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  • 51.
    Crosara, Alessandro
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. Pöyry.
    Tomasson, Egill
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Generation Adequacy in the Nordic and Baltic Region: Case Studies from 2020 to 2050: Flex4RES Project Report2019Report (Other academic)
    Abstract [en]

    Generation adequacy is a concern in today's electricity market where intermittent renewable energy sources are rapidly becoming a greater share of the generation mix. This study focuses on the Nordic and Baltic power system that is comprised of the system areas of the Nord Pool spot market. Sequential Monte Carlo Simulation is applied to assess the generation adequacy of this multi-area system for several future case studies, based on scenarios defined within the Nordic Flex4RES project. The report gives insights into the characteristics of these adequacy problems that the system could face in a more sustainable future, quantifies their magnitude and presents their characteristics. Finally, a solution based on the demand flexibility of residential electric heating is discussed, as a way to counter capacity deficit problems.

  • 52.
    Cuk, Vladimir
    et al.
    Einhoven University of Technology.
    Riberio, Paulo F.
    Einhoven University of Technology.
    Cobben, Joseph F.G.
    Einhoven University of Technology.
    Kling, Wil L.
    Einhoven University of Technology.
    Isleifsson, Fridrik R.
    Technical Universitu of Denmark.
    Bindner, Henrik W.
    Technical Universitu of Denmark.
    martensen, Nis
    Energynautics.
    Samadi, Afshin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Considerations on the Modeling of Photovoltaic Systems for Grid Impact Studies2011In: 1st International Workshop on Integration of Solar Power into Power Systems / [ed] Uta Betancourt/Thomas Ackermann, Germany: Energynautics Gmbh , 2011, p. 35-42Conference paper (Refereed)
  • 53.
    Dabar, Omar Assowe
    et al.
    CERD, Inst Sci Terre, Route Aeroport,BP 486, Ville, Djibouti..
    Awaleh, Mohamed Osman
    CERD, Inst Sci Terre, Route Aeroport,BP 486, Ville, Djibouti..
    Kirk-Davidoff, Daniel
    Univ Maryland, Dept Atmospher & Ocean Sci, College Pk, MD 20742 USA..
    Olauson, Jon
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Awaleh, Said Ismael
    CERD, Inst Sci Terre, Route Aeroport,BP 486, Ville, Djibouti..
    Wind resource assessment and economic analysis for electricity generation in three locations of the Republic of Djibouti2019In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 185, p. 884-894Article in journal (Refereed)
    Abstract [en]

    In the Republic of Djibouti, due to increasing electricity demands, the government has planned to increase power supply by using renewable resources such as geothermal, solar and wind energy. This work presents the first wind resource assessment in the Republic of Djibouti using measured wind speed data for the period of three years by meteorological stations at eight locations. The results confirmed that three of the eight locations (i.e. GaliMa-aba, Ghoubbet and Bada Wein) have the best resource, with mean annual wind speeds of more than 6.0 m/s. Wind simulations using NCEP-CFSR and ERA5 models reanalysis shows that the seasonal variations are stable between different years and are broadly consistent with the observed wind speed. The feasibility of three wind farms with total capacity of 275 MW at GaliMa-aba, Ghoubbet and Bada Wein is examined. Using the WindPRO program and two commercial wind turbines in according to IEC 61400-1 design criteria, the electricity generation were technically assessed. These wind farms can produce 1073 GWh of electricity per year, approximately equal to Djibouti's expected average annual electrical demand in 2030. The economic evaluation using the present value cost (PVC) method estimate that the generation cost per kWh at these locations varies from 7.03 US.$ cent/kWh to 9.67 US.$ cent/kWh. Elsevier Ltd. All rights reserved.

