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• 1.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Impact of Reward and Penalty Scheme on the Incentives for Distribution System Reliability2014In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 29, no 1, p. 386-394Article in journal (Refereed)

Performance-based regulations accompanied by quality regulations are gaining ground in the electricity distribution business. Several European countries apply quality regulations with reward and penalty schemes (RPSs), where the distribution system operator (DSO) is rewarded (or penalized) when fulfilling (or not fulfilling) an adequate level of reliability to its customers. This paper develops a method that the regulator can use before enforcing a regulation to get an understanding of the impact different RPS design solutions have on the DSO's financial risk and incentives to invest in reliability. The proposed method also includes a sensitivity analysis to identify which are the most important parameters in an RPS. The new method is applied to three regulatory challenges to evaluate their RPS design solutions. Results show that the choice of scheme design and cost model used to decide the incentive rate have a large impact on the DSO's financial risk and incentive to invest.

• 2.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
An Evaluation of Intraday Trading and Demand Response for a Predominantly Hydro-Wind System Under Nordic Market Rules2015In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 30, no 1, p. 3-12Article in journal (Refereed)

Many countries are planning for a large-scale expansion of wind power. This development will have a significant impact on power system operation and economics. One of the challenges is that the difficulty to forecast wind power generation will increase the need for real-time balancing. This paper presents a study of how the impact of wind power forecast errors can be reduced by changes in the market design. The study is based on the conditions in the Nordic electricity market. A characteristic of this market is that there is a large share of flexible hydro generation; hence, ramp and unit commitment constraints rarely constrain dispatch. The need for regulation during real-time is provided in a voluntary real-time balancing market, where players can be compensated for their redispatch costs. Case studies are presented which show that a shift from day-ahead to intraday trading and increased demand response can improve the performance when the share of wind power is increasing.

• 3.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Comparison of Capacity Credit Calculation Methods for Conventional Power Plants and Wind Power2009In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 24, no 2, p. 685-691Article in journal (Refereed)

Several methods for computing capacity credit values of power plants have been presented over the years. This paper uses an empirical approach to investigate and compare different properties of four typical capacity credit definitions. It is shown that the choice of definition indeed can have a significant impact on the results. Concerning three of the analyzed methods, it is found that important factors that influence the capacity credit are the overall generation adequacy and the penetration factor of the power plant; this means that the same generating unit will generally have a higher capacity credit if added to a system with high loss of load probability, and the unit will have a higher capacity credit if its installed capacity is small compared to the total installed capacity of the system. The results of the fourth method only depend on the size and availability of the generating units.

• 4.
KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
Distributed Frequency Control Through MTDC Transmission Systems2017In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 32, no 1, p. 250-260, article id 7456314Article in journal (Refereed)

In this paper, we propose distributed dynamic controllers for sharing both frequency containment and restoration reserves of asynchronous ac systems connected through a multi-terminal HVDC (MTDC) grid. The communication structure of the controller is distributed in the sense that only local and neighboring state information is needed, rather than the complete state. We derive sufficient stability conditions, which guarantee that the ac frequencies converge to the nominal frequency. Simultaneously, a global quadratic power generation cost function is minimized. The proposed controller also regulates the voltages of the MTDC grid, asymptotically minimizing a quadratic cost function of the deviations from the nominal dc voltages. The results are valid for distributed cable models of the HVDC grid (e.g., $\pi$-links), as well as ac systems of arbitrary number of synchronous machines, each modeled by the swing equation. We also propose a decentralized communication-free version of the controller. The proposed controllers are tested on a high-order dynamic model of a power system consisting of asynchronous ac grids, modeled as IEEE 14 bus networks, connected through a six-terminal HVDC grid. The performance of the controller is successfully evaluated through simulation. © 1969-2012 IEEE.

• 5.
KU Leuven.
KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF. KU Leuven.
A Quantitative Method to Determine ICT Delay Requirements for Wide-Area Power System Damping Controllers2015In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, ISSN 0885-8950, Vol. 30, no 4, p. 2023-2030Article in journal (Refereed)

This paper presents a quantitative method to determine delay requirements of the information and communication technology (ICT) system supporting wide-area power oscillation damping (WAPOD) controllers. An allowable time delay for the ICT infrastructure named “equivalent time delay (ETD)” is defined. The ETD is calculated by numerically comparing the damping behavior of the system when local input signals (LI) and remote input signals (RI) are used in the damping controller. The use of a WAPOD is only justified when its response outperforms that of a controller using local inputs. Therefore, the total time delay in the control loop must be below the calculated ETD. As such, the ETD serves as a design criteria to determine ICT latency requirements. The selection of an effective RI signal can be carried out by considering the maximum delays (ETDs) of different wide-area measurements. A damping improvement ETDx% has been proposed using the same methodology indicating a minimum outperformance of the remote signals. The proposed method is demonstrated using the well-known Klein-Rogers-Kundur multi-machine power system and the Vietnamese power system model.

