IEC TR 62544:2011

High-voltage direct current (HVDC) systems - Application of active filters

IEC/TR 62544:2011(E) gives general guidance on the subject of active filters for use in high-voltage direct current (HVDC) power transmission. It describes systems where active devices are used primarily to achieve a reduction in harmonics in the d.c. or a.c. systems. This excludes the use of automatically retuned components. The various types of circuit that can be used for active filters are described in the report, along with their principal operational characteristics and typical applications. The overall aim is to provide guidance for purchasers to assist with the task of specifying active filters as part of HVDC converters. Passive filters are specifically excluded from this report.

General Information

• Status: Published
• Publication Date: 04-Feb-2020
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.240.99 - Other equipment related to power transmission and distribution networks
• Technical Committee: SC 22F - Power electronics for electrical transmission and distribution systems
• Drafting Committee: WG 20 - TC 22/SC 22F/WG 20
• Current Stage: PPUB - Publication issued
• Start Date: 30-Nov-2011
• Completion Date: 19-Aug-2011

Relations

• Replaces: IEC PAS 62544:2008 - Active filters in HVDC applications
• Effective Date: 05-Sep-2023
• Amended By: IEC TR 62544:2011/AMD1:2016 - Amendment 1 - High-voltage direct current (HVDC) systems - Application of active filters
• Effective Date: 05-Sep-2023
• Amended By: IEC TR 62544:2011/AMD2:2020 - Amendment 2 - High-voltage direct current (HVDC) systems - Application of active filters
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC/TR 62544 ®
Edition 1.0 2011-08
TECHNICAL
REPORT
High-voltage direct current (HVDC) systems – Application of active filters

IEC/TR 62544:2011(E)
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
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please contact the address below or your local IEC member National Committee for further information.

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IEC/TR 62544 ®
Edition 1.0 2011-08
TECHNICAL
REPORT
High-voltage direct current (HVDC) systems – Application of active filters

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 29.240.99 ISBN 978-2-88912-627-9

– 2 – TR 62544 © IEC:2011(E)
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references. 7
3 Terms and definitions . 7
3.1 Active and passive filters . 8
3.2 Active filter topologies . 8
shunt active filter . 8
3.3 Power semiconductor terms . 9
3.4 Converter topologies . 9
4 Active filters in HVDC applications . 9
4.1 General . 9
4.2 Semiconductor devices available for active filters . 11
5 Active d.c. filters . 11
5.1 Harmonic disturbances on the d.c. side . 11
5.2 Description of active d.c. filters . 12
5.2.1 General . 12
5.2.2 Types of converters available . 12
5.2.3 Connections of the active d.c. filter . 13
5.2.4 Characteristics of installed active d.c. filters . 15
5.3 Main components in an d.c. active filter . 16
5.3.1 General . 16
5.3.2 Passive part . 16
5.3.3 Current transducer . 18
5.3.4 Control system . 18
5.3.5 Amplifier . 19
5.3.6 Transformer . 19
5.3.7 Protection circuit and arrester . 19
5.3.8 Bypass switch and disconnectors . 19
5.4 Active d.c. filter control . 19
5.4.1 General . 19
5.4.2 Active d.c. filter control methods . 20
5.5 Example – Performance of the Skagerrak 3 HVDC Intertie active d.c. filter . 23
5.6 Conclusions on active d.c. filters . 24
6 Active a.c. filters in HVDC applications . 25
6.1 General . 25
6.2 Harmonic disturbances on the a.c. side of a HVDC system . 25
6.3 Passive filters . 26
6.3.1 Conventional passive filters. 26
6.3.2 Continuously tuned passive filters . 26
6.4 Reasons for using active filters in HVDC systems . 27
6.5 Operation principles of active filters . 28
6.5.1 Shunt connected active filter . 28
6.5.2 Series connected active filter . 29
6.6 Parallel and series configuration . 29
6.6.1 General . 29
6.6.2 Hybrid filter schemes . 29
6.7 Converter configurations . 30