  • 54.
    Divshali, Poria Hasanpor
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Improving PV Dynamic Hosting Capacity Using Adaptive Controller for STATCOMs2019In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 34, no 1, p. 415-425Article in journal (Refereed)
    Abstract [en]

    High penetrations of renewable energy sources (RES) in distribution grids lead to new challenges in voltage regulation. These challenges are not just limited to the steady-state voltage rise, but they are extended to rapid voltage changes due to wind speed variations and moving clouds, casting shadows on photovoltaic panels. According to EN50160 in low-voltage (LV) grids, the steady-state voltage should not exceed 1.1 pu (static characteristic), and rapid voltage changes should be kept less than 0.05 pu (dynamic characteristic). These two characteristics may limit the maximum amount of RES that can be installed in LV grids, called, respectively, the static hosting capacity (SHC) and dynamic hosting capacity (DHC). Although existing research just evaluated SHC in distribution grids, high-penetrated RES grids can be faced with such large voltage changes, which cause a smaller DHC than the SHC. This paper studies both SHC and DHC in distribution grids and proposes an adaptive controller for static synchronous compensators to regulate the steady-state and dynamic voltage while avoiding the unnecessary increase in the reactive power. The simulation results in some German distribution grids show considerable effects of the proposed adaptive controller on improving both SHC and DHC.

  • 55.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Influence of Ambient Temperature on Transformer Overloading During Cold Load Pickup2013In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 28, no 1, p. 153-161Article in journal (Refereed)
    Abstract [en]

    This paper proposes a method to investigate the socioeconomical aspects of transformer overloading during a cold load pickup (CLPU) in residential areas. The method uses customer damage functions to estimate the cost for their power interruption and a deterioration model to estimate the cost for transformer wear due to the CLPU. A thermodynamic model is implemented to estimate the peak and the duration of cold residential load. A stochastic differential equation is used to capture the volatility of the load and to estimate the probability for transformer overloading. In a numerical example, an optimal cold load pickup for a two-area system is demonstrated where transformer overloading is allowed. In this example, an ambient temperature threshold is identified, where transformer overloading is socioeconomically beneficial.

  • 56.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling Impact of Cold Load Pickup on Transformer Aging Using Ornstein-Uhlenbeck Process2012In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 27, no 2, p. 590-595Article in journal (Refereed)
    Abstract [en]

    Thermostatically controlled devices, such as air conditioners, heaters, and heat pumps may cause cold load pickup (CLPU) problems after a prolonged blackout. This causes an increased load on the power components in the electrical grid. The result is unpredictable aging and increased risk of failure. Quantifying this risk is crucial for efficient asset management for cost-intensive components such as the transformer. This paper presents a new approach to model the loading profile of a CLPU using stochastic differential equations. The realization of the loading profile is used to determine the aging of a transformer. Two models for the deterioration of transformer solid insulation represent the loss of life due to the CLPU. A comparison between two models for the aging of the solid insulation in the transformer is made in a case study. Due to the stochastic behavior of the load, there is a probability for loading the transformer above the recommended ratings, and this probability is estimated with Monte Carlo simulations.

  • 57.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A circuit breaker reliability model for restoration planning considering risk of communication outage2011In: 2011 IEEE PES Trondheim PowerTech: The Power of Technology for a Sustainable Society, POWERTECH 2011, IEEE , 2011, p. 1-6Conference paper (Refereed)
    Abstract [en]

    A large scale blackout is a long term loss of electricity over a large geographical area. In order to succeed with the restoration, the electric utility SCADA system must be highly reliable not only in normal operation but also during a black out. The main contribution of this paper is a circuit breaker (CB) reliability model to be used in restoration planning. The model consider both the reliability of a SCADA system and the reliability of a communication system during a power outage. If a remote control of CB fails, due to battery undersizing, it is assumed in the paper that a manual operation of CB can be performed if field personal can communicate with the TSO head-quarter. The evaluation of the reliability to operate CB is performed by solving the so called s-t reliability problem for a graph with failure prone components. The method is applied in a case study where the SCADA architecture for an IEEE reliability test system is modeled.

