IEC TR 61400-21-3:2019
(Main)Wind energy generation systems - Part 21-3: Measurement and assessment of electrical characteristics - Wind turbine harmonic model and its application
Wind energy generation systems - Part 21-3: Measurement and assessment of electrical characteristics - Wind turbine harmonic model and its application
IEC TR 61400-21-3:2019 provides guidance on principles which can be used as the basis for determining the application, structure and recommendations for the WT harmonic model. For the purpose of this Technical Report, a harmonic model means a model that represents harmonic emissions of different WT types interacting with the connected network.
This document is focused on providing technical guidance concerning the WT harmonic model. It describes the harmonic model in detail, covering such aspects as application, structure, as well as validation. By introducing a common understanding of the WT representation from a harmonic performance perspective, this document aims to bring the overall concept of the harmonic model closer to the industry (e.g. suppliers, developers, system operators, academia, etc.).
A standardized approach of WT harmonic model representation is presented in this document. The harmonic model will find a broad application in many areas of electrical engineering related to design, analysis, and optimisation of electrical infrastructure of onshore as well as offshore WPPs.
General Information
Standards Content (sample)
IEC TR 61400-21-3
Edition 1.0 2019-09
TECHNICAL
REPORT
colour
inside
Wind energy generation systems –
Part 21-3: Measurement and assessment of electrical characteristics – Wind
turbine harmonic model and its application
IEC TR 61400-21-3:2019-09(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 61400-21-3
Edition 1.0 2019-09
TECHNICAL
REPORT
colour
inside
Wind energy generation systems –
Part 21-3: Measurement and assessment of electrical characteristics – Wind
turbine harmonic model and its application
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.180 ISBN 978-2-8322-7288-6
Warning! Make sure that you obtained this publication from an authorized distributor.
® Registered trademark of the International Electrotechnical Commission---------------------- Page: 3 ----------------------
– 2 – IEC TR 61400-21-3:2019 © IEC 2019
CONTENTS
FOREWORD ........................................................................................................................... 4
INTRODUCTION ..................................................................................................................... 6
1 Scope .............................................................................................................................. 7
2 Normative references ...................................................................................................... 8
3 Terms, definitions and abbreviations ............................................................................... 8
3.1 Terms and definitions .............................................................................................. 8
3.2 Abbreviations ........................................................................................................ 12
4 General description ....................................................................................................... 13
4.1 Overview............................................................................................................... 13
4.2 Background........................................................................................................... 14
5 Recommendations of minimal requirements ................................................................... 17
5.1 General ................................................................................................................. 17
5.2 Application ............................................................................................................ 18
5.3 Input parameters ................................................................................................... 18
5.4 Harmonic model terminal ...................................................................................... 18
5.5 Output variables.................................................................................................... 19
5.6 Structure ............................................................................................................... 19
6 Interfaces to other IEC documents ................................................................................. 20
6.1 IEC 61400-21-1:2019, Annex D – Harmonic evaluation ......................................... 20
6.2 IEC 61400-21-1:2019, Annex E – Assessment of power quality of windturbines and wind power plants ............................................................................. 21
7 Harmonic model ............................................................................................................ 21
7.1 General ................................................................................................................. 21
7.2 Thévenin/Norton equivalent circuit ........................................................................ 22
7.3 Equivalent harmonic voltage/current sources ........................................................ 22
7.3.1 General ......................................................................................................... 22
7.3.2 Harmonic equivalent impedance .................................................................... 23
7.4 Wind turbine types ................................................................................................ 24
7.4.1 General ......................................................................................................... 24
7.4.2 Type 1 and Type 2 ......................................................................................... 24
7.4.3 Type 3 ........................................................................................................... 25
7.4.4 Type 4 ........................................................................................................... 26
8 Validation ...................................................................................................................... 28
8.1 General ................................................................................................................. 28
8.2 Overview............................................................................................................... 28
8.3 Model validation .................................................................................................... 29
8.4 Fictitious grid ........................................................................................................ 30
9 Limitations ..................................................................................................................... 30
Bibliography .......................................................................................................................... 32
Figure 1 – Example of a phase angle between the harmonic current and the harmonic
