IEC TS 62578:2009

IEC/TS 62578 ®
Edition 1.0 2009-11
TECHNICAL
SPECIFICATION
colour
inside
Power electronics systems and equipment – Operation conditions and
characteristics of active infeed converter applications

IEC/TS 62578:2009(E)
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IEC/TS 62578 ®
Edition 1.0 2009-11
TECHNICAL
SPECIFICATION
colour
inside
Power electronics systems and equipment – Operation conditions and
characteristics of active infeed converter applications

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 29.200 ISBN 978-2-88910-768-1
– 2 – TS 62578 © IEC:2009(E)
CONTENTS
FOREWORD.6
INTRODUCTION.8
1 Scope.9
2 Normative references .9
3 Terms and definitions .10
4 General system characteristics of PWM AIC Connected to the power supply
system.13
4.1 Basic topologies and operating principles.13
4.2 AIC rating (details to be found in special sections) .19
4.3 Electromagnetic compatibility (EMC) aspects .19
4.4 Different converter topologies and their influences on the power supply
system .21
4.5 Active power / reactive power.23
4.6 Audible noise effects .28
4.7 Leakage currents.28
4.8 Aspects of system integration and dedicated tests .28
5 Characteristics of a PWM AIC of voltage source type and two level topology.29
5.1 General function, basic circuit topologies .29
5.2 Power control .31
5.3 Dynamic performance.32
5.4 Mains interference, desired .33
5.5 Mains interference, undesirable.33
5.6 Availability and system aspects .34
5.7 Operation in active filter mode.34
6 Characteristics of a PWM AIC of voltage source type and three level topology .34
6.1 General function, basic circuit topologies .34
6.2 Power control .35
6.3 Dynamic performance.36
6.4 Mains interference, undesirable.36
6.5 Availability and system aspects .37
7 Characteristics of a PWM AIC of voltage source type and multi-level topology .37
7.1 General function, basic circuit topologies .37
7.2 Power control .39
7.3 Dynamic performance.39
7.4 Mains interference.40
7.5 Availability and system aspects .40
8 Characteristics of a F3E AIC of voltage source type .40
8.1 General function, basic circuit topologies .40
8.2 Power control and line side filter.41
8.3 Dynamic performance.43
8.4 Mains interference, low frequency components .44
9 Characteristics of an AIC of voltage source type in pulse chopper topology.44
9.1 General function, basic circuit topologies .44
9.2 Mains interference, desired .46
9.3 Mains interference, undesired .46
9.4 Availability.46

TS 62578 © IEC:2009(E) – 3 –
9.5 Performance.46
9.6 Availability and system aspects .46
10 Characteristics of a two level PWM AIC of current source type .46
10.1 General function, basic converter connections.46
10.2 Power control .48
10.3 Dynamic performance.50
10.4 Mains interference.50
10.5 Operation in active filter mode.50
10.6 Availability and system aspects .51
Annex A (informative)  Control methods for AICs .52
Bibliography.62