• 6.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
A Multi-Option Unified Power Flow Approach for Hybrid AC/DC Grids Incorporating Multi-Terminal VSC-HVDC2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 3, p. 2376-2383Article in journal (Refereed)

This paper proposes a multi-option power flow approach for hybrid AC/DC grids. A unified AC-DC unit is introduced which can be used in two different cases: case a) AC grids with embedded VSC-based MTDC grids, and case b) asynchronous AC grids connected via a common VSC-based MTDC grid. In the proposed method for each MTDC grid (regardless of the number of converters), a new state variable is introduced to handle any kind of converter loss models. For the case (b), the AC-DC unit can be used in two different analyses, namely, a1) the separated analysis and a2) the integrated analysis. Both a1) and a2) can be used in the practical analysis of the real-size power systems. However, it is shown that the separated analysis not only offers a shorter computational time but it is also very suitable for the future connection between large existing AC systems and other AC systems or remote renewable energy sources through the DC grids. The proposed methodology is implemented in MATLAB software and verified using commercial software SIMPOW.

• 7.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Transmission Loss Minimisation in Power Systems with Embedded Smart-Grid Technologies2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679Article in journal (Other academic)
• 8.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems. KTH, School of Electrical Engineering (EES), Electric Power Systems.
Second-order cone programming for optimal power flow in VSC-type AC-DC grids2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 4, p. 4282-4291Article in journal (Refereed)

This paper presents a second order cone programming (SOCP) formulation of the optimal power flow problem for AC-DC systems with voltage source converter (VSC) technology. Approximation techniques have been used to derive the SOCP formulation of the AC-DC OPF problem. Later, the SOCP formulation can be solved using the interior point method (IPM) by considering the limits on AC-DC grid. The accuracy of SOCP formulation of AC OPF has been proven with numerical examples using IEEE 14-bus, IEEE 30-bus, and IEEE 57-bus example systems. The results of the SOCP formulation are compared with available commercial software. Then a DC system with VSC technology is modeled in the IEEE 30-bus example system. The SOCP formulation of AC-DC OPF is applied to the modified IEEE 30-bus example system and the results are discussed. The limitations of derived SOCP formulation are also discussed.

• 9.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
AC Power Flow Representation in Conic Format2015In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 30, no 1, p. 546-547Article in journal (Refereed)

This letter presents a second-order cone formulation for AC power flow problem. The power flow equations are first derived as functions of more practical variables of power systems and then placed in a second-order cone programming (SOCP) problem. The proposed conic power flow (CPF) model can be solved efficiently through IPMs, and at the same time, it has a very good accuracy as compared to the full AC power flow model. Also, the proposed CPF can efficiently handle the ill-conditioned networks. The numerical efficiency and good accuracy of the model are shown by simulating various case studies.

• 10.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
A reliability-centered asset maintenance method for assessing the impact of maintenance in power distribution systems2005In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 20, no 1, p. 75-82Article in journal (Refereed)

This paper proposes a method for comparing the effect of different maintenance strategies on system reliability and cost. This method relates reliability theory with the experience gained from statistics and practical knowledge of component failures and maintenance measures. The approach has been applied to rural and urban distribution systems. In particular, a functional relationship between failure rate and maintenance measures has been developed for a cable component. The results show the value of using a systematic quantitative approach for investigating the effect of different maintenance strategies.

• 11.
KTH, School of Electrical Engineering (EES), Electric power and energy systems.
KTH, School of Electrical Engineering (EES), Electric power and energy systems. KTH.
Power System Stability Analysis Using Feedback Control System Modeling Including HVDC Transmission Links2016In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 31, no 1, p. 116-124Article in journal (Refereed)

A general platform is introduced to study the dynamics of power systems with high voltage dc (HVDC) transmission links. Small-signal stability, voltage stability, and interaction phenomena of power systems with both line-commutated-converter HVDC (LCC-HVDC) and voltage-source-converter HVDC (VSC-HVDC) are addressed using the proposed platform. In this platform, the entire power system is modeled as a multivariable feedback control system (FCS) which consists of three interconnected blocks. The contents as well as the inputs and outputs of the blocks are selected such that the conventional analysis tools for power system stability are applicable, both in the time and frequency domains. In the FCS model, the relationships between different instabilities are clear, and participant agents of each instability can be determined. The model is developed in a modular and hybrid style, to make it feasible for a large power system. The proposed model is validated against an electromagnetic transient simulation program (PSCAD) using time responses.

