SIST EN 62751-1:2014

SLOVENSKI STANDARD
01-december-2014
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Determination of power losses in voltage sourced converter (VSC) valves for high-
voltage direct current (HVDC) systems - Part 1: General requirements
Bestimmung der Leistungsverluste in Spannungszwischenkreis-Stromrichtern (VSC) für
Hochspannungsgleichstrom(HGÜ)-Systeme -- Teil 1: Allgemeine Anforderungen
Détermination des pertes de puissance dans les valves à convertisseur de source de
tension (VSC) des systèmes de transport d’énergie en courant continu à haute tension
(CCHT) -- Partie 1: Exigences générales
Ta slovenski standard je istoveten z: EN 62751-1:2014
ICS:
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 62751-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2014
ICS 29.200; 29.240
English Version
Power losses in voltage sourced converter (VSC) valves for
high-voltage direct current (HVDC) systems - Part 1: General
requirements
(IEC 62751-1:2014)
Pertes de puissance dans les valves à convertisseur de Bestimmung der Leistungsverluste in
source de tension (VSC) des systèmes en courant continu Spannungszwischenkreis-Stromrichtern (VSC) für
à haute tension (CCHT) - Partie 1: Exigences générales Hochspannungsgleichstrom(HGÜ)-Systeme - Teil 1:
(CEI 62751-1:2014) Allgemeine Anforderungen
(IEC 62751-1:2014)
This European Standard was approved by CENELEC on 2014-10-01. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
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, 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: Avenue Marnix 17, B-1000 Brussels
© 2014 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 62751-1:2014 E
Foreword
The text of document 22F/302/CDV, future edition 1 of IEC 62751-1, prepared by SC 22F "Power
electronics for electrical transmission and distribution systems", of IEC/TC 22 "Power electronic
systems and equipment" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN 62751-1:2014.
The following dates are fixed:
– latest date by which the document has to be implemented at (dop) 2015-07-01
national level by publication of an identical national
standard or by endorsement
– latest date by which the national standards conflicting with (dow) 2017-10-01
the document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 62751-1:2014 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 61803:1999 NOTE Harmonised as EN 61803:1999.

- 3 - EN 62751-1:2014
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is
available here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60633 -  Terminology for high-voltage direct current EN 60633 -
(HVDC) transmission
IEC 60747-2 -  Semiconductor devices - Discrete devices - -
and integrated circuits -- Part 2: Rectifier
diodes
IEC 60747-9 2007 Semiconductor devices - Discrete devices - - -
Part 9: Insulated-gate bipolar transistors
(IGBTs)
IEC 62747 2014 Terminology for voltage-sourced EN 62747 2014
converters (VSC) for high-voltage direct
current (HVDC) systems
IEC 62751-1 ®
Edition 1.0 2014-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power losses in voltage sourced converter (VSC) valves for high-voltage direct

current (HVDC) systems –
Part 1: General requirements
Pertes de puissance dans les valves à convertisseur de source de tension (VSC)

des systèmes en courant continu à haute tension (CCHT) –

Partie 1: Exigences générales
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX V
ICS 29.200; 29.240 ISBN 978-2-8322-1835-8

– 2 – IEC 62751-1:2014 © IEC 2014
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
3.1 Converter types . 7
3.2 Semiconductor devices . 7
3.3 Converter operating states . 8
3.4 Device characteristics . 9
3.5 Other definitions . 9
4 General conditions. 10
4.1 General . 10
4.2 Causes of power losses . 11
4.3 Categories of valve losses . 11
4.4 Operating conditions . 12
4.4.1 General . 12
4.4.2 Reference ambient conditions . 12
4.4.3 Reference a.c. system conditions . 12
4.4.4 Converter operating states. 12
4.4.5 Treatment of redundancy . 12
4.5 Use of real measured data . 13
4.5.1 General . 13
4.5.2 Routine testing . 13
4.5.3 Characterisation testing . 13
5 Conduction losses . 14
5.1 General . 14
5.2 IGBT conduction losses . 16
5.3 Diode conduction losses . 16
5.4 Other conduction losses . 17
6 D.C. voltage-dependent losses . 17
7 Losses in d.c. capacitors . 18
8 Switching losses . 18
8.1 General . 18
8.2 IGBT switching losses . 19
8.3 Diode switching losses . 20
9 Other losses . 21
9.1 Snubber circuit losses . 21
9.2 Valve electronics power consumption. 21
10 Total valve losses per converter substation . 22
Annex A (informative) Determination of power losses in other HVDC substation
equipment . 25
A.1 General . 25
A.2 Guidance for calculating losses in each equipment . 25
A.2.1 Circuit breaker . 25
A.2.2 Pre-insertion resistor . 25
A.2.3 Line side harmonic filter . 26

