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Li, W. (2018). PMU-based State Estimation for Hybrid AC and DC Grids. (Doctoral dissertation). KTH Royal Institute of Technology
Open this publication in new window or tab >>PMU-based State Estimation for Hybrid AC and DC Grids
2018 (English)Doctoral 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.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 123
Series
TRITA-EECS-AVL
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-224445 (URN)978-91-7729-723-9 (ISBN)
Public defence
2018-04-12, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, 761651
Note

QC 20180319

Available from: 2018-03-19 Created: 2018-03-17 Last updated: 2018-03-19Bibliographically approved
Li, W. & Vanfretti, L. (2015). A PMU-based state estimator for networks containing FACTS devices. In: 2015 IEEE Eindhoven PowerTech, PowerTech 2015: . Paper presented at IEEE Eindhoven PowerTech, PowerTech 2015, 29 June 2015 through 2 July 2015. IEEE conference proceedings
Open this publication in new window or tab >>A PMU-based state estimator for networks containing FACTS devices
2015 (English)In: 2015 IEEE Eindhoven PowerTech, PowerTech 2015, IEEE conference proceedings, 2015Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
Keywords
Flexible AC transmission system, Phasor measurement units, State estimation, Algorithms, Power electronics, Units of measurement, AC network Model, Flexible ac transmission system (FACTS), Network modeling, Nonlinear weighted least-squares, PMU measurements, Simulation studies, State estimation algorithms, State Estimators, Flexible AC transmission systems
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-181174 (URN)10.1109/PTC.2015.7232725 (DOI)000380546800492 ()2-s2.0-84951309711 (Scopus ID)9781479976935 (ISBN)
Conference
IEEE Eindhoven PowerTech, PowerTech 2015, 29 June 2015 through 2 July 2015
Note

QC 20160210

Available from: 2016-02-10 Created: 2016-01-29 Last updated: 2016-10-06Bibliographically approved
Li, W. & Vanfretti, L. (2015). A PMU-Based State Estimator For Networks Containing VSC-HVDC links. In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING: . Paper presented at General Meeting of the IEEE-Power-and-Energy-Society, JUL 26-30, 2015, Denver, CO. IEEE
Open this publication in new window or tab >>A PMU-Based State Estimator For Networks Containing VSC-HVDC links
2015 (English)In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2015Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE, 2015
Series
IEEE Power and Energy Society General Meeting PESGM, ISSN 1944-9925
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-184579 (URN)10.1109/PESGM.2015.7285679 (DOI)000371397500087 ()2-s2.0-84956855663 (Scopus ID)978-1-4673-8040-9 (ISBN)
Conference
General Meeting of the IEEE-Power-and-Energy-Society, JUL 26-30, 2015, Denver, CO
Note

QC 20160404

Available from: 2016-04-04 Created: 2016-04-01 Last updated: 2016-04-04Bibliographically approved
Vanfretti, L., Li, W., Egea-Alvarez, A. & Gomis-Bellmunt, O. (2015). Generic VSC-Based DC Grid EMT Modeling, Simulation, and Validation on a Scaled Hardware Platform. In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING: . Paper presented at General Meeting of the IEEE-Power-and-Energy-Society, JUL 26-30, 2015, Denver, CO. IEEE
Open this publication in new window or tab >>Generic VSC-Based DC Grid EMT Modeling, Simulation, and Validation on a Scaled Hardware Platform
2015 (English)In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2015Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE, 2015
Series
IEEE Power and Energy Society General Meeting PESGM, ISSN 1944-9925
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-184588 (URN)10.1109/PESGM.2015.7285979 (DOI)000371397501117 ()2-s2.0-84956863359 (Scopus ID)978-1-4673-8040-9 (ISBN)
Conference
General Meeting of the IEEE-Power-and-Energy-Society, JUL 26-30, 2015, Denver, CO
Note

QC 20160404

Available from: 2016-04-04 Created: 2016-04-01 Last updated: 2016-04-04Bibliographically approved
Rogersten, R., Vanfretti, L. & Li, W. (2015). Towards Consistent Model Exchange and Simulation of VSC-HVdc Controls for EMT Studies. In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING: . Paper presented at General Meeting of the IEEE-Power-and-Energy-Society, JUL 26-30, 2015, Denver, CO. IEEE
Open this publication in new window or tab >>Towards Consistent Model Exchange and Simulation of VSC-HVdc Controls for EMT Studies
2015 (English)In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2015Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE, 2015
Series
IEEE Power and Energy Society General Meeting PESGM, ISSN 1944-9925
National Category
Embedded Systems
Identifiers
urn:nbn:se:kth:diva-184583 (URN)10.1109/PESGM.2015.7285986 (DOI)000371397501124 ()2-s2.0-84956858447 (Scopus ID)978-1-4673-8040-9 (ISBN)
Conference
General Meeting of the IEEE-Power-and-Energy-Society, JUL 26-30, 2015, Denver, CO
Note

QC 20160404

Available from: 2016-04-04 Created: 2016-04-01 Last updated: 2016-04-04Bibliographically approved
Rogersten, R., Vanfretti, L., Li, W., Zhang, L. & Mitra, P. (2014). A Quantitative Method for the Assessment of VSC-HVdc Controller Simulations in EMT Tools. In: Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), 2014 IEEE PES: . Paper presented at IEEE PES ISGT Europe,12-15 Oct. 2014, IStanbul, Turkey (pp. 1-5). IEEE conference proceedings
Open this publication in new window or tab >>A Quantitative Method for the Assessment of VSC-HVdc Controller Simulations in EMT Tools
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2014 (English)In: Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), 2014 IEEE PES, IEEE conference proceedings, 2014, p. 1-5Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
Keywords
VSC-HVdc modeling and control, EMT simulation tools, Quantitative assessment method, PSCAD, Simulink
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-161751 (URN)10.1109/ISGTEurope.2014.7028824 (DOI)
Conference
IEEE PES ISGT Europe,12-15 Oct. 2014, IStanbul, Turkey
Note

