Analysis of the Combined and Coordinated Control Method for HVDC Transmission. Dissertation

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Analysis of the Combined and Coordinated Control Method for HVDC Transmission

Dissertation

zur Erlangung des akademischen Grades Doktoringenieur (Dr.-Ing.)

vorgelegt der Fakultät für Elektrotechnik und Informationstechnik der Technischen Universität Ilmenau

von M.Sc. Pakorn Thepparat

geboren am 08.02.1978 in Ratchaburi, Thailand

vorgelegt am: 28.09.2009

Gutachter: 1. Univ.-Prof. Dr.-Ing. Dirk Westermann 2. Prof. Dr.-Ing. Dusan Povh

3. Prof. Dr. Rafael Mihalic

Verteidigung am: 05.02.2010

Verf.-Nr.: EI 248

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Shaker Verlag Aachen 2010

Berichte aus der Elektrotechnik

Pakorn Thepparat

Analysis of the Combined and Coordinated

Control Method for HVDC Transmission

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Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche

Nationalbibliografie; detailed bibliographic data are available in the Internet at http://dnb.d-nb.de.

Zugl.: Ilmenau, Techn. Univ., Diss., 2010

Copyright Shaker Verlag 2010

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publishers.

Printed in Germany.

ISBN 978-3-8322-9045-0 ISSN 0945-0718

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Abstract I

Abstract

High Voltage Direct Current (HVDC) is a state-of-the-art technology for bulk power transmission from rectifier stations to inverter stations where the AC systems are often weak. The weak AC systems are very sensitive to the disturbances and the variations of active and reactive powers;

the HVDC controls having a transient response time of only a few milliseconds with the accuracy of a fraction of an electrical degree for firing the converter valves can therefore play a significant role in stabilizing the systems. Since the conventional HVDC control has been used more than 50 years, the further enhancements in HVDC control technology are become challenge.

In this thesis, the difficulties of conventional control are demonstrated and the novel HVDC control is introduced. The concept of the novel control promises to improve the system stability, particularly in weak systems. Moreover, the analysis of control movements explains the background of the inherent oscillations. Studies on the CIGRE Benchmark HVDC model and the practical back-to-back HVDC model are therefore performed to prove the use of novel control in comparison with the conventional one.

The linear continuous model of CIGRE Benchmark HVDC is developed for eigenvalue analysis. The validation of the model according to time and frequency response shows the satisfactory fidelity.

The model allows for analyzing in different control modes at the rectifier and the inverter. In addition, the physical relationships of the subsystem interconnection variables are directly considered in the model, the influences of system strength at the rectifier and the inverter to the stability can therefore be revealed. With the CIGRE Benchmark HVDC model, also a number of time domain studies are performed to demonstrate the results of the novel control compared to the conventional one.

In addition to CIGRE Benchmark HVDC model, the novel HVDC control is implemented in the practical back-to-back HVDC model which comprises the complex control schemes and systems.

The disturbances occurring on one side of the back-to-back HVDC can influence directly the other side, the controls must therefore response fast to protect the systems from undesirable conditions. The system recovery after fault and the control performance after reactive power element switching causing high AC voltage transients and AC voltage oscillations are studied.

Finally to prove the flexibility of the novel control, the thesis proposes the feasibility to adjust the characteristic of novel control to improve systems in a certain condition.

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Kurzfassung III

Kurzfassung

Die Hochspannungsgleichstromübertragung (HGÜ) ist derzeit die dem Stand der Technik entsprechende Technologie zur Übertragung großer Leistungen. In vielen Fällen ist die Umrichterstation der HGÜ an ein schwaches AC-Netz angeschlossen, welches empfindlich auf Störungen und Veränderung im Wirk- und Blindleistungsfluss reagiert. Die Regelung der HGÜ hat um ein Vielfaches kleinere Zeitkonstanten als das AC-Netz und spielt daher eine wichtige Rolle in der Stabilisierung von AC-Netzen. Seit über 50 Jahren wird eine konventionelle HGÜ-Regelung angewandt. Umso mehr ist eine Weiterentwicklung eine große Herausforderung.