TR 62544 © IEC:2011(E) – 3 –
6.7.1 Converters . 30
6.8 Active a.c. filter configurations . 32
6.8.1 Active a.c. filters for low voltage application . 32
6.8.2 Active a.c. filters for medium voltage application . 33
6.8.3 Active a.c. filters for HVDC applications . 33
6.9 Series connected active filters . 34
6.10 Control system . 34
6.10.1 General . 34
6.10.2 Description of a generic active power filter controller . 35
6.10.3 Calculation of reference current . 36
6.10.4 Synchronous reference frame (SRF) . 37
6.10.5 Other control approaches . 37
6.10.6 HVDC a.c. active filter control approach . 38
6.11 Existing active a.c. filter applications . 38
6.11.1 Low and medium voltage. 38
6.11.2 High voltage applications . 38
6.12 Overview on filter solutions for HVDC systems . 39
6.12.1 Solution with conventional passive filters . 39
6.12.2 Solution with continuously tuned passive filters . 40
6.12.3 Solution with active filters . 40
6.12.4 Solution with continuously tuned passive filters and active filters . 41
6.12.5 Study cases with the CIGRÉ HVDC model . 41
6.13 ACfilters for HVDC installations using VSC . 43
6.14 Conclusions on active a.c. filters . 43
Bibliography . 45

Figure 1 – Shunt connection . 8
Figure 2 – Series connection . 8
Figure 3 – Conceptual diagram of allowable interference level and d.c. filter cost . 10
Figure 4 – Simple current source converter . 13
Figure 5 – Simple voltage sourced converter . 13
Figure 6 – Possible connections of active d.c. filters . 14
Figure 7 – Filter components in the active filter . 17
Figure 8 – Impedance characteristics of different passive filters . 17
Figure 9 – Basic control loop of an active d.c. filter . 21
Figure 10 – Measured transfer function of external system, Baltic Cable HVDC link . 22
Figure 11 – Feedforward control for the active d.c. filter . 22
Figure 12 – Measured line current spectra, pole 3 operated as monopole . 24
Figure 13 – Continuously tuned filter . 26
Figure 14 – Example of current waves . 28
Figure 15 – Series and parallel connection . 29
Figure 16 – Hybrid configuration . 30
Figure 17 – Three phase current-source converter . 31
Figure 18 – Three phase 2 level voltage-sourced converter (three-wire type) . 31
Figure 19 – Three phase 3 level voltage-sourced converter (three-wire type) . 32
Figure 20 – Single-phase voltage sourced converter . 32

– 4 – TR 62544 © IEC:2011(E)
Figure 21 – Active filter connected to the HV system through a single-tuned passive
filter . 33
Figure 22 – Active filter connected to the HV system through a double-tuned passive
filter . 34
Figure 23 – Using an LC circuit to divert the fundamental current component . 34
Figure 24 – Per-phase schematic diagram of active filter and controller . 35
Figure 25 – Block diagram of IRPT .
...

IEC/TR 62544 ®
Edition 1.0 2011-08
TECHNICAL
REPORT
High-voltage direct current (HVDC) systems – Application of active filters

IEC/TR 62544:2011(E)
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: [e-mail]
Web: www.iec.ch
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
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It also gives information on projects, withdrawn and replaced publications.
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in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
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If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
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Fax: [phone]
IEC/TR 62544 ®
Edition 1.0 2011-08
TECHNICAL
REPORT
High-voltage direct current (HVDC) systems – Application of active filters

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 29.240.99 ISBN 978-2-88912-627-9

