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  • 201.
    Olsson, Magnus
    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.
    Modeling real-time balancing power demands in wind power systems using stochastic differential equations2010In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, no 8, p. 966-974Article in journal (Refereed)
    Abstract [en]

    The inclusion of wind power into power systems has a significant impact on the demand for real-rime balancing power due to the stochastic nature of wind power production The overall aim of this paper is to present probabilistic models of the impact of large-scale integration of wind power on the continuous demand in MW for real-time balancing power This is important not only for system operators, but also for producers and consumers since they in most systems through various market solutions provide balancing power.

    Since there can occur situations where the wind power variations cancel out other types of deviations in the system, models on an hourly basis are not sufficient Therefore the developed model is in continuous time and is based on stochastic differential equations (SDE) The model can be used within an analytical framework or in Monte Carlo simulations.

  • 202.
    Olsson, Magnus
    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.
    Simulation of real-time balancing power demands in power systems with wind power2010In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, p. 966-974Article in journal (Refereed)
  • 203.
    Olsson, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Estimating real-time balancing prices in wind power systems2009In: Proceedings of the 2009 Power Systems Conference and Exposition (PSCE), 2009, p. 229-237Conference paper (Refereed)
    Abstract [en]

    As the amounts of installed wind power increases in the power system, the required real-time balancing quantities increases because of the unpredictability of wind power production. Real-time balancing power is usually provided through various market solutions and thus, the prices on such markets will be affected by the increase in wind power production. Consequently, there exist a need for planning and simulation tools concerning the increased balancing demand. This paper therefore describes an estimation model for real-time balancing prices in systems where significant levels of wind power will be added. The model is divided into two steps: The first estimating the changes in required real-time balancing quantities, and the second calculating the corresponding price changes.

  • 204.
    Olsson, Magnus
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Söder, Lennart
    KTH, Superseded Departments, Electrical Systems.
    Generation of regulating power price scenarios2004In: 2004 International Conference On Probabilistic Methods Applied To Power Systems, 2004, p. 26-31Conference paper (Refereed)
    Abstract [en]

    This paper presents a model of the regulating power market prices, based on ARIMA processes. The model can be used when creating scenario trees that are used in stochastic programming problems to generate optimal bids to the regulating power market. The model considers spot market price correlation and the design of the regulating power market, including the delay time of release of prices and submission time. The usual estimation methods associated with stochastic processes are not sufficient for this application. Therefore, new parameter estimation methods have been developed for the ARIMA process. The model and the estimation methods are used in a case study, where real data from the Nordic power market is used. A conclusion is that ARIMA processes are possible to use for this kind of models.

  • 205.
    Olsson, Magnus
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Söder, Lennart
    KTH, Superseded Departments.
    Hydropower planning including trade-off between energy and reserve markets2003In: 2003 IEEE Bologna Power Tech Conference Proceedings, 2003, Vol. 1Conference paper (Refereed)
    Abstract [en]

    An increase of wind power in the Nordic power system increases the need for regulating power because of variations in wind power production. Hydropower is the most likely power source to balance these fluctuations. This affects the power market and increases the demand for planning tools that are taking the extended need of regulating power into account. A short-term hydropower scheduling model has been developed to manage the trade-off between energy and reserve markets. The model is expressed as a stochastic optimization problem, where the objective function is the sum of sales on the spot market, the regulating market and the value of saved water. Constraints are hydrological balance and balance in produced power and traded power on the market.

  • 206.
    Olsson, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling power prices in wind power systems using non-constant mean and volatility modelsManuscript (Other academic)
  • 207.
    Olsson, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling real-time balancing power market prices using combined SARIMA and Markov processes2008In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 23, no 2, p. 443-450Article in journal (Refereed)
    Abstract [en]

    This paper describes modeling of real-time balancingpower market prices by using combined seasonal auto regressiveintegrated moving average (SARIMA) and discrete Markovprocesses. The combination of such processes allows generationof price series with periods where no demand for balancingpower exists. The purpose of the model is simulation of prices toconstruct scenario trees representing possible realization of thestochastic prices. Such scenario trees can be used in planningmodels based on stochastic optimization to generate bid sequencesto the balancing market. The spread of the prices in the treeand the shape of the scenarios are of central importance. Modelparameter estimation methods reflecting the demands on scenariotrees have therefore been used. The proposed model is also appliedto data from the Nordic power market. The conclusion of thispaper is that the developed model is appropriate for modelingreal-time balancing power prices.

