind power forecast error is represented as a stochastic process. The imbalance costs resulting from this strategy are then compared to the case when wind power production bids on a short-term power market are based directly on a wind speed forecast.

  • 456.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Optimal daily planning for hydro power system coordinated with wind power in areas with limited export capability2006In: 2006 International Conference on Probabilistic Methods Applied to Power Systems, NEW YORK: IEEE , 2006, p. 47-54Conference paper (Refereed)
    Abstract [en]

    The paper presents a daily planning algorithm for a multi-reservoir hydropower system coordinated with wind power. The planning algorithm applies to the real situation where wind power and hydropower are owned by different utilities, sharing same transmission lines, though, hydropower has a priority for transmission capacity. Coordination is, thus, necessary to minimize wind energy curtailments during the congestion situations. The planning algorithm considers an uncertainty of wind power forecast. Forecast error scenarios are modeled with ARMA series. A scenario reduction algorithm is applied to reduce computational time. Only the planning for the spot market is considered. Thus, once the hydropower production bid is placed on the market it cannot be changed. The solution of the stochastic optimization problem should, therefore, fulfill the transmission constraints for all wind power production scenarios. The developed planning algorithm is applied in a case study. The results are compared to the planning results without coordination.

  • 457.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Short Term Hydro Power Planning Coordinated with Wind Power in Areas with Congestion Problems2007In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 10, no 3, p. 195-208Article in journal (Refereed)
    Abstract [en]

    In this paper, a day-ahead planning algorithm for a multi-reservoir hydropower system coordinated with wind power is developed Coordination applies to real situations, where wind power and hydropower are owned by different utilities, sharing the same transmission lines, although hydropower has priority for transmission capacity. Coordination is thus necessary to minimize wind energy curtailments during congestion situations. The planning algorithm accounts for the uncertainty of wind power forecast. Only planning for the spot market is considered. Once the production bid is placed on the market, it cannot be changed. The solution of the stochastic optimization problem should, therefore, fulfill the transmission constraints for all wind power production scenarios. An evaluation algorithm is also developed to quantify the impact from the coordinated planning in the long run. The developed planning algorithm and the evaluation algorithm are applied in a case study. The results are compared with uncoordinated operation. The results of the case study show that coordination with wind power brings additional income to the hydropower utility and leads to significant reduction of wind energy curtailments.

  • 458.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Strategies for local coordination between wind and hydropower2009Report (Other academic)
  • 459.
    Mehmood, Shahid
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Transient Fault Protection of Multiterminal HVDC Grid with Overhead Lines2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 460.
    Milano, Federico
    et al.
    University College Dublin.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Role of non-commerical software in undergraduate electric energy systems programmes2015In: Edulearn15: 7th International Conference on Education and New Learning Technologies, IATED-INT ASSOC TECHNOLOGY EDUCATION A& DEVELOPMENT, , 2015, p. 318-328Conference paper (Refereed)
    Abstract [en]

    This paper describes the potential and challenges of open-source non-commercial software tools for undergraduate electric energy systems programmes, and their impact on student’s potential work opportunities. This paper also describes how different academic traditions have an impact on the choice of educational software, and how that has repercussions on the students' learning and the learning outcomes of programme modules. The matter presented in the paper is based on the authors' experience as both developers of open-source software tools, as PhD students and lecturers with several universities.

  • 461. Milligan, M.
    et al.
    Holttinen, H.
    Kiviluoma, J.
    Orths, A.
    Lynch, M. A.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Market designs for high levels of variable generation2014In: IEEE Power and Energy Society General Meeting, 2014, no OctoberConference paper (Refereed)
    Abstract [en]

    Variable renewable generation is increasing in penetration in modern power systems, leading to higher variability in the supply and price of electricity as well as lower average spot prices. This raises new challenges, particularly in ensuring sufficient capacity and flexibility from conventional technologies. As the fixed costs and lifetimes of electricity generation investments are significant, designing markets and regulations which ensure efficient integration of renewable generation is a significant challenge. This panel presentation reviews the state of play in the USA and Europe with regard to these issues and considers new developments in both regions.

  • 462. Milligan, M.
    et al.
    Holttinen, H.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Clark, C.
    Market structures to enable efficient wind and solar power integration2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, p. 6345591-Conference paper (Refereed)
    Abstract [en]

    The development of large amounts of wind and/or solar energy will have an impact on bulk electricity markets. These variable generation sources increase the level of variability and uncertainty that the power system operator must manage. In this paper we discuss the impact that electricity markets have on the wind producer, using examples from the Nordic system. We also describe two market structures that will help induce both the needed flexibility, whether from generation or load, and sufficient capacity. We also provide some general guidelines for market design and simple tests that can help identify how a proposed market would function. We close with suggestions for future research.

  • 463. Milligan, Michael
    et al.
    Porter, Kevin
    DeMeo, Edgar
    Denholm, Paul
    Holttinen, Hannele
    Kirby, Brendan
    Miller, Nicholas
    Mills, Andrew
    O'Malley, Mark
    Schuerger, Matthew
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wind Power Myths Debunked2009Article in journal (Refereed)
  • 464.
    Moiseeva, Ekaterina
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Impact of High levels of Wind Penetration on the Exercise of Market Power in the Multi-Area Systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    New European energy policies have set a goal of a high share of renewable energy in electricity markets. In the presence of high levels of renewable generation, and especially wind, there is more uncertainty in the supply. It is natural, that volatility in energy production induces the volatility in energy prices. This can create incentives for the generators to exercise market power by traditional means: withholding the output by conventional generators, bidding not the true marginal costs, or using locational market power. In addition, a new type of market power has been recently observed: exercise of market power on ramp rate. This dissertation focuses on modeling the exercise of market power in power systems with high penetration of wind power. The models consider a single, or multiple profit-maximizing generators. Flexibility is identified as one of the major issues in wind-integrated power systems. Therefore, part of the research studies the behavior of strategic hydropower producers as main providers of flexibility in systems, where hydropower is available.Developed models are formulated as mathematical and equilibrium problems with equilibrium constraints (MPECs and EPECs). The models are recast as mixed-integer linear programs (MILPs) using discretization. Resulting MILPs can be solved directly by commercially-available MILP solvers, or by applying decomposition. Proposed Modified Benders Decomposition Algorithm (MBDA) significantly improves the computational efficiency.

