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  • 1.
    Chompoobutrgool, Yuwa
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Development and Implementation of the Nordic Grid Model for Power System Small-Signal and Transient Stability Studies in a Free and Open Source Software2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, p. 6344571-Conference paper (Refereed)
    Abstract [en]

    This article presents an implementation of a Nordic grid model in Power System Analysis Toolbox (PSAT) -a free and open-source software. A newly developed hydro turbine and hydro governor (HTG) model is implemented with this grid model and compared with the currently available PSAT turbine and governor models. Small-signal and transient stability analyses of the system using the two models are carried out and compared to demonstrate the difference and necessity of accurate hydro turbine and governor model utilization. The paper ends with a validation of the linearized Nordic grid model generated by PSAT including the newly implemented HTG models. This validation is done through nonlinear time-domain simulation by applying both large and small disturbances.

  • 2.
    Hasan, Md Rokibul
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. SF, Norwegian Transmission System Operator, Norway .
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Khan, Naveed Ahmad
    Generic High Level VSC-HVDC Grid Controls and Test Systems for Offline and Real Time Simulation2014In: 9th International: 2014 Electric Power Quality and Supply Reliability Conference, PQ 2014 - Proceedings, IEEE Computer Society, 2014, p. 57-64Conference paper (Refereed)
    Abstract [en]

    This article describes generic high level control models for VSC-HVDC grid systems. An average value model of the voltage source converter (VSC) is used; it includes the vector current control strategy. As an improvement to traditional conventional high-level control systems, this paper includes dc voltage, negative sequence current and dc voltage droop control loops. To validate the controller's performances, two tests systems were developed: a point-to-point link and a four-terminal DC grid. Both offline and real-time simulations are carried out for several test scenarios. A methodology for calibrating controller parameters is presented and used to tune the controls of each test system considering the different scenarios presented. All simulation models were developed in SimPowerSystem/Simulink and prepared using the RT-LAB software from Opal-RT for real-time simulation; real-time simulation performance of the simulation models is also discussed.

  • 3.
    Khan, Naveed Ahmad
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. HVDC ABB AB, Dept Syst Studies, Ludvika, Sweden.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Stattnet SF, Oslo, Norway.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Haider, Arif
    KTH, School of Electrical Engineering (EES), Electric Power Systems. HVDC ABB AB, Dept Syst Studies, Ludvika, Sweden.
    Hybrid Nearest Level and open loop control of Modular Multilevel Converters with N+1 and 2N+1 levels2014In: Power Electronics and Applications (EPE'14-ECCE Europe), 2014 16th European Conference on, IEEE conference proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    In this paper a Nearest Level Control with open loop approach for modular multilevel converter (MMC) is proposed. By using open loop approach it is possible to suppress circulating currents without using feedback controllers. Moreover, with this method, both N+1 and 2N+1 levels (N=number of sub-modules) can be obtained at the output voltage. In addition, the voltage quality is improved and the total harmonic distortion is reduced at higher and lower modulation indices by increasing the number of levels up to 2N+1. Simulation results of 3-phase MMC are presented for both 2N+1 and N+1 levels together with the description of proposed Nearest Level Control scheme.