voltage component as well as the fundamental voltage ........................................................... 9
Figure 2 – Example of wind power plant typical components relevant for the harmonic
studies and potential challenges in harmonic performance .................................................... 14
Figure 3 – Example of a WPP complex structure ................................................................... 15
Figure 4 – Example of a WPP complex electrical infrastructure with many WTs .................... 16
---------------------- Page: 4 ----------------------IEC TR 61400-21-3:2019 © IEC 2019 – 3 –
Figure 5 – Harmonic impedance estimated at the point of connection specified in
Figure 4 ................................................................................................................................ 17
Figure 6 – Generic harmonic model structure represented as Norton/Théveninequivalent circuit ................................................................................................................... 20
Figure 7 – Main electrical and mechanical components of Type 3 WTs [6] ............................ 25
Figure 8 – Example of a structure of a DFAG harmonic model (from [13]) ............................. 26
Figure 9 – Main electrical and mechanical components of Type 4 WTs [6] ............................ 26
Figure 10 – Example of a converter harmonic model as Thévenin equivalent circuittogether with an example of a WT power circuit (from [9]) ..................................................... 27
Figure 11 – Harmonic voltage comparison for respective power bins .................................... 28
Table 1 – Example of a representation/template of the harmonic voltage source ................... 23
Table 2 – Example of a representation/template of the harmonic current source ................... 23
Table 3 – Example of a representation/template of the harmonic equivalent impedance ........ 24
---------------------- Page: 5 ----------------------– 4 – IEC TR 61400-21-3:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –
Part 21-3: Measurement and assessment of electrical characteristics –
Wind turbine harmonic model and its application
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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Publications.8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a Technical Report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".IEC TR 61400-21-3, which is a Technical Report, has been prepared by IEC Technical
Committee 88: Wind energy generation systems.The text of this Technical Report is based on the following documents:
DTR Report on voting
88/698/DTR 88/717/RVDTR
Full information on the voting for the approval of this Technical Report can be found in the
report on voting indicated in the above table.---------------------- Page: 6 ----------------------
IEC TR 61400-21-3:2019 © IEC 2019 – 5 –
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 61400 series, published under the general title Wind energy
generation systems, can be found on the IEC website.Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correctunderstanding of its contents. Users should therefore print this document using a
colour printer.---------------------- Page: 7 ----------------------
– 6 – IEC TR 61400-21-3:2019 © IEC 2019
INTRODUCTION
The purpose of this IEC Technical Report (TR) is to provide a methodology that will ensure
understanding, consistency and accuracy in application, structure and validation of the
harmonic model of grid connected wind turbines (WTs).There is an understandable requirement from wind power industry shareholders, e.g.
transmission system operators (TSOs) and distribution system operators (DSOs), wind power
plant (WPP) developers, WT manufacturers, WT component suppliers, academic units,
research institutions, certifying bodies and standardization groups (e.g. TC88 MT21), for
having a standardized WT harmonic model.The standardized harmonic model would find a broad application in many areas of electrical
engineering related to design, analysis, and optimisation of electrical infrastructure of onshore
as well as offshore WPPs. Among others, this could be the evaluation of the WT harmonic
performance, system-level harmonic studies, electrical infrastructure design and proposal of
harmonic mitigation measures.Standardized WT harmonic models as a performance measure starts to be important in such
multi stakeholder systems as large offshore WPPs where TSOs, WPP developers andoperators as well as WT manufacturers need to have a common understanding about
harmonic modelling of WTs and harmonic studies in WPPs.
---------------------- Page: 8 ----------------------
IEC TR 61400-21-3:2019 © IEC 2019 – 7 –
WIND ENERGY GENERATION SYSTEMS –
Part 21-3: Measurement and assessment of electrical characteristics –
Wind turbine harmonic model and its application
1 Scope
This part of IEC 61400 provides guidance on principles which can be used as the basis for
determining the application, structure and recommendations for the WT harmonic model. For
the purpose of this Technical Report, a harmonic model means a model that represents
harmonic emissions of different WT types interacting with the connected network.This document is focused on providing technical guidance concerning the WT harmonic
model. It describes the harmonic model in detail, covering such aspects as application,
structure, as well as validation. By introducing a common understanding of the WT
representation from a harmonic performance perspective, this document aims to bring the
overall concept of the harmonic model closer to the industry (e.g. suppliers, developers,
system operators, academia, etc.).A standardized approach of WT harmonic model representation is presented in this document.
The harmonic model will find a broad application in many areas of electrical engineering
related to design, analysis, and optimisation of electrical infrastructure of onshore as well as
offshore WPPs.The structure of the harmonic model presented in this document will find an application in the
following potential areas:– evaluation of the WT harmonic performance during the design of electrical
infrastructure and grid-connection studies;
– harmonic studies/analysis of modern power systems incorporating a number of WTs
with line side converters;– active or passive harmonic filter design to optimize electrical infrastructure (e.g.
resonance characteristic shaping) as well as meet requirements in various grid codes;
– sizing of electrical components (e.g. harmonic losses, static reactive powercompensation, noise emission, harmonic compatibility levels, etc.) within WPP
electrical infrastructure;
– evaluation of external network background distortion impact on WT harmonic
assessment;
– standardised communication interfaces in relation to WT harmonic data exchange
between different stakeholders (e.g. system operators, generators, developers, etc.);
– universal interface for harmonic studies for engineering software developers;– possible benchmark of WT introduced to the academia and the industry.