  • 465.
    Moiseeva, Ekaterina
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Impact of energy storage devices on energy price in decentralized wind-diesel utilities2013In: 2013 10th International Conference on the European Energy Market (EEM), IEEE conference proceedings, 2013, p. 6607282-Conference paper (Refereed)
    Abstract [en]

    The most widely spread method of supplying the customers in isolated areas is to use single or multiple diesel generators with constant or variable speed. The price of energy in such areas is highly influenced by the cost of fuel transportation to the place of consumption. We propose an approach to reduce this price by complementing the diesel generators with wind turbines and high-capacity energy storage devices. We create a model to define the proportion between the installed capacities and to provide the proper sizing of elements. The paper studies the case of an isolated area in central Russia, where the fuel transportation share of energy price reaches 65%. We propose a new energy supply system, which includes diesel generators, wind turbines and energy storage devices. We study the system statistically and model it in Homer software. To decrease the capital and operating costs, we introduce the specific algorithm: the diesel generator operates only when wind turbines are not covering the load and energy storage device is exhausted. We test the proposed algorithm using MATLAB to obtain both economic and technical operation results. The economic modeling then continues the system evaluation. We evaluate the investment criteria and define the new minimum price for electricity. The paper is concluded by a systematic analysis of the results and remarks towards the efficiency of investment into the new equipment.

  • 466.
    Moiseeva, Ekaterina
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling the Hedging Decisions in Electricity Markets Using Two-stage Games2013In: 2013 4th IEEE/PES Innovative Smart Grid Technologies Europe, ISGT Europe 2013, IEEE conference proceedings, 2013, p. 6695462-Conference paper (Refereed)
    Abstract [en]

    The electricity market structure aims to provide effective competition among producers. However, the exercise of market power considerably affects energy prices and induces the wealth transfer from consumers to generators. It is widely recognized that the incentive of generator to exercise market power depends on its hedging decision. The hedged generator has very little or no tendency to exercise market power. However, existing approaches for forecasting market power typically take the hedge cover level as an external input to the model, providing an open-loop analysis. In practice, the level of hedge is chosen by a generating firm and treated confidentially. Omitting this assumption results in equilibrium constraints in the forward and spot stages of the trade period. This type of problem can be modelled as a two-stage game, where in the first stage the generator decides on the profit-maximizing level of hedging and in the second stage it takes part in Cournot game on output in spot market. We show that in the oligopoly case with no constraints on installed capacity and transmission limits there is no equilibrium in pure strategies, which corresponds to the "all-or-nothing" decision. In the case when transmission and capacity constraints are binding, we use a backward induction approach and closed-loop analysis to find a sub-game perfect Nash equilibrium (SPNE) on the level of hedging and a corresponding SPNE in spot market. We show that the solution in this constrained network is similar to the unconstrained one.

  • 467.
    Moiseeva, Ekaterina
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Biggar, Darryl
    Exercise of Market Power on Ramp Rate in Wind-Integrated Power Systems2015In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 30, no 3, p. 1614-1623Article in journal (Refereed)
    Abstract [en]

    With an increasing penetration of wind power, there is likely to be an increasing need for fast-ramping generating units. These generators ensure that no load is lost if supply drops due to the uncertainties in wind power generation. However, it is observed in practice that, in a presence of network constraints, fast-ramping generating units are prone to act strategically and exercise market power by withholding their ramp rates. In this paper we model this gaming behavior on ramp rates. We assume a market operator who collects bids in form of marginal costs, quantities, and ramp rates. He runs a ramp-constrained economic dispatch given the generators' bids, forecasted demand, and contingencies. Following the game-theoretic concepts, we set up a multi-level optimization problem. The lower-level problem is the ramp-constrained economic dispatch and the higher-level represents the profit maximization problems solved by strategic generators. The whole problem is formulated as an equilibrium problem with equilibrium constraints (EPEC). The outcome of the EPEC problem is a set of Nash equilibria. To tackle the multiple Nash equilibria problem, the concept of the extremal-Nash equilibria is defined and formulated. We model the concept of extremal-Nash equilibria as a single-stage mixed-integer linear programming problem (MILP) and demonstrate the application of this mathematical framework on an illustrative case and on a more realistic case study with tractable results.

  • 468.
    Moiseeva, Ekaterina
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dimoulkas, Ilias
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Tacit Collusion with Imperfect Information: Ex-Ante Detection2014Conference paper (Refereed)
    Abstract [en]

    The liberalization of electricity markets had a significant impact on the whole process of optimal dispatch. The positive effect of competition is partly canceled out by profit-maximizing behavior of market participants. Strategic generators can exercise market power or collude tacitly with other participants to ensure higher electricity price and therefore higher profits. In this paper we study the generators' possibility to come to a tacit collusion by distributed computations. Due to the strategic nature of market interactions, the information corresponding to the power production by generating companies is often fully confidential outside the generating unit. Such information includes the data about planned and emergency outages, capacity constraints, ramping rates specific to the units, probability of failures, etc. Under certain assumptions the constraint set of a generating unit can be represented as a convex set. Using a novel multi-agent distributed constrained optimization algorithm we show how market participants with confidential constraint sets can reach the collusion on the production share, while maximizing their own profit. We compare this outcome to the outcome of Nash equilibrium over specified time horizon and conclude, if both generators find it profitable to collude. This modeling is important for early detection and prevention of tacit collusion.