  • 58.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Impact of remote control failure on power system restoration time2010In: 2010 IEEE 11th International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2010, IEEE , 2010, p. 343-347Conference paper (Refereed)
    Abstract [en]

    Extended blackouts are rare events but when they occur they cause severe stress on the society. After a blackout it is important to have a efficient restoration strategy and to be aware of the risks that could extend the restoration process. One important risk during the restoration process after a blackout is the dependence of limited back up power at substations. The back up power is needed to control circuit breakers and for communication equipment. If the outage time is extensive the back up power might run out and the ability to control the circuit breakers is lost and this will extend the restoration time even further. In this paper a stochastic model of the restoration process of a power system with several substations with an uncertain backup power is presented. The model uses a Monte Carlo simulation to identify the impact of remote control failure on power system restoration time. © 2010 IEEE.

  • 59.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On spectral graph theory in power system restoration2011In: IEEE PES Innovative. Smart Grid Technol. Conf. Europe, 2011Conference paper (Refereed)
    Abstract [en]

    A large penetration of renewable energy sources with volatile power generation imposes new challenges for efficient restoration of the power system after a blackout. Prolonged power outages are also characterized be uncertain load conditions due to cold load phenomena. To meet this challenge, this paper deals with the problem of how to restore a transmission system after a blackout under uncertain load conditions and volatile power generation. The main contribution is a approximate method which minimizes the expected dissipated power under random current injection and maximizes the short circuit power under random generator generator introduction. The method is demonstrated in a numerical example on the Nordic32 400 kV transmission system.

  • 60.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On uncontrolled system separation in power system restoration2011In: NAPS 2011 - 43rd North American Power Symposium, IEEE , 2011Conference paper (Refereed)
    Abstract [en]

    Since extended power outages causes severe stress on society and the restoration following a black out is a complex and time consuming task, efficient restoration strategies are needed. During the restoration, the power system undergoes continual changes and therefore it is subject to desired and undesired operations and failures which might be devastating. The main contribution of this paper is a new method to estimate the risk of an uncontrolled system separation in case of a loss of a transmission line or a transformer during a restoration process. The method in this paper assigns failure rates to the transformers and the transmission lines. Further, a graph theoretical method are used to find probability bounds for an uncontrolled system separation for a whole restoration sequence. In a numerical example are three restoration strategies applied to an IEEE 14 bus test system and evaluated. It is shown in the numerical example that the restoration strategy has an high impact on the probability for a system separation. © 2011 IEEE.

  • 61.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Using power system stabilisers in doubly fed induction generators2008In: 2008 Australasian Universities Power Engineering Conference, AUPEC 2008, 2008Conference paper (Refereed)
    Abstract [en]

    This article deals with the design and usage of a power system stabiliser (PSS) and its impact in the controller of a doubly fed induction generator (DFIG). Eigenvalue analysis and numerical simulations are used to design and tune the PSS for different types of input signals, and the suitability of the signals is assessed. The impact of large scale wind farms utilising DFIGs on the oscillations of a conventional power system is compared to the impact of conventional generators in a test power system. The dynamics of a wind farm can be represented by a third order DFIG model and a simple controller model. Modal analysis and dynamic simulations are used to demonstrate the contribution made by the wind farm to power system damping. Numerical simulations show that DFIGs, such as those found in wind farms, are capable of damping oscillations.

  • 62.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Coordinated control of multiple HVDC links using input-output exact linearization2010In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, no 12, p. 1406-1412Article in journal (Refereed)
    Abstract [en]

    This paper is concerned with the investigation of a new control technique for the conventional High Voltage Direct Current (HVDC) link. The proposed technique relies upon nonlinear state feedback linearization of the AC/DC power system. The idea in input-output exact feedback linearization is to algebraically transform nonlinear systems dynamics into a linear control problem using a nonlinear pre-feedback loop, and then for the linearized power system one can design another feedback loop using a well established technique such as a linear-quadratic regulator. The primary goal of the controller presented in this paper is to contribute to the enhancement of both the transient and the small-signal stability of the power system. Since the proposed state feedback linearization does not rely on the assumption that there is only small deviation of the states from an equilibrium, the enhancement of both is feasible. The simulation results obtained in the framework of the study show that the proposed controller is capable of stabilizing the system in various system operating conditions.