– 2 – TR 62544 © IEC:2011(E)
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references. 7
3 Terms and definitions . 7
3.1 Active and passive filters . 8
3.2 Active filter topologies . 8
shunt active filter . 8
3.3 Power semiconductor terms . 9
3.4 Converter topologies . 9
4 Active filters in HVDC applications . 9
4.1 General . 9
4.2 Semiconductor devices available for active filters . 11
5 Active d.c. filters . 11
5.1 Harmonic disturbances on the d.c. side . 11
5.2 Description of active d.c. filters . 12
5.2.1 General . 12
5.2.2 Types of converters available . 12
5.2.3 Connections of the active d.c. filter . 13
5.2.4 Characteristics of installed active d.c. filters . 15
5.3 Main components in an d.c. active filter . 16
5.3.1 General . 16
5.3.2 Passive part . 16
5.3.3 Current transducer . 18
5.3.4 Control system . 18
5.3.5 Amplifier . 19
5.3.6 Transformer . 19
5.3.7 Protection circuit and arrester . 19
5.3.8 Bypass switch and disconnectors . 19
5.4 Active d.c. filter control . 19
5.4.1 General . 19
5.4.2 Active d.c. filter control methods . 20
5.5 Example – Performance of the Skagerrak 3 HVDC Intertie active d.c. filter . 23
5.6 Conclusions on active d.c. filters . 24
6 Active a.c. filters in HVDC applications . 25
6.1 General . 25
6.2 Harmonic disturbances on the a.c. side of a HVDC system . 25
6.3 Passive filters . 26
6.3.1 Conventional passive filters. 26
6.3.2 Continuously tuned passive filters . 26
6.4 Reasons for using active filters in HVDC systems . 27
6.5 Operation principles of active filters . 28
6.5.1 Shunt connected active filter . 28
6.5.2 Series connected active filter . 29
6.6 Parallel and series configuration . 29
6.6.1 General . 29
6.6.2 Hybrid filter schemes . 29
6.7 Converter configurations . 30

TR 62544 © IEC:2011(E) – 3 –
6.7.1 Converters . 30
6.8 Active a.c. filter configurations . 32
6.8.1 Active a.c. filters for low voltage application . 32
6.8.2 Active a.c. filters for medium voltage application . 33
6.8.3 Active a.c. filters for HVDC applications . 33
6.9 Series connected active filters . 34
6.10 Control system . 34
6.10.1 General . 34
6.10.2 Description of a generic active power filter controller . 35
6.10.3 Calculation of reference current . 36
6.10.4 Synchronous reference frame (SRF) . 37
6.10.5 Other control approaches . 37
6.10.6 HVDC a.c. active filter control approach . 38
6.11 Existing active a.c. filter applications . 38
6.11.1 Low and medium voltage. 38
6.11.2 High voltage applications . 38
6.12 Overview on filter solutions for HVDC systems . 39
6.12.1 Solution with conventional passive filters . 39
6.12.2 Solution with continuously tuned passive filters . 40
6.12.3 Solution with active filters . 40
6.12.4 Solution with continuously tuned passive filters and active filters . 41
6.12.5 Study cases with the CIGRÉ HVDC model . 41
6.13 ACfilters for HVDC installations using VSC . 43
6.14 Conclusions on active a.c. filters . 43
Bibliography . 45

Figure 1 – Shunt connection . 8
Figure 2 – Series connection . 8
Figure 3 – Conceptual diagram of allowable interference level and d.c. filter cost . 10
Figure 4 – Simple current source converter . 13
Figure 5 – Simple voltage sourced converter . 13
Figure 6 – Possible connections of active d.c. filters . 14
Figure 7 – Filter components in the active filter . 17
Figure 8 – Impedance characteristics of different passive filters . 17
Figure 9 – Basic control loop of an active d.c. filter . 21
Figure 10 – Measured transfer function of external system, Baltic Cable HVDC link . 22
Figure 11 – Feedforward control for the active d.c. filter . 22
Figure 12 – Measured line current spectra, pole 3 operated as monopole . 24
Figure 13 – Continuously tuned filter . 26
Figure 14 – Example of current waves . 28
Figure 15 – Series and parallel connection . 29
Figure 16 – Hybrid configuration . 30
Figure 17 – Three phase current-source converter . 31
Figure 18 – Three phase 2 level voltage-sourced converter (three-wire type) . 31
Figure 19 – Three phase 3 level voltage-sourced converter (three-wire type) . 32
Figure 20 – Single-phase voltage sourced converter . 32