Figure 1 – AIC in VSC topology, basic structure.14
Figure 2 – AIC in CSC topology, basic structure .15
Figure 3 – Equivalent circuit for the interaction of the mains with an AIC .16
Figure 4 – Voltage and current phasors of line and converter at fundamental frequency
for different load conditions.18
Figure 5 – Block diagram of a typical PDS with high frequency EMC filter system .21
Figure 6 – Typical mains current and voltage of a phase controlled converter with d.c.-
output and inductive smoothing.22
Figure 7 – Typical mains current and voltage of an uncontrolled converter with d.c.-
output and capacitive smoothing.22
Figure 8 – Typical mains current and voltage of an AIC realized by a PWM Converter
with capacitive smoothing without additional filters .22
Figure 9 – Example of attainable active and reactive power of the AIC at different line
voltages in per unit (with 10 % combined transformer and filter inductor short circuit
voltage, X/R ratio = 10/1, d.c. voltage = 6,5 kV) .23
Figure 10 – Principle of compensating given harmonics in the power supply system by
using an AIC and suitable control simultaneously.24
Figure 11 – Typical voltage distortion in the line-to-line and line-to-neutral voltage
generated by an AIC without additional filters .25
Figure 12 – Typical relative voltage of the 60th harmonic of an AIC depending on R .26
SCe
Figure 13 – Typical relative current emission of the 60th harmonic of an AIC
depending on R .27
SCe
Figure 14 – Typical impact of additional filter measures to the voltage distortion level
of an AIC ( V * / V is the voltage distortion with only a line side inductive
Lh L1
impedance).27
Figure 15 – Basic topology of a two level PWM voltage source AIC .29
Figure 16 – Typical waveforms of voltages u / U and voltage u / U , at pulse
(S1-S2) P (S1-0) P
frequency of 4 kHz – Power supply frequency is 50 Hz .30
Figure 17 – Typical waveforms of the common mode voltage u / U , at pulse
CM P
frequency of 4 kHz – Power supply frequency is 50 Hz .31
Figure 18 – Waveform of the current i / I at pulse frequency of 4 kHz, relative
L1 equ
impedance of SCV = 6 % – Power supply frequency is 50 Hz.31
equ
Figure 19 – Block diagram of a two level PWM AIC.32
Figure 20 – Harmonics of the current i of reactance X , pulse frequency  4 kHz,
L1 equ
relative reactance of SCV = 6 %.33
equ
Figure 21 – Typical waveforms of voltages voltage u / U and u / U at pulse
(L1-0) P (L1-L2) P
frequency of 4 kHz, relative reactance of SCV = 6 %, R = 100 .34
equ SCe
– 4 – TS 62578 © IEC:2009(E)
Figure 22 – Basic topology of a three level AIC – For a Power Drive System (PDS),
the same topology may be used also on the load side.35
Figure 23 – Typical curve shape of the phase-to-phase voltage of a three level PWM
converter .35
Figure 24 – Example of a sudden load change of a 13 MW PDS three level converter
where the current control achieves a response time within 5 ms .36
Figure 25 – Typical topology of a flying capacitor (FC) four level AIC.38
Figure 26 – Typical curve shape of the phase-to-phase voltage of a multi-(four)-
level AIC.39
Figure 27 – Harmonic frequencies and amplitudes in the line voltage measured directly
at the bridge terminals in Figure 25 and the line current of a multilevel (four) AIC
(transformer with 10 % short circuit voltage) .40
Figure 28 – Topology of a F3E AIC .41
Figure 29 – Line side filter and equivalent circuit for the F3E-converter behaviour for
the power supply system.42
Figure 30 – Current transfer function together with R = 100 and R = 750 and a
SCe SCe
line side filter : G(f) = i / i .42
L1 conv
Figure 31 – PWM – voltage distortion over mains impedance for F3E-infeed including
mains side filter .43
Figure 32 – Input current spectrum of a 75kW-F3E-converter.43
Figure 33 – Harmonic spectrum of the input current of a F3E-converter
with R = 100 .44
SCe
Figure 34 – An example of distortion effect by a single phase converter with capacitive
load – The current waveforms of many units are similar and the effect on the power
supply system is multiplied .45
Figure 35 – a.c. to a.c. AIC pulse chopper, basic circuit.45
Figure 36 – Converter connection of a current source AIC .47
Figure 37 – Typical waveforms of currents and voltages of a current source AIC with
high switching frequency.48
Figure 38 – Typical block diagram of a current source PWM AIC .49
Figure 39 – Current source AIC used as an active filter to compensate the harmonic
currents generated by a nonlinear load .49
Figure 40 – Step response (reference value and actual value) of current source AIC
with low switching frequency [10.9] – I equals the rated current of the AIC.50
LN
Figure A.1 – Typical waveforms of electrical power supply system current and voltage
for a current source AIC with low switching frequency [10.9].53
Figure A.2 – Currents and voltages in a (semiconductor) valve device of an AIC and a
machine side converter both of the current source with low pulse frequency [10.9] .54
Figure A.3 – Total harmonic distortion of electrical power supply system and motor
current [10.9] remains always below 8 % (triangles in straight line) in this application.54
Figure A.4 – Basic topology of a AIC with commutation on the d.c. side (six pulse
variant) .55
Figure A.5 – Dynamic performance of a reactive power converter .56
Figure A.6 – Line side current for a twelve pulse reactive power converter in a
capacitive and inductive operation mode (SCV = 15 %) .57
equ
Figure A.7 – The origin of the current waveform of a RPC by the line voltage
(sinusoidal) and the converter voltage (rectangular).57
Figure A.7 – Two level topology with nominal voltage of maximum 1 200 V and
timescale of 5 ms/div .59