  • 63.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Linear HVDC Modeling for Small Signal Stability Studies2009In: MEPCON, IEEE, 2009Conference paper (Refereed)
  • 64.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On the assessment of the impact of a conventional HVDC on a test power system2007In: 2007 IREP SYMPOSIUM- BULK POWER SYSTEM DYNAMICS AND CONTROL: VII REVITALIZING OPERATIONAL RELIABLITY, VOLS 1 AND 2, NEW YORK: IEEE , 2007, p. 58-62Conference paper (Refereed)
    Abstract [en]

    There are several possibilities to improve the first swing transient stability in a power system. One adequate option is to use the high controllability of the HVDC if HVDC is available in the system. This paper presents a control strategy for HVDC to improve the first swing transient. The strategy controls the power through the HVDC to make the system more transient stable during disturbances. The proposed control strategy consists of the PD-controller and feed-forward control, the use of a PD-controller is appropriate since it has the property of fast response. To improve the first swing oscillation even more the feed-forward control is used, since the behavior of system due to the disconnection is known. Two bench mark power systems are subjected to large disturbances to examine the effectiveness of the proposed strategy. Depending on how the power through the HVDC is controlled the transients damp differently. The PD-controller works well and damps the first swing oscillation transient so the system remains stable. When a power step also is applied after the line is disconnected, the transient swing becomes lower and the behaviour of the system is better. There is also a possibility to improve the first swing oscillation even more, by applying a power step through the HVDC which will compensate for the lack of power due to the disconnection of the line caused by the disturbance.

  • 65.
    Eriksson, Robert
    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.
    Coordination of HVDC-links to increase dynamic stability margins2010In: 2010 IEEE International Conference on Power and Energy, PECon2010, 2010, p. 183-188Conference paper (Refereed)
    Abstract [en]

    The main contribution of this paper is a new method for adaptively coordinating the power modulation of multiple HVDC-links in a power system, to enhance the total transfer capacity. This in turn may lead to a more active electricity market. The increase in transfer capacity is obtained by an adaptive coordinated modulation control of multiple HVDC-links in the system. The control method is based on maximizing the distance to the bifurcation surface by adjusting the feedback gain of the HVDC-links modulation controllers.

  • 66.
    Eriksson, Robert
    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.
    Transfer capacity enhancement by adaptive coordinated controlof HVDC-links based on forecasted load paths2011In: European transactions on electrical power, ISSN 1430-144X, E-ISSN 1546-3109, Vol. 21, no 3, p. 1455-1466Article in journal (Refereed)
    Abstract [en]

    Due to the intensive use of the transmission networks one of the major issues in electric energy trading is bottlenecks limiting the transfer capacity between different system areas. In this article, a new method for increasing transfer capacity is suggested. The increase in transfer capacity is obtained by an adaptive coordinated modulation control of multiple HVDC-links in the system. The control method is based on maximizing the distance to the bifurcation surface by adjusting the feedback gain of the HVDC-links modulation controllers. The system is linearized along the forecasted load path. The feedback gains are then chosen in such a way that system remains stable, in a small signal sense, as long as possible along the forecasted load path. The arising optimization problem is then solved using a particle swarm optimization method. If the load is predicted to increase, instability will eventually occur when the loading reaches a critical limit. Using the proposed control method the point in load-space where instability occur will be at a significantly higher loading level. The main contribution of this paper is the proposed new method for adaptively coordinating the power modulation of multiple HVDC-links in a power system, to enhance the total transfer capacity. This in turn will lead to a possibility to increase the traded volumes on the electricity market.