– 4 – TR 62544 © IEC:2011(E)
Figure 21 – Active filter connected to the HV system through a single-tuned passive
filter . 33
Figure 22 – Active filter connected to the HV system through a double-tuned passive
filter . 34
Figure 23 – Using an LC circuit to divert the fundamental current component . 34
Figure 24 – Per-phase schematic diagram of active filter and controller . 35
Figure 25 – Block diagram of IRPT .
...

IEC TR 62544 ®
Edition 1.1 2016-04
CONSOLIDATED VERSION
TECHNICAL
REPORT
colour
inside
High-voltage direct current (HVDC) systems – Application of active filters

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

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variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
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Centre: [e-mail].
IEC TR 62544 ®
Edition 1.1 2016-04
CONSOLIDATED VERSION
TECHNICAL
REPORT
colour
inside
High-voltage direct current (HVDC) systems – Application of active filters

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.99 ISBN 978-2-8322-3332-0

IEC TR 62544 ®
Edition 1.1 2016-04
CONSOLIDATED VERSION
REDLINE VERSION
colour
inside
High-voltage direct current (HVDC) systems – Application of active filters

– 2 – IEC TR 62544:2011+AMD1:2016 CSV
© IEC 2016
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.1 Active and passive filters . 8
3.2 Active filter topologies . 8
shunt active filter . 8
3.3 Power semiconductor terms . 9
3.4 Converter topologies . 9
4 Active filters in HVDC applications . 10
4.1 General . 10
4.2 Semiconductor devices available for active filters. 11
5 Active d.c. filters . 11
5.1 Harmonic disturbances on the d.c. side . 11
5.2 Description of active d.c. filters . 12
5.2.1 General . 12
5.2.2 Types of converters available . 12
5.2.3 Connections of the active d.c. filter . 14
5.2.4 Characteristics of installed active d.c. filters . 16
5.3 Main components in a d.c. active filter . 17
5.3.1 General . 17
5.3.2 Passive part . 17
5.3.3 Current transducer . 19
5.3.4 Control system . 19
5.3.5 Amplifier . 20
5.3.6 Transformer . 20
5.3.7 Protection circuit and arrester . 20
5.3.8 Bypass switch and disconnectors . 20
5.4 Active d.c. filter control . 20
5.4.1 General . 20
5.4.2 Active d.c. filter control methods . 21
5.5 Example – Performance of the Skagerrak 3 HVDC Intertie active d.c. filter . 24
5.6 Conclusions on active d.c. filters . 25
6 Active a.c. filters in HVDC applications . 26
6.1 General . 26
6.2 Harmonic disturbances on the a.c. side of a HVDC system. 26
6.3 Passive filters . 27
6.3.1 Conventional passive filters . 27
6.3.2 Continuously tuned passive filters . 27
6.4 Reasons for using active filters in HVDC systems . 28
6.5 Operation principles of active filters . 29
6.5.1 Shunt connected active filter . 29
6.5.2 Series connected active filter . 30
6.6 Parallel and series configuration . 30
6.6.1 General . 30
6.6.2 Hybrid filter schemes . 30