IEC 62751-1:2014 © IEC 2014 – 3 –
A.2.4 Line side high frequency filter . 26
A.2.5 Interface transformer . 26
A.2.6 Converter side harmonic filter . 27
A.2.7 Converter side high frequency filter . 27
A.2.8 Phase reactor . 27
A.2.9 VSC unit . 27
A.2.10 VSC d.c. capacitor . 27
A.2.11 D.C. harmonic filter . 27
A.2.12 Dynamic braking system . 27
A.2.13 Neutral point grounding branch . 28
A.2.14 D.C. reactor . 28
A.2.15 Common mode blocking reactor . 28
A.2.16 D.C. side high frequency filter . 28
A.2.17 D.C. cable or overhead transmission line . 28
A.3 Auxiliaries and station service losses . 29
Bibliography . 30

Figure 1 – On-state voltage of an IGBT or diode . 14
Figure 2 – Piecewise-linear representation of IGBT or diode on-state voltage . 15
Figure 3 – IGBT switching energy as a function of collector current . 19
Figure 4 – Diode recovery energy as a function of current . 20
Figure A.1 – Major components that may be found in a VSC substation . 26

Table 1 – Matrix indicating the relationship of data needed for calculation of losses
and the type of valve losses (1 of 2) . 23

– 4 – IEC 62751-1:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER LOSSES IN VOLTAGE SOURCED CONVERTER (VSC)
VALVES FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –

Part 1: General requirements
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
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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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.
International Standard IEC 62751-1 has been prepared by subcommittee 22F: Power
electronics for electrical transmission and distribution systems, of IEC technical committee 22:
Power electronic systems and equipment.
The text of this standard is based on the following documents:
CDV Report on voting
22F/302/CDV 22F/321A/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

IEC 62751-1:2014 © IEC 2014 – 5 –
A list of all parts in the IEC 62751series, published under the general title Power losses in
voltage sourced converter (VSC) valves for high-voltage direct current (HVDC) systems, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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 correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 62751-1:2014 © IEC 2014
POWER LOSSES IN VOLTAGE SOURCED CONVERTER (VSC)
VALVES FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –

