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Aspects on Dynamic Power Flow Controllers and Related Devices for Increased Flexibility in Electric Power Systems
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies different aspects of Flexible AC Transmission System (FACTS) devices which are used to improve the power transfer capability and increase the controllability in electric power systems. In the thesis, different aspects on the usage and control of Dynamic Power Flow Controllers (DPFC) and related FACTS devices are studied. The DPFC is a combination of a Phase Shifting Transformer (PST) and a Thyristor Switched Series Capacitor (TSSC)/Thyristor Switched Series Reactor (TSSR).

The thesis proposes and studies a new method, the Ideal Phase-Shifter (IPS) method, for selection and rating of Power Flow Controllers (PFC) in a power grid. The IPS method, which is based on steady-state calculations, is proposed as a first step in the design process for a PFC. The method uses the Power controller plane, introduced by Brochu et al in 1999. The IPS method extends the usage of decoupling methods in the Power controller plane to a power system of arbitrary size. The IPS method was in the thesis used to compare the ratings of different PFC:s required to improve the power transfer capability in two test systems. The studied devices were here the PST, the TSSC/TSSR and the DPFC.

The thesis treats control of ideal Controlled Series Capacitors (CSC), TCSC, TSSC/TSSR, and DPFC. The goals of the FACTS controllers which are developed are Power Oscillation Damping (POD), fast power flow control, and transient stability improvement in the power system. New adaptive control strategies for POD and power flow control are proposed and studied in different models of power systems by time-domain simulations. A strategy for transient stability improvement is also proposed and studied.

Additionally, different methods for study of Subsynchronous Resonance (SSR), which is associated with series compensation in power systems, are investigated. Here, four of the most common methods for frequency scanning to determine the electrical damping of subsynchronous oscillations in a power grid are studied. The study reveals significant differences of the electrical damping estimates of the studied standard methods when applied to a four-machine test system.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology - KTH, Stockholm, Sweden , 2011. , x, 131 p.
Series
Trita-EE, ISSN 1653-5146 ; 2011:050
Keyword [en]
Adaptive Control, Controlled Series Compensator, Dynamic Power Flow Controller, Frequency Scanning, Phase-Shifting Transformer, Power Controller Plane, Power Flow Control, Power Oscillation Damping, Subsynchronous Resonance, Thyristor Controlled Series Compensator, Thyristor Switched Series Compensator, Transient Stability
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-37823ISBN: 978-91-7501-058-8 (print)OAI: oai:DiVA.org:kth-37823DiVA: diva2:435280
Public defence
2011-09-09, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20110819Available from: 2011-08-19 Created: 2011-08-17 Last updated: 2011-08-19Bibliographically approved
List of papers
1. Estimation of grid parameters for the control of variable series reactance FACTS devices
Open this publication in new window or tab >>Estimation of grid parameters for the control of variable series reactance FACTS devices
2006 (English)In: 2006 POWER ENGINEERING SOCIETY GENERAL MEETING, VOLS 1-9, 2006, 105-111 p.Conference paper, Published paper (Refereed)
Abstract [en]

For high performance control of Flexible AC Transmission System (FACTS) devices with controllable reactances, a representation of the surrounding grid is essential. Using such a model, an adaptive control strategy can be developed which optimizes the control in real time as the grid parameters change. This paper proposes such a generic grid model and derives the theory of how to estimate the main parameters using measurements of the line active power response from small step reactance changes. The estimation methods are verified using simple grid models in PSCAD simulations and more advanced grid models using SIMPOW simulations of a modified version of the CIGRE Nordic 32 grid. This work should be thought of as a foundation for developing control systems for variable series reactance FACTS devices.