TS 62578 © IEC:2009(E) – 5 –
Figure A.8 – Three level topology with nominal voltage of maximum 2 400 V and
timescale of 5 ms/div .59
Figure A.9 – Four level topology with nominal voltage of maximum 3 300 V and
timescale of 5 ms/div .60

Table A.1 – Comparison of different PWM AICs of VSC type .58

– 6 – TS 62578 © IEC:2009(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER ELECTRONICS SYSTEMS AND EQUIPMENT –

Operation conditions and characteristics
of active infeed converter applications

FOREWORD
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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The main task of IEC technical committees is to prepare International Standards. In
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specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• The subject is still under technical development or where, for any other reason, there is
the future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62578, which is a technical specification, has been prepared by IEC technical committee
22: Power electronic systems and equipment.

TS 62578 © IEC:2009(E) – 7 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
22/145/DTS 22/160/RVC
Full information on the voting for the approval of this technical specification 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.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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
• transformed into an International standard,
• 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 publication using a colour printer.

– 8 – TS 62578 © IEC:2009(E)
INTRODUCTION
This technical specification is necessary because Active Infeed Converters (AIC) are a state
of the art technology in power electronic products but which have not been described very
well by standardization up to now.
AICs are necessary to feed back some inertia or braking power from a load back to the power
supply system
Dispersed power generating equipment is using such AICs to synchronise their voltages and
currents to the power supply system.
Therefore the advantage of using AICs in industrial as well as in domestic premises becomes
more and more interesting under light of the energy efficiency discussion.
Different possible topologies of AICs are described in this technical specificaton with their
specific advantages in order to introduce them and to give an overview for users.
Also utilities are interested in information how the correct application of AICs can additionally
help to mitigate harmonics in the power supply system.

TS 62578 © IEC:2009(E) – 9 –
POWER ELECTRONICS SYSTEMS AND EQUIPMENT –

Operation conditions and characteristics
of active infeed converter applications

1 Scope
This technical specification describes the operation conditions and typical characteristics of
Active Infeed Converters (AIC) of all technologies and topologies which can be connected
between the electrical power supply system (lines) and a current or voltage stiff d.c.-side and
which can convert electrical power (active and reactive) in both directions (generative or
regenerative).
Applications with AIC are realized together for example with d.c.-sides of adjustable speed
Power Drive Systems (PDS), Uninterruptible Power Systems (UPS), active filters, photovoltaic
systems, wind turbine systems, etc., of all voltages and power sizes.
Active Infeed Converters are generally connected between the electrical power supply system
(lines) and a current or voltage d.c.-side, with the objective to disburden the system from low
frequency harmonics (e.g. less than 1 kHz) by a sinusoidal approach of the lines current.
Some of them can additionally control the harmonic distortion of an applied voltage or current.
AIC are able to control the power factor of a power supply system section by moving the
electrical power (active and reactive) in both directions (generative or regenerative), which
enables energy saving in the system and stabilization of the power supply voltage.
The following is excluded from the scope:
• requirements for the design, development or further functionality of active infeed
applications;
• probability of interactions or influences of the AIC with other equipment caused by
parasitic elements in an installation as well as their mitigation.
2 Normative references
The following referenced documents are indispensable for the application 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 61800-3, Adjustable speed electrical power drive systems – Part 3: EMC product
standard including specific test methods
IEC 61800-5-1, Adjustable speed electrical power drive systems – Part 5-1: Safety
requirements -electrical, thermal and energy
IEC 62040-1, Uninterruptible power systems (UPS) – Part 1: General and safety requirements
for UPS
IEC 62040-2, Uninterruptible power systems (UPS) – Part 2: Electromagnetic compatibility
(EMC) requirements
IEC 62103, Electronic equipment for use in power installations