Part 1: General requirements
1 Scope
This part of IEC 62751 sets out the general principles for calculating the power losses in the
converter valves of a voltage sourced converter (VSC) for high-voltage direct current (HVDC)
applications, independent of the converter topology. Clauses 6 and 8 and subclauses 9.1, 9.2
and A.2.12 of the standard can also be used for calculating the power losses in the dynamic
braking valves (where used) and as guidance for calculating the power losses of the valves
for a STATCOM installation.
Power losses in other items of equipment in the HVDC substation, apart from the converter
valves, are excluded from the scope of this standard. Power losses in most equipment in a
VSC substation can be calculated using similar procedures to those prescribed for HVDC
systems with line-commutated converters (LCC) in IEC 61803. Annex A presents the main
differences between LCC and VSC HVDC substations in so far as they influence the method
for determining power losses of other equipment.
This standard does not apply to converter valves for line-commutated converter HVDC
systems.
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.
IEC 60633, Terminology for high-voltage direct current (HVDC) transmission
IEC 60747-2, Semiconductor devices – Discrete devices and integrated circuits – Part 2:
Rectifier diodes
IEC 60747-9:2007, Semiconductor devices – Discrete devices – Part 9: Insulated-gate bipolar
transistors (IGBTs)
IEC 62747:2014, Terminology for voltage-sourced converters (VSC) for high-voltage direct
current (HVDC) systems
IEC 62751-1:2014 © IEC 2014 – 7 –
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60633, IEC 62747,
IEC 60747-2, IEC 60747-9 as well as the following apply.
NOTE 1 Related terms and definitions can also be found in IEC TR 62543, IEC 62751-2 and in the other relevant
parts of the IEC 60747 series.
NOTE 2 Throughout this standard, the term “insulated gate bipolar transistor (IGBT)” is used to indicate a turn-off
semiconductor device; however, the standard is equally applicable to other types of turn-off semiconductor devices
such as the GTO, IGCT, ETO, IEGT, etc.
3.1 Converter types
3.1.1
2-level converter
converter in which the voltage between the a.c. terminals of the VSC unit and VSC unit
midpoint is switched between two discrete d.c. voltage levels
Note 1 to entry: VSC unit midpoint is defined in 3.5.9.
3.1.2
multi-level converter
converter in which the voltage between the a.c. terminals of the VSC unit and VSC unit
midpoint is switched between more than three discrete d.c. voltage levels
Note 1 to entry: VSC unit midpoint is defined in 3.5.9.
3.1.3
modular multi-level converter
MMC
multi-level converter in which each VSC valve consists of a number of MMC building blocks
connected in series
Note 1 to entry: MMC building block is defined in 3.5.4.
Note 2 to entry: This note applies to the French language only.
3.1.4
cascaded two-level converter
CTL
modular multi-level converter in which each switch position consists of more than one IGBT-
diode pair connected in series
Note 1 to entry: IGBT-diode pair is defined in 3.2.4.
Note 2 to entry: This note applies to the French language only.
3.2 Semiconductor devices
3.2.1
turn-off semiconductor device
controllable semiconductor device which may be turned on and off by a control signal, for
example an IGBT
3.2.2
insulated gate bipolar transistor
IGBT
turn-off semiconductor device with three terminals: a gate terminal (G) and two load terminals
emitter (E) and collector (C)
– 8 – IEC 62751-1:2014 © IEC 2014
Note 1 to entry: By applying appropriate gate to emitter voltages, current in one direction can be controlled, i.e.
turned on and turned off.
Note 2 to entry: This note applies to the French language only.
3.2.3
free-wheeling diode
FWD
power semiconductor device with diode characteristic
Note 1 to entry: A FWD has two terminals: an anode (A) and a cathode (K). The current through FWDs is in
opposite direction to the IGBT current. FWDs are characterized by the capability to cope with high rates of
decrease of current caused by the switching behaviour of the IGBT.
Note 2 to entry: This note applies to the French language only.
3.2.4
IGBT-diode pair
arrangement of IGBT and FWD connected in inverse parallel
Note 1 to entry: An IGBT-diode pair is usually in one common package; however, it can include individual IGBTs
and/or diodes packages connected in parallel.
3.3 Converter operating states
3.3.1
no-load operating state
condition in which the VSC substation is energized but the IGBTs are blocked and all
substation service loads and auxiliary equipment are connected
3.3.2
idling operating state
condition in which the VSC substation is energized and the IGBTs are de-blocked but with no
active or reactive power output at the point of common connection to the a.c. network
Note 1 to entry: The “idling operating” and “no-load” conditions are similar but from the no-load state several
seconds may be needed before power can be transmitted, while from the idling operating state, power transmission
may be commenced almost immediately (less than 3 power frequency cycles).
Note 2 to entry: In the idling operating state, the converter is capable of actively controlling the d.c. voltage, in
contrast to the no-load state where the behaviour of the converter is essentially “passive”.
Note 3 to entry: Losses will generally be slightly lower in the no-load state than in the idling operating state,
therefore this operating mode is preferred where the arrangement of the VSC system permits it.
3.3.3
operating state
condition in which the VSC substation is energized and the converters are de-blocked
Note 1 to entry: Unlike line-commutated converter, VSC can operate with zero active/reactive power output.
3.3.4
no-load power losses
power losses in the VSC valve in the no-load state
Note 1 to entry: In some converter designs, it may be necessary to make occasional switching operations for the
purposes of balancing voltages between different parts of the converter. In such converters, the calculation of no-
load losses shall take into account the switching frequency of such an operating mode.
3.3.5
idling operating losses
losses in the VSC valve in the idling operating state