  • 469. Momber, I.
    et al.
    Gomez, T.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    PEV fleet scheduling with electricity market and grid signals Charging schedules with capacity pricing based on DSO's long run marginal cost2013In: European Energy Market (EEM), 2013 10th International Conference on the, IEEE , 2013, p. 6607364-Conference paper (Refereed)
    Abstract [en]

    Electricity market signals are deemed efficient to allocate resources at the transmission system level, yet they may not always sufficiently represent the local network status of the distribution system. Furthermore, high penetration levels of Plug-in Electric Vehicles (PEV) potentially cause network reinforcement, which would have an impact on investment, operation and maintenance costs. While long run marginal cost pricing for computing node dependent network Use-of-System (UoS) tariffs has been proposed for integrating distributed generation, it remains unexplored in the context of PEV charging. Hence, this paper formulates the PEV energy retail problem with interactions in day-ahead and balancing markets from the aggregator's perspective, taking into account location dependent network UoS tariffs in the form of capacity prices for active power. While the retail tariff for the final customer is supposed fixed in the medium term, these capacity prices are accounted as costs to the aggregator. By aligning the PEV charging schedule, in time and location, to the network signals, the aggregator can hence further minimize its perceived costs. Applied to a medium voltage system with urban characteristics and spatial PEV mobility, profit optimal charging schedules for the aggregator are found. The result analysis and concluding remarks focus on the relevance of including node dependent network UoS tariffs.

  • 470.
    Momber, Ilan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Benefits of Coordinating Plug-In Electric Vehicles in Electric Power Systems: Through Market Prices and Use-of-System Network Charges2015Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Both electric power systems and the transportation sector are essential constituents to modern life, enhancing social welfare, enabling economic prosperity and ultimately providing well-being to the people. However, to mitigate adverse climatological effects of emitting greenhouse gases, a rigorous de-carbonization of both industries has been set on the political agenda in many parts of the world. To this end, electrifying personal vehicles is believed to contribute to an affordable and reliable energy model that provides tolerable environmental impact. Representing an inherently flexible electricity demand, plug-in electric vehicles (PEVs) promise to facilitate the integration of variable renewable energy sources. Yet, how should the PEVs' system usage be ideally coordinated for providing benefits to electric power systems in the presence of resource scarcity?

    The thesis develops a model of an aggregation agent as the interface to the wholesale electricity generators, which is envisaged to be in charge of procuring energy in electricity markets, exposed to uncertainty in prices, fleet availability and demand requirements. This aggregator could coordinate the PEV charging either with direct load control (DLC), i.e., sending power set points to the individual vehicles, or with indirect load control (ILC), i.e., by sending retail price signals.

    Contributing to the technical literature this thesis has on the one hand proposed a two-stage stochastic linear program for the PEV aggregator's day-ahead and balancing decisions with DLC over a large fleet of PEVs, while accounting for conditional value at risk in the objective function. On the other hand, it has put forward a formulation of ILC coordination as a bi-level optimization problem given by mathematical programming with equilibrium constraints, in which 1) the upper level decisions on retail tariffs and optimal bidding in electricity markets are subject to 2) the lower level client-side optimization of PEV charging schedules. These decisions may respect a potential discomfort that could arise when PEV users have to deviate from their preferred charging schedule. Set in an existing, real medium voltage distribution network with urban characteristics and spatial PEV mobility, network UoS tariffs for capacity have been applied to both DLC and ILC scheduling by a PEV aggregator.

  • 471.
    Momber, Ilan
    et al.
    KTH, School of Electrical Engineering (EES).
    Morales-España, Germán
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ramos, Andres
    Gomez, Tomas
    PEV Storage in Multi-Bus Scheduling Problems2014In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 5, no 2, p. 1079-1087Article in journal (Refereed)
    Abstract [en]

    Modeling electricity storage to address challenges and opportunities of its applications for smart grids requires inter-temporal equalities to keep track of energy content over time. Prevalently, these constraints present crucial modeling elements as to what extent energy storage applications can enhance future electric power systems' sustainability, reliability, and efficiency. This paper presents a novel and improved mixed-integer linear problem (MILP) formulation for energy storage of plug-in (hybrid) electric vehicles (PEVs) for reserves in power system models. It is based on insights from the field of System Dynamics, in which complex interactions between different elements are studied by means of feedback loops as well as stocks, flows and co-flows. Generalized to a multi-bus system, this formulation includes improvements in the energy balance and surpasses shortcomings in the way existing literature deals with reserve constraints. Tested on the IEEE 14-bus system with realistic PEV mobility patterns, the deterministic results show changes in the scheduling of the units, often referred to as unit commitment (UC).

  • 472.
    Momber, Ilan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Siddiqui, A.
    Roman, T. G. S.
    Söder, Lennart H.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Risk averse scheduling by a PEV aggregator under uncertainty2015In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 30, no 2, p. 882-891, article id 6847245Article in journal (Refereed)
    Abstract [en]

    Research on electric power systems has considered the impact of foreseeable plug-in electric vehicle (PEV) penetration on its regulation, planning, and operation. Indeed, detailed treatment of PEV charging is necessary for efficient allocation of resources. It is envisaged that a coordinator of charging schedules, i.e., a PEV aggregator, could exercise some form of load control according to electricity market prices and network charges. In this context, it is important to consider the effects of uncertainty of key input parameters to optimization algorithms for PEV charging schedules. However, the modeling of the PEV aggregator's exposure to profit volatility has received less attention in detail. Hence, this paper develops a methodology to maximize PEV aggregator profits taking decisions in day-ahead and balancing markets while considering risk aversion. Under uncertain market prices and fleet mobility, the proposed two-stage linear stochastic program finds optimal PEV charging schedules at the vehicle level. A case study highlights the effects of including the conditional value-at-risk (CVaR) term in the objective function and calculates two metrics referred to as the expected value of aggregation and flexibility.