• 12. Billinton, R.
KTH, Superseded Departments, Electric Power Systems.
Bibliography on the application of probability methods in power system reliability evaluation 1996-19992001In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 16, no 4, p. 595-602Article in journal (Refereed)

This paper presents a bibliography of papers on the subject of power system reliability evaluation. Papers in such areas as: probabilistic load flow, probabilistic production costing, probabilistic transient stability evaluation etc. have not been included except where they specifically address power system reliability evaluation. It includes material which has been made available since the publication of six previous papers Bibliography on the Application of Probability Methods in Power System Reliability Evaluation, IEEE Transactions on Power Apparatus and Systems PAS-91, 1972, pp. 649-660, Pas-97, 1978, pp. 2235-2242, PAS-103, 1984, pp. 275-282, IEEE Transactions on Power Systems, Vol. 3, no. 4, Nov. 1988, pp. 1555-1564, Vol. 9, No. 1, Feb. 1994, pp. 41-49, and Vol. 14, no. 1, Feb. 1999, pp. 51-57.

• 13.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes2019In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, no 2, p. 1095-1104Article in journal (Refereed)

This paper considers power oscillation damping (POD) using active power modulation of high-voltage dc transmissions. An analytical study of how the proximity between interarea modal frequencies in two interconnected asynchronous grids puts a fundamental limit to the achievable performance is presented. It is shown that the ratio between the modal frequencies is the sole factor determining the achievable nominal performance. To illustrate the inherent limitations, simulations using a proportional controller tuned to optimize performance in terms of POD are done on a simplified two-machine model. The influence of limited system information and unmodeled dynamics is shown. The analytical result is then further validated on a realistic model with two interconnected 32-bus networks.

• 14. Bompard, E.
KTH, Superseded Departments.
Congestion-management schemes: A comparative analysis under a unified framework2003In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 18, no 1, p. 346-352Article in journal (Refereed)

The restructuring of the electricity industry has spawned the introduction of new independent grid operators (IGOs), typically called transmission system operators (TSOs); independent system operator (ISOs); or regional transmission organizations (RTOs), in various parts of the world. An important task of an IGO is congestion management (CM) and pricing. This activity has significant economic implications on every. market participant in the IGO's region. The paper briefly reviews the CM schemes and the associated pricing mechanism used by the IGOs in five representative schemes. These were selected to illustrate the various CM approaches in use: England and Wales, Norway, Sweden, PJM, and California. We develop a unified framework for the mathematical representation of the market dispatch and redispatch problems that the IGO must solve in CM in these various jurisdictions. We use this unified framework to develop meaningful metrics to compare the various CM approaches so as to assess their efficiency and the effectiveness of the market signals provided to the market participants. We compare, using a small test system, side by side, the performance of these schemes.

• 15.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Estimation of hydropower system equivalentsIn: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679Article in journal (Refereed)
• 16.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Identification of power system dominant inter-area oscillation paths2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 3, p. 2798-2807Article in journal (Refereed)

This paper presents three algorithms for identification of dominant inter-area oscillation paths: a series of interconnected corridors in which the highest content of the inter-area modes propagates through. The algorithms are developed to treat different sets of data: 1) known system model; 2) transient; and 3) ambient measurements from phasor measurement units (PMUs). These algorithms take feasibility into consideration by associating the network variables made available by PMUs, i.e., voltage and current phasors. All algorithms are demonstrated and implemented on a conceptualized Nordic Grid model. The results and comparison among three algorithms are provided. The applications of the algorithms not only facilitate in revealing critical corridors which are mostly stressed but also help in indicating relevant feedback input signals and inputs to mode meters which can be determined from the properties of dominant paths.

• 17. Chow, J. H.
Estimation of Radial Power System Transfer Path Dynamic Parameters Using Synchronized Phasor Data2008In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 23, no 2, p. 564-571Article in journal (Refereed)

This paper develops a measurement-based method for estimating a two-machine reduced model to represent the interarea dynamics of a radial, multimachine power system. The method uses synchronized bus voltage phasor measurements at two buses and the line current on the power transfer path. The innovation is the application of the interarea oscillation components in the voltage variables resulting from disturbances for extrapolating system impedances and inertias beyond the measured buses. Expressions for the amplitudes of the bus voltage and bus frequency oscillations as functions of the location on the transmission path are derived from a small-signal perturbation approach. The reduced model provides approximate response to disturbances on the transfer path and offers an alternative to model reduction techniques based on detailed system models and data.

