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  • 1.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Mitigation of Sub-Synchronous Control Interaction in DFIGs using a Power Oscillation Damper2017In: 2017 IEEE Manchester PowerTech, Powertech 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7980941Conference paper (Refereed)
    Abstract [en]

    The aim of this research work is to analyse subsynchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) and to design a supplementary control technique for the mitigation of SSCI. A mathematical model of the DFIG is derived and linearized in order to perform an eigenvalue analysis. This analysis pinpoints the parameters of the system which are sensitive in making sub-synchronous modes unstable and hence are responsible for causing SSCI. A power oscillation damper (POD) is designed using a residue method to make the DFIG system immune to the SSCI. The POD control signal acts as a supplementary control, which is fed to the controller of the grid-side converter (GSC). The POD signal is applied to different summation junctions of the GSC controller in order to determine the best placement of the POD for effective mitigation of SSCI and for the increased damping of the system.

  • 2.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Effect of control parameters on infliction of sub-synchronous control interaction in DFIGs2016In: 2016 IEEE International Conference on Power and Renewable Energy (ICPRE), IEEE conference proceedings, 2016, p. 72-78, article id 7871175Conference paper (Refereed)
    Abstract [en]

    This research work deals with the analysis of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs). The time-invariant model of the DFIG is linearized to perform eigenvalue analysis and to obtain the participation factor of each state variable for unstable modes. The sensitivity of system eigenvalues related to sub-synchronous modes is analyzed with respect to all the proportional and integral parameters of the controllers in the rotor-side-converters and grid-side-converters. The major contribution of this research work is the outcomes based on eigenvalue analysis that clearly point out the control parameters to which sub-synchronous modes are highly sensitive. The effect of series compensation level on DFIG system and on the sensitivity of converter control parameters is also studied.

  • 3.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Optimal tuning and placement of POD for SSCI mitigation in DFIG-based power system2019In: 2019 IEEE Milan PowerTech, PowerTech 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, article id 8810891Conference paper (Refereed)
    Abstract [en]

    The phenomenon of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) is investigated and the optimal tuning and placement of a power oscillation damper (POD) for its mitigation is proposed in this paper. The effect of the POD on the DFIG system is studied by placing it at all the summation junctions of rotor-side converter (RSC) and grid-side converter (GSC) controllers, turn by turn. Five local signals are examined as different input signals to the POD out of which three local signals gave promising results. These signals include the DFIG's active power, the magnitude of the DFIG's apparent power, and the magnitude of the current through the transmission line. Residues are calculated for each POD placement and for each input to the POD. The calculated residues are studied along with the root-locus plots to see the effect of the POD on the mitigation of SSCI and the stability of the DFIG-based system.

  • 4.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Nazari, Mohammad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems2014In: Proceedings of the 19th IFAC World Congress, 2014, IFAC Papers Online, 2014, Vol. 19, p. 11910-11916Conference paper (Refereed)
    Abstract [en]

    High-voltage direct current (HVDC) is a commonly used technology for long-distance power transmission, due to its low resistive losses and low costs. In this paper, a novel distributed controller for multi-terminal HVDC (MTDC) systems is proposed. Under certain conditions on the controller gains, it is shown to stabilize the MTDC system. The controller is shown to always keep the voltages close to the nominal voltage, while assuring that the injected power is shared fairly among the converters. The theoretical results are validated by simulations, where the affect of communication time-delays is also studied.

  • 5.
    Babazadeh, Davood
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nazari, Mohammad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fidai, Muhammad Hassan
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Implementation of agent-based power flow coordination in AC/DC grids using co-simulation platform2014In: 2014 IEEE International Conference on Smart Grid Communications, SmartGridComm 2014, 2014, p. 188-193Conference paper (Refereed)
    Abstract [en]

    This paper presents work on the coordination of power sharing contribution of converters in an overlaid HVDC grid using a Multi-Agent System (MAS) approach. This approach is further implemented in a real-time co-simulation platform in order to study the proposed control scheme including the supporting information and communication Technology (ICT) systems. The platform consists of OPNET, a communication network simulator, connected to a real-time power system simulator through virtualized and real devices. Furthermore, the impact of different supporting system parameters such as bit-error rate has been studied using this real-time co-simulation platform.

  • 6.
    Baradar, Mohamadreza
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    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)
    Abstract [en]

    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.
    Baradar, Mohamadreza
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Van Hertem, Dirk
    Electrical engineering.
    The Modeling Multi-Terminal VSC-HVDC in Power Flow Calculation Using Unified Methodology2011In: Innovative Smart Grid Technologies (ISGT) Conference, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper, a new unified method for power flowcalculation in AC grids with embedded multi-terminal HVDCsystems based on voltage source converter is proposed. In thismethod all DC and AC equations are solved simultaneously inthe same iteration while there is no need to rely on resultsobtained from other iterative loops unlike the other methods.The method can be applied for any number of converters,any DC network configuration and any converter loss model.The algorithm is implemented in MATLAB and to validate theresults, they are compared to results obtained from the simulationsoftware SIMPOW.