IEC 62751-1:2014 © IEC 2014 – 9 –
3.3.6
operating losses
losses in the VSC valve in the operating state
3.4 Device characteristics
3.4.1
IGBT collector-emitter saturation voltage
V
CE(sat)
collector-emitter voltage under conditions of gate-emitter voltage at which the collector current
is essentially independent of the gate-emitter voltage
3.4.2
IGBT turn-on energy
E
on
energy dissipated inside the IGBT during the turn-on of a single collector current pulse
3.4.3
IGBT turn-off energy
E
off
energy dissipated inside the IGBT during the turn-off procedure of a single collector current
pulse
3.4.4
diode forward voltage
V
F
voltage across the terminals of a diode which results from the flow of current in the forward
direction
3.4.5
diode reverse recovery energy
E
rec
energy dissipated inside the diode during the turn-off procedure
3.5 Other definitions
3.5.1
VSC valve level
smallest indivisible functional unit of VSC valve
Note 1 to entry: For any VSC valve in which IGBTs are connected in series and operated simultaneously, one
VSC valve level is one IGBT-diode pair including its auxiliaries. For MMC type valve, one valve level is one
submodule together with its auxiliaries.
3.5.2
redundant levels
maximum number of series connected VSC valve levels or diode valve levels in a valve that
may be short-circuited externally or internally during service without affecting the safe
operation of the valve as demonstrated by type tests, and which if and when exceeded, would
require shutdown of the valve to replace the failed levels or acceptance of increased risk of
failures
Note 1 to entry: In valve designs such as the cascaded two level converter, which contain two or more conduction
paths within each cell and have series-connected VSC valve levels in each path, redundant levels shall be counted
only in one conduction path in each cell
3.5.3
valve electronics
electronic circuits at valve potential(s) which perform control and protection functions for one
or more valve levels
– 10 – IEC 62751-1:2014 © IEC 2014
3.5.4
MMC building block
self-contained, two-terminal controllable voltage source together with d.c. capacitor(s) and
immediate auxiliaries, forming part of a MMC
3.5.5
switch position
semiconductor function which behaves as a single, indivisible switch
Note 1 to entry: A switch position may consist of a single IGBT-diode pair or, in the case of the cascaded two
level converter, a series connection of multiple IGBT-diode pairs.
3.5.6
submodule
MMC building block where each switch position consists of only one IGBT-diode pair cell
3.5.7
cell
MMC building block where each switch position consists of more than one IGBT-diode pair
connected in series
3.5.8
VSC unit
three VSC phase units, together with VSC unit control equipment, essential protective and
switching devices, d.c. storage capacitors, phase reactors and auxiliaries, if any, used for
conversion
3.5.9
VSC unit midpoint
point in a VSC unit whose electrical potential is equal to the average of the potentials of the
positive and negative d.c. terminals of the VSC unit
Note 1 to entry: In some applications the VSC unit midpoint may exist only as a virtual point, not corresponding to
a physical node in the circuit.
4 General conditions
4.1 General
Suppliers need to know in detail how and where losses are generated, since this affects
component and equipment ratings. Purchasers are interested in a verifiable loss figure which
allows equitable bid comparison and in a procedure after delivery which can objectively verify
the guaranteed performance requirements of the supplier.
As a general principle, it would be desirable to determine the efficiency of an HVDC converter
station by a direct measurement of its energy losses. However, attempts to determine the
station losses by subtracting the measured output power from the measured input power
should recognize that such measurements have an inherent inaccuracy, especially if
performed at high voltage. The losses of an HVDC converter station at full load are generally
of the order 1 % of the transmitted power. Therefore, the loss measured as a small difference
between two large quantities is not likely to be a sufficiently accurate indication of the actual
losses.
In some special circumstances it may be possible, for example, to arrange a temporary test
connection in which two converters are operated from the same a.c. source and also
connected together via their d.c. terminals. In this connection, the power drawn from the a.c.
source equals the losses in the circuit. However, the a.c. source also provides var support
and commutating voltage to the two converters. Once again, there are practical measurement
difficulties. In order to avoid the problems described above, this standard standardizes a
method of calculating the HVDC converter station losses by summing the losses calculated