• 18. Enyioha, Chinwendu
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH - Royal Institute of Technology. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
On Variability of Renewable Energy and Online Power Allocation2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 1, p. 451-462Article in journal (Refereed)

As electric power system operators shift from conventional energy to renewable energy sources, power distribution systems will experience increasing fluctuations in supply. These fluctuations present the need to not only design online decentralized power allocation algorithms, but also characterize how effective they are given fast-changing consumer demand and generation. In this paper, we present an online decentralized dual descent (OD3) power allocation algorithm and determine (in the worst case) how much of observed social welfare can be explained by fluctuations in generation capacity and consumer demand. Convergence properties and performance guarantees of the OD3 algorithm are analyzed by characterizing the difference between the online decision and the optimal decision. We demonstrate validity and accuracy of the theoretical results in the paper through numerical experiments using real power generation data.

• 19.
KTH, Superseded Departments, Electrical Systems.
Control Lyapunov functions for Controllable Series Devices2001In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 16, no 4, p. 689-694Article in journal (Refereed)

Controllable Series Devices (CSD), i.e., series-connected Flexible AC Transmission Systems (FACTS) devices, such as Unified Power Controller (UPFC), Controllable Series Capacitor (CSC) and Quadrature Boosting Transformer (QBT) with a suitable control scheme can improve transient stability and help to damp electromechanical oscillations. For these devices, a general model, which is referred to as injection model, is used. This model is valid for load flow and angle stability analysis and is helpful for understanding the impact of the CSD on power system stability. Also, based on Lyapunov theory a control strategy for damping of electromechanical power oscillations in a multi-machine power system Is derived. Lyapunov theory deals with dynamical systems without inputs. For this reason, it has traditionally been applied only to closed-loop control systems, that is, systems for which the input has been eliminated through the substitution of a predetermined feedback control. However, in this paper, we use Lyapunov function candidates in feedback design itself by making the l.yapunov derivative negative when choosing the control. This control strategy is called Control Lyapunov Function (CLF) for systems with control inputs.

• 20.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems. 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)

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.

• 21.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems. 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)

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.

• 22.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Transmission augmentation with mathematical modeling of market power and strategic generation expansion - Part I2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, ISSN 0885-8950, Vol. 26, no 4, p. 2040-2048Article in journal (Refereed)

This paper proposes a new mathematical structure for evaluating the economic efficiency of transmission investment in a liberalized electricity market. The problem faced by a transmission planner is modeled using the concept of social welfare from economics. The behavior of generators is modeled as the Nash equilibrium of a strategic game. The Nash solution concept is reformulated as an optimization problem and a new concept - the Stackelberg-Worst Nash equilibrium - is introduced to resolve the problem of multiple equilibria. The proposed structure can take into account the effects of a transmission augmentation on both market power and strategic generation investment. Accordingly, the optimal solution to the transmission planner's problem may allow additional transmission capacity both to reduce market power and to defer investment in the generation sector. A methodology is proposed to decompose the benefits of a transmission augmentation policy into the efficiency benefit, competition benefit, and the deferral benefit. The outcomes of the proposed approach to transmission augmentation are compared with the outcomes of two other approaches to transmission augmentation using a simple three-bus network example.

• 23.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Transmission augmentation with mathematical modeling of market power and strategic generation expansion - Part II2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, ISSN 0885-8950, Vol. 26, no 4, p. 2049-2057Article in journal (Refereed)

This paper describes a numerical approach to solving the mathematical structure proposed in the first part of this paper. The numerical approach employs a standard genetic algorithm (GA) embedded with an island parallel genetic algorithm (IPGA). The GA handles the decision variables of the transmission network service provider, (TNSP) while the IPGA module finds the equilibrium of the electricity market. The IPGA module uses the concept of parallel islands with limited communication. The islands evolve in parallel and communicate with each other at a specific rate and frequency. The communication pattern helps the IPGA module to spread the best-found genes across all isolated islands. The isolated evolution removes the fitness pressure of the already-found optima from the chromosomes in other islands. A stability operator has been developed which detects stabilized islands and through a strong mutation process re-employs them in exploring the search space. To improve the efficiency of the proposed numerical solution, two high performance computing (HPC) techniques are used - shared-memory architecture and distributed-memory architecture. The application of the proposed approach to the assessment of transmission augmentation is illustrated using an IEEE 14-bus example system.

• 24.
Swinburne University of Technology, Australia.
Transmission System Augmentation Based on the Concepts of Quantity Withheld and Monopoly Rent for Reducing Market Power2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, ISSN 0885-8950, Vol. 25, no 1, p. 167-180Article in journal (Refereed)

This paper proposes two mathematical structures for considering the market power effect of transmission capacity in transmission augmentation assessment. These mathematical structures use the concepts of monopoly rent and quantity withheld in economics for market power modeling in the assessment process of transmission augmentation. The simultaneous-move and sequential-move games in applied mathematics are used to model the interactions of the transmission network service provider, generating companies, and the market management company in the proposed mathematical structures. The solution concept of Nash equilibria is reformulated as an optimization problem, and the multiple Nash equilibria is tackled through an introduced concept termed worst Nash equilibrium. A numerical solution is developed to solve the proposed mathematical structures. The numerical solution is an island parallel genetic algorithm nested in a standard genetic algorithm. The six-bus Garver's example system and the IEEE 14-bus test system are modified and studied. The results prove the strong mechanism of the developed structures for modeling the market power effect of transmission capacity in the assessment of transmission augmentation.