In dieser Dissertation werden Grenzen in der Anwendung der konventionellen Regelung aufgezeigt und ein neuer Regelungsansatz vorgestellt. Das neuartige Regelungskonzept verbessert insbesondere das Stabilitätsverhalten im Zusammenhang mit schwachem AC-Netze. Darüber hinaus erklärt eine neu eingeführte Darstellungsart des „Reglerverhaltens“ die Grundlagen inhärenter Schwingungen. Untersuchungen mit dem „CIGRE HVDC Benchmark Model“ und einer back-to-back Anlage wurden durchgeführt um die Anwendbarkeit und Leistungsfähigkeit des neuen Regelungskonzeptes im Vergleich zur konventionellen Regelung zu zeigen.

Für eine Eigenwert-Analyse wird aus dem „CIGRE HVDC Benchmark Model“ ein lineares kontinuierliches Modell entwickelt. Die Validierung des Modells erfolgt durch die Untersuchung des Zeit- und Frequenzverhaltens und liefert eine zufriedenstellende Genauigkeit. Mit diesem Modell lassen sich verschiedene Reglerstrategien am Gleich- und Wechselrichter untersuchen.

Zusätzlich werden die physikalischen Zusammenhänge der Zustandsvariablen im Modell direkt berücksichtigt. Somit kann der Einfluss der Netzkurzschlussleistung am Anschlusspunkt der Gleich- und Wechselrichter auf das Stabilitätsverhalten deutlich gemacht werden. Mit dem „CIGRE HVDC Benchmark Model“ wurden zum Vergleich der konventionellen und der neuen Regelung auch Untersuchungen im Zeitbereich durchgeführt.

Neben dem „CIGRE HVDC Benchmark Model“ wird das neue Regelungsverfahren ebenfalls in das Modell einer realen back-to-back Anlage implementiert, welches eine genaue Regler- und Systemnachbildung beinhaltet. Netzstörungen auf der einen Seite einer back-to-back Anlage beeinflussen direkt das AC-Netz auf der anderen Seite. Dies führt dazu, dass die Regelung sehr schnell sein muss, um das Netz vor unerwünschten Betriebszuständen zu schützen. Das Systemverhalten nach einem 3-poligen Kurzschluss sowie die Reglerqualität nach dem Schalten von Blindleistungskompensationen – welches transiente Überspannungen und Schwingungen verursacht – wird dabei untersucht. Zum Schluss wird die Flexibilität der neuen Regelung aufgezeigt. Die Möglichkeit der Anpassung der Regelcharakteristik verbessert in bestimmten Fällen das Systemverhalten.

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Acknowledgement V

Acknowledgement

This work has been done during my time as a doctoral student in the Department of Electrical Energy Supply at Technical University of Ilmenau, Ilmenau, Germany and in the Energy Sector, Siemens AG, Erlangen, Germany. I have received a lot of kind supports from many parties and I would like to express my sincere gratitude and appreciation to them.

Firstly, I would like to thank my supervisor, Univ.-Prof. Dr.-Ing. Dirk Westermann for offering me a great opportunity to pursue my doctoral study in his department. His guidance, professional support and comments are valuable for my study.

I am very grateful to Prof. Dr.-Ing. Dusan Povh for his excellent support, comments, understanding and patience. I have learnt a lot from his professional work experience. He taught not only academic stuff but also life.

I would like to thank Prof. Dr. Rafael Mihalic, Univ.-Prof. Dr.-Ing. Frank Berger and promotion committee for your interest in my work.

I wish to show my deep gratitude to Mr. Wilfried Breuer for supporting and giving me a chance for my study. To Dr.-Ing. Hartmut Huang, I really appreciate your interest in my research and your arrangement for financial support.

Furthermore, I am indebted to Prof. Dr.-Ing. Dietmar Retzmann. I would like to say thank you very much for giving me a lot of great opportunities for my life. His character always encourages me to be a professional engineer. Also I would like to show my sincere gratitude to Mr. Klaus Bergmann for his excellent support and working atmosphere. To Mr. Franz Karlecik-Maier, I would thank you very much for your great supports which help me to break though the obstacle.

My thanks are extended to Dr. Mojtaba Mohaddes, Mr. Michael Bär, Dr.-Ing. Frank Schettler, Mr.

Norbert Hilfert and team for their patience in my queries.

My appreciations are to Mr. Christian Krieger, Mr. Torsten Priebe, Mr. Dennis Brandt, Mr. Johann Messner, Dr. Mark Davies, Dr.-Ing. Jürgen Rittiger and Mr. Reinhard Wagner for discussions.