  • 4.
    Li, Wei
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    PMU-based State Estimation for Hybrid AC and DC Grids2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Power system state estimation plays key role in the energy management systems(EMS) of providing the best estimates of the electrical variables in the grid that arefurther used in functions such as contingency analysis, automatic generation control,dispatch, and others. The invention of phasor measurement units (PMUs) takes thepower system operation and control into a new era, where PMUs’ high reportingrate and synchronization characteristics allow the development of new wide-areamonitoring, protection, and control (WAMPAC) application to enhance the grid’sresiliency. In addition, the large number of PMU installation allows the PMU-onlystate estimation, which is ready to leap forward today’s approach which is based onconventional measurements.At the same time, high voltage direct current (HVDC) techniques enable totransmit electric power over long distance and between different power systems,which have become a popular choice for connecting variable renewable energy sourcesin distant locations. HVDCs together with another type of power electronic-baseddevices, flexible AC transmission system (FACTS), have proven to successfullyenhance controllability and increase power transfer capability on a long-term costeffectivebasis. With the extensive integration of FACTS and HVDC transmissiontechniques, the present AC networks will merge, resulting in large-scale hybrid ACand DC networks. Consequently, power system state estimators need to considerDC grids/components into their network models and upgrade their estimationalgorithms.This thesis aims to develop a paradigm of using PMU data to solve stateestimations for hybrid AC/DC grids. It contains two aspects: (i) formulating thestate estimation problem and selecting a suitable state estimation algorithm; (ii)developing corresponding models, particularly for HVDCs and FACTS.This work starts by developing a linear power system model and applying thelinear weighted least squares (WLS) algorithm for estimation solution. Linear networkmodels for the AC transmission network and classic HVDC links are developed. Thislinear scheme simplifies the nonlinearities of the typical power flow network modelused in the conventional state estimations and has an explicit closed-form solution.However, as the states are voltage and current phasors in rectangular coordinates,phasor angle is not an explicit state in the modeling and estimation process. Thisalso limits the linear estimators’ ability to deal with the corrupt angle measurementsresulting from timing errors or GPS spoofing. Additionally, it is cumbersome toselect state variables for an inherently nonlinear network model, e.g., classic HVDClink, when trying to fulfill its linear formulation requirement.In contrast, it is more natural to use PMU measurements in polar coordinatesbecause they can provide an explicit state measurement set to be directly used inthe modeling and estimation process without form changes, and more importantly,it allows detection and correction for angle bias which emerges due to imperfectsynchronization or incorrect time-tagging by PMUs. To this end, the state estimationproblem needs to be formulated as a nonlinear one and the nonlinear WLS is applied for solution. We propose a novel measurement model for PMU-based state estimationwhich separates the errors due to modeling uncertainty and measurement noise sothat different weights can be assigned to them separately. In addition, nonlinearnetwork models for AC transmission network, classic HVDC link, voltage sourceconverter (VSC)-HVDC, and FACTS are developed and validated via simulation.The aforementioned linear/nonlinear modeling and estimation schemes belongto static state estimator category. They perform adequately when the system isunder steady-state or quasi-steady state, but less satisfactorily when the system isunder large dynamic changes and the power electronic devices react to these changes.Testing results indicate that additional modeling details need to be included toobtain higher accuracy during system dynamics involving fast responses from powerelectronics. Therefore, we propose a pseudo-dynamic modeling approach that canimprove estimation accuracy during transients without significantly increasing theestimation’s computational burden. To illustrate this approach, the pseudo-dynamicnetwork models for the static synchronous compensator (STATCOM), as an exampleof a FACTS device, and the VSC-HVDC link are developed and tested.Throughout this thesis, WLS is the main state estimation algorithm. It requiresa proper weight quantification which has not been subject to a sufficient attentionin literature. In the last part of thesis, we propose two approaches to quantify PMUmeasurement weights: off-line simulation and hardware-in-the-loop (HIL) simulation.The findings we conclude from these two approaches will provide better guidancefor selecting proper weights for power system state estimation.

  • 5.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric power and energy systems. Statnett SF, Norway.
    A PMU-based state estimator for networks containing FACTS devices2015In: 2015 IEEE Eindhoven PowerTech, PowerTech 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    This paper presents a PMU-based state estimation algorithm that considers the presence of flexible AC transmission system (FACTS). The models of FACTS devices, including thyristor- and converter-based devices, are developed and then combined with an AC network model. Considering the characteristics of PMU measurements, the network model for state estimation is separated from the measurements. By applying the nonlinear weighted least squares (WLS) algorithm, a PMU-based state estimator can estimate the states of an AC system and its embedded FACTS devices simultaneously. To validate the algorithm, simulation studies for a 9-bus system are performed.

