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  • 1. Beerten, J.
    et al.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem. Technical University of Denmark (DTU), Denmark.
    Van Hertem, D.
    A new approach to HVDC grid voltage control based on generalized state feedback2014Inngår i: 2014 IEEE PES General Meeting | Conference & Exposition, IEEE Computer Society, 2014, nr October, s. 6939418-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, a new approach to DC voltage control in a High Voltage Direct Current (HVDC) grid is introduced. In an HVDC grid, the power sharing after a converter outage can be influenced by the droop control values. However, when relying on a local feedback signal, the DC voltage drops in the system hamper a straight-forward definition of the power sharing. The use of a common DC voltage signal for the control can solve some of the problems. However, it disregards some of the benefits that are associated with the use of a local voltage control, such as the tendency of a controller using local voltage feedback signals to solve problems locally which can reduce the stress on the AC system. Furthermore, it provides no direct means to obtain different system responses for different converter outages. The control approach presented in this paper aims at improving the DC voltage droop control by combining the local voltage signal available at the converter terminals with remote voltage signals at different locations in the DC system by means of communication. The local voltage feedback control is used for a fast, reliable system response. The introduction of the remote voltage signals in the control allows to differentiate the system response for different converter outages. Simulation results show the validity of the proposed control scheme.

  • 2.
    Beerten, Jef
    et al.
    University of Leuven (KU Leuven).
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Belmans, Ronny
    University of Leuven (KU Leuven).
    Influence of DC voltage droop settings on AC system stability2012Inngår i: Proceedings on 10th International Conference on AC and DC Power Transmission, Institution of Engineering and Technology, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a methodology to study the impact of different DC voltage droop settings on the AC system stability. When several Voltage Source Converters (VSC) in a DC system jointly control the DC voltage by means of droop control, an outage of one converter results in an abrupt change of the active power set-points of several other converters. This relative power change is related to the relative droop settings of the other converters. In this paper, the influence of the power sharing on the AC system stability is discussed by means of a singular value decomposition.

  • 3.
    Chamorro, Harold
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Influence of the Increasing Non-Synchronous Generation on Small Signal Stability2014Inngår i: 2014 IEEE PES General Meeting | Conference & Exposition, IEEE conference proceedings, 2014, s. 6938796-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The increasing installation of aggregated renewable generation based Full Rated Converters (FRC) in current power systems is modifying their dynamic characteristics. This paper analyses the influence of large scale inclusion of non-synchronous generation through back-to-back Voltage Source Converters’(VSC) connection on power systems, by presenting the dynamic changes on inter-area oscillations in different penetration level cases. The aggregated model of VSC units is assumed. The Small Signal Stability Analysis (SSSA) is used to show thedynamic behaviour and presents the performance of the power systems related to the domain frequency modes in a test grid system. From the analysis, it is shown that the mode shapes and participation factors are displaced according to the penetration levels. Eigenvalue sensitivity analysis according to the inertia isalso applied, showing the impact of the large penetration of nonsynchronousgeneration.

  • 4.
    Chamorro, Harold
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Wind Power Impact on Power System Frequency Response2013Inngår i: 45th North American Power Symposium, NAPS 2013, IEEE , 2013, s. 6666880-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The use of high power electronics in the large scale integration of wind power in the transmission and distribution systems can affect the system inertia response and the ability to recover frequency stability after large disturbances. Different approaches have been presented to show the system dynamic behaviour, and to quantify the wind power impact on the system inertial and frequency response. This paper gives a short overview of studies performed regarding the system inertia issues under high penetrations of wind power. Also, it presents the results of a case study to show how the system inertia can be affected by high penetrations of wind power.

  • 5.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Coordinated Control of HVDC Links in Transmission Systems2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Dynamic security limits the power transfer capacity between regions and therefore has an economic impact. The power modulation control of high-voltage direct current (HVDC) links can improve the dynamic security of the power system. Having several HVDC links in a system creates the opportunity to coordinate such control, and coordination also ensures that negative interactions do not occur among the controllable devices.