IEC 62751-1:2014 © IEC 2014 – 11 –
for each item of equipment. The standardized calculation method will help the purchaser to
meaningfully compare the competing bids. It will also allow an easy generation of
performance curves for the wide range of operating conditions in which the performance has
to be known. In the absence of an inexpensive experimental method which could be employed
for an objective verification of losses during type tests, the calculation method is the next best
alternative as it uses, wherever possible, experimental data obtained from measurements on
individual equipment and components under conditions equivalent to those encountered in
real operation.
It is important to note that the power loss in each item of equipment will depend on the
ambient conditions under which it operates, as well as on the operating conditions or duty
cycles to which it is subjected. Therefore, the ambient and operating conditions shall be
defined for each item of equipment, based on the ambient and operating conditions of the
entire HVDC converter station.
4.2 Causes of power losses
Dependent on the converter topology, a VSC valve can either have the function to act like a
controllable switch or to act like a controllable voltage source.
For the controllable voltage source type converter, the VSC valve is a complete controllable
voltage source assembly, which is generally connected between one a.c. terminal and one
d.c. terminal.
For the switch type converter, the VSC valve is an arrangement of IGBT-diode pairs
connected in series and arranged to be switched simultaneously as a single functional unit.
Most of the power losses in VSC valves appear in IGBTs and diodes. In each case, two
mechanisms are involved:
• conduction losses;
• switching losses.
There may, in addition, be small losses in d.c. submodule or cell capacitors, voltage divider
and snubber circuits, valve electronics etc.
Since the technology of VSC transmission is developing rapidly with several quite different
VSC topologies being used, a detailed procedure for calculating the power losses is not yet
available for all possible converter topologies. As a result, the manufacturer of the VSC
equipment shall present a detailed report of the VSC valve loss calculation, explaining the
method used and justifying any assumptions made. This standard gives the general principles
to be followed in calculating valve losses and provides guidance for the preparation and
interpretation of such a report.
Due to the accuracy of d.c. metering systems (especially due to the poor accuracy of d.c.
voltage measurement) the approach of the standard rests on calculations based on routine
testing of devices (datasheet) together with some characterisation measurements.
4.3 Categories of valve losses
The various components of valve losses are subdivided into terms referred to as P to P :
V1 V9
• P : IGBT conduction losses
V1
• P : diode conduction losses
V2
• P : other valve conduction losses
V3
• P : d.c. voltage-dependent losses
V4
• P : losses in d.c. capacitors of the valve
V5
– 12 – IEC 62751-1:2014 © IEC 2014
• P : IGBT switching losses
V6
• P : diode turn-off losses
V7
• P : snubber losses
V8
• P : valve electronics power consumption
V9
4.4 Operating conditions
4.4.1 General
Purchasers of HVDC systems may specify their own standard reference conditions for
atmospheric pressure, ambient temperature, humidity, coolant temperature, power
transmission level etc, at which the power losses are to be determined. Where the purchaser
does not specify such reference conditions, losses shall be determined under the following
default conditions.
4.4.2 Reference ambient conditions
The following default reference ambient conditions are applied:
• dry-bulb ambient temperature = 20 °C
• wet-bulb ambient temperature = 14 °C
• atmospheric pressure = 101,3 kPa.
4.4.3 Reference a.c. system conditions
The following default reference a.c. system conditions are applied:
• nominal a.c. system frequency,
• nominal a.c. network voltage,
• balanced a.c. conditions (i.e. no negative phase sequence).
4.4.4 Converter operating states
As a minimum, VSC valve losses shall be determined for the following operating states:
• no-load operation;
• idling operation;
• operation with 100 % rated power in each relevant direction of power transmission, with
zero net reactive power exchange with the a.c. system, and with the d.c. voltage at the
value as applicable to the power being transmitted.
In some VSC systems, the interface transformer includes a tap changer, the purpose of which
is to adjust the valve-side a.c. voltage, in steady-state, to a value which allows the power
losses to be optimised. The tap position has a large effect on the power losses of both the
transformer and the converter and should therefore be correctly represented in all
calculations. The tap position of the transformer tap changer (where fitted) is important in the
determination of losses. The calculations of losses shall take into account the tap position
corresponding to the operating point at which losses are to be determined and the control and
protection strategies employed for the VSC system, including, for example, fault ride-through
requirements. The manufacturer is responsible for defining and justifying the tap position for
the loss calculation.
4.4.5 Treatment of redundancy
For the calculation of valve losses, all redundant VSC levels shall be assumed to be in
operation.
IEC 62751-1:2014 © IEC 2014 – 13 –
NOTE This approach yields the highest total losses in the valve, although it does not give the highest losses per
VSC valve level, which occur when redundant levels are shorted.
4.5 Use of real measured data
4.5.1 General
The characteristics of the IGBTs and diodes used in the valve shall be determined by a
combination of routine tests performed under standardised conditions on 100 % of production,
and more comprehensive characterisation tests performed on smaller samples under
conditions that are more representative of the conditions encountered in the real converter
valve.
The routine tests shall be used to derive a population average of all IGBTs and diodes
supplied for the project, but under standardised operating conditions which may not
necessarily be applicable to the project (for example, junction temperature). The
characterisation tests shall then be used to derive correction factors applicable for the exact
operating conditions of the project.
4.5.2 Routine testing
As a minimum, the following tests shall be performed in accordance with IEC Publications by
the device manufacturer on all IGBTs (IEC 60747-9), and diodes (IEC 60747-2) used for the
valve:
• IGBT on-state voltage V and diode forward voltage V at one typical value of current
CE(sat) F
and temperature;
• IGBT turn-on energy E and turn–off energy E at one typical commutating condition;
on off
• diode recovery energy E at one typical commutating condition.
rec
This data shall be used to calculate the average device properties for calculation of the losses
of the complete converter.
The conditions under which the routine tests are performed may not be fully representative of
the conditions encountered in the VSC valve, in respect of temperature, stray inductance,
gate drive behaviour, etc.
4.5.3 Characterisation testing
4.5.3.1 Characterisation testing of semiconductor devices
A minimum of 10 devices from at least 2 different production lots shall be subjected to a more
comprehensive programme of characterisation tests to permit the routine test data obtained in
4.4.1 above to be adjusted to the correct operating conditions of the VSC valve. The following
conditions shall be reproduced adequately.
Fixed values for a given design of VSC valve are as follows:
• stray inductance of commutating loop;
• other semiconductor devices affected by the commutation process;
• gate drive characteristics;
• snubber circuits (if any).
Operating variables are as follows:
• d.c capacitor or d.c. submodule capacitor voltage, scaled to one VSC level;
• device current (over the range from standby to operation at full power in either rectifier or
inverter mode);
– 14 – IEC 62751-1:2014 © IEC 2014
• junction temperature (over the range from standby to operation at full power in either
rectifier or inverter mode).
The characterization tests shall be performed in accordance with IEC 60747-2 and
IEC 60747-9.
4.5.3.2 Characterisation testing of other components
Characterization tests for components are as follows:
• R test;
ESR
• snubber turn-on and turn-off tests.
5 Conduction losses
5.1 General
When an IGBT or a diode is in the conducting state, it exhibits a small on-state voltage of a
few volts. This on-state voltage, multiplied by the current flowing through the device, gives
rise to “conduction losses”. The on-state voltage is referred to as V in diodes and V in
F CE(sat)
IGBTs.
The on-state voltage depends on current in a non-linear manner, and to a lesser extent also
on the “junction temperature” of the device, as shown on Figure 1.
I
25°C 125°C
V , V
F CE(sat)
IEC
Figure 1 – On-state voltage of an IGBT or diode
NOTE 1 The on-state voltage V of an IGBT also depends on the gate-emitter voltage V . For low values of
CE GE
V , increasing V reduces the value of V . However, above a certain value of V , little or no further reduction of
GE GE CE GE
V occurs and the IGBT is said to be “saturated”. It is assumed here that V is high enough to ensure that the
CE GE
IGBT remains fully saturated. Consequently V (the saturated value of V ) can be used for loss calculation.
CE(sat) CE
NOTE 2 On some types of semiconductor device, the “crossover” current can be very low, such that for most
practical values of current the on-state voltage always increases with temperature.
Calculation of power losses requires that the on-state voltage be represented mathematically,
so that the average conduction losses over a complete cycle may be evaluated as follows:

