CLC/TS 50654-1:2018
(Main)HVDC Grid Systems and connected Converter Stations - Guideline and Parameter Lists for Functional Specifications - Part 1: Guidelines
HVDC Grid Systems and connected Converter Stations - Guideline and Parameter Lists for Functional Specifications - Part 1: Guidelines
1.1 General These Guidelines and Parameter Lists to Functional Specifications describe specific functional requirements for HVDC Grid Systems. The terminology "HVDC Grid Systems" is used here describing HVDC systems for power transmission having more than two converter stations connected to a common d.c. circuit. While this document focuses on requirements, that are specific for HVDC Grid Systems, some requirements are considered applicable to all HVDC systems in general, i.e. including point-to-point HVDC systems. Existing IEC, Cigré or other documents relevant have been used for reference as far as possible. Corresponding to electric power transmission applications, this document is applicable to high voltage systems, i.e. .only nominal d.c. voltages equal or higher than 50 kV with respect to earth are considered in this document. NOTE While the physical principles of d.c. networks are basically voltage independent, the technical options for designing equipment get much wider with lower d.c. voltage levels, e.g. in case of converters or switchgear. Both parts have the same outline and headlines to aid the reader. 1.2 About the Present Release The present release of the Guidelines and Parameter Lists for Functional Specifications describes technical guidelines and specifications for HVDC Grid Systems which are characterized by having exactly one single connection between two converter stations, often referred to as radial systems. When developing the requirements for radial systems, care is taken not to build up potential show-stoppers for meshed systems. Meshed HVDC Grid Systems can be included into this specification at a later point in time. The Guidelines and Parameter List to the Functional Specification of HVDC Grid Systems cover technical aspects of - Coordination of HVDC Grid and a.c. Systems - HVDC Grid System Characteristics - HVDC Grid System Control - HVDC Grid System Protection - Models and Validation - Beyond the present scope, the following aspects are proposed for future work: - AC/DC converter stations - HVDC Grid System Equipment - HVDC Grid System Integration Tests
Hochspannungsgleichstrom-Netzsysteme - Leitfaden und Parameter-Listen für funktionale Spezifikationen - Teil 1: Leitfaden
Réseaux CCHT et stations de conversion connectées - Lignes directrices et listes de paramètres pour les spécifications fonctionnelles - Partie 1: Lignes directrices
Sistemi visokonapetostnega enosmernega omrežja in priključene pretvorniške postaje - Smernice in seznam parametrov za funkcijsko specifikacijo - 1. del: Smernice
Te smernice za funkcionalne specifikacije opisujejo določene funkcionalne zahteve za sisteme omrežja HVDC. Terminologija »sistemi omrežja HVDC« se tu uporablja za opis sistemov HVDC za prenos električne energije, ki imajo več kot dve pretvorniški postaji priključeni na običajen enosmerni tokokrog.
Čeprav se ta dokument osredotoča na zahteve, ki so značilne za sisteme omrežja HVDC, nekatere zahteve veljajo za vse sisteme HVDC na splošno, vključno s sistemi HVDC od točke do točke. Kot referenca so bili po možnosti uporabljeni obstoječe specifikacije, dokumenti Cigré ali drugi ustrezni dokumenti.
Ustrezno z aplikacijami prenosa električne energije se ta dokument uporablja za visokonapetostne sisteme, torej so v tem dokumentu upoštevane zgolj nazivne enosmerne napetosti, ki so enake ali višje od 50 kV glede na zemljo.
Opomba: Čeprav so po fizikalnih načelih omrežja enosmernega toka načeloma neodvisna od napetosti, so tehnične možnosti oblikovanja opreme večje pri nizkih ravneh napetosti enosmernega toka, npr. pri pretvornikih ali stikalnih napravah.
Ta 1. del bo treba prebrati v povezavi z 2. delom »Seznama parametrov«, za katere se vzporedno zažene predlog za nove delovne postavke.