    This thesis aims to increase dynamic security by coordinating HVDC links, as an alternative to decreasing the transfer capacity. This thesis contributes four control approaches for increasing the dynamic stability, based on feedforward control, adaptive control, optimal control, and exact-feedback linearization control. Depending on the available measurements, dynamic system model, and system topology, one of the developed methods can be applied. The wide-area measurement system provides the central controller with real-time data and sends control signals to the HVDC links.

    The feedforward controller applies rapid power dispatch, and the strategy used here is to link the N-1 criterion between two systems. The adaptive controller uses the modal analysis approach; based on forecasted load paths, the controller gains are adaptively adjusted to maximize the damping in the system. The optimal controller is designed based on an estimated reduced-order model; system identification develops the model based on the system response. The exact-feedback linearization approach uses a pre-feedback loop to cancel the nonlinearities; a stabilizing controller is designed for the remaining linear system.

    The conclusion is that coordinating the HVDC links improves the dynamic stability, which makes it possible to increase the transfer capacity. This conclusion is also supported by simulations of each control approach.

  • 6.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Coordinated Control of Multiterminal DC Grid Power Injections for Improved Rotor-Angle Stability Based on Lyapunov Theory2014Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 29, nr 4, s. 1789-1797Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stability of an interconnected ac/dc system is affected by disturbances occurring in the system. Disturbances, such as three-phase faults, may jeopardize the rotor-angle stability and, thus, the generators fall out of synchronism. The possibility of fast change of the injected powers by the multiterminal dc grid can, by proper control action, enhance this stability. This paper proposes a new time optimal control strategy for the injected power of multiterminal dc grids to enhance the rotor-angle stability. The controller is time optimal, since it reduces the impact of a disturbance as fast as possible, and is based on Lyapunov theory considering the nonlinear behavior. The time optimal controller is of a bang-bang type and uses wide-area measurements as feedback signals. Nonlinear simulations are run in the Nordic32 test system implemented in PowerFactory/DIgSILENT with an interface to Matlab where the controller is implemented.

  • 7.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    On the Centralized Nonlinear Control of HVDC Systems Using Lyapunov Theory2013Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 28, nr 2, s. 1156-1163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The security region of a power system is an important and timely issue; different stability criteria may be limiting. Rotor-angle stability can be improved by modulating active power of installed high-voltage direct current (HVDC) links. This paper proposes a new centralized nonlinear control strategy for coordinating several point-to-point and multiterminal HVDC systems based on Lyapunov theory. The proposed control Lyapunov function is negative semi-definite along the trajectories and uses the internal node representation of the system. The proposed control Lyapunov function increases the domain of attraction and, thus, improves the rotor-angle stability. Nonlinear simulations are performed on the IEEE 10-machine 39-bus system which shows the effectiveness of the controller. In comparison, simulations using the conventional lead-lag controller are also run.

  • 8.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Security-centered Coordinated Control in AC/DC Transmission Systems2008Licentiatavhandling, monografi (Annet vitenskapelig)
  • 9.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Beerten, J.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Belmans, R.
    Optimizing DC voltage droop settings for AC/DC system interactions2014Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 29, nr 1, s. 362-369Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a methodology is presented to optimize the dc voltage droop settings in a multiterminal voltage-source converter high-voltage direct-current system with respect to the ac system stability. Implementing dc voltage droop control enables having multiple converters assisting the system in case of a converter outage. However, the abrupt power setpoint changes create additional stress in the ac system, especially when multiple converters are connected to the same interconnected ac system. This paper presents a methodology to determine optimizd converter droop settings in order to not compromise the ac system stability, thereby taking into account the adverse effect the droop control actions have on the interconnected ac system. Developing a disturbance model of the interconnected ac/dc system, the principal directions indicate the gain and directionality of the disturbances; from this, optimal droop settings are derived to minimize the disturbance gain.

