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Distributed Control of HVDC Transmission Grids
KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.ORCID iD: 0000-0003-3946-7655
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recent issues such as priority access of renewable resources recommended by European energy directives and increase the electricity trading among countries lead to new requirements on the operation and expansion of transmission grids. Since AC grid expansions are limited by legislative issues and long distance transmission capacity, there is a considerable attention drawn to application of HVDC transmission grids on top of, or in complement to, existing AC power systems. The secure operation of HVDC grids requires a hierarchical control system. In HVDC grids, the primary control action to deal with power or DC voltage deviations is communication-free and local. In addition to primary control, the higher supervisory control actions are needed to guarantee the optimal operation of HVDC grids. However, the implementation of supervisory control functions is linked to the arrangement of system operators; i.e. an individual HVDC operator (central structure) or sharing tasks among AC system operators (distributed structure).

This thesis presents distributed control of an HVDC grid. To this end, three possible supervisory functions are investigated; coordination of power injection set-points, DC slack bus selection and network topology identification. In this thesis, all three functions are first studied for the central structure. For the distributed solution, two algorithms based on Alternating Direction Method of Multipliers (ADMM) and Auxiliary Problem Principle (APP) are adopted to solve the coordination of power injection. For distributed selection of DC slack bus, the choice of parameters for quantitative ranking of converters is important. These parameters should be calculated based on local measurements if distributed decision is desired. To this end, the short circuit capacity of connected AC grid and power margin of converters are considered. To estimate the short circuit capacity as one of the required selection parameters, the result shows that the recursive least square algorithm can be very efficiently used. Besides, it is possible to intelligently use a naturally occurring droop response in HVDC grids as a local measurement for this estimation algorithm. Regarding the network topology, a two-stage distributed algorithm is introduced to use the abstract information about the neighbouring substation topology to determine the grid connectivity.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , p. 51
Series
TRITA-EE, ISSN 1653-5146 ; 2017:018
Keyword [en]
co-simulation, cyber-physical system, DC slack bus, distributed control, HVDC grids, power injection, topology processor, wind farms
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-202753ISBN: 978-91-7729-310-1 (print)OAI: oai:DiVA.org:kth-202753DiVA, id: diva2:1078539
Public defence
2017-04-10, F3, Lindstedtsvägen 26 - KTH campus, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170306

Available from: 2017-03-06 Created: 2017-03-05 Last updated: 2017-03-10Bibliographically approved
List of papers
1. Study of Centralized and Distributed Coordination of Power Injection in Multi-TSO HVDC Grid with Large Off-shore Wind Integration
Open this publication in new window or tab >>Study of Centralized and Distributed Coordination of Power Injection in Multi-TSO HVDC Grid with Large Off-shore Wind Integration
2016 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 136, p. 281-288Article in journal (Refereed) Published
Abstract [en]

This paper studies centralized and distributed schemes for the coordinationof power injection in an HVDC grid connected to large wind generation.This coordination of power injection aims to keep the power balanced withinthe HVDC grid especially during large wind disturbances. Furthermore, thecoordination tries to follow the converters’ schedules set by the connectingAC-TSOs every 15−minutes. This schedule comes from an overall combinedAC/DC economic dispatch calculation with lower resolution compared to thiscoordination. In this paper, the coordination of power injection has been formulatedas a non-linear constrained optimization problem for the centralizedarchitecture. Next, the centralized optimization problem is decomposed tosub-problems using the Auxiliary Problem Principle (APP) method for thedistributed architecture. This distributed optimization problem is solved byexchanging the required information between the AC TSOs. These two differentapproaches have been evaluated for a 5-terminal HVDC grid. Furthermore,a sensitivity analysis has been carried out to find the optimal updatingrate of power injection set-points. The result shows that the more frequentupdating of power injection coordination in the centralized architecture improvesthe generation reserves in each AC area.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Distributed optimization, HVDC grid, Optimal power injection, Wind farm
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-178726 (URN)10.1016/j.epsr.2016.03.001 (DOI)000375505800028 ()2-s2.0-84960905190 (Scopus ID)
Note

QC 20160413

Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2017-12-01Bibliographically approved
2. Selection of DC Voltage Controlling Station in an HVDC Grid
Open this publication in new window or tab >>Selection of DC Voltage Controlling Station in an HVDC Grid
Show others...
2016 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 144, p. 224-232Article in journal (Refereed) Published
Abstract [en]

This paper proposes a real-time quantitative evaluation of HVDC converters’ in an HVDC grid to select the suitable DC slack converter. This real-time evaluation considers the strength of connecting AC grid and the converter's on-line capacity margin as selection metrics. The strength of AC grid is evaluated in real-time by the estimation of grid short circuit capacity using recursive lease square algorithm. Given these selection metrics, the credibility of HVDC stations in controlling the DC voltage can be offered to the system operator in real-time for further operational decisions. This paper also studies the practical aspect of the estimation algorithm regarding selection of the operating points. As major contribution, it suggests to intelligently use a naturally occurring droop response in HVDC grids as a second operating point in the estimation algorithm to calculate the short circuit capacity. The method has been tested through set of scenarios using a real-time co-simulation platform. This platform includes real-time power system simulator to model AC/DC grid, industrial HVDC controllers and corresponding ICT systems. The results show that the proper selection of DC slack station can improve the AC system response and DC voltage drops during disturbances.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
HVDC grid, Short circuit capacity, Slack bus selection, Voltage control
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-180715 (URN)10.1016/j.epsr.2016.12.008 (DOI)000392889700024 ()2-s2.0-85006978465 (Scopus ID)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Note