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
01-maj-2018
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HVDC Grid Systems and connected Converter Stations - Guideline and Parameter Lists
for Functional Specifications - Part 1: Guidelines
Ta slovenski standard je istoveten z: CLC/TS 50654-1:2018
ICS:
29.240.01 2PUHåMD]DSUHQRVLQ Power transmission and
GLVWULEXFLMRHOHNWULþQHHQHUJLMH distribution networks in
QDVSORãQR general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
TECHNICAL SPECIFICATION CLC/TS 50654-1
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
March 2018
ICS 29.240.01
English Version
HVDC Grid Systems and connected Converter Stations -
Guideline and Parameter Lists for Functional Specifications -
Part 1: Guidelines
Réseaux CCHT et stations de conversion connectées - Hochspannungsgleichstrom-Netzsysteme - Leitfaden und
Lignes directrices et listes de paramètres pour les Parameter-Listen für funktionale Spezifikationen - Teil 1:
spécifications fonctionnelles - Partie 1: Lignes directrices Leitfaden
This Technical Specification was approved by CENELEC on 2018-01-22.
CENELEC members are required to announce the existence of this TS in the same way as for an EN and to make the TS available promptly
at national level in an appropriate form. It is permissible to keep conflicting national standards in force.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. CLC/TS 50654-1:2018 E
Contents Page
European foreword . 5
Introduction . 6
1 Scope . 7
1.1 General . 7
1.2 About the Present Release . 7
2 Normative references . 7
3 Terms, definitions and abbreviations . 8
3.1 Terms and definitions . 8
3.2 Abbreviations . 10
4 Coordination of HVDC Grid System and AC Systems . 10
4.1 Purpose of the HVDC Grid System and Power Network Diagram . 10
4.2 Hybrid AC/DC Power Flow Optimization . 11
4.3 Basic Operation Functions – Converter Normal Operation State . 12
4.3.1 General . 12
4.3.2 AC System Frequency by a Frequency / Power Droop . 12
4.3.3 DC Voltage / DC Power Droop . 13
4.4 Basic Operation Functions – Converter Abnormal Operation State . 14
4.4.1 General . 14
4.4.2 Network Conditions and Power Flow Requirements . 14
4.4.3 Abnormal AC Voltage Conditions . 14
4.5 Ancillary Services . 15
4.5.1 General . 15
4.5.2 Frequency Control Related Services . 15
4.5.3 AC Voltage Control Related Services . 17
4.5.4 Power Oscillation Damping Services . 18
4.5.5 System Restoration Services . 18
5 HVDC Grid System Characteristics . 18
5.1 HVDC Circuit Topologies . 18
5.1.1 Basic Characteristics and Nomenclature . 18
5.1.2 Attributes of HVDC Grid Systems or HVDC Grid Sub-Systems . 23
5.1.3 Attributes of a Converter Station . 24
5.2 Grid Operating States . 25
5.2.1 Normal State . 25
5.2.2 Alert State . 25
5.2.3 Emergency State . 25
5.2.4 Blackout State . 25
5.2.5 Restoration . 25
5.3 DC Voltages . 26
5.3.1 General . 26
5.3.2 Nominal DC System Voltage . 26
5.3.3 Steady-State DC Voltage . 26
5.3.4 Temporary DC Voltage . 26
5.4 Insulation Coordination . 28
5.5 Short-Circuit Characteristics . 28
5.5.1 General Remarks . 28
5.5.2 Calculation of Short-Circuit Currents in HVDC Grid Systems . 28
5.5.3 Short Circuit Current Design Requirements . 29
5.6 Steady-State Voltage and Current Distortions . 29
6 HVDC Grid System Control . 30
6.1 Closed-Loop Control Functions . 30
6.1.1 General . 30
6.1.2 Core Control Functions . 30
6.1.3 Coordinating Control Functions . 30
6.2 Controller Hierarchy . 30
6.2.1 General . 30
6.2.2 Internal Converter Control . 31
6.2.3 DC Node Voltage Control . 32
6.2.4 Coordinated System Control . 33
6.2.5 AC/DC Grid Control . 35
6.3 Propagation of Information . 36
6.4 Open-Loop Controls . 37
6.4.1 Operating Sequences for Grid Installations . 37
6.4.2 Operating Sequences for the Return Path . 38
6.4.3 Recovery . 38
7 HVDC Grid System Protection . 39
7.1 General . 39
7.2 DC Fault Separation . 40
7.3 Protection System Related Installations and Equipment . 40
7.3.1 AC/DC Converter Station . 40
7.3.2 HVDC Grid System Topology and Equipment . 41
7.4 HVDC Grid System Protection Zones . 41
7.4.1 General . 41
7.4.2 Permanent Stop P . 43
7.4.3 Permanent Stop PQ . 45
7.4.4 Temporary Stop P . 46
7.4.5 Temporary Stop PQ . 48
7.4.6 Continued Operation . 48
7.4.7 Example of a Protection Zone Matrix . 50
7.5 DC Protection . 51
7.5.1 General . 51
7.5.2 DC Converter Protections . 52
7.5.3 HVDC Grid System Protections . 52