  • 10.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Knazkins, Valerijs
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Nonlinear Coordinated Control of Multiple HVDC Links2008Inngår i: 2008 IEEE 2ND INTERNATIONAL POWER AND ENERGY CONFERENCE: PECON, VOLS 1-3, NEW YORK: IEEE , 2008, s. 497-501Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 11.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Knazkins, Valerijs
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    On the coordinated control of multiple HVDC links2008Inngår i: 2008 IEEE/PES TRANSMISSION AND DISTRIBUTION CONFERENCE AND EXPOSITION: LATIN AMERICA, 2008, s. 500-505Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, coordinated control of multiple HVDC links in a small AC/DC power system is investigated. A coordinated control strategy is proposed to increase the transient stability and the damping in the AC/DC system. The system power loading is set by the well-known N - 1 criteria, i.e. that the system should remain intact (in the sense of both transient and small-signal stability) despite the loss of any important component. Since both transient stability and damping are increased by coordination of the control of the HVDC links, the allowed transmission capacity can be increased. The control strategy proposed in this paper posses the ability of damping power oscillations and improving the transient stability in the test system, it can also be used in a large scale power system. In the test system, the HVDC links are not operating in parallel with the ac lines, therefore coordination of the HVDC links is necessary to achieve significant better damping and transient stability.

  • 12.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Knazkins, Valerijs
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Coordinated control of multiple HVDC links using input-output exact linearization2010Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, nr 12, s. 1406-1412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 13.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Knazkins, Valerijs
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Linear HVDC Modeling for Small Signal Stability Studies2009Inngår i: MEPCON, IEEE, 2009Konferansepaper (Fagfellevurdert)
  • 14.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Knazkins, Valerijs
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    On the assessment of the impact of a conventional HVDC on a test power system2007Inngår i: 2007 IREP SYMPOSIUM- BULK POWER SYSTEM DYNAMICS AND CONTROL: VII REVITALIZING OPERATIONAL RELIABLITY, VOLS 1 AND 2, NEW YORK: IEEE , 2007, s. 58-62Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 15.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Perninge, Magnus
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Coordination of HVDC-links to increase dynamic stability margins2010Inngår i: 2010 IEEE International Conference on Power and Energy, PECon2010, 2010, s. 183-188Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 16.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Perninge, Magnus
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Transfer capacity enhancement by adaptive coordinated controlof HVDC-links based on forecasted load paths2011Inngår i: European transactions on electrical power, ISSN 1430-144X, E-ISSN 1546-3109, Vol. 21, nr 3, s. 1455-1466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 17.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    A general approach to coordinated control of multiple HVDC links using input-output exact linearizationArtikkel i tidsskrift (Annet vitenskapelig)
  • 18.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Centrally coordinated control of multiple HVDC links for power oscillation damping2010Inngår i: POWER CONTROL AND OPTIMIZATION, 2010, Vol. 1239, s. 134-140Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 19.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Coordinated control design of multiple HVDC links based on model identification2010Inngår i: Computers and Mathematics with Applications, ISSN 0898-1221, E-ISSN 1873-7668, Vol. 60, nr 4, s. 944-953Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 20.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    On the coordinated control of multiple HVDC links using input-output exact linearization in large power systems2012Inngår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 43, nr 1, s. 118-125Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 21.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Optimal coordinated control of multiple HVDC links for power oscillation damping based on model identification2012Inngår i: European transactions on electrical power, ISSN 1430-144X, E-ISSN 1546-3109, Vol. 22, nr 2, s. 188-205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 22.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    System identification techniques for obtaining linear models of large power systems with controllable devices from noisy measurements2010Inngår i: 2010 IREP Symposium - Bulk Power System Dynamics and Control - VIII, IREP2010, 2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