– 10 – TS 62578 © IEC:2009(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
Active Infeed Converter
AIC
self-commutated electronic power converters of all technologies, topologies, voltages and
sizes which are connected between the a.c. power supply system (lines) and a stiff d.c.-side
(current source or voltage source) and which can convert electric power in both directions
(generative or regenerative) and which can control the reactive power or the power factor
Some of them can additionally control the harmonics to reduce the distortion of an applied
voltage or current.
Basic topologies may be realized as a Voltage Source Converter (VSC) or a Current Source
Converter (CSC).
NOTE In the IEV, these terms (VSC and CSC) are defined as voltage stiff a.c./d.c. converter [551-12-03] and
current stiff a.c./d.c. converter [551-12-04]. Most of the AICs are bi-directional converters and have sources on the
d.c. side. So, they are known as voltage source converters and current source converters in this technical
specification.
3.2
active infeed application
application using the advantages of an Active Infeed Converter
3.3
active filter
AIC operating as a filter to control the specific a.c.-side harmonic and interharmonic voltages
or currents usually without a d.c.-side load
3.4
PWM converter
converter generally using a pulse-width modulation technique in order to control the switching
of its semiconductor valve devices
3.5
switching frequency
mean value of the frequency with which the semiconductor valve devices of a PWM converter
are operated
NOTE In some converters the switching frequency may not be the same for all semiconductor valve devices.
3.6
pulse frequency
frequency, resulting from the switching frequency and the converter topology, which
characterizes, together with the selected pulse pattern, the lowest frequency of non-
controllable harmonics or interharmonics at the In-plant Point of Coupling (IPC)
NOTE The switching frequency itself may not be present as a harmonic or interharmonic.
3.7
pulse pattern
pattern of the switched voltages or currents, measurable at the terminal of the converter,
resulting from pulse frequency and modulation schemes used

TS 62578 © IEC:2009(E) – 11 –
3.8
In-plant Point of Coupling
IPC
point on a network inside a system or an installation, electrically nearest to a particular load,
at which other loads are, or could be, connected
NOTE The IPC is usually the point for which electromagnetic compatibility is to be considered. In case of
connection to the public supply system the IPC is equivalent to the Point of Common Coupling (PCC).
3.9
d.c.-side load
electrical device optionally connected to the d.c.-Side
NOTE The load may either consume or feed electrical energy.
3.10
short-time energy storage device
one or more inductors or capacitors providing rated power for about 1 ms to 10 ms and
directly connected to the d.c.-Side
3.11
long-time energy storage device
device connected to the d.c.-link directly or by a semiconductor valve device, providing rated
power for typically seconds to minutes
3.12
DC filter
a filter on the DC side of a converter, designed to reduce the ripple in the associated system
[IEV 551-14-18]
3.13
AC filter
a filter on the AC side of a converter, designed to reduce the circulation of harmonic currents
in the associated system
[IEV 551-14-19]
3.14
supply impedance
the actual resulting impedance of the power supply system at the IPC
3.15
total impedance
resulting impedance consisting of the supply impedance and the supply-side filter impedance
of the AIC
NOTE In the range of controllable harmonics the total impedance can normally be approximated as purely
inductive.
3.16
effective supply-side filter impedance
effective impedance of the supply-side filter of the AIC for frequencies in the range of the
controllable harmonics or interharmonics
NOTE If no value for this range of frequencies can be given, the value for the fundamental frequency should
explicitly be given
3.17
control
purposeful action on or in a process to meet specified objectives

– 12 – TS 62578 © IEC:2009(E)
[IEV 351-21-29]
3.18
fundamental component (of a Fourier series)
sinusoidal component of the Fourier series of a periodic quantity having the frequency of the
quantity itself
NOTE For practical analysis, an approximation of the periodicity may be necessary.
[IEV 551-20-01]
3.19
harmonic frequency
frequency which is an integer multiple greater than one of the fundamental frequency or of the
reference fundamental frequency
[IEV 551-20-05]
3.20
harmonic component
sinusoidal component of a periodic quantity having a harmonic frequency
NOTE For practical analysis, an approximation of the periodicity may be necessary.
[IEV 551-20-07]
3.21
controllable harmonics or interharmonics
set of harmonic or interharmonic components which can be influenced directly by the control
strategy of the AIC
3.22
generated harmonics or interharmonics
set of harmonic or interharmonic components which result from the pulse frequency and the
pulse pattern
3.23
electric power supply flux (supply flux)
arithmetical flux quantity resulting from integrating the supply voltage
3.24
converter flux
arithmetical flux quantity resulting from integrating the supply-side converter voltage
3.25
controlled freewheeling circuit
a secondary circuit with a controllable valve device, not with a freewheeling diode
3.26
short circuit power
S
SC
value of the three-phase short-circuit power calculated from the nominal phase-to-phase
system voltage U and the impedance Z of the system at the Point of Common Coupling
nominal
(PCC)
S = U / Z
SC nominal
Where Z is the supply impedance at the power frequency