7.5.4 HVDC Hub Respective HVDC Node Protections . 53
7.5.5 DC Grid Protection Communication . 54
8 AC/DC Converter Stations . 54
8.1 General . 54
8.2 AC/DC Converter Station Types . 54
9 HVDC Grid System Installations . 55
10 Models and Validation . 55
10.1 Introduction . 55
10.2 HVDC Grid System Studies . 56
10.2.1 Type of Studies . 56
10.2.2 Tools and Methods . 57
10.3 Model General Specifications . 57
10.3.1 Model Capability . 57
10.3.2 Model Format and Data Type . 58
10.3.3 Model Aggregation . 58
10.4 Model Specific Recommendations . 59
10.4.1 Load Flow Models . 59
10.4.2 Short-Circuit Models . 59
10.4.3 Protection System Models . 59
10.4.4 Insulation Coordination Related Models . 60
10.4.5 Electromechanical Transient Models . 60
10.4.6 Electromagnetic Transient Models . 61
10.4.7 Power Quality Models . 62
10.5 Model Validation . 62
10.6 Compliance Simulation . 64
10.7 Outputs/Results . 64
10.7.1 Model Data . 64
10.7.2 Model Documentation . 65
10.7.3 Model Example . 65
10.7.4 Model Compliance Documentation . 65
10.7.5 Model Validation Documentation – Model Final Version . 65
10.7.6 Model Guarantee . 66
11 HVDC Grid System Integration Tests . 66
Bibliography . 67
European foreword
This document (CLC/TS 50654-1:2018) has been prepared by CLC/TC8X/WG 06 “System Aspects of HVDC
Grid”.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Introduction
HVDC Grid Systems are a new field of technology. There are very few systems with a small number of
converter stations in operation; some more are in execution or in detailed planning.
The Guidelines and Parameter Lists to Functional Specifications are presented featuring planning,
specification and execution of multi-vendor HVDC Grid Systems in Europe. Being elaborated by a team of
experts from leading manufacturers of HVDC technology, Transmission System Operators (TSO's), Academia
and Institutions in Europe, the present document provides a commonly agreed basis for an open market of
compatible equipment and solutions for HVDC Grid Systems. Executing such systems and gaining operational
experience is seen an important prerequisite for developing corresponding technical standards in the future.
By elaborating this document, special care has been taken to as far as possible describe the requirements in a
technologically independent way. In order to achieve that, a function of interest is described by a
comprehensive set of parameters. The parameters are selected based on a systematic analysis of physical
phenomena relevant to achieve the requested functionality. The physical phenomena are categorized in order
to show the mutual dependence of the individual parameters and ensure completeness of the physical aspects
to be considered. Based on a clearly defined common language describing the functionalities requested,
existing technologies can be applied or new dedicated technical solutions can be developed.
Reflecting the early stage of technology, these Guidelines and Parameter Lists to Functional Specifications
need comprehensive explanations and background information for the technical parameters. This dual
character of the content will be represented by two corresponding parts:
• Part I “Guidelines” containing the explanations and the background information in context with the
Parameter Lists.
• Part II “Parameter Lists” containing the essential lists of parameters and values describing properties of
the a.c. respectively d.c. system (operating conditions) and parameters describing the performance of the
newly installed component (performance requirements).
1 Scope
1.1 General
These Guidelines and Parameter Lists to Functional Specifications describe specific functional requirements
for HVDC Grid Systems. The terminology “HVDC Grid Systems” is used here describing HVDC systems for
power transmission having more than two converter stations connected to a common d.c. circuit.
While this document focuses on requirements, that are specific for HVDC Grid Systems, some requirements
are considered applicable to all HVDC systems in general, i.e. including point-to-point HVDC systems. Existing
IEC, Cigré or other documents relevant have been used for reference as far as possible.
Corresponding to electric power transmission applications, this document is applicable to high voltage
systems, i.e. .only nominal d.c. voltages equal or higher than 50 kV with respect to earth are considered in this
document.