Series
IEEE Power Engineering Society General Meeting, ISSN 1932-5517
Keyword
parameter estimation, power system stability, power transmission control, prediction methods, FACTS
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8038 (URN)10.1109/PES.2006.1708919 (DOI)000247080000022 ()978-1-4244-0492-6 (ISBN)
Conference
General Meeting of the Power-Engineering-Society, Montreal, CANADA, JUN 18-22, 2006
Note
QC 20101112Available from: 2008-02-27 Created: 2008-02-27 Last updated: 2011-10-10Bibliographically approved
2. Discrete open loop control for power oscillation damping utilizing variable series reactance FACTS devices
Open this publication in new window or tab >>Discrete open loop control for power oscillation damping utilizing variable series reactance FACTS devices
2006 (English)In: PROCEEDINGS OF THE 41ST INTERNATIONAL UNIVERSITIES POWER ENGINEERING CONFERENCE, 2006, 785-789 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes an open loop method of controlling FACTS devices for power oscillation damping. The method is based on step-wise series reactance modulation. The principle of the method is to stabilize an oscillation in a power system which is characterized by one major mode of oscillation by switching a reactance in series with one transmission line, thereby changing the total reactance between the areas participating in the oscillation. In order to stabilize the system during an oscillation, the stationary voltage angle difference between the areas is changed to coincide with the present angle at a point where the speed of the lumped machine representations of the areas is nominal. This is the case at the peaks of the oscillation. To determine the required size of the reactance step, a reduced model of the power system is used. The model parameters are continuously updated using local measurements of the active power on the reactance controlled line. Several approaches for damping with different numbers of steps are presented and verified using digital simulations of power system models.

Keyword
Damping, Electric impedance, Electric power systems, Electric power transmission networks, Model structures, Modulation, Active Power (CO), angle difference, Digital simulations, FACTS (Flexible AC Transmission System) devices, In order, International (CO), Local measurements, machine representations, Model parameters, Open loop controlling, Open-loop method, power engineering, Power oscillation damping, Power system modelling, power systems, Reduced models, Transmission line (TL)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8039 (URN)10.1109/UPEC.2006.367586 (DOI)000256054900159 ()2-s2.0-46849086754 (Scopus ID)
Conference
41st International Universities Power Engineering Conference, Newcastle upon Tyne, ENGLAND, SEP 06, 2006-SEP 08, 2008
Note
QC 20101112Available from: 2008-02-27 Created: 2008-02-27 Last updated: 2011-08-19Bibliographically approved
3. An adaptive model predictive approach to power oscillation damping utilizing variable series reactance FACTS devices
Open this publication in new window or tab >>An adaptive model predictive approach to power oscillation damping utilizing variable series reactance FACTS devices
2006 (English)In: PROCEEDINGS OF THE 41ST INTERNATIONAL UNIVERSITIES POWER ENGINEERING CONFERENCE, 2006, 790-794 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes an adaptive method of controlling FACTS devices for power oscillation damping. The method is based on step-wise series reactance modulation. Here, a reduced model of the power system with only two rotating masses is used as a basis for the control design. The model parameters are updated using local measurements of the active power on the controlled line. An adaptive closed loop controller is developed based on the principle that it is possible to stabilize an oscillation in a power system which is characterized by one major mode of oscillation by switching a reactance in series with one transmission line in a small number of steps. The reduced model parameters are recomputed when new information of the system response is known making the control scheme an adaptive one. The paper also includes the derivation of a damping controller with a power flow control feature and a verification of the controllers using digital simulations of power system models of different complexities.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8040 (URN)10.1109/UPEC.2006.367587 (DOI)000256054900160 ()2-s2.0-46849089203 (Scopus ID)978-1-86135-342-9 (ISBN)
Conference
41st International Universities Power Engineering Conference, Newcastle upon Tyne, ENGLAND, SEP 06, 2006-SEP 08, 2008
Note
QC 20101112Available from: 2008-02-27 Created: 2008-02-27 Last updated: 2011-08-19Bibliographically approved
4. Adaptive control of controlled series compensators for power system stability improvement
Open this publication in new window or tab >>Adaptive control of controlled series compensators for power system stability improvement
2007 (English)In: 2007 IEEE LAUSANNE POWERTECH, 2007, 355-360 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes the design and verification of a time-discrete adaptive controller for damping of inter-area power oscillations, power flow control, and transient stability improvement Only locally measured signals are used as inputs to the controller. The controller may be used with any FACTS device which operates as a variable series reactance in the power grid, such as for example the TCSC. The controller is based on a reduced system model which relies on the assumption of one dominating inter-area oscillation mode in the power system where the FACTS device is placed. Verification of the controller is performed by means of digital simulations of a four-machine system commonly used to study inter-area oscillations.