• 25.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Computation of extremal-nash equilibria in a wholesale power market using a single-stage MILP2012In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 27, no 3, p. 1706-1707Article in journal (Refereed)

This letter proposes a new approach to the computation of extremal-Nash equilibria in a wholesale power market with transmission constraints. The approach uses linearization techniques to formulate the extremal-Nash equilibrium problem as a single-stage mixed-integer linear programming problem which can be solved with standard software. Through the introduced concept of extremal-Nash equilibria, the derived structure can efficiently locate all Nash equilibria of the game. We show that this approach offers significant performance improvements over existing approaches to computing Nash equilibria.

• 26.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Merger Analysis in Wholesale Power Markets Using the Equilibria-Band Methodology2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 2, p. 819-827Article in journal (Refereed)

Around the world, electricity market regulators and competition authorities are struggling to find ways to reliably assess the likely market impact of mergers of generators. Conventional indicators of market power fail to capture key aspects of the exercise of market power in wholesale electricity markets. On the other hand, full-scale computation of Nash equilibria has historically been time consuming, non-transparent, and typically results in multiple Nash equilibria. In this paper we propose two methodological advances: an efficient approach to computing extremal-Nash equilibria in a wholesale power market with market power and the application of this approach in the assessment of wholesale market mergers. The extremal-Nash equilibria are those equilibria which have the highest or the lowest social cost to the society. The resulting formulation is a Mixed Integer Linear Program which efficiently finds the full set of extremal-Nash equilibria. The continuum of these extremal-Nash equilibria over a range of demand conditions describes the upper and lower envelopes of the Equilibria Band. To illustrate the advantages of the proposed approach, two case studies are explored, involving the New South Wales region of the Australian National Electricity Market, on the one hand, and the IEEE 14-Bus Test System, on the other.

• 27.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Transmission Capacity Expansion in Imperfectly Competitive Power Markets2014In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 29, no 1, p. 62-71Article in journal (Refereed)

This paper proposes a mathematical model for transmission planning in an environment where there is imperfect competition in electricity supply industry. The model is developed based on the concept of the leader-followers game in applied mathematics. The leader of the game is the transmission planner and the followers are the strategic electricity producing firms. The reaction of the strategic electricity producing firms to the transmission planning decision is modeled using the introduced concept of the worst-Cournot-Nash equilibrium. The worst-Cournot-Nash equilibrium can handle the multiple Nash equilibria problem. The whole mathematical formulation is a bilevel mixed-integer linear programming problem. This formulation is achieved using the Karush-Kuhn-Tucker optimality conditions and a binary mapping approach. The application of the proposed approach to the three-node example system and the modified six-node Garver's example system are studied. The transmission planning with perfect competition is formulated and used as the benchmark. The numerical results show that the proposed approach in this paper can efficiently allocate the additional transmission capacity to the transmission grid such that it reduces the market power cost in the electricity supply industry. However, further studies should be carried out to scale up the proposed approach to the larger case studies.

• 28.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Faculty of Engineering, University of Porto. Faculty of Engineering, University of Porto. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Multiobjective Optimization Applied to Maintenance Policy for Electrical Networks2007In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 22, no 4, p. 1675-1682Article in journal (Refereed)

A major goal for managers of electric power networks is maximum asset performance. Minimal life cycle cost and maintenance optimization becomes crucial in reaching this goal, while meeting demands from customers and regulators. This necessitates the determination of the optimal balance between preventive and corrective maintenance in order to obtain the lowest total cost.

The approach of this paper is to study the problem of balance between preventive and corrective maintenance as a multiobjective optimization problem, with customer interruptions on one hand and the maintenance budget of the network operator on the other. The problem is solved with meta-heuristics developed for the specific problem, in conjunction with an evolutionary particle swarm optimization algorithm.

The maintenance optimization is applied in a case study to an urban distribution system in Stockholm, Sweden. Despite a general decreased level of maintenance (lower total maintenance cost), better network performance can be offered to the customers. This is achieved by focusing the preventive maintenance on components with a high potential for improvements. Besides this, this paper displays the value of introducing more maintenance alternatives for every component and choosing the right level of maintenance for the components with respect to network performance.