NOTE While the physical principles of d.c. networks are basically voltage independent, the technical options for
designing equipment get much wider with lower d.c. voltage levels, e.g. in case of converters or switchgear.
Both parts have the same outline and headlines to aid the reader.
1.2 About the Present Release
The present release of the Guidelines and Parameter Lists for Functional Specifications describes technical
guidelines and specifications for HVDC Grid Systems which are characterized by having exactly one single
connection between two converter stations, often referred to as radial systems. When developing the
requirements for radial systems, care is taken not to build up potential show-stoppers for meshed systems.
Meshed HVDC Grid Systems can be included into this specification at a later point in time.
The Guidelines and Parameter List to the Functional Specification of HVDC Grid Systems cover technical
aspects of
• Coordination of HVDC Grid and a.c. Systems
• HVDC Grid System Characteristics
• HVDC Grid System Control
• HVDC Grid System Protection
• Models and Validation
• Beyond the present scope, the following aspects are proposed for future work:
• AC/DC converter stations
• HVDC Grid System Equipment
• HVDC Grid System Integration Tests
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 62747:2014, Terminology for voltage-sourced converters (VSC) for high-voltage direct current (HVDC)
systems (IEC 62747:2014)
EN 60909 (all parts), Short-circuit currents in three-phase A.C. systems
EN 61660-1:1997, Short-circuit currents in d.c. auxiliary installations in power plants and substations — Part 1:
Calculation of short-circuit currents (IEC 61660-1:1997)
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain
terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
AC/DC converter unit
indivisible operative unit comprising all equipment between the point of connection on the a.c. side and the
point of connection on the d.c. side, essentially one or more converters, together with converter transformers,
control equipment, essential protective and switching devices and auxiliaries, if any, used for conversion
[SOURCE: EN 62747:2014, modified – The definition was neutralised with respect to technology (not only
VSC converters) and uses the terms PoC as defined in the present document]
3.1.2
AC/DC converter station
part of an HVDC system which consists of one or more AC/DC converter units including d.c. switchgear, d.c.
fault current controlling devices, if any, installed in a single location together with buildings, reactors, filters,
reactive power supply, control, monitoring, protective, measuring and auxiliary equipment
[SOURCE: EN 62747:2014, modified – The definition was made specific with respect to AC/DC converter
units, differentiating from DC/DC converter units. Furthermore, only the term AC/DC converter station is used
in the present document]
3.1.3
point of connection-DC (PoC-DC)
electrical interface point at d.c. voltage
3.1.4
point of connection-AC (PoC-AC)
electrical interface point at a.c. voltage
AC/DC converter
station
a.c. side d.c. side
point of connection point of connection HVDC grid
(PoC-AC) (PoC-DC) system
Figure 1 — Definition of the Point Of Connection-AC and the Point Of Connection-DC at an AC/DC
converter station
3.1.5
DC/DC converter unit
indivisible operative unit comprising all equipment between the points of connection to the HVDC Grid System,
essentially one or more converters, together with converter transformers, if any, control equipment, essential
protective and switching devices and auxiliaries, if any, used for conversion
3.1.6
DC/DC converter station
part of an HVDC Grid System which consists of one or more DC/DC converter units including d.c. switchgear,
d.c. fault current controlling devices, if any, installed in a single location together with buildings, reactors,
filters, control, monitoring, protective, measuring and auxiliary equipment
3.1.7
HVDC Grid System
high voltage direct current transmission network connecting more than two AC/DC converter stations
transferring energy in the form of high-voltage direct current including related transmission lines, switching
stations, DC/DC converter stations, if any, as well as other equipment and sub-systems needed for operation
3.1.8
meshed HVDC Grid System
HVDC Grid System having more than one direct current connection between at least two converter stations
3.1.9
DC protection zone
physical part of a HVDC Grid System with a common response to d.c. faults
3.1.10
radial HVDC Grid System
HVDC Grid System having exactly one direct current connection between two arbitrary converter stations
3.1.11
rigid bipolar (HVDC) system
bipolar (HVDC) system without Dedicated Return Path or electrodes as illustrated in Figure 2
Note 1 to entry: Monopolar operation is possible by means of bypass switches during a converter pole outage, but not
during an HVDC conductor outage. A short bipolar outage will follow a converter pole outage before bypass operation can
be established.