  • 473. Montano, R
    et al.
    Ackermann, T
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Impact of the Utgrunden Offshore Windfarm on Network losses2001In: European Wind Energy Conference, Copenhagen, Denmark, 2001Conference paper (Refereed)
  • 474.
    Morales-España, Germán
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
    Unit Commitment: Computational Performance, System Representation and Wind Uncertainty Management2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years, high penetration of variable generating sources, such as wind power, has challenged independent system operators (ISO) in keeping a cheap and reliable power system operation. Any deviation between expected and real wind production must be absorbed by the power system resources (reserves), which must be available and ready to be deployed in real time. To guarantee this resource availability, the system resources must be committed in advance, usually the day-ahead, by solving the so-called unit commitment (UC) problem. If the quantity of committed resources is extremely low, there will be devastating and costly consequences in the system, such as significant load shedding. On the other hand, if this quantity is extremely high, the system operation will be excessively expensive, mainly because facilities will not be fully exploited.

    This thesis proposes computationally efficient models for optimal day-ahead planning in (thermal) power systems to adequately face the stochastic nature of wind production in the real-time system operation. The models can support ISOs to face the new challenges in short-term planning as uncertainty increases dramatically due to the integration of variable generating resources. This thesis then tackles the UC problem in the following aspects: 

    • Power system representation: This thesis identifies drawbacks of the traditional energy-block scheduling approach, which make it unable to adequately prepare the power system to face deterministic and perfectly known events. To overcome those drawbacks, we propose the ramp-based scheduling approach that more accurately describes the system operation, thus better exploiting the system flexibility.
    • UC computational performance: Developing more accurate models would be pointless if these models considerably increase the computational burden of the UC problem, which is already a complex integer and non-convex problem. We then devise simultaneously tight and compact formulations under the mixed-integer programming (MIP) approach. This simultaneous characteristic reinforces the convergence speed by reducing the search space (tightness) and simultaneously increasing the searching speed (compactness) with which solvers explore that reduced space.
    • Uncertainty management in UC: By putting together the improvements in the previous two aspects, this thesis contributes to a better management of wind uncertainty in UC, even though these two aspects are in conflict and improving one often means harming the other. If compared with a traditional energy-block UC model under the stochastic (deterministic) paradigm, a stochastic (deterministic) ramp-based UC model: 1) leads to more economic operation, due to a better and more detailed system representation, while 2) being solved significantly faster, because the core of the model is built upon simultaneously tight and compact MIP formulations.
    • To further improve the uncertainty management in the proposed ramp-based UC, we extend the formulation to a network-constrained UC with robust reserve modelling. Based on robust optimization insights, the UC solution guarantees feasibility for any realization of the uncertain wind production, within the considered uncertainty ranges. This final model remains as a pure linear MIP problem whose size does not depend on the uncertainty representation, thus avoiding the inherent computational complications of the stochastic and robust UCs commonly found in the literature.
  • 475.
    Morales-España, Germán
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
    Baldick, Ross
    University of Texas.
    García-González, Javier
    Universidad Pontificia Comillas.
    Ramos, Andres
    Universidad Pontificia Comillas.
    Robustified Reserve Modelling for Wind PowerIntegration in Ramp-Based Unit CommitmentManuscript (preprint) (Other academic)
    Abstract [en]

    This paper proposes a “robustified” network-constrained Unit Commitment (UC) formulation as an altern-ative to the robust and stochastic UC formulations under windgeneration uncertainty. The formulation draws a clear distinctionbetween power-capacity and ramp-capability reserves to deal withwind production uncertainty. These power and ramp require-ments can be obtained from wind forecast information. The modelis formulated under the ramp-based scheduling approach, whichschedules power-trajectories instead of the traditional energy-blocks and takes into account the inherent startup and shutdownpower trajectories of thermal units. These characteristics allowa correct representation of unit’s ramp schedule which definetheir ramp availability for reserves. The proposed formulationsignificantly decreases operation costs if compared to traditionaldeterministic and stochastic UC formulations while simultan-eously lowering the computational burden. The operation costcomparison is made through 5-min economic dispatch simulationunder hundreds of out-of-sample wind generation scenarios.

  • 476.
    Morales-España, Germán
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
    Gentile, Claudio
    Ramos, Andres
    Universidad Pontificia Comillas.
    Tight MIP Formulations of the Power-Based Unit Commitment ProblemManuscript (preprint) (Other academic)
    Abstract [en]

    This paper provides the convex hull description for the basic operation of slow- and quick-startunits in power-based unit commitment (UC) problems. The basic operating constraints that are modeled forboth types of units are: 1) generation limits and 2) minimum up and down times. Apart from this, the startupand shutdown processes are also modeled, using 3) startup and shutdown power trajectories for slow-startunits, and 4) startup and shutdown capabilities for quick-start units. In the conventional UC problem, powerschedules are used to represent the staircase energy schedule; however, this simplification leads to infeasibleenergy delivery, as stated in the literature. To overcome this drawback, this paper provides a power-basedUC formulation drawing a clear distinction between power and energy. The proposed constraints can be usedas the core of any power-based UC formulation, thus tightening the final mixed-integer programming UCproblem. We provide evidence that dramatic improvements in computational time are obtained by solvingdifferent case studies, for self-UC and network-constrained UC problems.