• 29.
KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301). KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
Evaluating Strategies for Defending Electric Power Networks against Antagonistic Attacks2007In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 22, no 1, p. 76-84Article in journal (Refereed)

We show how concepts from game theory can be used to find and evaluate strategies for defending an electric power system against antagonistic attacks. Consequently, the interaction between the antagonist and the defender of the system is envisaged as a game. In a numerical example, we study the performance of different defense strategies against a number of attack scenarios. Particularly, we study whether there is a dominant defense strategy and an optimal allocation of resources between protection of components and recovery.

• 30.
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics. KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
A Comparison of Different Frequency Scanning Methods for Study of Subsynchronous Resonance2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 1, p. 356-363Article in journal (Refereed)

This paper compares four different methods for determining the electrical damping of a power system seen from one generator as a function of frequency. This information is useful when the risk for subsynchronous resonance (SSR) in the system is evaluated. The study compares one frequency scanning method which is implemented in a time-domain digital simulation program with three methods of different complexity based on analytical calculations. The time-domain simulation method is easily implemented with a detailed model of the power system including complex load and generator models, whereas the analytical methods are based on simpler models of the power system. The computational effort is much larger for the time-domain method than for the analytical methods. In the study, all methods were used to determine the damping characteristics of a four-machine power system in different configurations. The study shows that fast analytical methods may provide results which closely agree with the detailed method of time-domain simulation. However, the study also shows that the level of accuracy in the analytical model is very important.

• 31.
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics. KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
An Adaptive Controller for Power System Stability Improvement and Power Flow Control by Means of a Thyristor Switched Series Capacitor (TSSC)2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 1, p. 381-391Article in journal (Refereed)

In this paper, a controller for a thyristor switched series capacitor (TSSC) is presented. The controller aims to stabilize the power system by damping interarea power oscillations and by improving the transient stability of the system. In addition to this, a power flow control feature is included in the controller. The power oscillation damping controller is designed based on a nonlinear control law, while the transient stability improvement feature works in open loop. The damping controller is adaptive and estimates the power system parameters according to a simplified generic model of a two-area power system. It is designed for systems where one poorly damped dominant mode of power oscillation exists. In the paper, a verification of the controller by means of digital simulations of one two-area, four-machine power system, and one 23-machine power system is presented. The results show that the controller improves the stability of both test systems significantly in a number of fault cases at different levels of interarea power flow.

• 32.
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics. KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
An Adaptive Controller for Power System Stability Improvement and Power Flow Control by Means of a Thyristor Switched Series Capacitor (TSSC) (vol 25, pg 381, 2010)2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 2, p. 1200-1200Article in journal (Refereed)
• 33. Keane, A.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Capacity value of wind power2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 2, p. 564-572Article in journal (Refereed)

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

• 34.
KTH, Superseded Departments, Electrical Systems.
KTH, Superseded Departments, Electrical Systems.
On the parameter estimation and modeling of aggregate power system loads2004In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 19, no 2, p. 1023-1031Article in journal (Refereed)

This paper addressed some theoretical and practical issues relevant to the problem of Power system load modeling and identification. Two identification techniques are developed in the theoretical framework of stochastic system identification. The identification techniques presented in this paper belong to the family of output error models; both techniques are based on well-established equations describing load recovery mechanisms having a commonly recognized physical appeal. Numerical experiments with artificially created data were first performed on the proposed techniques and the estimates obtained proved to be asymptotically unbiased and achieved the corresponding Cramer-Rao lower bound. The proposed techniques were then tested using actual field measurements taken at a paper mill, and the corresponding results were used to validate a commonly used aggregate load model. The results reported in this paper indicate that the existing load models satisfactorily describe the actual behavior of the physical load and can be reliably estimated using the identification techniques presented herein.

KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Impact of Optimal Storage Allocation on Price Volatility in Energy-Only Electricity Markets2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 2, p. 1903-1914Article in journal (Refereed)

Recent studies show that the fast growing expansion of wind power generation may lead to extremely high levels of price volatility in wholesale electricity markets. Storage technologies, regardless of their specific forms, e.g., pump-storage hydro, large-scale, or distributed batteries, are capable of alleviating the extreme price volatility levels due to their energy usage time shifting, fast-ramping, and price arbitrage capabilities. In this paper, we propose a stochastic bilevel optimization model to find the optimal nodal storage capacities required to achieve a certain price volatility level in a highly volatile energy-only electricity market. The decision on storage capacities is made in the upper level problem and the operation of strategic/regulated generation, storage, and transmission players is modeled in the lower level problem using an extended stochastic (Bayesian) Cournot-based game. The South Australia (SA) electricity market, which has recently experienced high levels of price volatility, and a 30-bus IEEE system are considered as the case studies. Our numerical results indicate that 50% price volatility reduction in the SA electricity market can be achieved by installing either 430-MWh regulated storage or 530-MWh strategic storage. In other words, regulated storage firms are more efficient in reducing the price volatility than strategic storage firms.