  • 6.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, Research and Development, Oslo, Norway.
    A PMU-Based State Estimator For Networks Containing VSC-HVDC links2015In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    This paper presents a PMU-based state estimation algorithm that considers the presence of voltage source converter-based high voltage direct current (VSC-HVDC) links. The network model of a VSC-HVDC link with its control modes is developed and then combined with an AC model to accomplish a hybrid AC/DC network model. The measurement model in this algorithm considers the properties of PMU measurements, thus separating the network model with measurements. Additionally, DC link measurements are assumed to be sampled synchronously, time-stamped and reported at the same rate as PMU measurements. Then, by applying the nonlinear weighted least squares (WLS) algorithm, a PMU-based state estimator can solve for both AC and DC states simultaneously. To validate the algorithm, a simulation study for a 6-bus hybrid AC/DC test system is shown in this paper.

  • 7.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Inclusion of Classic HVDC links in a PMU-based state estimator2014In: PES General Meeting | Conference & Exposition, 2014 IEEE, IEEE conference proceedings, 2014, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This article presents a PMU-based state estimator algorithm that considers the presence of classic HVDC links. A hybrid AC/DC network model is developed to combine the AC network and DC links. The algorithm assumes that DC link measurements can be sampled synchronously, are time-stamped and reported at the same rate as PMU measurements. Then, by applying the weighted least squares algorithm, a linear state estimator can solve for both AC and DC states simultaneously. To validate the algorithm, a state estimation model is built for a 9-bus and the KTH-Nordic 32 systems, for both AC-only and hybrid AC/DC networks. In addition, the influence of losing DC measurements and effects of measurement noise on the state estimator are briefly discussed.

  • 8.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Chompoobutrgool, Yuwa
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Development and implementation of hydro turbine and governor models in a free and open source software package2012In: Simulation (San Diego, Calif.), ISSN 1569-190X, E-ISSN 1878-1462, Vol. 24, p. 84-102Article in journal (Refereed)
    Abstract [en]

    This article studies accurate and detailed hydro turbine and governor models, and implements these models in Power System Analysis Toolbox (PSAT)-a free and open source software. The implementation of these models in PSAT is approached using a general methodology, which is described in detail. To evaluate the performances of the developed hydro turbine and governor models, simulation studies are carried out on test systems of different scales, from a single-machine infinite-bus (SMIB) system to a larger system which includes 20 generators. Further more, transient stability analysis and small signal stability analysis are carried out to assess the performance of the implemented models.

  • 9.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Farrokhabadi, Mostafa
    Modeling of Custom Hydro Turbine and Governor Models for Real-Time Simulation2012In: 2012 IEEE COMPENG 2012: Workshop on Complexity in Engineering, IEEE conference proceedings, 2012, p. 83-88Conference paper (Refereed)
    Abstract [en]

    This article develops three different hydro turbineand governor (HTG) models to fulfill adequate modeling requirements for the representation of hydro power generation inthe Nordic grid. To validate the performance of the developed models, both off-line and real-time simulation studies on a single machine infinite-bus (SMIB) system are carried out. Apart from SMIB system, real-time simulations are also executed for alarger scale power system—the IEEE Reliability Test System1996 (IEEE RTS 96) in this article to determine the models’dynamic performance in larger and more complex networks. Inaddition, how to properly transfer an off-line models developedin SimPowerSystems (SPS) for real-time simulation in RT-LAB is addressed; including valuable experiences obtained from these simulation exercises.

  • 10.
    Rogersten, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, R and D, Oslo, Norway.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Towards Consistent Model Exchange and Simulation of VSC-HVdc Controls for EMT Studies2015In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Design of voltage source converters (VSC) for high-voltage direct current (HVdc) systems requires extensive simulation tools that are accurate and reliable. Before the installation of VSC-HVdc links, different simulation-based studies need to be performed by different parties and using different electromagnetic transient (EMT) simulation platforms. Previous work shows that even with a pedantic re-implementation of the models from the ground up, simulation results are still inconsistent between different EMT tools. This paper demonstrates a methodology, which provides a higher consistency between the simulation tools Simulink and PSCAD. This methodology is complex and exposes several limitations. Hence, the is a need for the adoption of a standardized equation-based modeling language for EMT model exchange.