The advantage of having standardized WT harmonic performance assessment by means of
the harmonic model is getting more and more crucial in case of large systems with different
types of WTs connected to them, e.g. multi-cluster wind power plants incorporating different
types of WTs connected to the same offshore or onshore substation.th th th
The WT harmonic model can cover the integer harmonic range up to the 40 , 50 , or 100 .
And can be expanded, depending on requirements and application, to higher harmonic range
as well as can also cover interharmonic components.---------------------- Page: 9 ----------------------
– 8 – IEC TR 61400-21-3:2019 © IEC 2019
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.IEC 60050-415:1999, International Electrotechnical Vocabulary – Part 415: Wind turbine
generator systems (available atIEC TR 61000-3-6:2008, Electromagnetic compatibility (EMC) – Part 3-6: Limits – Assessment
of emission limits for the connection of distorting installations to MV, HV and EHV power
systemsIEC 61000-4-7:2002, Electromagnetic compatibility (EMC) – Part 4-7: Testing and
measurement techniques – General guide on harmonics and interharmonics measurements
and instrumentation, for power supply systems and equipment connected theretoIEC 61400-21-1:2019, Wind energy generation systems – Part 21-1: Measurement and
assessment of electrical characteristics – Part 1 – Wind turbines
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-415 and the
following 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
compatibility levels
reference levels of a particular disturbance in a particular environment defined for co-
ordinating the emission and immunity of equipment which is part of, or supplied by, a supply
system in order to ensure the EMC in the whole system (including system and connected
equipment)Note 1 to entry: Compatibility levels are generally based on the 95 % probability levels of entire systems, using
statistical distributions which represent both time and space variations of disturbances.
Note 2 to entry: There is allowance for the fact that the system operator or owner cannot control all points of a
system at all times. Therefore, evaluation with respect to compatibility levels should be made on a system-wide
basis and no assessment method is provided for evaluation at a specific location.
3.1.2factor K
indicator of the ability of a transformer to be loaded with non-sinusoidal currents
Note 1 to entry: The equivalent power rating is equal to the power based on the RMS value of the non-sinusoidal
current multiplied by the factor K.[SOURCE: EN 50464-3:2007, modified – additional elaboration, creation of a note to entry
and deletion of the formula]---------------------- Page: 10 ----------------------
IEC TR 61400-21-3:2019 © IEC 2019 – 9 –
3.1.3
harmonic phase or angle
phase (angle) α of the spectral component y , that is, the phase between the harmonic
h hcurrent component or harmonic voltage component and the fundamental component voltage
defined in Figure 1 and equation belowy = c sin htω+α
h h 1h
where c is the spectral component magnitude
Figure 1 – Example of a phase angle between the harmonic current and the harmonic
voltage component as well as the fundamental voltageNote 1 to entry: The sign convention used for the voltages and currents is the generator convention as defined in
IEC 61400-21-1:2019, Annex C.Note 2 to entry: Please check IEC 61400-21-1:2019, Annex D for more details.
3.1.4
harmonic distortion
cyclic departure of a waveform from the sinusoidal shape
Note 1 to entry: This can be described by the addition of one or more harmonics to the fundamental.
3.1.5harmonic model
model that represents harmonic emissions of a WT interacting with the connected network
Note 1 to entry: Different WT types may be modelled by changing the model parameters.
3.1.6harmonic model terminals
reference point on the electric power system where here the harmonic model is connected
3.1.7negative-sequence component of 3-phase voltages (or currents)
symmetrical vector system derived by application of the Fortescue’s transformation matrix,
and that rotates in the opposite direction to the power frequency voltage (or current)
[SOURCE: IEC TR 61000-3-13:2008, 3.26.4, modified – the formula has been deleted]
3.1.8operational mode
operation according to control setting, for example voltage control mode,
frequency control mode, reactive power control mode, active power control mode, etc.