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

  • 23.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    WAMS based identification for obtaining linear models to coordinate controllable devices2012Inngår i: Electrical engineering (Berlin. Print), ISSN 0948-7921, E-ISSN 1432-0487, Vol. 94, nr 1, s. 27-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 24.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Wide-Area measurement system-based subspace identification for obtaining linear models to centrally coordinate controllable devices2011Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 26, nr 2, s. 988-997Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 25.
    Eriksson, Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart H.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Wide-area measurement system control to coordinate HVDC links in large scale power systems2011Inngår i: Int. Conf. Intelligent Syst. Appl. Power Syst., ISAP, 2011, s. 6082169-Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 26.
    Nasri, Amin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Suitable placements of multiple FACTS devices to improve the transient stability using trajectory sensitivity analysis2013Inngår i: North American Power Symposium (NAPS), 2013, IEEE conference proceedings, 2013, s. 1-6Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 27.
    Nasri, Amin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Using trajectory sensitivity analysis to find suitable locations of series compensators for improving rotor angle stability2014Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 111, s. 1-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 28.
    Nasri, Amin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    Appropriate placement of series compensators to improve transient stability of power system2012Inngår i: Innovative Smart Grid Technologies-Asia (ISGT Asia), 2012 IEEE, IEEE conference proceedings, 2012, s. 1-6Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 29.
    Nasri, Amin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Transient stability assessment of power systems in the presence of shunt compensators using trajectory sensitivity analysis2013Inngår i: 2013 IEEE Power and Energy Society General Meeting (PES), IEEE , 2013, s. 6672163-Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 30.
    Nilsson, Martin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ghandari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ericsson, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Designing new proactive control-room strategies to decrease the need for automatic reserves2017Inngår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017 - Proceedings, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Maintaining automatic reserve capacities is essential for a sustainable and reliable power system. Today, many power systems experience more frequent frequency deviations coming from increased power variations. This implies an increased utilization of automatic reserves. To decrease frequency deviations, one can increase the automatic reserve capacities. However, the solution tends to be costly and ineffective. Therefore, it is urgent to develop better solutions to cease this trend. Here we have designed new proactive control-room strategies to decrease the need for automatic reserves. We design strategies for a process called Re-Scheduling of Generation and for the Tertiary Frequency Control process. The new control-room strategies are tested using an intra-hour model comparing already used strategies against new ones. It is shown that the historical used strategies are well executed. Nevertheless, results show that the proactive TFC-strategy using a forecasted frequency as control parameter would improve system security significantly.

  • 31.
    Nycander, Elis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Olauson, Jon
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Eriksson, Robert ()
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Curtailment analysis for the Nordic power system considering transmission capacity, inertia limits and generation flexibility2020Inngår i: Renewable Energy, Vol. 152, s. 942-960Artikkel i tidsskrift (Fagfellevurdert)
  • 32.
    Nycander, Elis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Söder, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Eriksson, Robert
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hamon, Camille
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Minimising wind power curtailments using OPF considering voltage stability2019Inngår i: The Journal of Engineering, ISSN 1872-3284, E-ISSN 2051-3305, nr 18, s. 5064-5068Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As the amount of wind power in power systems has increased, it has become necessary to curtail wind power in some high-penetration situations. In order to assess the need for curtailment arising from voltage stability considerations the authors develop a security constrained optimal power flow (SCOPF) for minimising the expected curtailment. The authors find that with a very high wind penetration and wind farms operating at unity power factor curtailment becomes necessary to satisfy voltage limits. In this case, the optimal solution in the studied system is to curtail at a single bus rather than curtailing by a smaller amount at several buses. However, allowing for reactive power production from wind farms reduces the need for curtailments.