  • 208.
    Olsson, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling swedish real-time balancing power prices using nonlinear time series models2010In: 2010 IEEE 11th International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2010, 2010, p. 358-363Conference paper (Refereed)
    Abstract [en]

    The liberalization of electricity markets and the rapid establishment of renewable power sources in the power system increases the need for decision support tools for planning, trading and operation. A suitable approach to model such decision problems is the use of stochastic optimization, where uncertain parameters, e.g. prices, are represented by a scenario tree. A scenario tree consists of possible outcomes of the stochastic prices. This paper describes a probabilistic model of real-time balancing prices. Real-time here refers to market places where balance power is traded with the TSO close to real-time. The proposed model reflects real-time markets applying hourly marginal pricing with different prices for upward and downward balancing. Further, the model is aimed for Monte Carlo simulation and generation of scenario trees. The model is based on nonlinear time series processes and use hourly day-ahead spot prices and real-time balancing demands as exogenous variables. By adjusting these prices and demands, future production mixes can be considered.

  • 209. P., Fischer
    et al.
    Ekström, Å.
    Söder, Lennart
    KTH, Superseded Departments.
    Benefits on New Voltage Source Converter HVDC Configurations for City Infeed2002In: European Power and Energy Systems: EuroPES 2002 / [ed] George Contaxis, Manolis Antonidakis, 2002Conference paper (Refereed)
    Abstract [en]

    Today most of the city centers infeed use HVAC transmission systems bringing large quantities of power to load centers. Many of theses systems are operating close to the designed short circuit capacity and have low network stability. In addition, there is an increase in environmental concern when overhead lines are used. The VSC (Voltage Source Converters) HVDC Cable Transmission system may become an interesting option for these cases. The aim of the paper is to describe possible VSC HVDC configurations that can be used for city center infeed. In the paper some of these are applied to real cases in Stockholm, Göteborg and São Paulo.

  • 210.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    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.
    Estimating Upper Confidence Bounds of Electric Power Consumption2009In: THIRTEEN INTERNATIONAL MIDDLE- EAST POWER SYSTEMS CONFERENCE, MEPCON'2009, 2009Conference paper (Refereed)
  • 211.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    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.
    Modeling the electric power consumption in a multi-area system2011In: European transactions on electrical power, ISSN 1430-144X, E-ISSN 1546-3109, Vol. 21, no 1, p. 413-423Article in journal (Refereed)
    Abstract [en]

    In this article a model of the electric power consumption in a multi-area power system is derived. The model is based on stochastic differential equations to mimic the stochastic behavior of electric power consumption in large systems. The developed model considers correlations between the consumptions in the different areas. A numerical example showing how to find the parameters of the process will be given. The load data used in the numerical example is hourly energy consumption data for the Nordic countries: Sweden, Norway, and Finland.

  • 212.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    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.
    Risk Estimation of Critical Time to Voltage Instability Induced by Saddle-Node Bifurcation2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 3, p. 1600-1610Article in journal (Refereed)
    Abstract [en]

    Prevention of voltage instability in electric power systems is an important objective that the system operators have to meet. Under certain circumstances the operating point of the power system may start drifting towards the set of voltage unstable operating points. If no preventive measures are taken, after some time the operating point may eventually become voltage unstable. It will thus be preferable to have a measure of the risk of voltage collapse in future loading states. This paper presents a novel method for estimation of the probability distribution of the time to voltage instability for a power system with uncertain future loading scenarios. The method uses a distance from the predicted load-path to the set of voltage unstable operating points when finding an estimate of the time to voltage instability. This will reduce the problem to a one-dimensional problem which for large systems decreases the computation time significantly.

  • 213.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    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.
    The Impact of a Given Trading Limit on a Two-Area Test System2009In: 2009 IEEE BUCHAREST POWERTECH / [ed] Toma L; Otomega B, NEW YORK: IEEE , 2009, p. 2122-2127Conference paper (Refereed)
    Abstract [en]

    This paper uses methods from stochastic analysis and stochastic modeling to determine the impact of a certain trading limit on the transfer between the two areas of a benchmark two-area power system. We also try to state which uncertainties are important to consider when calculating this power transfer.

  • 214.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Lindskog, Filip
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Importance Sampling of Injected Powers for Electric Power System Security Analysis2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 27, no 1, p. 3-11Article in journal (Refereed)
    Abstract [en]

    Power system security analysis is often strongly tied with contingency analysis. To improve Monte Carlo simulation, many different contingency selection techniques have been proposed in the literature.

  • 215.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A probabilistic distance to the power system secure operation boundary2010In: 2010 IREP Symposium - Bulk Power System Dynamics and Control - VIII, IREP2010, 2010Conference paper (Refereed)
    Abstract [en]

    Estimation of power system operation boundaries is an important issue in power system engineering. To make an adequate approximation of the operation boundary, not only the geometric properties of the boundary have to be taken under consideration but also the stochastic properties of the future injected power. In this paper two different distance functions on the power system operation boundary are suggested. The methods used to find the distance functions assumes that the future injected power can be modeled by a diffusion process. The proposed distance functions can be used when an approximation such as a Taylor's expansion of the power system operation boundary is needed. It is then suggested to use the point on the operation boundary that minimizes one of the proposed distance functions, as the basis for the approximation. Another possible application of the distance functions is when wanting to control power system equipment in order to increase stability margins.