QC 20150319

Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2015-03-19Bibliographically approved
Hasan, M. R., Vanfretti, L., Li, W. & Khan, N. A. (2014). Generic High Level VSC-HVDC Grid Controls and Test Systems for Offline and Real Time Simulation. In: 9th International: 2014 Electric Power Quality and Supply Reliability Conference, PQ 2014 - Proceedings. Paper presented at 9th International Conference on Electric Power Quality and Supply Reliability, PQ 2014, Rakvere, Estonia, 11 June 2014 through 13 June 2014 (pp. 57-64). IEEE Computer Society
Open this publication in new window or tab >>Generic High Level VSC-HVDC Grid Controls and Test Systems for Offline and Real Time Simulation
2014 (English)In: 9th International: 2014 Electric Power Quality and Supply Reliability Conference, PQ 2014 - Proceedings, IEEE Computer Society, 2014, p. 57-64Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE Computer Society, 2014
Keywords
Voltage Source Converter, High-level control, HVDC grid test system, controller calibration, Real-time simulation
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-158301 (URN)10.1109/PQ.2014.6866784 (DOI)000345736800009 ()2-s2.0-84907373307 (Scopus ID)978-1-4799-5022-5 (ISBN)
Conference
9th International Conference on Electric Power Quality and Supply Reliability, PQ 2014, Rakvere, Estonia, 11 June 2014 through 13 June 2014
Note

QC 20150116

Available from: 2015-01-16 Created: 2015-01-07 Last updated: 2015-01-16Bibliographically approved
Vanfretti, L., Khan, N. A., Li, W., Hasan, M. R. & Haider, A. (2014). Generic VSC and low level switching control models for offline simulation of VSC-HVDC systems. In: 9th International: 2014 Electric Power Quality and Supply Reliability Conference, PQ 2014 - Proceedings. Paper presented at 9th International Conference on Electric Power Quality and Supply Reliability, PQ 2014, 11 June 2014 through 13 June 2014, Rakvere, Estonia (pp. 265-272). IEEE Computer Society
Open this publication in new window or tab >>Generic VSC and low level switching control models for offline simulation of VSC-HVDC systems
Show others...
2014 (English)In: 9th International: 2014 Electric Power Quality and Supply Reliability Conference, PQ 2014 - Proceedings, IEEE Computer Society, 2014, p. 265-272Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE Computer Society, 2014
Keywords
controller calibration, HVDC grid test system, Low level controls, Modulation Schemes, Voltage Source Converter
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-157958 (URN)10.1109/PQ.2014.6866825 (DOI)000345736800046 ()2-s2.0-84907342299 (Scopus ID)978-147995020-1 (ISBN)
Conference
9th International Conference on Electric Power Quality and Supply Reliability, PQ 2014, 11 June 2014 through 13 June 2014, Rakvere, Estonia
Note

QC 20141219

Available from: 2014-12-19 Created: 2014-12-18 Last updated: 2015-01-09Bibliographically approved
Khan, N. A., Vanfretti, L., Li, W. & Haider, A. (2014). Hybrid Nearest Level and open loop control of Modular Multilevel Converters with N+1 and 2N+1 levels. In: Power Electronics and Applications (EPE'14-ECCE Europe), 2014 16th European Conference on: . Paper presented at EPE’14-ECCE Europe,26-28 Aug. 2014,Lappeenranta. IEEE conference proceedings
Open this publication in new window or tab >>Hybrid Nearest Level and open loop control of Modular Multilevel Converters with N+1 and 2N+1 levels
2014 (English)In: Power Electronics and Applications (EPE'14-ECCE Europe), 2014 16th European Conference on, IEEE conference proceedings, 2014Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
Keywords
Multilevel Converters, Voltage Source Converter (VSC), Modulation Strategy, Modeling, Simulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-161752 (URN)10.1109/EPE.2014.6910866 (DOI)000361460002052 ()2-s2.0-84923917534 (Scopus ID)
Conference
EPE’14-ECCE Europe,26-28 Aug. 2014,Lappeenranta
Note

QC 20150319

Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2015-10-20Bibliographically approved
Li, W. & Vanfretti, L. (2014). Inclusion of Classic HVDC links in a PMU-based state estimator. In: PES General Meeting | Conference & Exposition, 2014 IEEE: . Paper presented at 2014 IEEE PES General Meeting,27-31 July 2014,National Harbor, MD (pp. 1-5). IEEE conference proceedings
Open this publication in new window or tab >>Inclusion of Classic HVDC links in a PMU-based state estimator
2014 (English)In: PES General Meeting | Conference & Exposition, 2014 IEEE, IEEE conference proceedings, 2014, p. 1-5Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
Keywords
State estimation, Classic HVDC link, PMU, Hybrid AC and DC state estimation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-161729 (URN)10.1109/PESGM.2014.6938841 (DOI)000349551500039 ()
Conference
2014 IEEE PES General Meeting,27-31 July 2014,National Harbor, MD
Note

QC 20150319

Available from: 2015-03-15 Created: 2015-03-15 Last updated: 2015-04-17Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2845-8043

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