TS 62578 © IEC:2009(E) – 13 –
3.27
rated apparent power of equipment
S
equ
value calculated from the rated r.m.s. line current I of the piece of equipment stated by
equ
)
the manufacturer and the rated interphase voltage U .
i
1)
S = 3 × U × I
equ i equ
3.28
short circuit ratio
1)
R
SCe
characteristic value of a piece of equipment derived from the short circuit power S divided
SC
by the rated apparent power of the equipment (S )
equ
1)
R = S / S
SCe SC equ
3.29
F3E-infeed (F3E = fundamental frequency front end)
voltage source converter with its commutation capacitor on the a.c. side which uses line-
frequency switched semiconductor valve devices and has a regenerative capability.
NOTE The d.c.-link capacitor which is normally a electrolytic capacitor is basically replaced by an a.c. line side
filter, designed to limit the voltage distortion caused by the PWM currents of the inverter stage.
3.30
converter topology
converter topology is the family term for different possible arrangements and their
connections
3.31
reactive power converter
converter for reactive power compensation that generates or consumes reactive power
without the flow of active power except for the power losses in the converter
[IEV 551-12-15]
4 General system characteristics of PWM AIC Connected to the power supply
system
In this clause, the voltage source AIC, which is used in large numbers, is chosen as the
example.
4.1 Basic topologies and operating principles
4.1.1 General
Active infeed applications are mainly available with capacitive (VSC) and inductive (CSC)
smoothing on the d.c. side. Some converter concepts use no or nearly no d.c.-side smoothing.
The majority of installed units utilize capacitive smoothing.
Depending on the rated power and the power supply system availability the connection to the
power supply system may be single-phase or three-phase. The three-phase version is
selected for the examples.
———————
)
for balanced three-phase equipment.

– 14 – TS 62578 © IEC:2009(E)
The main operation principle is to switch the d.c.-side potentials or the d.c.-side currents
between the a.c.-side conductors with a pulse frequency of normally between 300 Hz and
20 kHz. In this way the desired voltages or currents on the a.c. side are realised as mean
values. The pulse frequency is normally high compared to the line frequency and allows quick
and accurate control of the voltages and currents on the a.c. side. However, switching
between fixed potentials or currents generates undesirable disturbances in the high-frequency
range. Passive a.c.-side filters are normally required to mitigate these disturbances.
A control system allows the precise control of fundamental and additional harmonic
components. The frequency up to which harmonics can be controlled is determined by the
pulse frequency of the converter.
The usual structure of VSC and CSC systems is shown in Figure 1 and Figure 2, respectively.

IEC  2280/09
Figure 1 – AIC in VSC topology, basic structure
(Note that the valve device symbols are just used for illustration)