  • 216.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A Stochastic Control Approach to Manage Operational Risk in Power SystemsManuscript (preprint) (Other academic)
    Abstract [en]

    In this article the novel method Operational Risk Managing Optimal Power Flow (ORMOPF), for minimizing the expected cost of power system operation, is proposed. In contrast to previous research in the area, the proposed method does not use a security criterion. Instead the expected cost of operation includes expected costs of system failures.

    This will lead to more flexible operating limits, giving a more adequate balance between risk and economic benefit of transmission.

    The method assumes a set of observable system variables such as transfers through specific transmission corridors, system frequency, or distance to a bifurcation surface. Then impulse control is applied to find an optimal strategy for activation of tertiary reserves, based on the values of the observables.

  • 217.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A Stochastic Control Approach to Manage Operational Risk in Power Systems2012In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 27, no 2, p. 1021-1031Article in journal (Refereed)
    Abstract [en]

    In this paper, the novel method operational risk managing optimal power flow (ORMOPF), for minimizing the expected cost of power system operation, is proposed. In contrast to previous research in the area, the proposed method does not use a security criterion. Instead the expected cost of operation includes expected costs of system failures. This will lead to more flexible operating limits, giving a more adequate balance between risk and economic benefit of transmission. The method assumes a set of observable system variables such as transfers through specific transmission corridors, system frequency, or distance to a bifurcation surface. Then impulse control is applied to find an optimal strategy for activation of tertiary reserves, based on the values of the observables.

  • 218.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Analysis of Transfer Capability by Markov Chain Monte Carlo Simulation2010In: PECon2010 - 2010 IEEE International Conference on Power and Energy, 2010, p. 232-237Conference paper (Refereed)
  • 219.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Analysis of transfer-limit induced power system security by Markov chain Monte Carlo simulation2012In: European transactions on electrical power, ISSN 1430-144X, E-ISSN 1546-3109, Vol. 22, no 2, p. 140-151Article in journal (Refereed)
    Abstract [en]

    Adequate security margins are commonly applied in power systems by keeping predefined transfer limits through certain transmission corridors in the system. These limits are often set to keep the criterion stating that the system should remain stable after the loss of any component. For many stability criteria such as, voltage stability, and voltage limits at specific nodes, the distribution of the injected power amongst the nodes of the system will be of vital importance. To incorporate this into the analysis of transfer limits the uncertainties in nodal loading and wind power production will have to be considered. In this article we propose a new method for generating samples of the power at all nodes given a set of transfers through specified corridors of the power system. It is then shown how the method can be used to evaluate the risk of violating the system stability limits induced by choosing a specific set of transfer limits. The method can be used in power system operations planning when setting the limits for trading and transfer between the different nodes of the power system.

  • 220.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Geometric Properties of the Loadability Surface at SNB-SLL Intersections and Tangential Intersection Points2011In: 16th International Conference on Intelligent System Application to Power Systems (ISAP) 2011, 2011, p. 1-5Conference paper (Refereed)
  • 221.
    Perninge, Magnus
    et al.
    Department of Automatic Control, Lund University.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Irreversible Investments with Delayed Reaction: An Application to Generation Re-Dispatch in Power System Operation2014In: Mathematical Methods of Operations Research, ISSN 1432-2994, E-ISSN 1432-5217, Vol. 79, no 2, p. 195-224Article in journal (Refereed)
    Abstract [en]

    In this article we consider how the operator of an electric power system should activate bids on the regulating power market in order to minimize the expected operation cost. Important characteristics of the problem are reaction times of actors on the regulating market and ramp-rates for production changes in power plants. Neglecting these will in general lead to major underestimation of the operation cost. Including reaction times and ramp-rates leads to an impulse control problem with delayed reaction. Two numerical schemes to solve this problem are proposed. The first scheme is based on the least-squares Monte Carlo method developed by Longstaff and Schwartz (Rev Financ Stud 14:113-148, 2001). The second scheme which turns out to be more efficient when solving problems with delays, is based on the regression Monte Carlo method developed by Tsitsiklis and van Roy (IEEE Trans Autom Control 44(10):1840-1851, 1999) and (IEEE Trans Neural Netw 12(4):694-703, 2001). The main contribution of the article is the idea of using stochastic control to find an optimal strategy for power system operation and the numerical solution schemes proposed to solve impulse control problems with delayed reaction.

  • 222.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On the validity of local approximations of the power system loadability surface2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 4, p. 2143-2153Article in journal (Refereed)
    Abstract [en]

    Power system voltage security assessment is generally applied by considering the power system loadability surface. For a large power system, the loadability surface is a complicated hyper-surface in parameter space, and local approximations are a necessity for any analysis. Unfortunately, inequality constraints due to for example generator overexitation limiters and higher codimension bifurcations makes the loadability surface nonsmooth. This makes the use of local approximations limited and calls for a method for estimating the distance to a nonsmooth part of the surface. This paper suggests a method for calculating the distance from a point on the loadability surface to the closest point of nonsmoothness of the loadability surface.