  • 8.
    Baradar, Mohamadreza
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Van Hertem, Dirk
    Electrical engineering, Katholieke Universiteit Leuven, Heverlee, Belgium.
    Kargarian, Amin
    Electrical and Computer Engineering, Mississippi State University.
    Power flow calculation of hybrid AC/DC power systems2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, p. 6343958-Conference paper (Refereed)
    Abstract [en]

    Multi-terminal HVDC systems have recently become an attractive option for interconnection of isolated AC systems such as offshore wind farms and oil platforms to asynchronous large AC systems. This paper deals with power flow calculation (PFC) of hybrid AC/DC power systems where several asynchronous AC systems are interconnected via a common multiterminal VSC-HVDC system. This paper proposes a unified AC-DC approach for PFC of a hybrid AC/DC power system. The proposed approach is then employed for two different analyses, namely a) the separated analysis where the entire hybrid AC/DC system is divided into two groups. The first group (named external AC system) comprises all asynchronous AC systems which are not directly connected to the slack convertor of the DC network, and the second group comprises an AC/DC system where the selected AC system is directly connected to the slack convertor. In this method, a PFC is firstly performed for the the first group, and its relevant obtained results will be used for PFC of the second group. b) the integrated analysis where the entire hybrid system is considered as a unit. Both a) and b) can be used in the practical analysis of the real-size power systems. However, due to practical issues and computational costs the separated analysis may be a more acceptable method. The simulations have been performed using MATLAB, and the obtained results have been compared with those obtained in SIMPOW.

  • 9.
    Baradar, Mohamadreza
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ohmic loss minimization in AC transmission systems with embedded DC grids2013In: 39th Annual Conference of the IEEE Industrial Electronics Society, IECON, IEEE conference proceedings, 2013, p. 2117-2120Conference paper (Refereed)
    Abstract [en]

    The HVDC systems built based on the voltage source converters (VSC) can bring several benefits to the AC power systems. Better voltage profile, increasing power flow controllability, lower ohmic loss, and higher transfer capability are some major benefits of such systems. This paper investigate the impact of VSC-type DC grids installed in the AC power systems on the ohmic network losses. This is done by formulating a convex optimization problem which minimises the ohmic losses (both in AC and DC grids) subject to the technical constraints of both AC and DC system. The formulated optimisation problem is a conic optimisation problem which can be solved using the commercially available optimisation softwares. The conic AC-DC optimal power flow, CAD-OPF, is coded in GAMS platform and solved using the MOSEK solver. The IEEE 30-bus example system is modeled and studied.

  • 10.
    Baradar, Mohamadreza
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad R.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    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)
    Abstract [en]

    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.

  • 11.
    Baradar, Mohamadreza
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modelling of multi-terminal HVDC systems in optimal power flow formulation2012In: 2012 IEEE Electrical Power and Energy Conference, EPEC 2012, IEEE , 2012, p. 170-175Conference paper (Refereed)
    Abstract [en]

    The multi-terminal HVDC systems and their embedded DC networks are considered as smart grids technology which improve economic efficiency of the power system. This technology allows better voltage profile in the power system by better allocation of the generation sources. Also, it can help in improving the economic efficiency of the system by substituting the high-cost generation with low-cost generation. In order to assess the technical benefit of this smart grids technology, this paper presents an optimal power flow formulation for AC grids with embedded DC networks built from multi-terminal HVDC systems. The objective function of this AC-DC OPF formulation is the total active dispatch costs. The constraints consist of (a) AC grid constraints, (b) constraints from multi-terminal HVDC systems, and (c) DC grid constraints. The formulated AC-DC OPF is a mixed-integer nonlinear optimisation problem. The formulation is coded in GAMS platform and tested on IEEE 30 Bus system.

  • 12.
    Chamorro, Harold
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Influence of the Increasing Non-Synchronous Generation on Small Signal Stability2014In: 2014 IEEE PES General Meeting | Conference & Exposition, IEEE conference proceedings, 2014, p. 6938796-Conference paper (Refereed)
    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.

  • 13.
    Chamorro, Harold
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wind Power Impact on Power System Frequency Response2013In: 45th North American Power Symposium, NAPS 2013, IEEE , 2013, p. 6666880-Conference paper (Refereed)
    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.