Keyword
control, FACTS, power oscillation, TCSC, TSSC, transient stability
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8041 (URN)10.1109/PCT.2007.4538343 (DOI)000258730100062 ()2-s2.0-50849087016 (Scopus ID)978-1-4244-2189-3 (ISBN)
Conference
IEEE Lausanne Powertech, Lausanne, SWITZERLAND, JUL 01-05, 2007
Note
QC 20101112Available from: 2008-02-27 Created: 2008-02-27 Last updated: 2011-08-19Bibliographically approved
5. A dynamic power flow controller for power system stability improvement and loss reduction
Open this publication in new window or tab >>A dynamic power flow controller for power system stability improvement and loss reduction
2008 (English)In: The 16th Power Systems Computation Conference, Power Systems Computation Conference ( PSCC ) , 2008Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, a novel FACTS device denoted Dynamic Power Flow Controller (DPFC) is described. The device consists of a Phase-Shifting Transformer (PST) connected in series with a set of thyristor-switched capacitive and/or inductive elements. When compared to a normal PST, this device has faster dynamic properties and in addition to the normal PST functions, it also allows for power oscillation damping, transient stability improvement, and voltage stability improvement in a power grid. The DPFC is believed to be less costly than other FACTS devices with the same functionalities. In this paper, the benefits and functions of the DPFC are discussed. Additionally, an adaptive controller for DPFC power oscillation damping, transient stability improvement, and power flow control is presented and verified by means of digital simulations.

Place, publisher, year, edition, pages
Power Systems Computation Conference ( PSCC ), 2008
Keyword
Adaptive control, Dynamic Power Flow Controller, FACTS, Phase-Shifting Transformer, Power Oscillation Damping, Transient Stability, Power Flow Control
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8042 (URN)2-s2.0-84944111649 (Scopus ID)
Conference
16th PSCC, Glasgow, Scotland, July 14-18, 2008
Note

QC 20101112

Available from: 2008-02-27 Created: 2008-02-27 Last updated: 2016-03-07Bibliographically approved
6. An Adaptive Controller for Power System Stability Improvement and Power Flow Control by Means of a Thyristor Switched Series Capacitor (TSSC)
Open this publication in new window or tab >>An Adaptive Controller for Power System Stability Improvement and Power Flow Control by Means of a Thyristor Switched Series Capacitor (TSSC)
2010 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, Vol. 25, no 1, 381-391 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a controller for a thyristor switched series capacitor (TSSC) is presented. The controller aims to stabilize the power system by damping interarea power oscillations and by improving the transient stability of the system. In addition to this, a power flow control feature is included in the controller. The power oscillation damping controller is designed based on a nonlinear control law, while the transient stability improvement feature works in open loop. The damping controller is adaptive and estimates the power system parameters according to a simplified generic model of a two-area power system. It is designed for systems where one poorly damped dominant mode of power oscillation exists. In the paper, a verification of the controller by means of digital simulations of one two-area, four-machine power system, and one 23-machine power system is presented. The results show that the controller improves the stability of both test systems significantly in a number of fault cases at different levels of interarea power flow.

Keyword
Power flow control, power oscillation damping (POD), thyristor, controlled series capacitor (TCSC), thyristor switched series capacitor, (TSSC), transient stability, interarea oscillations, design, strategy, model
Identifiers
urn:nbn:se:kth:diva-19144 (URN)10.1109/tpwrs.2009.2036484 (DOI)000273930800040 ()2-s2.0-76649100765 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-08-19Bibliographically approved
7. A Comparison of Different Frequency Scanning Methods for Study of Subsynchronous Resonance
Open this publication in new window or tab >>A Comparison of Different Frequency Scanning Methods for Study of Subsynchronous Resonance
2011 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 1, 356-363 p.Article in journal (Refereed) Published
Abstract [en]