  • 11.
    Rogersten, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Zhang, Lidong
    ABB, Sweden.
    Mitra, Pinaki
    ABB, Sweden.
    A Quantitative Method for the Assessment of VSC-HVdc Controller Simulations in EMT Tools2014In: Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), 2014 IEEE PES, IEEE conference proceedings, 2014, p. 1-5Conference paper (Refereed)
    Abstract [en]

    Voltage-Source Converter-Based High-voltage dc (VSC-HVdc) technology has received growing interest during recent years due to its benefits for separated active and reactive power control. Before the installation of VSC-HVdc links, different simulation-based studies need to be performed, usually by different parties and using different electromagnetic transient (EMT) simulation platforms. This paper provides a systematic method to assess discrepancies between simulation tools. Models of the VSC and its control systems are implemented from scratch in two different tools. A metric and a methodology to quantitatively assess the discrepancies between simulation results is proposed and illustrated. The paper shows that even with a pedantic re-implementation of the models from the ground up, simulation results are still inconsistent. The objective of this paper is to develop a quantification method for comparing the models developed in different EMT simulation tool and to emphasize differences that can arise with the numerical solvers in such tools.

  • 12.
    Vanfretti, Luigi
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Khan, N. A.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hasan, Md Rokibul
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Haider, A.
    Generic VSC and low level switching control models for offline simulation of VSC-HVDC systems2014In: 9th International: 2014 Electric Power Quality and Supply Reliability Conference, PQ 2014 - Proceedings, IEEE Computer Society, 2014, p. 265-272Conference paper (Refereed)
    Abstract [en]

    This article proposes and implements generic and detailed voltage source converter (VSC) models, and low-level switching control models for simulation of HVDC networks using Modular Multilevel Converters (MMCs) or conventional two-level converters. The low level control approaches for both MMCs and two-level converters are explained. The behavior of the test HVDC networks is analyzed with the detailed model of both types of converter. In addition, high level controls are briefly explained, focusing on their application in DC grids. The simulation results of test networks validate the proposed high level controls and low level switching controls for simulation with detailed models of MMCs and conventional two-level converters.

  • 13.
    Vanfretti, Luigi
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Bogodorova, Tetiana
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Panciatici, Patrick
    RTE, France.
    Unambiguous Power System Dynamic Modeling and Simulation using Modelica Tools2013In: 2013 IEEE Power and Energy Society General Meeting (PES), IEEE , 2013, p. 21-25Conference paper (Refereed)
    Abstract [en]

    Dynamic modeling and time-domain simulation for power systems is inconsistent across different simulation platforms, which makes it difficult for engineers to consistently exchange models and assess model quality. Therefore, there is a clear need for unambiguous dynamic model exchange. In this article, a possible solution is proposed by using open modeling equation-based Modelica tools. The nature of the Modelica modeling language supports model exchange at the 'equation-level', this allows for unambiguous model exchange between different Modelica-based simulation tools without loss of information about the model. An example of power system dynamic model exchange between two Modelica-based software Scilab/Xcos and Dymola is presented. In addition, common issues related to simulation, including the extended modeling of complex controls, the capabilities of the DAE solvers and initialization problems are discussed. In order to integrate power system Modelica models into other simulation tools (Matlab/Simulink), the utilization of the FMI Toolbox is investigated as well.

  • 14.
    Vanfretti, Luigi
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, R&D, Oslo, Norway.
    Li, Wei
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Egea-Alvarez, Agusti
    Gomis-Bellmunt, Oriol
    Generic VSC-Based DC Grid EMT Modeling, Simulation, and Validation on a Scaled Hardware Platform2015In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    This paper presents results from the KIC InnoEnergy project: Generic DC grid off-line and real-time simulation models and tools (Action 2.1, Subtask 2.1.1). The work reported here is focused on the development of a generic voltage source converter (VSC) model and its control schemes. Different test systems were designed and implemented in simulation tools and an experimental platform to verify the proposed generic model. Consistent simulation and emulation performances indicate that the generic model and its control schemes are applicable for VSC-HVDC operation, and thus, they can facilitate further research and development in DC grids.

1 - 14 of 14
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