QC 20160901

Available from: 2016-01-21 Created: 2016-01-21 Last updated: 2017-11-30Bibliographically approved
3. Real-Time Estimation of AC-Grid Short Circuit Capacity for HVDC Control Application
Open this publication in new window or tab >>Real-Time Estimation of AC-Grid Short Circuit Capacity for HVDC Control Application
Show others...
2016 (English)In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695Article in journal (Refereed) Published
Abstract [en]

Being able to estimate the AC grid strength using Short Circuit Capacity (SCC) fromthe perspective of a connected HVDC station allows adjustment of converter control parameters orto select the converter’s operational control mode. The short circuit capacity can be calculated byestimation of the grid’s impedance and its equivalent voltage. This paper presents the operationaland practical challenges in real-time implementation of the grid estimation algorithms especiallyfor HVDC applications. This paper shows that the Recursive Least Square (RLS) algorithm can bevery efficiently used for the real-time estimation of SCC. This technique forms a regression prob-lem using algebraic complex equations with an objective to minimize the error between estimatedand measured parameters. The algorithm has been reformulated and simplified to make it non-complex without the use of matrices, in order to facilitate further implementation on an industrialreal-time controller. The performance of the real-time implementation has been evaluated usinga HIL platform. A sensitivity analysis has been also carriedout to study the impact of differentparameters and operational conditions on the performance of the estimation algorithm. Finally, theactual application of real-time SCC estimation for the HVDCsystems has been demonstrated.

Place, publisher, year, edition, pages
IET, 2016
Keyword
estimation, HVDC, real-time, recursive least square, short circuit capacity
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-180714 (URN)10.1049/iet-gtd.2016.0465 (DOI)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Note

QC 20160901

Available from: 2016-01-21 Created: 2016-01-21 Last updated: 2017-11-30Bibliographically approved
4. Distributed Security-Constrained Secondary Control of HVDC grids in the Presence of Wind Uncertainty
Open this publication in new window or tab >>Distributed Security-Constrained Secondary Control of HVDC grids in the Presence of Wind Uncertainty
(English)In: Sustainable Energy, Grids and Networks, ISSN 0284-4354, E-ISSN 2352-4677Article in journal (Refereed) Submitted
Abstract [en]

This paper proposes a distributed coordination of converters in an HVDC grid in order to provide close-to-real-time optimal DCvoltage and power profiles in the presence of wind uncertainty. This coordination is a part of HVDC grid secondary control actionthat carries out after the automatic primary control response by DC voltage droop controlling converters. It aims to optimize thegrid operation by finding the new DC power and voltage set-points that minimize the operational costs due to wind fluctuations andprediction error. Furthermore, the N-1 secure operation of HVDC grid is considered in this distributed coordination by adding a setof security constraints that tightens the upper and lower bounds of the problem variables. The coordination problem is formulatedas a convex optimization problem and therefore a modified version of alternating direction method of multipliers is adopted to solvethe problem in distributed manner. The performance of distributed coordination has been tested by a set of scenarios. The resultsimply that the distributed coordination is eligible in terms of time and complexity to be considered as either the main option forsecondary coordination or a complementary back-up solution for the central coordination.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-202751 (URN)
Note

QCR 20170306

Available from: 2017-03-05 Created: 2017-03-05 Last updated: 2017-11-29Bibliographically approved
5. Distributed Two-stage Network Topology Processor for HVDC Grid Operation
Open this publication in new window or tab >>Distributed Two-stage Network Topology Processor for HVDC Grid Operation
2017 (English)In: 2017 IEEE Manchester PowerTech, Powertech 2017, IEEE, 2017, article id 7980841Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the results of an analysis of distributed two-stage coordination of network topology processor for HVDC grids. In the first stage of the two-stage processor, the substation topology is analyzed locally using an automated graph-based algorithm. Thereafter, a distributed algorithm is proposed to used the neighboring information to realize the grid connectivity. For distributed islanding detection, the connectivity problem is formulated as a set of linear equations and solved iteratively using successive-over-relaxation method. The performance of the proposed methods versus conventional one-stage method has been tested in an islanding scenario for a 5-terminal HVDC grid.

Place, publisher, year, edition, pages
IEEE, 2017
Keyword
distributed coordination, HVDC grid, topology processor
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-202752 (URN)10.1109/PTC.2017.7980841 (DOI)000411142500054 ()2-s2.0-85034774933 (Scopus ID)9781509042371 (ISBN)
Conference
12th IEEE PES PowerTech Conference, Towards and Beyond Sustainable Energy Systems, juni 18-22, Manchester, UK
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Note

QC 20170627

Available from: 2017-03-05 Created: 2017-03-05 Last updated: 2018-02-26Bibliographically approved
6. Implementation of agent-based power flow coordination in AC/DC grids using co-simulation platform
Open this publication in new window or tab >>Implementation of agent-based power flow coordination in AC/DC grids using co-simulation platform
Show others...
2014 (English)In: 2014 IEEE International Conference on Smart Grid Communications, SmartGridComm 2014, 2014, p. 188-193Conference paper, Published 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.

Keyword
Co-Simulation, DMU, Graph Theory, HVDC grid, Multi-Agent System, PSMIX-P
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-138036 (URN)10.1109/SmartGridComm.2014.7007644 (DOI)2-s2.0-84922422813 (Scopus ID)9781479949342 (ISBN)
Conference
2014 IEEE International Conference on Smart Grid Communications, SmartGridComm 2014; Venice; Italy; 3 November 2014 through 6 November 2014
Funder
StandUp
Note

QC 20150601

Available from: 2013-12-17 Created: 2013-12-17 Last updated: 2017-03-05Bibliographically approved

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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
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Output format
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