  • 33.
    Perninge, Magnus
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Using a fixed point method to compute the parameter space distance to the surface of constant critical energy2012Inngår i: 2012 11th International Conference on Environment and Electrical Engineering, EEEIC 2012 - Conference Proceedings, IEEE , 2012, s. 298-302Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Power system voltage security assessment is generally applied by considering the steady-state stability surface. However, as seen in the literature, random perturbations can drive the system away from stable operation, long before the steady-state stability surface is reached. In this article we include the value of the critical energy for the transient energy function, as a stability criterion when defining the stability boundary surface in parameter space. We show how the closest point on the surface of constant critical energy can be computed. The main contribution of this article is that it serves as a first step to include dynamic voltage collapse issues in the analysis of bulk power transfer security.

  • 34.
    Samadi, Afshin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Jose, Della
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Mahmood, Farhan
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Comparison of a Three-Phase Single-Stage PV System in PSCAD and PowerFactory2012Inngår i: Proceedings of the 2nd International Workshop on Integration of Solar Power into Power Systems, Energynautics GmbH , 2012, s. 237-244Konferansepaper (Fagfellevurdert)
  • 35.
    Samadi, Afshin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Evaluation of Reactive Power Support Interactions Among PV Systems Using Sensitivity Analysis2012Inngår i: 2nd International Workshop on Integration of Solar Power into Power Systems, 2012, s. 245-252Konferansepaper (Fagfellevurdert)
  • 36.
    Samadi, Afshin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Rawn, Barry
    Boemer, Jens C.
    Coordinated Active Power-Dependent Voltage Regulation in Distribution Grids With PV Systems2014Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 29, nr 3, s. 1454-1464Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 37.
    Samadi, Afshin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Shayesteh, Ebrahim
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Rawn, Barry
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems2014Inngår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 71, s. 315-323Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 38.
    Samadi, Afshin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Shayesteh, Ebrahim
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Static Equivalent of Distribution Grids with High Penetration of PV SystemsManuskript (preprint) (Annet vitenskapelig)
  • 39.
    Samadi, Afshin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Shayesteh, Ebrahim
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Static Equivalent of Distribution Grids With High Penetration of PV Systems2015Inngår i: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 6, nr 4, s. 1763-1774Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High penetrations of photovoltaic (PV) systems within load pockets in distribution grids have changed pure consumers to prosumers. This can cause technical challenges in distribution and transmission grids, such as overvoltage and reverse power flow. Embedding voltage support schemes into PVs, such as standard cos phi(P) characteristic proposed by the German grid codes, may cause more changes in the steady-state behavior of distribution grids and, in turn, the transmission side. Accordingly, it is important to properly model active distribution grids to analyze the system impacts of these changes to plan and operate future smart power grids. However, due to the high dimension of distribution grids, considering a detailed distribution grid to study the transmission side or a fraction of the distribution grid is either cumbersome or impractical. Therefore, it is required to develop a reasonable equivalent that can fairly capture the dominant behavior of the distribution grids. The aim of this paper is to use gray-box modeling concepts to develop a static equivalent of distribution grids comprising a large number of PV systems embedded with voltage support schemes. In the proposed model, the PV systems are aggregated as a separate entity, and not as a negative load, which is traditionally done. The results demonstrate the superior quality of the proposed model compared with the model with PV systems as the negative load.

  • 40.
    Van Hertem, Dirk
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Coordination of multiple power flow controlling devices in transmission systems2010Inngår i: ACDC 2010: 9th International Conference on AC and DC Power Transmission, 2010Konferansepaper (Fagfellevurdert)
  • 41.
    van Hertem, Dirk
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, Robert
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Coordination of multiple power flow controlling devices in transmission titles2010Inngår i: Proceedings of 9th international conference on AC and DC transmission, 2010, Vol. 9Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Power flow controlling devices are increasingly present in meshed systems. These devices have strong influence on the power flows throughout the power system. As such, they influence each others operation. In order to make a more optimal and efficient use of their controllability, coordination is needed. This coordination can increase transmission capacity and security, both in steady-state and dynamically. The effect of coordination is shown using two simple examples.

1 - 41 of 41
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