  • 14.
    Chamorro, Harold R.
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Nazari, Mohammad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Babazadeh, Davood
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Malik, Naveed ur Rehman
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Consensus Control for Induction Motors Speed Regulation2014In: 2014 16TH European Conference on Power Electronics and Applications, 2014Conference paper (Refereed)
    Abstract [en]

    Cyber Physical Energy Systems (CPES) development requires the combination of distributed intelligence to fulfill the future complex tasks and reach the increase the energy demands. Electrical Industrial Systems (EIS) are in continuous evolving integrating new technologies allowing to a better performance and increase the efficiency. This paper applies the consensus protocol for Multi-Agent Systems (MAS) to control the speed of multiple induction motors. In this paper, the behaviour of the system under different disturbances and scenarios has been simulated, thus, confirming the suitability and simplicity of this method for coordinating the control actions.

  • 15.
    Chamorro, Harold R.
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Ordonez, Camilo A.
    Peng, Jimmy C.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Non-synchronous generation impact on power systems coherency2016In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 10, no 10, p. 2443-2453Article in journal (Refereed)
    Abstract [en]

    The increasing integration of renewables into the grid based on power electronics converters interfaces is affecting the power systems dynamics, requiring effective monitoring and visualisation to provide appropriate assessment during extreme events. The coherent group identification in power systems is of importance for dynamic studies and transmission capability improvement. This study analyses the coherency based on the mode shapes, the application of the Koopman mode analysis (KMA) and a Prony analysis (PA) on-line variation for the identification of coherent groups in power systems. KMA and PA use the voltage angle measurements obtained from simulation. The clustering of the coherent groups are evaluated in two test systems. The coherency methods are also evaluated taking into account the impact of a large gradual scale inclusion of non-synchronous generation under different penetration level cases. From the comparison and visualisation of the different methods it is possible to observe the impact of the large inclusion of non-synchronous generation on the coherency.

  • 16.
    Chamorro, Harold R.
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Ordonez, Camilo A.
    Peng, Jimmy C. -H.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    On-line Oscillations Monitoring under High Penetration of Non-Synchronous Generation2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON SMART GRID COMMUNICATIONS (SMARTGRIDCOMM), IEEE , 2015, p. 278-282Conference paper (Refereed)
    Abstract [en]

    The large scale penetration of non-synchronous generation based power electronics converters interfaces in current power systems is modifying their dynamic characteristics. The observation, monitoring and supervision of the electromechanical oscillation changes due to this integration is a requirement in order to protect the system from undesired events. This paper uses the Prony analysis to estimate the critical modes by using the tie-lines which interconnect the operative areas as measurement points and evaluating the impact of the large gradual scale inclusion of non-synchronous generation on power systems. The modes monitoring involved in the transient dynamic response are shown in the different penetration level cases. From the computed measurements, the frequency and damping variation in the different cases studied on the test system is obtained, which shows the impact of the large inclusion of non-synchronous generation.

  • 17.
    Chamorro Vera, Harold R
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Eriksson, R.
    Coherent groups identification under high penetration of non-synchronous generation2016In: IEEE Power and Energy Society General Meeting, IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    The current power systems are facing an important transition due to the integration of non-synchronous generation through back-to-back Full Rated Converters' (FRC). Coherency behaviour under the presence of large inclusion of renewables requires special attention in order to understand the swing oscillations when the inertia is decreasing due to the decoupling. This paper presents the application of the so-called Koopman operator for the identification of coherent groups in power systems with the influence of non-synchronous generation. The method provides a clustering observation tool based on measurement signals allowing to identify the dynamic changes effected through the derived spectral analysis of the Koopman modes. The applied method of coherency identification is evaluated in the Nordic test system through gradually increasing integration and different fault locations.

  • 18.
    Chompoobutrgool, Yuwa
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Survey on Power System Stabilizers Control and their Prospective Applications for Power System Damping using Synchrophasor-Based Wide-Area Systems2011In: European transactions on electrical power, ISSN 1430-144X, E-ISSN 1546-3109, Vol. 21, no 8, p. 2098-2111Article in journal (Refereed)
    Abstract [en]

    Powersystemoscillationdampingremains as one of the major concerns for secure and reliable operation of largepowersystems, and is of great current interest to both industry and academia. The principal reason for this is that the inception of poorly-damped low-frequency inter-areaoscillations (LFIOs) whenpowersystemsare operating under stringent conditions may lead tosystem-widebreakups or considerably reduce thepowertransfers over critical corridors. With the availability of high-sampling rate phasor measurement units (PMUs), there is an increasing interest for effectively exploiting conventionaldampingcontroldevices, such aspowersystemstabilizers(PSSs), by using these measurements ascontrolinput signals. In this paper, we provide a comprehensive overview of distinct elements (or "building blocks") necessary forwide-areapowersystemdampingusing synchrophasors and PSSs. These building blocks together shape a tentative methodical framework, and are disposed as follows: (1) fundamental understanding of the main characteristics of inter-areaoscillations, (2)wide-areameasurement andcontrolsystems(WAMS and WACS) andwide-areadampingcontrol(WADC), (3) advanced signal processing techniques for mode property identification, (4) methods for model-basedsmall-signal analysis, (5)controlinput signals selection, and (6) methods for PSScontroldesign. We also describe the latest developments in the implementation ofsynchrophasormeasurements in WAMS and WACS as well as their prospectives for WADCapplications. This paper serves both to abridge the state-of-the-art in each of these elements, and to accentuate aspiring ideas in each building block.