I would like to thank Mr. Georg Wild and Mr. Wolfgang Zink for giving me a chance to learn HVDC.

I would like to thank Dr.-Ing. Lu, Miguel, Tuan, Dr.-Ing Moreno and Cerda. Also to team E T PS E24 and E T PS E5, I deeply appreciate for their friendly and excellent working atmosphere.

To Sudarat, Yodsaya, Karapin, Siritassanakul Family, Phuangtong, Supawadee, Montha, Suwanasri Family, Chawanakorn, Senawong, Chanchai, Burin, Wolfgang, Todsaporn, Piyapatt, Channarong and friends in Aachen, and Thailand, I am very thankful for your friendship and encouragements.

To my mother, father and brother, I would like to thank for your support, encouragements and sacrifices which help me to conquer the hindrances. Especially my brother, he does the excellent responsibility to our family during my time in Germany.

Erlangen, February 2010 Pakorn Thepparat

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Contents VII

List of Frequently Used Abbreviations and Symbols

Abbreviations

CC Current Control

CCCM Combined and Coordinated Control Method CEA Constant Extinction Angle

CEC Current Error Control

ESCR Effective Short-Circuit Ratio

FC Fixed Capacitor

FR Fixed Reactor

GTO Gate Turn-Off Thyristor IGBT Insulated Gate Bipolar Transistors MCCM Marginal Current Control Method

MIMO Multi-Input Multi-Output

PI Proportional and Integral

PLL Phase Locked Loop

PLUS Power Link Universal Systems

SCC Short-Circuit Capacity

SCR Short-Circuit Ratio

SISO Single-Input Single-Output

VC Voltage Control

VCO Voltage Controlled Oscillator VDCOL Voltage Dependent Current Order Limit VDPOL Voltage Dependent Power Order Limit VSC Voltage Sourced Converters Symbols

Current error coefficient at rectifier

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X List of Frequently Used Abbreviations and Symbols

a Transformer ratio defined as ^{Pr imary} ^Secondary

Seconadry Pr imary

I V

Voltage error coefficient at rectifier Current error coefficient at inverter Voltage error coefficient at inverter

Eaci Line-to-Line inverter AC voltage on the secondary side Eacr Line-to-Line rectifier AC voltage on the secondary side

Id Measured DC current

Idif Inverter DC current after filtering Idref DC current reference

Idrf Rectifier DC current after filtering

mi Pr iL N

I Crest line to neutral inverter AC current on the primary side

mr Pr iL N

I Crest line to neutral rectifier AC current on the primary side

ʹ

Is Crest current of line-to-line short circuit on AC system Isc Three-phase short-circuit current

KcPLL Phase Locked Loop amplified gain KiiI Integrator gain for inverter DC current KiiU Integrator gain for inverter DC voltage KiPLL Phase Locked Loop integral gain KirI Integrator gain for rectifier DC current KirU Integrator gain for rectifier DC voltage KpPLL Phase Locked Loop proportional gain

Lc Commutating inductance

Pd DC power

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List of Frequently Used Abbreviations and Symbols XI

Pdref DC power reference

Qc Reactive power compensations at AC bus TIdi Inverter time constant for DC current filter TIdr Rectifier time constant for DC current filter TUdi Inverter time constant for DC voltage filter TUdr Rectifier time constant for DC voltage filter

Ud Measured DC voltage

Ͳ

Ud i Ideal no-load DC voltage at inverter

Ͳ

Ud r Ideal no-load DC voltage at rectifier Udref DC voltage reference

Udrf Rectifier DC voltage after filtering

A B C

v , v , v Commutating three-phase AC voltages

mi Pr iL N

V Crest line to neutral inverter AC voltage on the primary side

mr Pr iL N

V Crest line to neutral rectifier AC voltage on the primary side

v , v_D _E Direct and quadrature axes voltages

Xci Commutating reactance referred to the valve side of converter transformer per phase in ohms at inverter

Xcr Commutating reactance referred to the valve side of converter transformer per phase in ohms at rectifier

D Delay angle (Firing angle)

E^Advance^angle

I Power factor angle

J Extinction angle

U Input matrix

X State matrix

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XII List of Frequently Used Abbreviations and Symbols

Y Output matrix

[ AC current angle

T

Phase angle output of PLL

P^Overlap^angle

] Damping ratio

M AC voltage angle

Z^Angular^frequency