© IEC 2016
6.7 Converter configurations . 31
6.7.1 Converters . 31
6.8 Active a.c. filter configurations . 34
6.8.1 Active a.c. filters for low voltage application . 34
6.8.2 Active a.c. filters for medium voltage application . 34
6.8.3 Active a.c. filters for HVDC applications . 34
6.9 Series connected active filters . 36
6.10 Control system . 36
6.10.1 General . 36
6.10.2 Description of a generic active power filter controller . 36
6.10.3 Calculation of reference current . 37
6.10.4 Synchronous reference frame (SRF) . 38
6.10.5 Other control approaches . 39
6.10.6 HVDC a.c. active filter control approach . 39
6.11 Existing active a.c. filter applications . 39
6.11.1 Low and medium voltage . 39
6.11.2 High voltage applications . 39
6.12 Overview on filter solutions for HVDC systems . 40
6.12.1 Solution with conventional passive filters . 40
6.12.2 Solution with continuously tuned passive filters . 41
6.12.3 Solution with active filters . 42
6.12.4 Solution with continuously tuned passive filters and active filters . 42
6.12.5 Study cases with the CIGRÉ HVDC model . 42
6.13 ACfilters for HVDC installations using VSC . 44
6.14 Conclusions on active a.c. filters . 45
Bibliography . 46

Figure 1 – Shunt connection . 8
Figure 2 – Series connection . 8
Figure 3 – Conceptual diagram of allowable interference level and d.c. filter cost . 10
Figure 4 – Simple current source converter . 13
Figure 5 – Simple voltage sourced converter . 14
Figure 6 – Possible connections of active d.c. filters . 15
Figure 7 – Filter components in the active filter . 18
Figure 8 – Impedance characteristics of different passive filters . 18
Figure 9 – Basic control loop of an active d.c. filter . 22
Figure 10 – Measured transfer function of external system, Baltic Cable HVDC link . 23
Figure 11 – Feedforward control for the active d.c. filter . 23
Figure 12 – Measured line current spectra, pole 3 operated as monopole . 25
Figure 13 – Continuously tuned filter . 27
Figure 14 – Example of current waves . 30
Figure 15 – Series and parallel connection . 31
Figure 16 – Hybrid configuration . 31
Figure 17 – Three phase current-source converter . 32
Figure 18 – Three phase 2 level voltage-sourced converter (three-wire type) . 33
Figure 19 – Three phase 3 level voltage-sourced converter (three-wire type) . 33

– 4 – IEC TR 62544:2011+AMD1:2016 CSV
© IEC 2016
Figure 20 – Single-phase voltage sourced converter . 34
Figure 21 – Active filter connected to the HV system through a single-tuned passive
filter .
...

IEC TR 62544 ®
Edition 1.2 2020-02
CONSOLIDATED VERSION
TECHNICAL
REPORT
High-voltage direct current (HVDC) systems – Application of active filters

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and 67 000 electrotechnical terminology entries in English and
once a month by email. French extracted from the Terms and definitions clause of
IEC publications issued between 2002 and 2015. Some
IEC Customer Service Centre - webstore.iec.ch/csc entries have been collected from earlier publications of IEC
If you wish to give us your feedback on this publication or TC 37, 77, 86 and CISPR.

need further assistance, please contact the Customer Service

Centre: [e-mail].
IEC TR 62544 ®
Edition 1.2 2020-02
CONSOLIDATED VERSION
TECHNICAL
REPORT
High-voltage direct current (HVDC) systems – Application of active filters

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.99 ISBN 978-2-8322-7860-4

IEC TR 62544 ®
Edition 1.2 2020-02
CONSOLIDATED VERSION
REDLINE VERSION
High-voltage direct current (HVDC) systems – Application of active filters