  • 19.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Comparison of reduced order doubly fed induction generator models for nonlinear analysis2009In: 2009 IEEE Electrical Power and Energy Conference, EPEC 2009, 2009Conference paper (Refereed)
    Abstract [en]

    This article compares the behaviour of different order models, for large scale wind farms comprising doubly fed induction generators (DFIGs). While it is important to have a model which is detailed enough that all interesting phenomena can be examined, it is also important to have simple models, not only to reduce computation time, but also to simplify the design of controllers. This article compares the characteristics of different order models for DFIGs and their responses to control. Eigenvalue analysis and numerical simulations are used to compare the characteristics of the different order models.

  • 20.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Nonlinear Power Oscillation Damping Controllers for Doubly Fed Induction Generators in Wind Farms2013In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 7, no 2, p. 172-179Article in journal (Refereed)
    Abstract [en]

    This study presents two methods for designing power oscillation damping (POD) controllers for wind farms comprising doubly fed induction generators (DFIGs). The first is the residue method, which uses linear feedback. The second method uses a non-linear signal as feedback. Here linear matrix inequalities (LMIs) and regional pole placement are used to determine the feedback gains for multiple wind farms simultaneously so that the power system satisfies a minimum damping ratio. The impact of the designed POD controllers in wind farms is demonstrated in a test power system. Modal analysis is used to design controllers using both the residue and LMI methods, and dynamic simulations are used to demonstrate the contribution of the wind farms to power system damping. Numerical simulations show that DFIGs, such as those found in wind farms, are capable of damping oscillations, and also illustrate the effectiveness of using non-linear feedback controllers.

  • 21.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Using power system stabilisers in doubly fed induction generators2008In: 2008 Australasian Universities Power Engineering Conference, AUPEC 2008, 2008Conference paper (Refereed)
    Abstract [en]

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

  • 22.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modal analysis of power systems with doubly fed induction generators2007In: 2007 IREP SYMPOSIUM- BULK POWER SYSTEM DYNAMICS AND CONTROL: VII REVITALIZING OPERATIONAL RELIABLITY, VOLS 1 AND 2, NEW YORK: IEEE , 2007, p. 140-147Conference paper (Refereed)
    Abstract [en]

    This article is concerned with the impact of large scale wind farms utilising doubly fed induction generators on the stability of a conventional power system. Inspection of the eigenstructure of the system provides a foundation for assessment of the impact, which is then quantified by means of detailed numerical simulations. Simplified state-space models are used to describe the dynamics of generators in a very simple system, whose network is described by algebraic relations. A third order model is derived for a doubly fed induction generator. Mathematical models are used to identify the behavioural patterns of the system when it is subject to disturbances. Eigenvalue analysis reveals certain interesting properties of the system when it is subject to small disturbances. Numerical simulations show that the addition to a power system of doubly fed induction generators, such as those found in wind farms, improves the response of the system to small disturbances, but can have an adverse impact after larger disturbances.

  • 23.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On the rotor angle stability of power systems with Doubly Fed Induction Generators2007In: 2007 IEEE LAUSANNE POWERTECH, VOLS 1-5, NEW YORK: IEEE , 2007, p. 213-218Conference paper (Refereed)
    Abstract [en]

    This article is concerned with the impact of large scale wind farms utilising doubly fed induction generators on the stability of a traditional thermal power system. Inspection of the eigenstructure of the power system provides a foundation for assessment of the impact, which is then quantifted by means of detailed numerical simulations. Simplified state-space models are used to describe the dynamics of the generators in a very simple system., whose network is described by algebraic relations. A third order model is derived for a doubly fed induction generator. Mathematical models are used to identify the behavioural patterns of the system when it is subject to disturbances. Eigenvalue analysis reveals certain interesting properties of the system when it is subject to small disturbances. Numerical simulations show that the addition to a power system of doubly fed induction generators, such as those found in wind farms, improves the response of the system to small disturbances, but can have an adverse impact after larger disturbances.