(SOURCE: IEEE P1899 [1])
Pole
DC Line or Cable
~ ~
= =
~
~
DC Line or Cable
=
=
Pole
Figure 2 — Rigid Bipolar HVDC system
3.2 Abbreviations
AC/DC alternating current / direct current (conversion)
DC/DC direct current / direct current (conversion)
DPT dynamic performance tests
ENTSO-E European Network of Transmission System Operators for Electricity
FAT factory acceptance tests
FCR frequency containment reserve
FRR frequency restoration reserve
GOOSE generic object-oriented substation events
HSS high-speed switches
HV high voltage
HVDC high-voltage direct current
IEEE Institute of Electrical and Electronics Engineers
LAT laboratory acceptance test
LVRT low-voltage ride through
MMC modular multilevel converter
NC Network Code
OHL overhead line
OP operating point
OPF optimum power flow
OVRT over-voltage ride through
PoC-AC point of connection on a.c. side
PoC-DC point of connection on d.c. side
POD power oscillation damping
STATCOM static synchronous compensator
THD total harmonic distortion
TSO transmission system operator
UVRT under-voltage ride through
VSC voltage-sourced converter
4 Coordination of HVDC Grid System and AC Systems
4.1 Purpose of the HVDC Grid System and Power Network Diagram
To provide an overall understanding of the HVDC Grid System, the purposes and basic functions of the HVDC
Grid System including all AC/DC converter stations shall be explained.
To explain the a.c. and HVDC Grid System structure, a Power Network Diagram shall be specified. This
diagram shall contain the following information as a minimum:
• a.c. networks showing the connection of each AC/DC converter station to the synchronous zones
• HVDC Grid System showing in detail, how the AC/DC converter stations are interconnected on the d.c.
side, including, if any, lines, reactors, switches, DC Breakers, DC/DC converters, energy storages,
braking choppers, pre-insertion resistors
The main electrical parameters of all installations listed above shall be specified.
4.2 Hybrid AC/DC Power Flow Optimization
The behaviour of an HVDC Grid System and its AC/DC converter stations within their a.c. system environment
is typically described in corresponding network codes for the respective a.c. systems. This chapter describes
typical requirements from the a.c. system perspective with respect to their implications on the design of HVDC
Grid Systems.
An HVDC Grid System with more than two AC/DC converter stations in operation requires superordinate
coordination of the power flow between the individual converter stations. The requirements for such
coordination are described in chapter HVDC Grid System Control.
The steady-state active and reactive power capabilities of an AC/DC converter station are described by the
maximum and minimum reactive power exchange capability charts (inductive and capacitive) depending on
active power and voltage (P ,U ) at the PoC-AC of each station as shown in Figure 3. This diagram can
AC AC
be specified for different a.c. voltage levels. There can be similar diagrams describing the boundaries under
temporary conditions, e.g. overload operation.
U =const.
AC
Q
OP3 OP2
OP11 OP10
OP1
OP4
OP12 OP9
P
OP13 OP16
OP5 OP8
OP14 OP15
OP6 OP7
Figure 3 — Example of a PQ-diagram showing maximum and minimum reactive power
(inductive and capacitive) exchange capability of an AC/DC converter station
Compared to a.c. infrastructures, AC/DC converter stations provide the capability to set and control active
power flow going through them. The active power set points as well as the control droop parameters have an
impact on the global grid power flows (a.c. and d.c.). Optimizing the static power flow, can aim at different
objectives, e.g. minimizing the overall losses, while remaining below the limits of individual equipment
(converters, ampacity of lines, breakers, etc.) and minimizing the consequences of contingencies such as loss
of transmissible power.
In this chapter a general categorization of converter operational functions into basic operation functions during
normal operation states, basic operation functions during abnormal operation states and functions for ancillary
service provision is provided. Basic operation functions both during normal and abnormal operating state are
functions which need to be parameterized since they are basic to the coordination of an HVDC grid with a.c.
systems. The consecutive chapters will further outline these functions.
4.3 Basic Operation Functions – Converter Normal Operation State
4.3.1 General
The converter station control has two fundamental degrees of freedom on the a.c. side:
• active power injection
• reactive power injection
In general for active current exchange, reference values can be given for the following control objectives:
• active power control
• a.c. frequency control
• d.c. voltage control
The corresponding control objectives for active current exchange cannot be reached independently from one
another.