  • 223.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Optimal activation of regulating bids to handle bottlenecks in power system operation2012In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 83, no 1, p. 151-159Article in journal (Refereed)
    Abstract [en]

    In this article we investigate how to optimally activate regulating bids to handle bottlenecks inpower system operation. This will lead to an optimal stopping problem, and activation of aregulating bid is to be performed when the transfer through a specific system bottleneck reachesa certain value. Compared to previous research in the area the work presented in this articleincludes a more detailed model of the structure of the regulating market, and reaction times ofactors on the regulating market is taken into consideration. The emphasis of the presentation willbe application to a two area test system. The method is compared to Monte Carlo simulation ina numerical example. The example shows a promising result for the suggested method.

  • 224.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Optimal distribution of primary control participation with respect to voltage stability2010In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, no 11, p. 1357-1363Article in journal (Refereed)
    Abstract [en]

    In competitive electricity markets the transmission system will at times be heavily loaded. At these occasions prevention of voltage instability is an important objective that the system operator has to meet. In this paper a method for finding the primary control participation that maximizes the margin from an operating point to the saddle-node bifurcation surface is proposed. The arising optimization problem is solved using a steepest descent method. The proposed method can find its applications both in generation planning and in real-time operation of electric power systems.

  • 225.
    Perninge, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Risk estimation of the distance to voltage instability using a second order approximation of the saddle-node bifurcation surface2011In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 81, no 2, p. 625-635Article in journal (Refereed)
    Abstract [en]

    Prevention of voltage instability in electric power systems is an important objective that the systemoperators have to meet. Under certain circumstances the operating point of the power system may startdrifting towards the set of voltage unstable operating points. If no preventive measures are taken, aftersome time, the operating point may eventually become voltage unstable. It will thus be preferable to havea measure of the risk of voltage collapse in future loading states. This paper presents a novel method forestimation of the probability distribution of the load-space distance to the point where voltage instabilityinduced by saddle-node bifurcation occurs. Another result of the method is an estimate of the probabilitydistribution of the time to voltage instability for a power system with uncertain future loading scenarios.The method uses a second order approximation of the saddle-node bifurcation surface. The proposedmethod can be used in power system security assessments.

  • 226.
    Persson, Jonas
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Rouco, L.
    Söder, Lennart
    KTH, Superseded Departments.
    Linear analysis with two linear models of a thyristor-controlled series capacitor2003In: 2003 IEEE Bologna Power Tech Conference Proceedings, 2003, Vol. 3Conference paper (Refereed)
    Abstract [en]

    In this paper two reduced order models of a thyristor-controlled series capacitor (TCSC) are built. The models are identified from frequency response and time-domain simulation of the detailed original model of the TCSC. The reduced models are linear and with them, linear analysis can be done in a more proper way compared to doing linear analysis with the detailed original model of the TCSC that contains non-linearities, for instance the thyristors as well as the non-linear control algorithm. The performances of the linear models are compared with the fully detailed original TCSC-model using linear analysis and time-domain simulations. When doing linear analysis with the original detailed model, eigenvalues derived from the control algorithm of the TCSC are generated. These are ignored in the two linear models.

  • 227.
    Persson, Jonas
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Rouco, L.
    Söder, Lennart
    KTH, Superseded Departments.
    Time-domain comparisons of two linear models of a thyristor-controlled series capacitor2003In: IPEC 2003: Proceedings of the 6th International Power Engineering Conference, Vols 1 and 2, 2003, p. 746-751Conference paper (Refereed)
    Abstract [en]

    This paper describes a method to construct a linear model of a Thyristor-Controlled Series Capacitor (TCSC) by analyzing its frequency response obtained from time-domain simulations of a detailed model of the device. Such linear model represents the low frequency behavior of the device as needed in power system stability studies. The linear model is validated comparing the time-domain simulations obtained using the original detailed TCSC-model, the developed linear model and a previously obtained linear model. The latter one has been built by disturbing the TCSC with two events and identified with Matlab's System Identification ToolBox from time-domain simulations. By using a linear model, the computing time can be reduced significantly compared to simulations with a detailed TCSC-model, maintaining dominant behavior of the TCSC. All simulations are done with the power system simulation software Simpow.

  • 228.
    Persson, Jonas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Comparison of threes linearization methods2008In: Proceedings of 16th Power System Computation Conference, Power Systems Computation Conference ( PSCC ) , 2008Conference paper (Refereed)
    Abstract [en]

    Eigenvalues of a power system give a picture of the stability in the current operating point. The eigenvalues are calculated from the system matrix of a dynamic system. To create the system matrix, the dynamic system has to be linearized and to do that, linearization methods are utilized. Three linearization methods are compared in the paper. The performance of two software which use two of the methods are also compared and evaluated. It is shown how the linearization methods influence the results. Conclusions drawn from eigenvalue analysis are thus not only dependent on the properties of the investigated system, but also on used linearization method. It is shown how results obtained from three engineers working in parallel, studying the same power system but using three different linearization methods differ.