  • 477.
    Morales-España, Germán
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
    Latorre, Jesus Maria
    Universidad Pontificia Comillas.
    Ramos, Andres
    Universidad Pontificia Comillas.
    Tight and Compact MILP Formulation for the Thermal Unit Commitment Problem2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 4, p. 4897-4908Article in journal (Refereed)
    Abstract [en]

    This paper presents a mixed-integer linear programming (MILP) reformulation of the thermal unit commitment (UC) problem. The proposed formulation is simultaneously tight and compact. The tighter characteristic reduces the search space and the more compact characteristic increases the searching speed with which solvers explore that reduced space. Therefore, as a natural consequence, the proposed formulation significantly reduces the computational burden in comparison with analogous MILP-based UC formulations. We provide computational results comparing the proposed formulation with two others which have been recognized as computationally efficient in the literature. The experiments were carried out on 40 different power system mixes and sizes, running from 28 to 1870 generating units.

  • 478.
    Morales-España, Germán
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
    Latorre, Jesus Maria
    Universidad Pontificia Comillas.
    Ramos, Andres
    Universidad Pontificia Comillas.
    Tight and Compact MILP Formulation of Start-Up and Shut-Down Ramping in Unit Commitment2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 2, p. 1288-1296Article in journal (Refereed)
    Abstract [en]

    This paper presents a mixed-integer linear programming (MILP) formulation of start-up (SU) and shut-down (SD) power trajectories of thermal units. Multiple SU power-trajectories and costs are modeled according to how long the unit has been offline. The proposed formulation significantly reduces the computational burden in comparison with others commonly found in the literature. This is because the formulation is 1) tighter, i.e., the relaxed solution is nearer to the optimal integer solution; and 2) more compact, i.e., it needs fewer constraints, variables and nonzero elements in the constraint matrix. For illustration, the self-unit commitment problem faced by a thermal unit is employed. We provide computational results comparing the proposed formulation with others found in the literature.

  • 479.
    Morales-España, Germán
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Mora-Florez, Juan
    Univ Tecnol Pereira, Pereira, Colombia..
    Vargas-Torres, Hermann
    Univ Ind Santander, Santander, Spain..
    Elimination of Multiple Estimation for Fault Location in Radial Power Systems by Using Fundamental Single-End Measurements2013In: 2013 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PES), IEEE , 2013Conference paper (Refereed)
  • 480.
    Morales-España, Germán
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
    Ramos, Andres
    Universidad Pontificia Comillas.
    Garcia-Gonzalez, Javier
    Universidad Pontificia Comillas.
    An MIP Formulation for Joint Market-Clearing of Energy and Reserves Based on Ramp Scheduling2014In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 29, no 1, p. 476-488Article in journal (Refereed)
    Abstract [en]

    The day-ahead unit-commitment (UC)-based market-clearing (MC) is widely acknowledged to be the most economically efficient mechanism for scheduling resources in power systems. In conventional UC problems, power schedules are used to represent the staircase energy schedule. However, the realizability of this schedule cannot be guaranteed due to the violation of ramping limits, and hence conventional UC formulations do not manage the flexibility of generating units efficiently. This paper provides a UC-based MC formulation, drawing a clear distinction between power and energy. Demand and generation are modeled as hourly piecewise-linear functions representing their instantaneous power trajectories. The schedule of generating unit output is no longer a staircase function, but a smoother function that respects all ramp constraints. The formulation represents in detail the operating reserves (online and offline), their time deployment limits (e.g., 15 min), their potential substitution, and their limits according to the actual ramp schedule. Startup and shutdown power trajectories are also modeled, and thus a more efficient energy and reserves schedule is obtained. The model is formulated as a mixed-integer programming (MIP) problem, and was tested with a 10-unit and 100-unit system in which its computational performance was compared with a traditional UC formulation.

  • 481. Morthorst, P. E.
    et al.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Economic Aspects of Wind Power in Power Systems2012In: Wind Power in Power Systems, Second Edition, John Wiley & Sons, 2012, 2, p. 489-516Chapter in book (Refereed)
    Abstract [en]

    The integration of large amounts of wind power into the energy system requires a strong interplay with power markets. In this respect the power exchange is an important instrument, defining a single market clearing price for each trading period. Following the liberalisation of the EU electricity industry power markets are increasingly being organised as power exchanges to a certain extent following the same lines, where a number of if not identical then closely related services are being provided. Using the NordPool power market as an example this chapter outlines the basic characteristics of the two key markets, the day-ahead market and the regulating market. The determination of the day-ahead price is described and the impact of wind power on power prices investigated. Finally, the cost of regulation is addressed.

  • 482.
    Mossberg, Mats
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeller för studier av ursprungsmärkt el2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The EU has decided that it should be possible for consumers to get information about the origin of the electricity they buy. Therefore, there is a need to examine different systems for electricity disclosure. In this thesis two ways of disclosure have been studied:

    � Certificate system. A certificate system involves two parallel markets, one for trading electrical energy and one for trading certificates of origin.

    � Separated Markets. In this system there are different electricity commodities where each electricity commodity is equivalent to a mix of different power sources. Examples of these commodities are pure bio electricity, pure hydro electricity, pure wind electricity and gray electricity. Gray electricity is an unspecified mix of different power sources where origin does not matter.

    The aim of this thesis was to create models which can be used to study the consequences of implementing the above described disclosure systems.

    Two test systems were constructed in order to develop suitable models; a single- and a multiarea model. The focus of the single-area model simulations was how to model consumers willingness to pay for electricity of a certain origin as well as the pricing. In the multi-area model impacts of transmission were included. The constructed multi-area model was a simplified model of the Nordic power market, with possibility to randomize demand and supply.

    Simulations showed that the social surplus increase after introducing systems for electricity disclosure. The choice of disclosure system is dependent on market characteristics. Nondispatchable power plants (for example wind power) are most favored by certificate systems.