  • 24. Elkington, Katherine
    et al.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On the stability of power systems containing doubly fed induction generator-based generation2008In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 78, no 9, p. 1477-1484Article in journal (Refereed)
    Abstract [en]

    This article is concerned with the impact of large-scale wind farms utilising doubly fed induction generators on the stability of a general power system. Inspection of the eigenstructure of the power system provides a foundation for assessing the impact, which is then quantified by means of detailed numerical simulations. Simplified state-space models are used to describe the dynamics of the generators in a very simple system, whose network is described by algebraic relations. A third order model is derived for a doubly fed induction generator. Mathematical models are then used to identify the behavioural patterns of the system when it is subject to disturbances. Eigenvalue analysis reveals some interesting properties of the system for small disturbances, and shows that the addition to a power system of doubly fed generators, such as those in wind farms, improves the response of the system to small disturbances. However, numerical simulations show that it can have an adverse impact after larger disturbances.

  • 25.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Latorre, Hector
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Operation of Doubly Fed Induction Generators in Power Systems with VSC-HVDC Transmission2010In: AC and DC Power Transmission, 2010. ACDC, 2010, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this article we investigate the interaction of a wind park comprising doubly fed induction generators and a VSC-HVDC link in a test power system. We look at the combined impact of the components on power oscillation damping and voltage support.

  • 26.
    Elkington, Katherine
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Slootweg, J. G.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Kling, W. L.
    Reduced-Order Modelling of Wind Turbines2012In: Wind Power in Power Systems, John Wiley & Sons, 2012, 2, p. 821-847Chapter in book (Refereed)
    Abstract [en]

    In this chapter power system dynamics simulation(PSDS) isused to study the dynamics of large-scale power systems. It is necessary to incorporate models of wind turbine generating systems into PSDS software packages in order to analyse the impact of high wind power penetration on electrical power systems. These models need to match the assumptions and simplifications applied in this type of simulation. This chapter presents models that can be used to represent wind turbines in PSDSs. We give a brief introduction to PSDS, and describe the three main wind turbine types and the assumptions on which they are modelled. We then present the models of the various subsystems of each of the most important current wind turbine types are then presented. The response of the models to a simulated wind speed sequence is then shown.

  • 27.
    Eriksson, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Beerten, J.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Belmans, R.
    Optimizing DC voltage droop settings for AC/DC system interactions2014In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 29, no 1, p. 362-369Article in journal (Refereed)
    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.

  • 28.
    Ghandari, Mehrdad
    KTH, Superseded Departments, Electric Power Systems.
    Control of power oscillations in transmission systems using controllable series devices1997Licentiate thesis, monograph (Other scientific)
  • 29.
    Ghandhari, M.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Application of control Lyapunov functions to static var compensator2002In: IEEE Conference on Control Applications - Proceedings, Glasgow, 2002, Vol. 1, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper a control strategy for Static Var Compensator (SVC) is derived. The derived control strategy is based on Control Lyapunov Functions (CLF). The input signals of the derived control strategy can be relied on local or remote information. In this paper, the remote input signals will be used. These signals can be identified by applying the Single Machine Equivalent (SIME) method.

  • 30.
    Ghandhari, M
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Andersson, G
    Noroozian, M
    Angquist, L
    Non-linear Control of Controllable Series Devices (CSD)1997In: Proc. of the 29th NAPS, Wyoming, USA, pp. 398-403, Oct. 1997, 1997, p. 398-403Conference paper (Refereed)
  • 31.
    Ghandhari, Mehrdad
    KTH, Superseded Departments, Electric Power Systems.
    Control Lyapunov Functions: A Control Strategy for Damping of Power Oscillations in Large Power Systems2000Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    In the present climate of deregulation and privatisation, theutilities are often separated into generation, transmission anddistribution companies so as to help promote economic efficiencyand encourage competition. Also, environmental concerns,right-of-way and cost problems have delayed the construction ofboth generation facilities and new transmission lines while thedemand for electric power has continued to grow, which must bemet by increased loading of available lines. A consequence isthat power system damping is often reduced which leads to a poordamping of electromechanical power oscillations and/or impairmentof transient stability. The aim of this thesis is to examine theability of Controllable Series Devices (CSDs), such as

    Unified Power Flow Controller (UPFC)

     

    Controllable Series Capacitor (CSC)

     

    Quadrature Boosting Transformer (QBT)

     

    for improving transient stability and damping ofelectromechanical oscillations in a power system.

    For these devices, a general model is used in power systemanalysis. This model is referred to as injection model which isvalid for load flow and angle stability analysis. The model isalso helpful for understanding the impact of the CSDs on powersystem stability.

    A control strategy for damping of electromechanical poweroscillations is also derived based on Lyapunov theory. Lyapunovtheory deals with dynamical systems without input. For thisreason, it has traditionally been applied only to closed-loopcontrol systems, that is, systems for which the input has beeneliminated through the substitution of a predetermined feedbackcontrol. However, in this thesis, Lyapunov function candidatesare used in feedback design itself by making the Lyapunovderivative negative when choosing the control. This controlstrategy is called Control Lyapunov Function (CLF) for systemswith control input.