  • 229.
    Persson, Jonas
    et al.
    KTH, Superseded Departments, Electric Power Systems.
    Söder, Lennart
    KTH, Superseded Departments, Electric Power Systems.
    Linear analysis of a two-area system including a linear model of a thyristor-controlled series capacitor2001In: 2001 IEEE Porto Power Tech Proceedings, 2001, Vol. 2Conference paper (Refereed)
    Abstract [en]

    This paper describes a method to construct a linear model of a thyristor-controlled series capacitor (TCSC) by analyzing its response in a time domain simulation wherein the TCSC is represented by a detailed instantaneous value model. To create the linear model Matlab’s System Identification ToolBox is used. The linear model in the classic ABCD-form is included in both time simulations and linear analysis of the power system. With this technique, dynamic behavior of the TCSC are included in linear analysis of the power system. The studied power system is a simplified model of the TCSC compensated south-north link in Brazil. Comparisons between the linear and the instantaneous value model of the TCSC are performed. By using the linear model, simulations can be done much faster (the computing time is reduced) and still includes the dominant behavior of the TCSC.

  • 230.
    Persson, Jonas
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Slootweg, J. G.
    Rouco, L.
    Kling, W. L.
    A comparison of eigenvalues obtained with two dynamic simulation software packages2003In: 2003 IEEE Bologna Power Tech Conference Proceedings, IEEE , 2003, Vol. 2Conference paper (Refereed)
    Abstract [en]

    Eigenvalues of a power system give a good picture of the stability in the current operating point. In this paper the linear analysis capabilities of two software packages are evaluated and compared. It is shown in which way the linearization method influences the results, i.e., the location of the obtained eigenvalues in the complex plane. Further, the paper illustrates the impact of the models of the power system components (such as generators) on the location of the eigenvalues. The conclusions drawn from eigenvalue analysis are thus not only dependent on the properties of the investigated system, but also on the software package which is used, as well as on how the components of the power system are modeled. Therefore, conclusions can differ when studying the same power system with different software packages.

  • 231.
    Picciariello, Angela
    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.
    Impact of Network Regulation on the Incentive for DG Integration for the DSO: Opportunities for a Transition Toward a Smart Grid2015In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 6, no 4, p. 1730-1739Article in journal (Refereed)
    Abstract [en]

    The integration of distributed generation (DG) in distribution grids is one of the pillars of smart grid deployment. However, an increasing amount of DG connected to distribution grids is likely to affect the operation of the grids themselves, e.g., changing the magnitude, and in some cases the direction, of power flows. In order to perform the transition to a smart grid, it is therefore essential to have the distribution system operators (DSOs) involved in the process. However, being that the DSOs' business is controlled by regulators, regulation has a fundamental impact on the speed and the actual performance of DSOs' involvement in the transition toward a smart grid. Therefore, a method is needed to assess network regulation impact on DSOs' incentive to integrate DG into their grids. This paper proposes a new method for the calculation of such incentive, and the method has been applied on a case study to the Portuguese, Danish, and Swedish regulations for different scenarios of DG penetration. The focus is on DSOs' operational costs and revenues. The analyses indicate that DG has a different impact on DSOs business, depending on the different regulations, the most relevant aspects being the structure of customer tariffs and the regulatory treatment of network losses.

  • 232.
    Picciariello, Angela
    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.
    Incentive from network regulation for distribution system operators to integrate distributed generation: The Portuguese case2013In: European Energy Market (EEM), 2013 10th International Conference on the, IEEE , 2013, p. 6607376-Conference paper (Refereed)
    Abstract [en]

    Increasing amount of distributed generation (DG) connected to distribution grids is likely to affect the operation of the grids themselves, for example by changing the magnitude and, in some cases also the directions, of the power flows in the networks. This can have different economic consequences on the Distribution System Operators (DSOs) depending on the different enforced network regulations. This paper proposes a method for how to calculate the incentive for DSOs to integrate DG into their grids. The calculation of this incentive is carried out for the Portuguese case. Only the operational aspects are considered to calculate costs and benefits for the DSO, including network tariffs, ancillary services costs, Operation and Maintenance (O&M) costs, and economic treatment of losses. The IEEE 34 Node Test Feeder is used to perform power flow analyses under different scenarios of DG penetration. The analysis shows that the Portuguese DSO would have an incentive to integrate a low level of DG penetration; in case of a higher level of DG penetration, however, this incentive would turn into a small disadvantage for the DSO. In both cases, the regulatory treatment of network losses turns out to be the relevant factor to determine such a result.