  • 483.
    Mountouri, Dona
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Identification of saddle-node bifurcation point for a forecasted path of future loading2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 484. Munkhammar, J.
    et al.
    Widén, J.
    Grahn, Pia
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rydén, J.
    A Bernoulli distribution model for plug-in electric vehicle charging based on time-use data for driving patterns2014In: 2014 IEEE International Electric Vehicle Conference, IEVC 2014, IEEE conference proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    This paper presents a Bernoulli distribution model for plug-in electric vehicle (PEV) charging based on high resolution activity data for Swedish driving patterns. Based on the activity 'driving vehicle' from a time diary study a Monte Carlo simulation is made of PEV state of charge which is then condensed down to Bernoulli distributions representing charging for each hour during weekday and weekend day. These distributions are then used as a basis for simulations of PEV charging patterns. Results regarding charging patterns for a number of different PEV parameters are shown along with a comparison with results from a different stochastic model for PEV charging. A convergence test for Monte Carlo simulations of the distributions is also provided. In addition to this we show that multiple PEV charging patterns are represented by Binomial distributions via convolution of Bernoulli distributions. Also the distribution for aggregate charging of many PEVs is shown to be normally distributed. Finally a few remarks regarding the applicability of the model are given along with a discussion on potential extensions.

  • 485.
    Munkhammar, Joakim
    et al.
    Uppsala Universitet.
    Grahn, Pia
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Widén, Joakim
    Uppsala Universitet.
    Quantifying self-consumption of on-site photovoltaic power generation in households with electric vehicle home charging2013In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 97, p. 208-216Article in journal (Refereed)
    Abstract [en]

    Photovoltaic (PV) power production and residential power demand are negatively correlated at high latitudes on both annual and diurnal basis. If PV penetration levels increase, methods to deal with power overproduction in the local distribution grids are needed to avoid costly grid reinforcements. Increased local consumption is one such option. The introduction of a home-charged plug-in electric vehicle (PEV) has a significant impact on the household load and potentially changes the coincidence between household load and photovoltaic power production. This paper uses a stochastic model to investigate the effect on the coincidence between household load and photovoltaic power production when including a PEV load. The investigation is based on two system levels: (I) individual household level and (II) aggregate household level. The stochastic model produces theoretical high-resolution load profiles for household load and home charged PEV load over time. The photovoltaic power production model is based on high-resolution irradiance data for Uppsala, Sweden. It is shown that the introduction of a PEV improves the self-consumption of the photovoltaic power both on an individual and an aggregate level, but the increase is limited due to the low coincidence between the photovoltaic power production pattern and the charging patterns of the PEV.

  • 486.
    Murad, Mohammad Ahsan Adib
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Phasor Time-Domain Power System Modeling and Simulation using the Standardized Modelica Language: Conventional and Power Electronic-Based Devices2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Modern electric power systems are complex networks that ensure continuous supply of

    electricity. For the planning and operation of these complex networks, modeling and simulations

    are essential to satisfy operational requirements or planning constraints. Traditionally,

    dynamic modeling and simulation of power systems is performed by using

    di erent and mostly incompatible software packages. This issue is currently being addressed

    through the Common Information Model (CIM) for power system applications,

    however, there are still many challenges for Power system dynamic modeling and simulation

    without any ambiguity.

    To overcome these challenges, this thesis develops unambiguous models for consistent

    model exchange, which are compatible in di erent simulation environments that support

    the Modelica language. Modelica, an object-oriented equation-based standardized

    language, is proposed as possible solution to these challenges as it can represent and

    exchange dynamic models with a strict mathematical description.

    In this thesis, modeling and simulation of controllable power electronic-based components

    and conventional components for phasor time-domain simulation is carried out

    using Modelica. The work in this thesis contributes to a Modelica power systems library

    being developed by KTH SmartTS Lab under the FP7 iTesla project and other projects

    supported by Statnett SF. Both software implementation in Modelica of each component,

    and software-to-software validation against PSAT is carried out.

  • 487.
    Nasri, Amin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Appropriate placement of series compensators to improve small signal stability of power system2012In: IEEE International Energy Conference and Exhibition (ENERGYCON), 2012, IEEE conference proceedings, 2012, p. 421-426Conference paper (Refereed)
    Abstract [en]

    Series FACTS devices like thyristor controlled series capacitors (TCSC) equipped with appropriate supplementary damping controller can improve the small signal stability of power system if they are located properly. In this paper, trajectory sensitivity analysis (TSA) is used to determine the best locations for installing TCSC to damp out the inter-area mode of oscillation. Based on the modal analysis, an equivalent angle is defined by determining critical and non-critical machines, and then using trajectory sensitivities of this angle with respect to the impedances of the transmission lines; appropriate locations for placing TCSC are found. To verify the accuracy of the proposed method, the residue technique for optimal placement of FACTS devices is also implemented in this paper. Both methods are applied to the IEEE 3-machines 9-buses test system, and the obtained results show the validity and efficiency of the proposed method.

  • 488.
    Nasri, Amin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On the Dynamics and Statics of Power System Operation: Optimal Utilization of FACTS Devicesand Management of Wind Power Uncertainty2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nowadays, power systems are dealing with some new challenges raisedby the major changes that have been taken place since 80’s, e.g., deregu-lation in electricity markets, significant increase of electricity demands andmore recently large-scale integration of renewable energy resources such aswind power. Therefore, system operators must make some adjustments toaccommodate these changes into the future of power systems.One of the main challenges is maintaining the system stability since theextra stress caused by the above changes reduces the stability margin, andmay lead to rise of many undesirable phenomena. The other important chal-lenge is to cope with uncertainty and variability of renewable energy sourceswhich make power systems to become more stochastic in nature, and lesscontrollable.Flexible AC Transmission Systems (FACTS) have emerged as a solutionto help power systems with these new challenges. This thesis aims to ap-propriately utilize such devices in order to increase the transmission capacityand flexibility, improve the dynamic behavior of power systems and integratemore renewable energy into the system. To this end, the most appropriatelocations and settings of these controllable devices need to be determined.This thesis mainly looks at (i) rotor angle stability, i.e., small signal andtransient stability (ii) system operation under wind uncertainty. In the firstpart of this thesis, trajectory sensitivity analysis is used to determine themost suitable placement of FACTS devices for improving rotor angle sta-bility, while in the second part, optimal settings of such devices are foundto maximize the level of wind power integration. As a general conclusion,it was demonstrated that FACTS devices, installed in proper locations andtuned appropriately, are effective means to enhance the system stability andto handle wind uncertainty.The last objective of this thesis work is to propose an efficient solutionapproach based on Benders’ decomposition to solve a network-constrained acunit commitment problem in a wind-integrated power system. The numericalresults show validity, accuracy and efficiency of the proposed approach.