  • 32.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dynamic Analysis of Power Systems, Part I2006Other (Other academic)
  • 33.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dynamic Analysis of Power Systems, Part II2006Other (Other academic)
  • 34.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Stability of Power Systems, An Introduction2011Other (Other academic)
  • 35.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The impact of FACTS and HVDC Systems on Transient Stability and Power Oscillation Damping2007Other (Other academic)
  • 36.
    Ghandhari, Mehrdad
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Andersson, G.
    A damping control strategy for controllable series capacitor (CSC)1999Conference paper (Refereed)
  • 37.
    Ghandhari, Mehrdad
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Andersson, G.
    KTH, Superseded Departments, Electrical Systems.
    Two various control laws for controllable series capacitor (CSC)1999In: Electric Power Engineering, 1999. PowerTech Budapest 99. International Conference on, 1999Conference paper (Refereed)
    Abstract [en]

    A controllable series capacitor (CSC) with suitable control schemes can improve power system transient stability and help to damp electromechanical oscillations. This paper examines the improvement of power system dynamics when a CSC is controlled by either a control Lyapunov function (CLF) or variable structure control (VSC). The effectiveness of the proposed control laws are demonstrated in a single machine infinite bus (SMIB) power system.

  • 38.
    Ghandhari, Mehrdad
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Andersson, G.
    Hiskens, I. A.
    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)
    Abstract [en]

    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.

  • 39.
    Ghandhari, Mehrdad
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Andersson, G.
    Pavella, M.
    Ernst, D.
    A control strategy for controllable series capacitor in electric power systems2001In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 37, no 10, p. 1575-1583Article in journal (Refereed)
    Abstract [en]

    It has been verified that a controllable series capacitor with a suitable control scheme can improve transient stability and help to damp electromechanical oscillations. A question of great importance is the selection of the input signals and a control strategy for this device in order to damp power oscillations in an effective and robust manner. 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 Lyapunov derivative negative when choosing the control. This control strategy is called control Lyapunov function for systems with control inputs. Also, two input signals for this control strategy are used. The first one is based on local information and the second one on remote information derived by the single machine equivalent method.

  • 40.
    Hamon, Camille
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Elkington, Katherine
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Doubly-fed Induction Generator Modeling and Control in DigSilent PowerFactory2010In: 2010 International Conference on Power System Technology: Technological Innovations Making Power Grid Smarter, POWERCON2010, IEEE , 2010, p. 1-7Conference paper (Refereed)
    Abstract [en]

    Several computer programs exist to carry out dynamicsimulations and this study will focus on one of them,namely DigDilent PowerFactory. It offers two built-in modelsof doubly-fed induction generator. A new model has also beendeveloped, based upon a controllable voltage source. Thesethree models are compared, in terms of dynamic behavior andsimulation time. One of them is then used to study the impact ofan input control signal based on the single machine equivalentmethod. This signal provides power oscillation damping.

  • 41. Hejri, Mohammad
    et al.
    Mokhtari, Hossein
    Azizian, Mohammad Reza
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    On the Parameter Extraction of a Five-Parameter Double-Diode Model of Photovoltaic Cells and Modules2014In: IEEE Journal of Photovoltaics, ISSN 2156-3381, Vol. 4, no 3, p. 915-923Article in journal (Refereed)
    Abstract [en]

    The main contribution of this paper is to present a new set of approximate analytical solutions for the parameters of a photovoltaic (PV) five-parameter double-diode model that can be used as initial values for the numerical solutions based on the Newton-Raphson method. The proposed formulations are developed based on only the limited information given by the PV manufacturers, i.e., the open-circuit voltage (V-oc), the short circuit current (I-sc), and the current and voltage at the maximum power point (I-m and V-m). Compared with the existing techniques that require the entire experimental I-V curve or additional information such as the slope of the I-V curves of the open circuit and the short circuit points, the proposed technique is quite independent of these additional data, and, it is therefore, a low cost and fast parameter extraction method. The accuracy of the theoretical I-V curves is evaluated through the comparison of the simulation results and experimental data. The results of the application of the proposed technique to different PV modules show the accuracy and validity of the proposed analytical-numerical method.