  • 67.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A general approach to coordinated control of multiple HVDC links using input-output exact linearizationArticle in journal (Other academic)
  • 68.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Centrally coordinated control of multiple HVDC links for power oscillation damping2010In: POWER CONTROL AND OPTIMIZATION, 2010, Vol. 1239, p. 134-140Conference paper (Refereed)
    Abstract [en]

    This paper presents a method of how to design a centrally coordinated controller for several HVDC links. The controller increases the damping of the power oscillations by modulating the current through the HVDC links coordinately. To design a centrally coordinated controller a reduced order open system model is estimated. The open system model of the power system is developed by using black-box system identifications techniques. The current setpoint change through the HVDC links is the set of input signals and, the speeds of the generators are the set of outputs. Numerical Algorithms for Subspace State-Space System Identification (N4SID) is used to identify a model. This controller design method increases the damping significantly which is shown for a small power system.

  • 69.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Coordinated control design of multiple HVDC links based on model identification2010In: Computers and Mathematics with Applications, ISSN 0898-1221, E-ISSN 1873-7668, Vol. 60, no 4, p. 944-953Article in journal (Refereed)
    Abstract [en]

    This paper presents a method for designing a centralized coordinated controller for several HVDC links. The controller increases the damping of the power oscillations by modulating the current through the HVDC links in a coordinated fashion. To design a centralized coordinated controller a reduced order open system model is estimated. The open system model of the power system is estimated using the Numerical Algorithms for Subspace State-Space System Identification (N4SID) algorithm which is a black-box system identification technique. The current set-point change through the HVDC links is the set of input signals and the speeds of the generators are the set of outputs. This controller design method increases the damping significantly, which is shown for a small power system.

  • 70.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On the coordinated control of multiple HVDC links using input-output exact linearization in large power systems2012In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 43, no 1, p. 118-125Article in journal (Refereed)
    Abstract [en]

    Stability of power systems may limit the amount of transfer capacity between areas as the systems tend to be more utilized. The controllability brought by the high voltage direct current (HVDC) links is a possible access to increase the stability and thereby the power transfer. The main contribution of this article is a coordinated control strategy for multiple HVDC links to improve both transient and small signal stability. The input-output exact feedback linearization is used to map the nonlinear system model to a linear model seen from the input to the output. Linear control design can now be used, such as the linear quadratic regulator (LQR). This linearization is not the commonly used Taylor linearization, the input-output exact feedback linearization cancels the nonlinearities by a pre-feedback loop. An extension of the internal node representation by including the dynamics of the HVDC links in the nonlinear differential swing equations is also developed, which is needed for the feedback control design.

  • 71.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Optimal coordinated control of multiple HVDC links for power oscillation damping based on model identification2012In: European transactions on electrical power, ISSN 1430-144X, E-ISSN 1546-3109, Vol. 22, no 2, p. 188-205Article in journal (Refereed)
    Abstract [en]

    This paper deals with optimal coordinated control of several high voltage direct current (HVDC) links based on an estimated model of large power systems. The model of the power system is estimated by using subspace system identification techniques. An optimal controller is designed based on the estimated model with the aim to improve the damping in the system. The main contribution of this paper is the development of a new method which uses global Phasor measurement units (PMUs) signals for coordinated damping control of multiple HVDC links. The input signals are the controllable set-points of the HVDC links, the output signals are the speed signals of selected generators obtained from PMU. The PMU signals are used to estimate the current state of the model, i.e., the state of the system, an appropriate control action can then be applied to dampen the system. The benefit of the method is that the used output signals, i.e., the used PMU signals, are independent of the system equilibrium and therefore makes it possible to use state-feedback control, i.e., coordinated control. The method is applied to the Cigre Nordic 32-bus system including two HVDC links. The consistent results show that the damping can be significantly increased.