  • 233.
    Picciariello, Angela
    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.
    State-of-art review on regulation for distributed generation integration in distribution systems2012Conference paper (Refereed)
    Abstract [en]

    Integration of distributed generation (DG) into distribution networks may affect many different factors, such as network reliability, voltage quality and network planning. Network regulation, therefore, is needed to provide the distribution system operators (DSOs) with fair business, meanwhile protecting the consumers and producers from any potential exploitation by the DSOs because of their monopoly situation. EU Member States have implemented different regulations, but there is no consensus yet as to what is the most appropriate mechanism for a successful and efficient integration of DG in distribution grids. This paper reviews the state-of-art of the regulatory frameworks for the integration of DG in some EU countries, and methods to model the regulation impact on DG integration in distribution systems. For each regulatory scheme, the main critical issues concerning DG integration are identified.

  • 234.
    Picciariello, Angela
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Lindfeldt, Erik
    Vattenfall, Sweden .
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Distributed generation exemption from network tariffs: general implications and analysis of a case study2015Conference paper (Refereed)
  • 235.
    Picciariello, Angela
    et al.
    KTH, School of Electrical Engineering (EES).
    Reneses, Javier
    KTH, School of Electrical Engineering (EES).
    Frias, P.
    KTH, School of Electrical Engineering (EES).
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Distributed generation and distribution pricing: Why do we need new tariff design methodologies?2015In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 119, p. 370-376Article, review/survey (Refereed)
    Abstract [en]

    Due to the increasing amount of DG (distributed generation) in distribution grids, new challenges are arising in the distribution sector in many countries. Depending on the DG penetration, location, concentration, size and generation technology, the DG impact on network costs can be either negative or positive. These additional costs or benefits can be allocated to the DG owners through network tariffs. New cost allocation methodologies, based on a cost causation principle, are therefore required. This paper addresses several issues arising within network tariff design due to the integration of DG. Furthermore, it reviews the methodologies proposed so far to tackle those issues. Recommendations for setting up a new, cost causation-based, methodology are finally drawn.

  • 236.
    Picciariello, Angela
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Vergara, Claudio
    Reneses, Javier
    Frías, Pablo
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Electricity distribution tariffs and distributed generation: quantifying cross-subsidies from consumers to prosumers2015In: Utilities Policy, ISSN 0957-1787, E-ISSN 1878-4356, Vol. 37, p. 23-33Article in journal (Refereed)
    Abstract [en]

    An increasing amount of distributed generation (DG) can cause an increase or a decrease on distribution network costs. Tariff design is the main tool for allocating these costs to customers who own and operate DG resources. Currently, however, either DG units are exempt from paying distribution tariffs or they are subject to tariffs originally designed according to a traditional pricing model without DG in the grids, also known as load-based pricing. Partial recovery of the allowed distribution company revenue requirements or cross-subsidies between customers may ensue from such tariff arrangements. In this article, pricing, as represented by a combination of net metering and pure volumetric tariffs, is applied in the context of increasing DG. The paper presents a methodology where a Reference Network Model (RNM) is used to investigate the effect of this pricing scheme on the magnitude of cross-subsidies from consumers towards the so-called prosumers for a set of twelve simulations based on real-size networks in the U.S.For the considered scenarios, the analysis reveals substantial cross-subsidies from consumers toward prosumers. The degree of subsidy varies with the amount of DG connected to the grid and network characteristics. The rate of cross-subsidy tends to be higher for low-density grids. This paper contributes to the net metering literature with a quantitative assessment of cross-subsidies by comparing allocated payments to different actors with the costs they impose on the system, estimated through an RNM. Moreover, the paper proposed a tariff structure based on cost causality by proposing a cost-reflective, volumetric tariff approach through which aggregate load-driven and DG-driven network costs are accordingly allocated to loads and DG units.

  • 237.
    Ren, Guorui
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. Harbin Institute of Technology, Harbin, Heilongjiang, China.
    Wan, J.
    Liu, J.
    Yu, D.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Analysis of wind power intermittency based on historical wind power data2018In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 150, p. 482-492Article in journal (Refereed)
    Abstract [en]

    As wind power provides an increasingly larger share of electricity supply, the challenges caused by wind power intermittency have become more and more prominent. A better understanding of wind power intermittency would contribute to mitigate it effectively. In the present study, the definition of wind power intermittency is given firstly. Based on the definition, wind power intermittency is quantified by duty ratio of wind power ramp (DRWPR). This index provides system operators quantitative insights into wind power intermittency. Furthermore, some characteristics of wind power intermittency can be extracted by the index, such as the differences between wind speed intermittency and wind power intermittency, the differences of wind power intermittency between different scales and so on. The wind power intermittency of a Chinese wind farm is studied in detail based on the proposed index and historical data.

  • 238.
    Risberg, Daniel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hydro Power Equivalents of Complex River Systems2017In: 2017 IEEE Manchester PowerTech, Powertech 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7981057Conference paper (Refereed)
    Abstract [en]

    When a hydro power producer wants to plan the production for the next day in an optimal way a precise and detailed model is needed. But when using this model to plan for a longer period of time the computational complexity increases. To overcome this problem there is a need to do a model reduction of the original system into a smaller equivalent system with almost the same properties. This paper compares the performance and computation time of different setups in the equivalent representation of the original hydro power system. This includes different setups in both topology and the piecewise linear production equivalents. It is tested independently on two rivers with 21 and 28 stations respectively and also for the case if both of these rivers were to represented by one equivalent system. The performance is evaluated with respect to error in production and computation time. It is shown that with model reduction the relative error lies between 11.5 and 5.1 percent of installed capacity and the computation time is then reduced by 99.3 and 92.5 percent respectively.