– 2 – IEC TR 62544:2011+AMD1:2016
+AMD2:2020 CSV © IEC 2020
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.1 Active and passive filters . 8
3.2 Active filter topologies . 8
shunt active filter . 8
3.3 Power semiconductor terms . 9
3.4 Converter topologies . 9
4 Active filters in HVDC applications . 10
4.1 General . 10
4.2 Semiconductor devices available for active filters . 11
5 Active d.c. filters . 11
5.1 Harmonic disturbances on the d.c. side . 11
5.2 Description of active d.c. filters. 12
5.2.1 General . 12
5.2.2 Types of converters available . 12
5.2.3 Connections of the active d.c. filter . 14
5.2.4 Characteristics of installed active d.c. filters . 16
5.3 Main components in a d.c. active filter . 17
5.3.1 General . 17
5.3.2 Passive part . 17
5.3.3 Current transducer . 19
5.3.4 Control system . 19
5.3.5 Amplifier . 20
5.3.6 Transformer . 20
5.3.7 Protection circuit and arrester . 20
5.3.8 Bypass switch and disconnectors . 20
5.4 Active d.c. filter control . 20
5.4.1 General . 20
5.4.2 Active d.c. filter control methods . 21
5.5 Example – Performance of the Skagerrak 3 HVDC Intertie active d.c. filter . 24
5.6 Conclusions on active d.c. filters . 25
6 Active a.c. filters in HVDC applications . 26
6.1 General . 26
6.2 Harmonic disturbances on the a.c. side of a HVDC system . 26
6.3 Passive filters . 27
6.3.1 Conventional passive filters . 27
6.3.2 Continuously tuned passive filters . 27
6.4 Reasons for using active filters in HVDC systems. 28
6.5 Operation principles of active filters . 29
6.5.1 Shunt connected active filter. 29
6.5.2 Series connected active filter . 30
6.6 Parallel and series configuration . 30
6.6.1 General . 30
6.6.2 Hybrid filter schemes . 30

+AMD2:2020 CSV © IEC 2020
6.7 Converter configurations . 31
6.7.1 Converters . 31
6.8 Active a.c. filter configurations. 34
6.8.1 Active a.c. filters for low voltage application . 34
6.8.2 Active a.c. filters for medium voltage application . 34
6.8.3 Active a.c. filters for HVDC applications. 34
6.9 Series connected active filters . 36
6.10 Control system . 36
6.10.1 General . 36
6.10.2 Description of a generic active power filter controller . 36
6.10.3 Calculation of reference current . 37
6.10.4 Synchronous reference frame (SRF) . 38
6.10.5 Other control approaches . 39
6.10.6 HVDC a.c. active filter control approach . 39
6.11 Existing active a.c. filter applications . 39
6.11.1 Low and medium voltage . 39
6.11.2 High voltage applications . 39
6.12 Overview on filter solutions for HVDC systems . 40
6.12.1 Solution with conventional passive filters . 40
6.12.2 Solution with continuously tuned passive filters . 41
6.12.3 Solution with active filters . 42
6.12.4 Solution with continuously tuned passive filters and active filters . 42
6.12.5 Study cases with the CIGRÉ HVDC model . 42
6.13 ACfilters for HVDC installations using VSC . 44
6.14 Conclusions on active a.c. filters . 45
Bibliography . 46

Figure 1 – Shunt connection . 8
Figure 2 – Series connection . 8
Figure 3 – Conceptual diagram of allowable interference level and d.c. filter cost . 10
Figure 4 – Simple current source converter . 13
Figure 5 – Simple voltage sourced converter . 14
Figure 6 – Possible connections of active d.c. filters . 15
Figure 7 – Filter components in the active filter . 18
Figure 8 – Impedance characteristics of different passive filters. 18
Figure 9 – Basic control loop of an active d.c. filter . 22
Figure 10 – Measured transfer function of external system, Baltic Cable HVDC link . 23
Figure 11 – Feedforward control for the active d.c. filter . 23
Figure 12 – Measured line current spectra, pole 3 operated as monopole . 25
Figure 13 – Continuously tuned filter. 27
Figure 14 – Example of current waves . 30
Figure 15 – Series and parallel connection . 31
Figure 16 – Hybrid configuration . 31
Figure 17 – Three phase current-source converter . 32
Figure 18 – Three phase 2 level voltage-sourced converter (three-wire type) . 33
Figure 19 – Three phase 3 level voltage-sourced converter (three-wire type) . 33

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Figure 20 – Single-phase voltage sourced converter . 34
Figure 21 – Active filter connected to the HV system through a single-tuned passive
filter . 35
Figure 22 – Active filter connected to the HV system through
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