  • 72.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    System identification techniques for obtaining linear models of large power systems with controllable devices from noisy measurements2010In: 2010 IREP Symposium - Bulk Power System Dynamics and Control - VIII, IREP2010, 2010Conference paper (Other academic)
    Abstract [en]

    This paper deals with the use of system identification techniques for estimating low-order black-box state-space models formodal analysis. It presents a method to estimate state-space models for large power systems with many controllable devices from noisy measurements. To excite the system low-energy pulses generated by the controllable devices are used. The input signals are the controllable set-points of the devices, the output signals are the speed signals of some generators obtained from Phasor Measurement Units (PMU). The Subspace State-Space System Identification (N4SID) and Prediction Error Method (PEM) are compared in sense of robustness using measurement with different signal to noise ratios noisy measurements. The method is applied in an extended version of the Cigré Nordic 32-bus test system. This model approach can be used directly for the design of a centralized controller coordinating the controllable devices with the aim to increase the damping in the system.

  • 73.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    WAMS based identification for obtaining linear models to coordinate controllable devices2012In: Electrical engineering (Berlin. Print), ISSN 0948-7921, E-ISSN 1432-0487, Vol. 94, no 1, p. 27-36Article in journal (Refereed)
    Abstract [en]

    This paper is concerned with the use of subspace system identification techniques to derive a low-order black-box state-space model of a power system with many controllable devices. This is a multi-input multi-output open system model describing the power oscillatory behavior of the power system. The input signals are the controllable set points of the controllable devices, the output signals are the speed of some generators measured by a wide-area measurement system. This paper describes how to achieve and pre-process the data to use the subspace method to estimate and validate to finally assign an accurate model. This new approach can be used directly for the design of a centrally coordinated controller coordinating all the relevant controllable devices, with the aim to increase the damping of the modes in the system. Previously presented models, using input signals from controllable devices, use local measurements or output signals dependent on the actual operational point. The benefit of the presented method is that the used output signals are independent of the system state. This makes it possible to use a state-feedback controller, i.e., coordinated control. The presented method is applied in the Cigré Nordic 32-bus system including two high-voltage direct current (HVDC) links. The case study demonstrates that accurate low-order state-space models can be estimated and validated using the described method to accurately model the system's power oscillatory behavior. 

  • 74.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wide-Area measurement system-based subspace identification for obtaining linear models to centrally coordinate controllable devices2011In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 26, no 2, p. 988-997Article in journal (Refereed)
    Abstract [en]

    The contribution of this paper is the application of subspace system identification techniques, to derive a low-order black-box state-space model of a power system with many controllable devices using global signals. This model is a multiinput, multioutput open system model describing the power oscillatory behavior of the power system. The input signals are the controllable setpoints of the controllable devices, the output signals are the speed of selected generators measured by a wide-area measurement system. This paper describes how to achieve and preprocess the data to use subspace techniques to estimate and validate to finally assign an accurate model. This new approach can be used directly to design a central coordinating controller for all of the relevant controllable devices, with the aim to increase the damping of the modes in the system. Previously presented methods use local measurements or output signals dependent on the actual operational point. The benefit of the presented method is that the used output signals are independent of the system state. This makes it possible to use state-feedback control to combine the controllable devices to coordinately damp the modes. The presented method is applied in the CIGRÉ Nordic 32-bus system including two HVDC links. The case study demonstrates that accurate low-order state-space models can be estimated and validated by using the described method to accurately model the system's power oscillatory behavior.

  • 75.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart H.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wide-area measurement system control to coordinate HVDC links in large scale power systems2011In: Int. Conf. Intelligent Syst. Appl. Power Syst., ISAP, 2011, p. 6082169-Conference paper (Refereed)
    Abstract [en]

    The paper develops wide-area measurement coordinated control for several high-voltage direct current (HVDC) links. The coordinating state-feedback controller is designed based on an estimated reduced order model aiming to improve the damping of the power oscillations.