For reactive current exchange, reference values can be given for the following control objectives
• reactive power control
• a.c. voltage magnitude control
These functions are described under subchapter Ancillary Services.
The corresponding control objectives for reactive current exchange cannot be reached independently from one
another.
The two fundamental degrees of freedom are reflected in the following three basic operation functions of a
converter station:
• maintaining the a.c. system frequency
• maintaining the d.c. voltage
• transmitting scheduled power at a defined power factor
The basic operating functions are specified by as follows:
• a.c. system frequency by a frequency / power droop (s )
PF
• d.c. voltage by a d.c. voltage / d.c. power droop (s ) or a d.c. voltage / d.c. current droop
P_UDC
s )
IDC_UDC
The capabilities and requirements of all converter stations connected to an HVDC Grid System have to be
coordinated with the a.c. system needs.
4.3.2 AC System Frequency by a Frequency / Power Droop
The a.c. system frequency by frequency power droop describes the change of active power in response to a
deviation of the a.c. system frequency from its reference value. It is defined by
s = (Δf/f ) / (ΔP/P )
PF nom nom
where:
Δf is the frequency change
f is the nominal a.c. system frequency
nom
ΔP is the change of the active power output of the converter station
P is the nominal active power of an AC/DC converter station
nom
There are two extreme cases:
a) scheduled power, |s | → ∞
PF
In this case, the converter station will operate at a power reference value and does not contribute to a.c.
system frequency control
b) constant a.c. system frequency s = 0
PF
In this case, the converter station will exchange the power needed to keep the a.c. system frequency constant.
Case b) as well as all other cases with |s | ≠ ∞ require at least one independent source of active power
PF
connected to the HVDC Grid System, such as an asynchronous a.c. system.
4.3.3 DC Voltage / DC Power Droop
The d.c. voltage by a d.c. voltage / d.c. power droop (s ) describes the change of active power in
P_UDC
response to a deviation of the d.c. voltage from its reference value.
s = (ΔU /U ) / (ΔP/P )
P_UDC DC DCnom n
Similarly, the d.c. voltage by a d.c. voltage / d.c. current droop (s ) describes the change of d.c.
IDC_UDC
current in response to a deviation of the d.c. voltage from its reference value. It is defined by
s = (ΔU /U ) / (ΔI /I )
IDC_UDC DC DCnom DC DCnom
There are two extreme cases:
a) scheduled power, s = ∞, s = ∞
P_UDC IDC_UDC
In this case, the converter station will operate at a power reference value and does not contribute to d.c.
voltage control.
b) constant d.c. voltage, s = 0, s = 0
P_UDC IDC_UDC
In this case, the converter station will exchange the power needed to keep the d.c. voltage at its terminals
constant.
In all other cases, the contributions of a converter station to the d.c. voltage control is specified by
corresponding droop values s , s between these two extremes.
P_UDC IDC_UDC
The above droop characteristics are the most common, but there could be others along with all other control
modes as defined in chapter Converter Control Modes where it is explained that droop constants could be a
function of active power, d.c. voltage, etc. Several droop constants s(P) could be used to model dead bands
etc.
4.4 Basic Operation Functions – Converter Abnormal Operation State
4.4.1 General
In this context basic operation functions in abnormal operation state are functions which need to be
parameterized since they are basic to the operation of an HVDC grid. Abnormal operation states are
conditions induced by faults.
4.4.2 Network Conditions and Power Flow Requirements
Pre- and post-fault a.c. system strengths are defined by the minimum and maximum short circuit currents at
the PoC-AC of a converter station without considering possible contributions by that particular converter
station, if any.
With respect to maintaining a.c. and d.c. system stability, maximum times of interruption of active and reactive
power exchange at an AC/DC converter station shall be specified.
Permanent faults may require a reconfiguration of the a.c. or d.c. grid, respectively, resulting in different post-
fault capabilities of the AC/DC converter stations. This shall be reflected in the post fault target values for
active or reactive power.
During an a.c. fault the current contribution by a converter station can be specified with respect to the positive,
negative and zero sequence voltage content. The active and reactive power flow requirements during a fault
condition may depend on the residual a.c. voltage level. Various power levels can be specified for different
voltage levels.