This paper compares four different methods for determining the electrical damping of a power system seen from one generator as a function of frequency. This information is useful when the risk for subsynchronous resonance (SSR) in the system is evaluated. The study compares one frequency scanning method which is implemented in a time-domain digital simulation program with three methods of different complexity based on analytical calculations. The time-domain simulation method is easily implemented with a detailed model of the power system including complex load and generator models, whereas the analytical methods are based on simpler models of the power system. The computational effort is much larger for the time-domain method than for the analytical methods. In the study, all methods were used to determine the damping characteristics of a four-machine power system in different configurations. The study shows that fast analytical methods may provide results which closely agree with the detailed method of time-domain simulation. However, the study also shows that the level of accuracy in the analytical model is very important.

Keyword
Frequency scanning, subsynchronous oscillations, subsynchronous resonance (SSR), torsional interaction
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-31345 (URN)10.1109/TPWRS.2010.2046345 (DOI)000286516100039 ()2-s2.0-79151473380 (Scopus ID)
Note
QC 20110317Available from: 2011-03-17 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
8. Designing power flow control devices using the power controller plane: An improved method
Open this publication in new window or tab >>Designing power flow control devices using the power controller plane: An improved method
(English)Article in journal (Other academic) Submitted
Abstract [en]

This paper introduces an improved method for design of Power Flow Controllers (PFC) in the power controller plane where the active power of the PFC line is plotted versus the difference in voltage angle between the PFC terminals. The power controller plane makes it possible to graphically visualize the working area of a PFC in a power grid and thus determine the grid situations which are dimensioning for the PFC. The paper extends the existing methods for design of PFC:s in the power controller plane by introducing a method to decouple the power grid- and PFC characteristics in a power system of arbitrary size. With this approach, it is possible to graphically compare and design PFC:s of different types and with different characteristics in the same plot by simple geometrical considerations. The method is intended to provide additional insight into how the power flow control capabilities of different PFC:s depend on the selected PFC characteristics and the grid conditions. Additionally, the method has the potential to simplify the process for selection and design of a PFC. The paper includes a study of the accuracy of the proposed method in two test systems of different complexity.

Keyword
Flexible ac transmission systems (FACTS), Phase shifting transformer (PST), Power controller plane, Power flow control, Thyristor switched series capacitor (TSSC)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-37916 (URN)
Note
QS 2011 QS 20120327Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2012-03-27Bibliographically approved
9. Aspects on Power Flow Control by means of a Dynamic Power Flow Controller
Open this publication in new window or tab >>Aspects on Power Flow Control by means of a Dynamic Power Flow Controller
(English)Article in journal (Other academic) Submitted
Abstract [en]

This paper, which is focused on steady-state power flow control, investigates the capability of three different Power Flow Controllers (PFC) to control power flows in two test systems. The studied devices are the Dynamic Power Flow Controller (DPFC), the Phase Shifting Transformer (PST) and the Thyristor Switched Series Capacitor (TSSC). The DPFC is actually a combination of the PST and the TSSC and the study thus attempts to solve the power flow control problems either by a PST, a TSSC or a combination of these devices. The different PFC:s are designed using the Power controller plane where it is possible to decouple the surrounding grid characteristics from the PFC characteristics in a convenient way. It is found that the installation of a PFC can improve the power transfer capacity significantly in the studied test systems. In some of the studied cases, it is found that the power flow control problem can only be solved by a PST or a DPFC. One main conclusion of the study is that a DPFC may be an attractive alternative to a traditional PST installation in some cases due to a lower required rating, a better voltage control capability and a higher speed of control.

Keyword
Terms—Dynamic power flow controller (DPFC), Flexible ac transmission systems (FACTS), Hybrid flow controller (HFC), Phase shifting transformer (PST), Power controller plane, Power flow control, Thyristor switched series capacitor (TSSC)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-37913 (URN)
Note
QS 2011 QS 20120327Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2012-03-27Bibliographically approved

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  • harvard1
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