  • 76.
    Estanqueiro, Ana
    et al.
    National Laboratory on Energy and Geology (LNEG).
    Ahlrot, Claes
    E.ON AB.
    Duque, Joaquim
    National Laboratory on Energy and Geology (LNEG).
    Santos, Duarte
    National Laboratory on Energy and Geology (LNEG).
    Gentle, Jake P.
    Idaho National Laboratory (INL).
    Abboud, Alexander W.
    Idaho National Laboratory (INL).
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Kanefendt, Thomas
    Fraunhofer IEE.
    DLR use for optimization of network design withvery large wind (and VRE) penetration2018Conference paper (Refereed)
    Abstract [en]

    Due to the stochastic nature of wind and clouds,the integration of wind and PV generation in the powersystem poses serious challenges to the long-term planning oftransmission systems. Grid reinforcements always involverelevant direct costs while the average load factor of the windand solar PV dedicated transmission lines is usually low.Additionally, in very windy sites, the same high windresource that produces large amounts of wind generation andmay congest the transmission lines transporting it to distantconsumption centres may also have a beneficial effect inincreasing the transmission capacity of those lines. In fact, theoccurrence of wind not only contributes to the loading of theconnecting line, but also increases the line capacity, via theconvective cooling of the cables - one of the main heattransfer mechanisms in conductor heat balance; in otherwords, higher winds speeds contribute to faster cooling ofconductor and therefore higher conductor’s capacitypotential. In this paper the existing methodologies tocharacterize those thermal effects in electrical cables - usuallyreferred as dynamic line rating (DLR) - are applied to severalIEA Task 25 countries case studies to characterize thetechnical value of the dynamic operation of thermallycongested lines, as well as its potential economic benefits.

  • 77.
    Fernández Martínez, Alberto
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Huang, Yalin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Distribution network planning with a large amount of small scale photovoltaic power2013In: 2013 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC), IEEE Computer Society, 2013, p. 1-6Conference paper (Refereed)
    Abstract [en]

    This paper presents a new method to assist distribution system operators assessing the capacity of each bus for connecting more photovoltaic power in a low voltage distribution network. The developed method takes the uncertainties from load and generation into account. Moreover, it applies probabilistic voltage limits in the assessment process. An improved linear power flow analysis is used in the process. Furthermore, a case study in a Swedish low voltage network is discussed to apply the proposed method on assessing the maximum photovoltaic peak power that can be installed into a distribution network without violating probabilistic voltage limits. A comparison between deterministic approach and probabilistic approach is also performed.

  • 78. Fischer, P.
    et al.
    Söder, Lennart
    KTH, Superseded Departments.
    The Benefits on New Voltage Source Converter HVDC Configurations for City Infeed2002In: IASTED Conference, Power and Energy Systems, EuroPES 2002, Creta Greece, 2002Conference paper (Refereed)
  • 79.
    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.

  • 80.
    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.

  • 81.
    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)
  • 82.
    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.

  • 83.
    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.

  • 84.
    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.

  • 85.
    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.

  • 86.
    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)
  • 87.
    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.

  • 88.
    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.

  • 89.
    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.

  • 90.
    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.

  • 91.
    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.

  • 92.
    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.

  • 93.
    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.

  • 94.
    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)
  • 95.
    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.

  • 96.
    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.

  • 97.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Review Paper on Wind Power Impact on Operation of Reserves2011In: 2011 8th International Conference on the European Energy Market, EEM 11, 2011, p. 895-903Conference paper (Refereed)
    Abstract [en]

    This paper reviews studies concerning new challengesfor European transmission system operators (TSOs) when operating primary, secondary and tertiary reserves in a systemwith large amounts of wind power. The review adopts three perspectives. First, the impact on existing markets is discussed and it is shown that need for additional reserve requirements does not necessarily mean need for new reserve capacity. Secondly, possible designs of improved load-frequency control schemes are presented.The proposed solutions exhibit a trend towards market-based procurement mechanisms and automation of reserve operations. Finally, participation of wind power in load-frequency control is examined. Technical designs are presented for participation inprimary control.