4.4.3 Abnormal AC Voltage Conditions
The operational requirements for abnormal a.c. voltage conditions are specified by a.c. Under-Voltage Ride
Through (UVRT), also known as a.c. Low Voltage Ride Through Capability (LVRT); as well as a.c. Over-
Voltage Ride Through (OVRT),
An exemplary generic combined a.c. under and over voltage ride through characteristic is shown in Figure 4.
The x-axis is the time and the y-axis is the rms voltage at the PoC-AC. This relates to symmetrical faults.
Voltage profiles for unsymmetrical faults shall be specified similar to the one for symmetrical faults.
A converter shall maintain controllability of current inside the grey shaped area depicted in Figure 4. Each
converter shall withstand several consecutive voltage disturbances.
When considering unsymmetrical events, the AC/DC converter station may trip in case of an over voltage
affecting one phase. The AC/DC converter station shall remain connected and maintain controllability of
current in case of an under voltage affecting one phase.
Although Figure 4 displays a deterministic number of over voltage / time tuples, this number is not subject of
specification; it could be any number “n” greater or less than the breaking points illustrated.
t t
t t t
AC_OV0 AC_OV1 AC_OV2 AC_OV3 AC_OV(i)
t(s)
U
AC_OV1
U
AC_OV2
U
AC_OV3
U
AC_OV(i)
U
ACmax_ss
U
ACmin_ss
U
AC_UV2
U
AC_UV1
t t t t
AC_UV0 AC_UV1 AC_UV2 AC_UV3
t(s)
Figure 4 — Exemplary generic AC Over- and Under Voltage Ride Through profile
of a HVDC converter station
4.5 Ancillary Services
4.5.1 General
Ancillary services comprise operation functions which are optional, i.e. they can be activated in order to
improve or support the rest of the power system but they are not mandatory for the operation of the power
system. An HVDC Grid System can provide the following ancillary services to an a.c. system:
• Frequency control related services
• Voltage control related services
• Power oscillation damping service
• System restoration service
These categories of ancillary services are further outlined in the following.
4.5.2 Frequency Control Related Services
4.5.2.1 Synthetic Inertia (Differential Frequency Control)
An HVDC Grid System connecting a minimum of two asynchronous a.c. grid zones can be specified to provide
synthetic inertia to be transmitted from at least one asynchronous a.c. grid zone to another one.
In the absence of commonly agreed principles, the details of such services are to be agreed on a case by
case basis.
4.5.2.2 Frequency Containment Reserve (Primary Frequency Control)
An HVDC Grid System connecting a minimum of two asynchronous areas can be specified to provide
frequency containment reserve (FCR) to be transmitted from at least one asynchronous zone to another one.
The corresponding requirements for one synchronous zone supported by the primary frequency control can be
distributed among all AC/DC converter stations interconnecting the supported synchronous zone and the
HVDC Grid System. The contribution of one of the AC/DC converter stations can be specified as shown in
Figure 5.
∆P
MaximumActivePowerTransmissionCapacity
P
max
(import)
∆P 100 ∆f
Range available for FSM
= − ⋅
(for0 < f ≤ f )
P s [%] f
max 1 n
transmitted active power
(operation setpoint)
∆P 100 ∆f
= − ⋅
(for 0 < f ≤ f )
P s [%] f
max 2 n
Minimum Active Power Transmission Capacity
(import)
− ∆f
(f − f ) (f f )
2 n 1 n
f
f
f n
n n
Key
ΔP: Change in P triggered by the step change in frequency (MW)
SETPOINT
Δf: Frequency change in a.c. network(s) where the HVDC is connected to, measured continuously by the
average of the rate of change of the a.c. network frequency (df/dt) for a defined time span; (Hz)
P : Maximum HVDC Active Power Transmission Capacity (MW)
max
f : Target frequency in the a.c. network (Hz)
n
f = [f , f ]: Frequency Response Dead-band (indicative range 0 – ± 500 mHz)
DEADBAND min max
s : upward regulation ‘droop’ (indicative value ≥ 0,1 %)
s : downward regulation ‘droop’ (indicative value ≥ 0,1 %)
f : Over-frequency threshold (Hz)
f : Under-frequency threshold (Hz)
Frequency response insensitivity: ≤ 30 mHz
Figure 5 — Active po
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