• 36.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Minimization of Imbalance Cost Trading Wind Power on the Short-Term Power Market2006In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 21, no 3, p. 1396-1404Article in journal (Refereed)

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

• 37.
KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
Strategic Bidding of a Hydropower Producer under Uncertainty: Modified Benders Approach2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 1, p. 861-873Article in journal (Refereed)

This paper proposes a stochastic bilevel program for strategic bidding of a hydropower producer. The price, quantity and ramp-rate bids are considered. The uncertainty of wind power generation, variation of inflows for the hydropower producer, and demand variability are modeled through the moment-matching scenario generation technique. Using discretization the stochastic bilevel program is reformulated as a stochastic mixed-integer linear program (MILP) with disjunctive constraints. We propose a modified Benders decomposition algorithm (MBDA), which fully exploits the disjunctive structure of reformatted MILP model. More importantly, the MBDA does not require optimal tuning of disjunctive parameters and it can be efficiently parallelized. Through an illustrative 5-node example, we identify possible strategies (specific to a hydropower producer) for maximizing profit, which in turn leads to market insights. We also use the IEEE 24-node, 118-node, and 300-node case studies to show how our parallelized MBDA outperforms the standard benders decomposition algorithm. The parallelized MBDA is also compared to the state-of-the-art CPLEX solver.

• 38.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Exercise of Market Power on Ramp Rate in Wind-Integrated Power Systems2015In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 30, no 3, p. 1614-1623Article in journal (Refereed)

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

• 39.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
Risk averse scheduling by a PEV aggregator under uncertainty2015In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 30, no 2, p. 882-891, article id 6847245Article in journal (Refereed)

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

• 40.
KTH, School of Electrical Engineering (EES), Electric power and energy systems. Comillas University, Spain.
Retail Pricing: A Bilevel Program for PEV Aggregator Decisions Using Indirect Load Control2016In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 31, no 1, p. 464-473Article in journal (Refereed)

Charging schedules of plug-in electric vehicles (PEVs) coordinated by an aggregating agent may increase system efficiency of allocating generation, transmission and distribution resources. Decentralized self-scheduling and local charging control appear to be preferred by vehicle manufacturers and PEV drivers who are simultaneously concerned about the longevity and reliability of their energy storage systems. In such a setting, the aggregator would have to determine energy retail prices as means to indirect load control. This paper proposes a mathematical program with equilibrium constraints optimizing the aggregator's decisions. It endogenously determines the profit-optimal price level subject to the cost minimizing charging schedule of the final customers, who are reacting to a combination of retail price signals and distribution use-of-system network charges. This active response follows an affine demand-price relationship, which is individually parametrized for each vehicle by local information of vehicle characteristics and mobility pattern. The proposed program is applied to two cases: 1) a small case study with 3 vehicles, which highlights the model functionality with detailed hourly information per vehicle; 2) a large-scale fleet of 1000 vehicles provides insights on computational burden. Numerical results indicate that adequate competition in the retail market is necessary to limit the aggregator's monopolistic profitability. Finally, sensitivity runs show dependency on the individual's willingness to pay, the cost of alternative fueling opportunities and minimum state-of-charge requirements.

• 41.
KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
Tight and Compact MILP Formulation for the Thermal Unit Commitment Problem2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 4, p. 4897-4908Article in journal (Refereed)

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

• 42.
KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
Tight and Compact MILP Formulation of Start-Up and Shut-Down Ramping in Unit Commitment2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 2, p. 1288-1296Article in journal (Refereed)

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

• 43.
KTH, School of Electrical Engineering (EES), Electric Power Systems. Universidad Pontificia Comillas.
An MIP Formulation for Joint Market-Clearing of Energy and Reserves Based on Ramp Scheduling2014In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 29, no 1, p. 476-488Article in journal (Refereed)

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

• 44.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
University of Castilla-la Mancha. University of Castilla-la Mancha. KTH, School of Electrical Engineering (EES), Electric Power Systems.
Minimizing Wind Power Spillage Using an OPF With FACTS Devices2014In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 29, no 5, p. 2150-2159Article in journal (Refereed)

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

• 45.
KTH, School of Electrical Engineering (EES).
KTH, School of Electrical Engineering (EES).
Network-Constrained AC Unit Commitment Under Uncertainty: A Benders' Decomposition Approach2016In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 31, no 1, p. 412-422Article in journal (Refereed)

This paper proposes an efficient solution approach based on Benders' decomposition to solve a network-constrained ac unit commitment problem under uncertainty. The wind power production is the only source of uncertainty considered in this paper, which is modeled through a suitable set of scenarios. The proposed model is formulated as a two-stage stochastic programming problem, whose first-stage refers to the day-ahead market, and whose second-stage represents real-time operation. The proposed Benders' approach allows decomposing the original problem, which is mixed-integer nonlinear and generally intractable, into a mixed-integer linear master problem and a set of nonlinear, but continuous subproblems, one per scenario. In addition, to temporally decompose the proposed ac unit commitment problem, a heuristic technique is used to relax the inter-temporal ramping constraints of the generating units. Numerical results from a case study based on the IEEE one-area reliability test system (RTS) demonstrate the usefulness of the proposed approach.