  • 42.
    Herbig, Arnim
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Ghandhari Alavijh, Mehrdad
    KTH, Superseded Departments, Electrical Systems.
    Jones, Lawrence Edmund
    KTH, Superseded Departments, Electrical Systems.
    Lee, Denis
    KTH, Superseded Departments, Electrical Systems.
    Andersson, Göran
    KTH, Superseded Departments, Electrical Systems.
    Power flow and stability control in power systems1998In: Bulk Power Systems Dynamics and Control IV Restructuring: Symposium Proceedings / [ed] Fink, L. H.; Vournas, C. D., 1998, p. 91-104Conference paper (Refereed)
  • 43.
    Knyazkin, Valerijs
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Ghandhari, Mehrdad
    KTH, Superseded Departments, Electrical Systems.
    Canizares, Claudio A.
    On the Transient Stability of Large Wind Farms2004In: Proc.11th International Power Electronics and Motion Control Conference, EPEPEMC, 2004Conference paper (Refereed)
  • 44.
    Knyazkin, Valery
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Mehrdad, Ghandhari
    KTH, Superseded Departments, Electrical Systems.
    Canizaris, Claudio
    Application of Extended Invariance Principle to Transient Stability Analysis of Asynchronous Generators2004In: Bulk Power System Dynamics and Control - VI, 2004, p. 513-521Conference paper (Refereed)
    Abstract [en]

    This paper reports preliminary results of a studyconcerned with the questions related to the transient stabilityof power systems with asynchronous generators. In this studythe asynchronous generators represent a large-scale wind farmconsisting of fixed-speed wind turbines with fixed pitch. Theobjective of the study is to develop a framework for studyingthe transient stability of the asynchronous generators similar tothat of synchronous generators, i.e., an attempt is made to applya Lyapunov/energy function method to the simple power systemwith asynchronous generators.Detailed analysis is performed in order to verify the existenceof a proper Lyapunov function for the system at hand.It was demonstrated analytically that four commonly knownmethods for the construction Lyapunov functions cannot yielda Lyapunov function for the system under consideration, whichindicates that the construction of such a function might be avery difficult mathematical task.A recent development of the theory of nonlinear differentialequations resulted in the discovery of the Extended InvariancePrinciple, which substantially broadens the class of functionsthat can be utilized as Lyapunov functions. The ExtendedInvariance Principle is found capable of constructing an energylikefunction for the power system treated in this paper.Although the Extended Invariance Principle allows a largerclass of functions to be applied for stability studies of powersystems, it comes at the expense of having to perform certainoperations on sets of reals.This paper also addresses the numerical problems inherentin the Extended Invariance Principle by utilizing the methodsof interval arithmetics and, based on the results obtained,presents an extended Lyapunov function for the assessment ofthe transient stability properties of a simple power system.A numerical example is used to illustrate the applicationof Extended Invariance Principle and interval arithmetics forsystem stability analysis of a simplified model of a wind farm.

  • 45.
    Kotb, Omar
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Eriksson, Robert
    Tech Univ Denmark, Dept Elect Engn, Bldg 325, DK-2800 Lyngby, Denmark..
    Sood, Vijay K.
    UOIT, Dept Elect & Comp Engn, Oshawa, ON L1H 7K4, Canada..
    Control of a Hybrid HVDC Link to Increase Inter-regional Power Transfer2016In: PROCEEDINGS OF THE 18TH MEDITERRANEAN ELECTROTECHNICAL CONFERENCE MELECON 2016 / [ed] Kyriakides, E Kyriacou, E Ellinas, G Louca, S Mavromoustakis, C Michael, D Vassiliou, V Hadjichristofi, G Georgiou, J Panayiotou, C Paschalidou, A Loizou, C Pattichis, CS, IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    This paper examines the application of a hybrid HVDC link in a two area power system with the purpose of increasing the inter-regional power transfer. A hybrid HVDC system combines both LCCs and VSCs, and hence it is capable of combining the benefits of both converter technologies, such as reduced cost and power losses due to the LCCs, and ability to connect to weak AC grids due to the VSCs. The mathematical model of the power system including the HVDC link is presented. The increase in inter-area power transfer is demonstrated and compared to the case when the hybrid HVDC link is not used. Furthermore, the transient stability of the AC/DC power system was enhanced using auxiliary controllers for Power Oscillation Damping (POD). The results show the ability of the hybrid HVDC link to increase the unidirectional inter-area power transfer, while enhancing the transient stability of the power system.

  • 46.
    Kotb, Omar
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Renedo, Javier
    Comillas Pontifical Univ, IIT Inst Res Technol, Madrid 28015, Spain..
    Rouco, Luis
    Comillas Pontifical Univ, IIT Inst Res Technol, Madrid 28015, Spain..
    Eriksson, Robert
    Swedish Natl Grid, Svenska Kraftnat, S-17224 Sundbyberg, Sweden..
    On the Design and Placement of a Supplementary Damping Controller in an Embedded VSC-MTDC Network2017In: 2017 IEEE PES INNOVATIVE SMART GRID TECHNOLOGIES CONFERENCE EUROPE (ISGT-EUROPE), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    This paper investigates the optimal placement and design of a Power Oscillation Damping (POD) controller within an embedded VSC-MTDC network. As VSC-MTDC networks are expected to play an eminent role in interconnecting AC grids, there is a growing need to optimize the placement and design of supplementary controllers in the MTDC converters, in order to maximize their benefit to the connected AC systems. Based on small signal stability analysis of the system, the location of damping controller within the MTDC network is selected according to the eigenvalue sensitivity of poorly damped oscillatory modes. On the other hand, the design of the damping controller is based on Modal Linear Quadratic Gaussian (MLQG) control that uses Wide Area Measurement Signals (WAMS). The results show the ability of the controller to enhance the damping in the system in case of disturbances, as well as to improve the small signal stability by boosting the damping of inter-area modes.