  • 489.
    Nasri, Amin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Chamorro Vera, Harold Rene
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Multi-parameter trajectory sensitivity approach to analyze the impacts of wind powerpenetration on power system transient stability2014In: CIGRE, AORC Technical meeting 2014, 2014, p. 7-Conference paper (Refereed)
    Abstract [en]

    In the most real-world power systems, the share of wind power penetration in total installed generationcapacity is rapidly increasing. This large-scale integration of wind power into an electric power systemposes challenges to the power system operators and planners. One of the main challenges is tomaintain sufficient margins for transient stability. High penetration of wind power causes reduction ofthe total kinetic energy stored in through rotating masses since wind generators are decoupled from thegrid by power electronic converters, and therefore, cannot contribute to the inertia of the grid. Theresulting reduction of grid inertia may cause higher risk of transient instability. In this paper, trajectorysensitivity analysis (TSA) technique is used to determine the impacts of decreasing inertia of differentgenerating units on the transient stability of power system. Numerical results from IEEE 10-machine39-bus test system demonstrate the usefulness of the proposed approach.

  • 490.
    Nasri, Amin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Conejo, Antonio J.
    University of Castilla-la Mancha.
    Kazempour, Seyed Jalal
    University of Castilla-la Mancha.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Minimizing Wind Power Spillage Using an OPF With FACTS Devices2014In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 29, no 5, p. 2150-2159Article in journal (Refereed)
    Abstract [en]

    This paper proposes an optimal power flow (OPF) model with flexible AC transmission system (FACTS) devices to minimize wind power spillage. The uncertain wind power production is modeled through a set of scenarios. Once the balancing market is cleared, and the final values of active power productions and consumptions are assigned, the proposed model is used by the system operator to determine optimal reactive power outputs of generating units, voltage magnitude and angles of buses, deployed reserves, and optimal setting of FACTS devices. This system operator tool is formulated as a two-stage stochastic programming model, whose first-stage describes decisions prior to uncertainty realization, and whose second-stage represents the operating conditions involving wind scenarios. Numerical results from a case study based on the IEEE RTS demonstrate the usefulness of the proposed tool.

  • 491.
    Nasri, Amin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Suitable placements of multiple FACTS devices to improve the transient stability using trajectory sensitivity analysis2013In: North American Power Symposium (NAPS), 2013, IEEE conference proceedings, 2013, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Trajectory sensitivity analysis (TSA) is used as a tool for suitable placement of multiple series compensators in the power system. The goal is to maximize the benefit of these devices in order to enhance the transient stability of the system. For this purpose, the trajectory sensitivities of the rotor angles of the most critical generators with respect to the reactances of transmission lines are calculated in the presence of the most severe faults. Based on the obtained trajectory sensitivities, a method is proposed to determine how effective the series compensation of each transmission line is for improving the transient stability. This method is applied to the Nordic-32 test system to find the priorities of the transmission lines for installation of several series compensators. Simulation with industrial software shows the validity and efficiency of the proposed method.

  • 492.
    Nasri, Amin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Using trajectory sensitivity analysis to find suitable locations of series compensators for improving rotor angle stability2014In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 111, p. 1-8Article in journal (Refereed)
    Abstract [en]

    This paper proposes an approach based on trajectory sensitivity analysis (TSA) to find most suitable placement of series compensators in the power system. The main objective is to maximize the benefit of these devices in order to enhance the rotor angle stability. This approach is formulated as a two-stage problem, whose first-stage describes prior to fault occurrence and whose second-stage represents the power system behavior involving a set of severe faults. The first-stage focuses on small signal stability, while the second-stage deals with transient stability of power system. In this vein, the trajectory sensitivities of the rotor angles of generators with respect to the reactances of transmission lines are calculated. Two equivalent rotor angles are introduced to find stability indices corresponding to the first- and the second-stage of the proposed approach. Numerical results from IEEE 10-machine 39-bus test system demonstrate the usefulness of the proposed method.

  • 493.
    Nasri, Amin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    Appropriate placement of series compensators to improve transient stability of power system2012In: Innovative Smart Grid Technologies-Asia (ISGT Asia), 2012 IEEE, IEEE conference proceedings, 2012, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Trajectory sensitivity analysis is used to find the best places for installation of thyristor controlled series capacitors (TCSC) to improve transient stability of the power system. Based on the rotor angles of generators, an equivalent angle (δeq) is defined by determining accelerating and decelerating machines, and then using trajectory sensitivities of this angle with respect to the impedances of the transmission lines in the post-fault system, appropriate locations for placing TCSC will be found. Severity of the faults is also considered in this calculation. This method is applied to the IEEE 3-machine 9-bus test system to find the priorities of the transmission lines for installation of TCSC. Simulation with industrial software verifies the obtained results.