• 46. Nilsson, Martin
KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
Balancing Strategies Evaluation Framework Using Available Multi-Area Data2017In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679Article in journal (Refereed)

The penetration of variable RES, the deregulation of electricity markets, and the expansion of HVDC- transmission capacities all increase the variability, uncertainty, and imbalances for System Operators (SOs) to handle. Meanwhile, frequency quality has deteriorated and occurrence of balancing problems has increased. Therefore, there is an increased need for SOs to improve their balancing strategies. In this paper we present a new balancing evaluation framework. The main idea of the framework is to be applicable for real and large power systems and provide support for SOs when comparing already used balancing strategies with new ones using historical available data. This is important as only comparatively low-resolution data measurements, such as hourly-mean-values for production, consumption, and HVDC-transmission are stored in many power systems. The framework consists of model building, system parameter identification, testing different strategies and targets supporting the corporate missions of the SOs. In a case study, the framework is tested for a real power system where the model set-up mimics measured frequency accurately. The case study illustrates how the framework can be used to evaluate the impact of different balancing strategies on a series of selected targets which support the cooperate missions of ENTSO-E.

• 47.
KTH, Superseded Departments, Electrical Systems.
KTH, Superseded Departments, Electrical Systems.
Integer modelling of spinning reserve requirements in short term scheduling of hydro systems1998In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 13, no 3, p. 959-964Article in journal (Refereed)

In short term power system scheduling, reserve margins are kept in order to maintain the security of the system if a non-forecasted event occurs. The security is maintained by re-dispatch of the generators in the system. During the first seconds of the disturbance it is only possible to re-dispatch the on-line units. The maximal increase of the generation during these first seconds of the disturbance is called the spinning reserve. In hydro dominated power systems the spinning reserve is kept in the hydro system, since hydro units are easy to re-dispatch. For an on-line hydro unit the spinning reserve is the marginal between maximum generation and the actual generation. If a hydro plant has several units, only the on-line units will contribute to the spinning reserve. This means that we need to introduce integer variables to model the spinning reserve contribution from a hydro plant with several units. In the literature there are several examples of integer models for representation of the generation of hydro plants. The contribution of this paper is that it incorporates the integer representation of the spinning reserve into an integer model of generation scheduling. To this model we apply variable splitting and Lagrange relaxation to decompose the problem into one subproblem for the hydrological constraints and one subproblem for each hydro plant. In order to find feasible solutions we use a combination of network programming and heuristic search. The dual problem constructed by the decomposition is solved by a subgradient method. In the paper we apply the proposed method to a numerical example.

• 48.
KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems. KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
A Multi-Disciplinary Course Portfolio on Computer Applications in Power Systems2014In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 29, no 4, p. 1919-1927Article in journal (Refereed)

As a response to the new requirements posed by the shift towards Smartgrids, there have been many initiatives worldwide to develop and update power engineering education curricula. This paper reports efforts to develop courses with the purpose to cross the gap between the disciplines of power engineering and information communication technology at KTH-the Royal Institute of Technology in Sweden. The course portfolio is engineered to complement several master programs offered by the university, and the intended audience are students and practitioners both with and without the power engineering background. This paper primarily focuses on details of a keystone course, Computer Applications in Power Systems, and its connection with the other courses in the portfolio. To prove the popularity and relevance of the reported course portfolio, increasingly positive feedback from students, recognition from industry partners, and accomplishments in terms of meeting several strategic goals in education set by the IEEE Power & Energy Society are also reported by this paper.

• 49.
KTH, Superseded Departments, Electric Power Systems.
KTH, Superseded Departments, Electric Power Systems. KTH, Superseded Departments, Electric Power Systems.
Linear programming based optimal power flow using second order sensitivities1995In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 10, no 3, p. 1691-1697Article in journal (Refereed)

For the electric railway traction in Sweden, a system of 130 kV transmission lines connected parallel to the contact lines is being build. Within this system, the generation costs differs only slightly between different nodes with power injections. In order to optimize the power flow in the system, an extended optimal power flow algorithm based on successive linear programming, has been developed. To improve the convergence, a method based on a second order sensitivity approximation of the active power losses of the total system is applied. Numerical examples are given to show the enhanced convergence properties.

• 50.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
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)

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.

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