  • 47.
    Kotb, Omar
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Eriksson, R.
    Leelaruji, R.
    Sood, V. K.
    Stability enhancement of an interconnected AC/DC power system through VSC-MTDC operating point adjustment2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 151, p. 308-318Article in journal (Refereed)
    Abstract [en]

    This paper investigates the improvement of dynamic and transient stability in interconnected AC/DC power systems through operating point adjustment in an embedded VSC-MTDC network. Hopf Bifurcation (HB) is known to result in oscillatory instability in the power system, therefore a sufficient margin to HB has to be maintained to enhance the dynamic stability and ensure a secure operation of the system. The enhancement of dynamic stability is based on the adjustment of the MTDC converters’ controller setpoints to drive the system away from HB point and increase the damping of oscillatory modes. The variation of each setpoint is calculated in proportion to the eigenvalue sensitivity to the respective setpoint. On the other hand, transient stability enhancement is based on operating point adjustment according to Power Transfer Distribution Factors (PTDFs) with the aim to reduce inter-area power flow over AC lines. The proposed method is applied to a VSC-MTDC network interconnecting two IEEE 14-bus sections. The results show an improvement in the system's stability margin in case of various disturbances such as load increase and short circuit fault. Time-domain simulations in DIgSILENT are used to corroborate the results obtained through small signal stability analysis.

  • 48.
    Kotb, Omar
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems. KTH.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Eriksson, Robert
    Svenska Kraftnät.
    Sood, Vijay
    UOIT.
    On small signal stability of an AC/DC power system with a hybrid MTDC network2016In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 136Article in journal (Refereed)
    Abstract [en]

    Multi-terminal HVDC (MTDC) networks are being contemplated for large scale integration of renewable energy sources, as well as for the interconnection of asynchronous AC systems. A hybrid MTDC network that combines line commutated converters (LCCs) and voltage source converters (VSCs) can combine the benefits of both technologies. This paper presents a mathematical model of an AC/DC power system with an embedded hybrid MTDC network interconnection. Small signal stability analysis of the power system is conducted based on the linearization of the model. The impact of VSC controller gains on the dominant modes in the system is investigated. The contributions of the converters and generators to different modes of the system are investigated based on the participation matrix analysis. Auxiliary controllers are applied at the converters for the purpose of damping power oscillations in case of disturbances. The results of small signal stability analysis are validated by time-domain simulations in MATLAB.

  • 49.
    Kotb, Omar
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    Sood, Vijay K.
    A study on the control of a hybrid MTDC system supplying a passive network2014In: POWERCON 2014 - 2014 International Conference on Power System Technology: Towards Green, Efficient and Smart Power System, Proceedings, 2014, p. 2427-2432Conference paper (Refereed)
    Abstract [en]

    A hybrid Multi-Terminal DC (MTDC) system can combine the benefits of both Line Commutated Converter (LCC) and Voltage Source Converter (VSC) technologies in the form of reduced losses and flexibility to connect to weak and passive grids. In this paper, an analysis of control strategies used in a hybrid MTDC system is presented. A case study of a four terminal hybrid MTDC system supplying a passive AC network was considered for simulation study. A control scheme based on voltage margin was developed to cope with the condition of main DC voltage controlling station tripping. Two various control scenarios for controlling the VSCs connected to the passive network were presented and compared. The system performance was studied through EMTP-RV simulations under different disturbances. The results show the ability of selected converter control modes and proposed control schemes to operate the hybrid MTDC system under different disturbance conditions.

  • 50.
    Latorre, Hector F.
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari Alavijh, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Improvement of Voltage Stability by Using VSC-HVdc2009In: T& D ASIA: 2009 TRANSMISSION & DISTRIBUTION CONFERENCE & EXPOSITION: ASIA AND PACIFIC, NEW YORK: IEEE , 2009, p. 275-278Conference paper (Refereed)
    Abstract [en]

    This paper analyzes and compares the stability of a power system when either a new ac transmission line or a dc link based on VSCs is connected in the grid. The location of the new transmission line is determined by the restrictions in the transfer of power. From the controllability point of view, this is not the most suitable location for a VSC-HVdc to provide damping. However the voltage support capability of the VSC-HVdc can be exploited to keep the system from losing synchronism due to voltage collapse.

12 1 - 50 of 93
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