  • 98. Hannele, Holttinen
    et al.
    Meibom, Peter
    Orths, Antje
    Lange, Bernhard
    O’Malley, Mark
    Tande, John Olav
    Estanqueiro, Ana
    Gomez, Emilio
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Strbac, Goran
    Smith, J. Charles
    van Hulle, Frans
    Impacts of large amounts of wind power on design and operation of power systems, results of IEA collaboration2009In: 8th International Workshop on LargeScale Integration of Wind Power into Power Systems as well as on Transmission Networks of Offshore Wind Farms, 2009Conference paper (Refereed)
    Abstract [en]

    IEA WIND R&D Task 25 on “Design and Operation of Power Systems with Large Amounts of Wind Power” collects and shares information on wind power impacts on power systems, with analyses and guidelines on methodologies. There are dozens of studies made and ongoing related to wind integration, however, the results are not easy to compare. In the stateoftheart report (October, 2007), and the final report of the 3 years period (July, 2009) the most relevant wind power grid integration studies have been analysed especially regarding methodologies and input data. Several issues that impact on the amount of wind power that can be integrated have been identified. Large balancing areas and aggregation benefits of large areas help in reducing the variability and forecast errors of wind power as well as help in pooling more cost effective balancing resources. System operation and functioning electricity markets at less than dayahead time scales help reduce forecast errors of wind power. Transmission is the key to aggregation benefits, electricity markets and larger balancing areas. Best practices in wind integration studies are described. There is also benefit when adding wind power to power systems: it reduces the total operating costs and emissions as wind replaces fossil fuels and this should be highlighted more in future studies.

  • 99.
    Hasanpor Divshali, Poria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. State University of New York, USA.
    Choi, Bong Jun
    Liang, Hao
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Transactive Demand Side Management Programs in Smart Grids with High Penetration of EVs2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 10, article id 1640Article in journal (Refereed)
    Abstract [en]

    Due to environmental concerns, economic issues, and emerging new loads, such as electrical vehicles (EVs), the importance of demand side management (DSM) programs has increased in recent years. DSM programs using a dynamic real-time pricing (RTP) method can help to adaptively control the electricity consumption. However, the existing RTP methods, particularly when they consider the EVs and the power system constraints, have many limitations, such as computational complexity and the need for centralized control. Therefore, a new transactive DSM program is proposed in this paper using an imperfect competition model with high EV penetration levels. In particular, a heuristic two-stage iterative method, considering the influence of decisions made independently by customers to minimize their own costs, is developed to find the market equilibrium quickly in a distributed manner. Simulations in the IEEE 37-bus system with 1141 customers and 670 EVs are performed to demonstrate the effectiveness of the proposed method. The results show that the proposed method can better manage the EVs and elastic appliances than the existing methods in terms of power constraints and cost. Also, the proposed method can solve the optimization problem quick enough to run in real-time.

  • 100.
    Hasanpor Divshali, Poria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Improvement of RES hosting capacity using a central energy storage system2017In: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1-6Conference paper (Refereed)
    Abstract [en]

    High penetration of renewable energy sources (RESs) in distribution systems leads to reverse active power and voltage rise in low voltage (LV) grids, which limits the hosting capacity. Energy storage systems (ESSs) have been used to improve the hosting capacity by decreasing the reverse active power in some literature. ESSs can still improve the hosting capacity more by providing reactive power. The reactive power shows a little effect in existing researches, because they have mostly simulate LV grids without modeling transformers. However, the high reactance of the transformer magnifies the effectiveness of the reactive power control even more than the active power in some buses. This paper develops an optimal method for placement, sizing, and active and reactive power control of a central ESS to improve the hosting capacity. The simulation results in highly RES penetrated grids at Germany show the effectiveness of the proposed method.

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