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IEC 62751-2
Edition 1.0 2019-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 1
AM ENDEMENT 1
Power losses in voltage sourced converter (VSC) valves for high-voltage direct
current (HVDC) systems –
Part 2: Modular multilevel converters
Pertes de puissance dans les valves à convertisseur de source de tension (VSC)
des systèmes en courant continu à haute tension (CCHT) –
Partie 2: Convertisseurs multiniveaux modulaires
IEC 62751-2:2014-08/AMD1:2019-08(en-fr)
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IEC 62751-2
Edition 1.0 2019-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 1
AM ENDEMENT 1
Power losses in voltage sourced converter (VSC) valves for high-voltage direct
current (HVDC) systems –
Part 2: Modular multilevel converters
Pertes de puissance dans les valves à convertisseur de source de tension (VSC)
des systèmes en courant continu à haute tension (CCHT) –
Partie 2: Convertisseurs multiniveaux modulaires
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.200; 29.240 ISBN 978-2-8322-7218-3
– 2 – IEC 62751-2:2014/AMD1:2019
© IEC 2019
FOREWORD
This amendment 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 amendment is based on the following documents:
CDV Report on voting
22F/479/CDV 22F/488B/RVC
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC website 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• withdrawn,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.
_____________
2 Normative references
Add the following new reference:
IEC 61803, Determination of power losses in high-voltage direct current (HVDC) converter
stations
3.1.11
no-load operating state
Add, after the existing definition, the following new note:
Note 1 to entry: In the no-load state, in principle no switching should occur as the valve is blocked. However, in
some designs, it may be necessary to make occasional switching operations to balance voltages between different
parts of the converter. Here, some losses may occur and need to be accounted for.
© IEC 2019
4 General conditions
4.1 General
Replace, in the third sentence of the existing paragraph, the abbreviated term "CTLC" by
"CTL".
4.2 Principles for loss determination
Add, to the end of the first existing paragraph, the following new sentence:
The manufacturer shall justify, in the loss calculation report, how the uncertainties have been
considered.
Replace the last two sentences of the third existing paragraph by the following new sentences:
In practice, this measurement would require the use of state-of-the-art measurement
equipment that rivals the best equipment available at national metrology institutes. To date,
although some industry/academic partnership projects have demonstrated prototypes of
measurement equipment claiming sufficient accuracy, there is little industry experience with
using such equipment on site. The feasibility of using laboratory measurements on VSC
valves to support a more accurate determination of valve losses is now under study in
CIGRÉ WG B4-75.
4.4 Loss calculation method
Replace the first sentence of the existing second paragraph by the following new sentence:
An important requirement for such simulations is an accurate modelling of the system under
investigation.
4.5.2 Input data for numerical simulations
Replace the last item of the existing dash list by the following new items:
– For calculating converter valve currents and MMC building block capacitor currents, which
are the basis for the calculation of corresponding losses, it is sufficient to use a simplified
model in which the on-state and switching characteristics of the IGBTs and diodes are
represented by worst-case characteristics applicable to their maximum rated junction
temperature.
– For the detailed calculation of losses, the simulation shall also consider the junction
temperature dependent semiconductor properties, such as on-state voltages, switching
and recovery losses. These properties are based on the characterisation testing as
described in IEC 62751-1:2014, 4.4.2. The steady-state junction temperatures of the
semiconductors are calculated iteratively for the relevant operating point to derive the
semiconductor losses.
4.5.3 Input data coming from numerical simulations
Add, to the last existing paragraph, the following new sentence:
The mean and rms currents in IGBTs and diodes are not required if conduction losses in
IGBTs and diodes are calculated using polynomials as discussed in 5.1.
4.5.4 Converter station data
Add, to the sixth dash of the existing list, the words "(for CTL designs)".
– 4 – IEC 62751-2:2014/AMD1:2019
© IEC 2019
Add, after the existing 4.5.5, the following new subclause:
4.6 Contents and structure of valve loss determination report
The manufacturer or bidder shall prepare and submit to the purchaser a detailed report
explaining how the losses in the VSC valves have been determined and including a
breakdown of the valve losses into the constituent parts P to P for each operating
V1 V9
condition at which losses are required to be guaranteed.
At the bid stage, and (where requested in the contract) after contract award but before the
manufacturing of valve components, the report shall document the assumptions used in
arriving at the calculated value of losses. After manufacturing, the report shall document the
actual values of test data derived from characterisation tests and routine tests on components.
Although a breakdown of the valve losses into the constituent parts P to P is requested,
V1 V9
only the total valve losses P shall be subject to financial evaluation.
Vt
A recommended list of data to be included in the report is presented in Annex B.
5.1 General
Add, after the existing Figure 2, the following new paragraphs:
To simplify the process of mathematically analysing conduction losses, the on-state voltage of
IGBTs and diodes is usually represented as a piecewise-linear approximation with a threshold
voltage V and a slope resistance R , as shown in Figure 2 of IEC 62751-1:2014.
0 0
It is possible to obtain greater accuracy by using a more exact model of the device on-state
voltage (for example, using a polynomial function to represent the on-state voltage) rather
than the piecewise-linear approximation, and then performing a direct numerical integration.
However, the piecewise-linear approximation is preferred because it simplifies the calculation
process, allows greater transparency and still permits good accuracy to be obtained, provided
the measurements used to derive the piecewise-linear approximation are made at appropriate
values of current. Therefore, it is recommended that V and R are determined by measuring
0 0
on-state voltage at 100 % and 33 % of the device rated current and performing a linear
extrapolation.
In the event that the purchaser prefers to use the more accurate method using a polynomial
function, then this shall be clearly stated in the purchasing specification, and all bidders are
expected to calculate power losses in a comparable way.
5.2 IGBT conduction loss
Replace the existing second paragraph, starting with "By means of…" and including
Equations (2) to (5) and their key, as well as the existing third paragraph, by the following new
text:
By means of numerical simulation, the currents shall be calculated for the IGBTs T1 and T2
for each MMC building block, respectively:
t
i
I =⋅⋅i ()t dt (2)
T1av T1
∫
t
i 0
t
i
I =⋅⋅i ()t dt (3)
T2av T2
∫
t
i 0
© IEC 2019
t
i
I =⋅⋅i ()t dt (4)
T1rms T1
∫
t
i
t
i
I =⋅⋅i ()t dt (5)
T2rms T2
∫
t
i 0
where
t is the integration time used in the simulation;
i
t shall not be less than 1 s.
i
If different IGBT types are used for T1 and T2, corresponding values for threshold voltages
and slope resistances shall be used accordingly.
5.3 Diode conduction losses
Replace the existing second paragraph, starting with "By means of…", including Equations (7)
to (10), the key to these equations and the note, by the following new text:
By means of numerical simulation, the currents shall be calculated for the diodes D1 and D2
for each MMC building block, respectively:
t
i
I =⋅⋅i t dt (7)
()
D1av D1
∫
t
i 0
t
i
I =⋅⋅i t dt (8)
()
D2av D2
∫
t
i 0
t
i
1 2
I =⋅⋅i t dt (9)
()
D1rms D1
∫
t
i 0
t
i
1 2
I =⋅⋅i t dt (10)
()
D2rms D2
∫
t
i 0
where
t is the integration time used in the simulation;
i
shall not be less than 1 s.
t
i
If different diode types are used for D1 and
...