[SOURCE: IEC 61400-21-1:2019, 3.9]---------------------- Page: 11 ----------------------
– 10 – IEC TR 61400-21-3:2019 © IEC 2019
3.1.9
percentile
the value of a variable below which a certain percent of observations fall
3.1.10
planning level
level of a particular disturbance in a particular environment, adopted as a reference value for
the limits to be set for the emissions from the installations in a particular system, in order to
co-ordinate those limits with all the limits adopted for equipment and installations intended to
be connected to the power supply systemNote 1 to entry: Planning levels are considered internal quality objectives to be specified at a local level by those
responsible for planning and operating the power supply system in the relevant area.
[SOURCE: IEC TR 61000-3-6:2008, 3.16]3.1.11
point of connection
reference point on the electric power system where here the WPP is connected
[SOURCE: IEC 60050-617:2009, 617-04-01, modified – "user’s electrical facility" has been
replaced by WPP]3.1.12
positive-sequence component of 3-phase voltages (or currents)
symmetrical vector system derived by application of the Fortescue’s transformation matrix,
and that rotates in the same direction as the power frequency voltage (or current)
[SOURCE: IEC TR 61000-3-13:2008, 3.26.3, modified – the formula has been deleted]
3.1.13power bin
consecutive, non-overlapping intervals of WT active power measured at WT terminals
Note 1 to entry: The bins (intervals) shall be adjacent, and are usually equal size, e.g. 0, 10, 20, … , 100 % of P .
0, 10, 20, … , 100 % are the bin midpoints.[SOURCE: IEC 61400-21-1:2019, 3.62, modified – "active" has been deleted from the term
defined; in the note, "shall be adjacent" has been added and the text has been slightly
modified]3.1.14
prevailing angle
phase of the spectral component is described by
Im C
( )
∑ h,i
i=1
α = arctan , if Re C ≥ 0
( )
h,avg ∑ h,i
Re C
i=1
( )
∑ h,i
i=1
Im C
( )
h,i
i=1
α = π + arctan , if Re C <0
( )
h,avg ∑ h,i
Re C i=1
( )
∑ h,i
i=1
where
n is the number of DFT windows;
---------------------- Page: 12 ----------------------
IEC TR 61400-21-3:2019 © IEC 2019 – 11 –
C is the complex value of the h-th harmonic from the estimated spectrum from each of i-th
h,i10-cycle or 12-cycle window, and
C is the h-th harmonic magnitude.
Note 1 to entry: Definition of rectangular window as in IEC 61000-4-7:2002.
3.1.15
prevailing angle ratio
ratio describing the phase randomness of spectral component and expressed by
C a +jb
( )
∑∑h,i h,i h,i
ii==11
PAR==
C a +jb
∑∑h,i h,i h,i
ii==11
where
C is the complex spectral component from DFT;
h,i
a and b are the real and imaginary components of the complex spectral component of
h,i h,ithe i-th window, respectively.
3.1.16
short-circuit power
product of the current in the short-circuit I at a point of a system and a nominal voltage U ,
k ngenerally the operating voltage
S = 3IU
k kn
Note 1 to entry: Using physical units for line current (A) and nominal phase-to-phase voltage (V), the product
should also include the factor 3.[SOURCE: IEC 60050-601:1985, 601-01-14, modified – "conventional" has been replaced by
"nominal"]3.1.17
short-circuit ratio
ratio of the short-circuit power S at the point of connection to the nominal power S of the
k nWPP or WT
SCR=
[SOURCE: IEC 61400-27-1:2015, 3.1.18, modified – "active" has been deleted and the
equation has been added]3.1.18
system operator or responsible
entity responsible for making technical connection agreements with customers who are
seeking connection of load or generation to a distribution or transmission system
[SOURCE: IEC TR 61000-3-6:2008, 3.23, modified – “owner” has been changed toresponsible]
3.1.19
total harmonic distortion
ratio of the RMS value of the sum of all the harmonic components up to a specified order to
the RMS value of the fundamental component---------------------- Page: 13 ----------------------
– 12 – IEC TR 61400-21-3:2019 © IEC 2019
THD=
h=2
1
where
Q represents either current or voltage;
Q is the RMS value of the fundamental component;
h is the harmonic order;
Q is the RMS value of the harmonic component of order h;
H is generally 40, 50 or 100 depending on the application.
[SOURCE: IEC TR 61000-3-6:2008, 3.26.7, modified – H is defined differently]
3.1.20
wind power plant
power station comprising one or more WTs, auxiliary equipment and plant control
[SOURCE: IEC 61400-27-1:2015, 3.1.25]
3.1.21
wind turbine
rotating machinery in which the kinetic wind energy is transformed into another form of energy
[SOURCE: IEC 60050-415:1999, 415-01-01]3.1.22
wind turbine terminals
point being a part of the WT and identified by the WT supplier at which the WT is connecte
...
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