  • 494.
    Nasri, Amin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Transient stability assessment of power systems in the presence of shunt compensators using trajectory sensitivity analysis2013In: 2013 IEEE Power and Energy Society General Meeting (PES), IEEE , 2013, p. 6672163-Conference paper (Refereed)
    Abstract [en]

    Trajectory sensitivity analysis (TSA) is used as analysis tool for suitable placement of shunt compensators in the power system. The goal is to maximize the benefit of these devices in order to enhance the transient stability of the system. For this purpose, the trajectory sensitivities of the rotor angles of generators with respect to the reactive power injected into different nodes of the system are calculated in the presence of most probable severe faults. Based on the obtained trajectory sensitivities, a method is proposed to determine how effective the shunt compensation in each node is for improving the transient stability. This method is applied to the IEEE 3-machine 9-bus to find the priorities of system's nodes for installation of shunt compensators. Simulation with industrial software shows the validity and efficiency of the proposed method.

  • 495.
    Nasri, Amin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Seyed Jalal, Kazempour
    Mechanical Engineering, Johns Hopkins University.
    Conejo, Antonio J.
    The Ohio State University.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Network-constrained AC Unit Commitment under Uncertainty: A Benders’ Decomposition ApproachManuscript (preprint) (Other academic)
    Abstract [en]

    This paper proposes an efficient solution approachbased on Benders’ decomposition to solve a network-constrainedac unit commitment problem under uncertainty. The wind powerproduction is the only source of uncertainty considered in thispaper, which is modeled through a suitable set of scenarios.The proposed model is formulated as a two-stage stochasticprogramming problem, whose first-stage refers to the day-aheadmarket, and whose second-stage represents real-time operation.The proposed Benders’ approach allows decomposing the originalproblem, which is mixed-integer non-linear and generallyintractable, into a mixed-integer linear master problem and aset of non-linear, but continuous subproblems, one per scenario.In addition, to temporally decompose the proposed ac unitcommitment problem, a heuristic technique is used to relaxthe inter-temporal ramping constraints of the generating units.Numerical results from a case study based on the IEEE one-areareliability test system (RTS) demonstrate the usefulness of theproposed approach.

  • 496.
    Nazari, Mohammad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Control of DC voltage in Multi-Terminal HVDC Transmission (MTDC) Systems2014Licentiate thesis, monograph (Other academic)
    Abstract [en]

    With recent advances in power electronic technology, High-Voltage Direct Current (HVDC) transmission system has become an alternative for transmitting power especially over long distances. Multi-Terminal HVDC (MTDC) systems are proposed as HVDC systems with more than two terminals. These systems can be geographically wide. While in AC grids, frequency is a global variable, in MTDC systems, DC voltage can be considered as its dual. However, unlike frequency, DC voltage can not be equal across the MTDC system. Control of DC voltage in MTDC systems is one of the important challenges in MTDC systems. Since the dynamic of MTDC system is very fast, DC voltage control methods cannot rely only on remote information. Therefore, they can work based on either local information or a combination of local and remote information. In this thesis, first, the MTDC system is modeled. One of the models presented in this thesis considers only the DC grid, and effects of the AC grids are modeled with DC current sources, while in the other one, the connections of the DC grid to the AC grids are also considered. Next, the proposed methods in the literature for controlling the DC voltage are described and in addition to these methods, some control methods are proposed to control the DC voltage in MTDC system. These control methods include two groups. The first group (such as Multi-Agent Control methods) uses remote and local information, while the second group (such as Sliding Mode Control and H¥ control) uses local information.The proposed multi-agent control uses local information for immediate response, while uses remote information for a better fast response. Application of Multi-Agent Control systems leads to equal deviation of DC voltages from their reference values. Using remote information leads to better results comparing to the case only local information is used. Moreover, the proposed methods can also work in the absence of remote information. When AC grid is considered in the modeling, the MTDC system has anon-linear dynamic. Sliding Mode Control, a non-linear control method with high disturbance rejection capability, which is non-sensitive to the parameter variations, is applied to the MTDC system. It controls the DC voltage very fast and with small or without overshoot. Afterward, a static state feedback H¥ control is applied to the system which minimizes the voltage deviation after a disturbance and keeps the injected power of the terminals within the limits. Finally, some case studies are presented and the effectiveness of the proposed methods are shown. All simulations have been done in MATLAB and SIMULINK.

  • 497.
    Nazari, Mohammad
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Baradar, Mohamadreza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On-line control of multi-terminal HVDC systems connected to offshore wind farms using the POF-based multi-agent approarch2015Conference paper (Other academic)
    Abstract [en]

    Multi-terminal HVDC systems are an attractive option to connect offshore wind farms to onshore grids. Although scheduling the multi-terminal HVDC system is based on forecasted wind power, the forecasted values may differ from their real time ones. This paper presents a new controller based on multi-agent system which optimally tries to follow the variations of real time wind power outputs. Since a fast optimal power flow algorithm is needed, a convexified AC-OPF model which can be efficiently solved through interior point methods (IPMs) is embedded into the proposed online controller. Simulations are carried out and validated using GAMS platform and MATLAB/Simulink.

  • 498.
    Nazari, Mohammad
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Application of Multi-Agent Control to Multi-Terminal HVDC Systems2013In: 2013 IEEE Electrical Power & Energy Conference (EPEC), IEEE Computer Society, 2013, p. 6802960-Conference paper (Refereed)
    Abstract [en]

     This paper addresses control of DC voltage in a multi-terminal HVDC system. The proposed control strategy in this paper utilizes multi-agent control methodology to control the set values of the DC voltages of converters. The input data used for the proposed control is based on either local or a combination of local and remote information. For the remote data, a time delay for received information is considered. Some case studies are presented using MATLAB / Simulink to show the performance of the proposed control method.

  • 499.
    Nechma, Nadira
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Solcellspaneler på hustak2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 500. Negra, N. B.
    et al.
    Todorovic, J.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Loss evaluation of HVAC and HVDC transmission solutions for large offshore wind farms2006In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 76, no 11, p. 916-927Article in journal (Refereed)
78910111213 451 - 500 of 806
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