IEC 62751-1:2014 © IEC 2014 – 15 –
2π
P =⋅⋅I ()ωωtV (I )⋅d()t (1)
cond_T T CE(sat) T
∫
2π
for an IGBT, or
2π
P =⋅ I ()ωωt⋅⋅VI( ) d()t (2)
cond_D D F D
∫
2π
for a diode.
The conduction losses of semiconductors in a complete valve are then found by summing the
conduction losses calculated as above for each IGBT and each diode in the valve.
To simplify this process, the on-state voltage shown in Figure 1 is usually represented as a
piecewise-linear approximation with a threshold voltage V and a slope resistance R , as
0 0
shown on Figure 2.
I
R
V , V
F CE(sat)
V
IEC
Figure 2 – Piecewise-linear representation of IGBT or diode on-state voltage
Having made this approximation, the conduction losses in each semiconductor device are
then determined by using the average and rms currents through that device:
P =V⋅ I+⋅R I (3)
cond 0 av 0 rms
where
V , R are the threshold voltage and slope resistance of the device;
0 0
I is the mean current in the device, averaged over one power-frequency cycle.
av
2π
I=⋅⋅I()ωωtd()t (4)
av
∫
2π
I is the rms current in the device, averaged over one power-frequency cycle.
rms
– 16 – IEC 62751-1:2014 © IEC 2014
2π
I=⋅⋅I()ωωt dt() (5)
rms
∫
2π
In general, rectifier mode gives rise to the largest diode conduction losses, while inverter
operation gives rise to the largest IGBT conduction losses.
It is possible to
...