  • 239.
    Rosenlind, Johanna
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edström, Fredrik
    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 Process2013In: 2013 IEEE Power And Energy Society General Meeting (PES), IEEE , 2013Conference paper (Refereed)
  • 240.
    Rosenlind, Johanna
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edström, Fredrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On optimal transformer capacity ratingManuscript (preprint) (Other academic)
  • 241.
    Rosenlind, Johanna
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Setréus, Johan
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Reliability screening for identifying critical power transformers in real size transmission systemManuscript (preprint) (Other academic)
  • 242.
    Salomonsson, Daniel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Comparison of different solutions for emergency and standby power systems for commercial consumers2006In: INTELEC 2006: 28th Annual International Telecommunications Energy Conference, 2006Conference paper (Refereed)
    Abstract [en]

    In this paper a new improved method to evaluate the design of commercial power systems is described. The power system is divided into seven design criteria and each criterion Is evaluated separately. The aim with the method is to identify problems with the present design which can be modified to improve the performance of the system. The method is applied to four sensitive commercial consumers: substation; hospital; voice and data communication facility; and data center. They are all equipped with emergency and standby power systems. Different requirements and solutions for each systems are analyzed and presented. The study shows that the voice and data communication facility and especially the data center both have possibilities of improvements. The data center power systems has a potential to improve the efficiency, and therefore also to reduce the energy cost, improve the availability, and to use the local energy source and energy storage to sell power to the utility grid during peak load.

  • 243.
    Salomonsson, Daniel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Sannino, Ambra
    An Adaptive Control System for a dc Microgrid for Data Centers2007In: CONFERENCE RECORD OF THE 2007 IEEE INDUSTRY APPLICATIONS CONFERENCE FORTY-SECOND IAS ANNUAL MEETING, 2007, p. 2414-2421Conference paper (Refereed)
    Abstract [en]

    In this paper, an adaptive control system for a de microgrid for data centers is proposed. Data centers call For electric power with high availability and a possibility to reduce the electric losses and hence the need for cooling. By using local energy sources, high reliability can be achieved, and by using dc the number of conversion steps, and therefore also the losses, can be reduced. The dc microgrid can also be used to supply closely located sensitive ac loads during outages on the utility grid. The proposed dc microgrid can be operated in eight different operation modes described here, resulting in 23 transitions. The adaptive control system coordinates the control of converters, sources and switches used in the dc microgrid. The adaptive control system is tested in the simulation software packages PSCAD/EMTDC, and the results of the most interesting operation modes and transitions are presented. The results show that it is possible to use the proposed dc microgrid to supply sensitive electronic loads, and also during utility grid outages, supply closely located sensitive ac loads. To reduce transients in the voltage experienced by the sensitive ac loads, the dc microgrid requires fast utility outage detection and fast switches.

  • 244.
    Salomonsson, Daniel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Sannino, Ambra
    Power Technologies Division, ABB Corporate Research.
    An adaptive control system for a dc microgrid for data centers2008In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 44, no 6, p. 1910-1917Article in journal (Refereed)
    Abstract [en]

    In this paper, an adaptive control system for a dc microgrid for data centers is proposed. Data centers call for electric power with high availability, and a possibility to reduce the electric losses and, consequently, the need for cooling. High reliability can be achieved by using local energy sources, and by using a dc power system, the number of conversion steps, and therefore also the losses, can be reduced. The dc microgrid can also supply closely located sensitive ac loads during outages in the ac grid. The proposed dc microgrid can be operated in eight different operation modes described here, resulting in 23 transitions. The control system coordinates the operation of converters, sources, and switches used in the dc microgrid. The control system is tested in the simulation software package PSCAD/EMTDC, and the results of the most interesting transitions are presented. The results show that it is possible to use the proposed dc microgrid to supply sensitive electronic loads and also, during ac-grid outages, supply closely located sensitive ac loads. To reduce the current transients experienced by grid-connected ac/dc converters, fast grid-outage detection and fast switches are required.

  • 245.
    Salomonsson, Daniel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Sannino, Ambra
    ABB Corporate Research, Power Technologies, Västerås .
    Protection of low-voltage dc microgrids2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 3, p. 1045-1053Article in journal (Refereed)
    Abstract [en]

    In this paper, a low-voltage (LV) dc microgrid protection system design is proposed. The LV de microgrid is used to interconnect distributed resources and sensitive electronic loads. When designing an LV de microgrid protection system, knowledge from existing dc power systems can be used. However, in most cases, these systems use grid-connected rectifiers with current-limiting capability during dc faults. In contrast, an LV dc microgrid must be connected to an ac grid through converters with bidirectional power flow and, therefore, a different protection-system design is needed. In this paper, the operating principles and technical data of LV dc protection devices, both available and in the research stage, are presented. Furthermore, different fault-detection and grounding methods are discussed. The influence of the selected protection devices and grounding method on an LV dc microgrid is studied through simulations. The results show that it is possible to use available devices to protect such a system. Problems may arise with high-impedance ground faults which can be difficult to detect.