TS 62578 © IEC:2009(E) – 15 –
IEC  2281/09
Figure 2 – AIC in CSC topology, basic structure
(Note that the valve device symbols are just used for illustration)
Figures 1 and 2 show that the structure of voltage and current source converter systems is
very similar. The main differences can be found on the d.c.-side and the a.c.-side filters and in
the type of semiconductors used for the valve device part of the converter. Details can be
found in the sections covering the different topologies.
The structure can be separated into three parts:
• Supply impedance at the internal point of coupling (IPC) which is mainly inductive.
• Converter and control up to d.c.-side. This part usually contains an a.c.-side filter, typically
as supply side inductance or LCL-filter with T-structure. A converter transformer, if used,
is part of (or designed to be used as) supply-side filter choke. Next in chain is the valve
device part, which may vary in structure see following subclauses of different topologies
as well as the d.c. side load character (capacitive smoothing or inductive smoothing). The
control typically uses space vector modulation, pulse width modulation, optimised
synchronous pulse patterns or hysteresis or sliding mode control for pulse pattern
generation. In case of pulse width modulation the pulse frequency is fixed. In case of
optimised synchronous pulse patterns the pulse pattern is fixed and synchronous with
respect to the line frequency. In case of line flux guidance the pulse pattern is
asynchronous to the line frequency and varies from period to period.
• Load part. The majority of loads connected are renewable energy equipment and PWM-
converter-fed machines. Another typical application are converters to feed passive or
mixed loads, as for example in uninterruptible power systems (UPS). This part is not
necessary in case of AICs for compensation. In case of voltage source converters long-
term energy storage units may be easily connected in parallel to the d.c.-side smoothing
capacitor. In typical applications the d.c.-side smoothing capacitor supplies the rated
power for about 1 ms to 10 ms without tripping of the converter. The long-term storage
typically may provide rated power for seconds to minutes.
4.1.2 Equivalent circuit of an AIC
The stationary behaviour of AICs is best described by equivalent sources and impedances.
These are shown in Figure 3.
– 16 – TS 62578 © IEC:2009(E)
supply-side
supply impedance T-filter impedance
PCC
V
PCC,harm
V
C ,μ
Undesired
distortion part
(high-frequency)
harmonics
V
S,harm
harmonic/interharmonic
components
Desired
V
C
,ν
(controllable)
harmonics
fundamental part
V
V C,1
S,1 fundamental component
V
PCC,1
IEC  2282/09
Power supply system            AIC
Figure 3 – Equivalent circuit for the interaction of the mains with an AIC
For better understanding it might be advantageous to separate the line voltages and the
converter voltages into their fundamentals and the remaining harmonics. For the converter
voltages, two sets of harmonic voltages may be distinguished.
• One set of harmonics which can be controlled directly. This set is defined as
controllable or desired harmonics and characterised by the index ν.
• One set of harmonics results from the pulse frequency and the pulse pattern. This set
is defined as undesired (generated) harmonics and characterised by the index μ.
The voltage V is the superposition of all (desired and undesired) harmonics caused by the
sharm
AIC and other loads together.
NOTE Similar conclusions can be drawn concerning current source AICs. In this case the set of voltages in
Figure 3 has to be replaced by a set of currents.
4.1.3 Filters
In the light of economical constraints the supply-side filter might be dimensioned in a way, that
the desired harmonics pass through the filter and the undesired harmonics are attenuated to a
degree prescribed by EMC specifications of the line. Additional design perspectives may
result from the power-supply system conditions at the IPC.
It should be noted that the frequency of the undesired harmonics is mainly from pulse
frequency on upward. The specification of the converter-side filter inductor has to take these
high frequencies into account, otherwise the inductor will overheat.
The d.c.-side filter, if used, has to attenuate the ripple of the d.c. voltage such, that the
converter and the eventually connected load function properly. The specification of a d.c.-link
capacitor has to take the amount of harmonic current into account, otherwise the capacitor
may overheat.
In some cases the energy-storage capability of the d.c.-side filter is adapted to dynamic
requirements. One application is the ride-through (continue operation during and after a short
interruption of the power supply system). Dynamic changes of energy flow of converter or
load also need larger d.c.-side energy storage. Otherwise the characterising d.c.-link quantity

TS 62578 © IEC:2009(E) – 17 –
(voltage or current) may leave a tolerance band in which proper function of the PWM
converter is guaranteed. An overshoot of voltage or current, even for a very short time, may
destroy the semiconductor valve devices of the converter.
For the fundamental frequency and the controllable harmonics, the supply-side filter may be
regarded as purely inductive. The voltage drop across the total impedance drives the supply-
side current. Quick changes of this supply-side current obviously require high values of the
voltage across the total impedance and therefore a higher rated supply-side and thus d.c.-
side voltage of the converter. Such quick changes of the line current are required for the
control of higher-frequency current components and during dynamic changes.
4.1.4 Pulse patterns
The selected pulse pattern generation influences the characteristics of the converter very
much. Three main basic pattern generation schemes are space vector modulation, optimised
synchronous pulse patterns and line flux guidance.
It should be noted that space vector modulation and symmetric pulse width modulation lead to
identical pulse patterns.
In case of space-vector modulation a sequence of zero states and non-zero voltage space
vectors is selected in such a way that the voltage space vector requested by the control
results as a mean value of the sequence. The zero states selected have to be of equal
duration
In case
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