  • 246.
    Samadi, Afshin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Jose, Della
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Mahmood, Farhan
    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.
    Comparison of a Three-Phase Single-Stage PV System in PSCAD and PowerFactory2012In: Proceedings of the 2nd International Workshop on Integration of Solar Power into Power Systems, Energynautics GmbH , 2012, p. 237-244Conference paper (Refereed)
  • 247.
    Samadi, Afshin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Evaluation of Reactive Power Support Interactions Among PV Systems Using Sensitivity Analysis2012In: 2nd International Workshop on Integration of Solar Power into Power Systems, 2012, p. 245-252Conference paper (Refereed)
  • 248.
    Samadi, Afshin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rawn, Barry
    Boemer, Jens C.
    Coordinated Active Power-Dependent Voltage Regulation in Distribution Grids With PV Systems2014In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 29, no 3, p. 1454-1464Article in journal (Refereed)
    Abstract [en]

    High penetrations of photovoltaic (PV) systems in distribution grids have brought about new challenges such as reverse power flow and voltage rise. One of the proposed remedies for voltage rise is reactive power contribution by PV systems. Recent German Grid Codes (GGC) introduce an active power dependent (APD) standard characteristic curve, Q(P), for inverter-coupled distributed generators. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to locally and systematically develop a coordinated Q(P) characteristic for each PV system along a feeder. The main aim of this paper is to evaluate the technical performance of different aspects of proposed Q(P) characteristics. In fact, the proposed method is a systematic approach to set parameters in the GGC Q(P) characteristic. In the proposed APD method the reactive power is determined based on the local feed-in active power of each PV system. However, the local voltage is also indirectly taken into account. Therefore, this method regulates the voltage in order to keep it under the upper steady-state voltage limit. Moreover, several variants of the proposed method are considered and implemented in a simple grid and a complex utility grid. The results demonstrate the voltage-regulation advantages of the proposed method in contrast to the GGC standard characteristic.

  • 249.
    Samadi, Afshin
    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.
    Reactive Power Dynamic Assessment of a PV System in a Distribution Grid2012In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 20, p. 98-107Article in journal (Refereed)
    Abstract [en]

    Accommodating more and more PV systems in grids has raised new challenges that formerly had not been considered and addressed in standards. According to recently under-discussed standards, each PV unit is allowed to participate in reactive power contributions to the grid to assist voltage control. There are some PV models in the literature however those models mostly assumed unity power factor operation for PV systems owing to the contemporary standards. Therefore, there is a need to develop a PV model considering the reactive power contribution and its dynamic influence on power system. This paper describes non-proprietary modeling of a three-phase, single stage PV system consisting of controller scheme design procedure and coping with the important aspects of three different reactive power regulation strategies and their impact assessment studies. The model is implemented in PSCAD to examine the behavior of the proposed model for recently codified reactive power strategies. Furthermore, this model is integrated in a distribution grid with two PV systems in order to effectively investigate consequences of the different reactive power control strategies on the distribution network.

  • 250.
    Samadi, Afshin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rawn, Barry
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems2014In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 71, p. 315-323Article in journal (Refereed)
    Abstract [en]

    High penetrations of photovoltaic (PV) systems in distribution grids have caused new challenges such as reverse power flow and voltage rise. Reactive power contribution by PV systems has been proposed by grid codes and literature as one of the remedies for voltage profile violation. Recent German Grid Codes (GGC), for instance, introduce a standard active power dependent reactive power characteristic, Q(P), for inverter-coupled distributed generators. Nevertheless, the GGC recommends a voltage dependent reactive power characteristic Q(V) for the near future, recognizing that the Q(P) characteristic cannot explicitly address voltage limits. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to develop a coordinated Q(V) characteristic for each PV system along a radial feeder using only the local measurement and drooping technique concepts. The aim of this paper is using a multi-objective design to adjust the parameters of the Q(V) characteristic in the proposed droop-based voltage regulation in order to minimize the reactive power consumption and line losses. On the other hand, it is also possible to adjust the parameters in order to reach equal reactive power sharing among all PV systems. A radial test distribution grid, which consist of five PV systems, is used to calculate power flow and, in turn, the voltage sensitivity matrix. The comparison of results demonstrates that both approaches in the proposed droop-based voltage regulation can successfully regulate the voltage to the steady-state limit. Moreover, it is shown that the profile of reactive power consumption and line losses are considerably reduced by the multi-objective design.

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