IEC TR 63575:2025

IEC TR 63575 ®
Edition 1.0 2025-07
TECHNICAL
REPORT
Performance of power electronic reactive power shunt compensators in high
voltage alternating current (HVAC) systems

ICS 29.240.99  ISBN 978-2-8327-0594-0

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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Overview of reactive power shunt compensators . 6
5 Applications . 7
5.1 General . 7
5.2 Power generation plant . 8
5.3 Transmission network . 8
5.4 Distribution network and industry plant . 9
6 Performance . 9
6.1 Step response . 9
6.2 Operation on weak system . 11
6.3 Fault ride-through . 13
6.4 Coordination with other electrically close reactive power devices . 15
6.5 Negative-sequence control . 16
6.6 Subsynchronous resonance and oscillation . 16
6.7 Power oscillation damping (POD) . 17
6.8 Geomagnetically induced currents (GIC) . 18
6.9 Harmonic interaction . 19
Annex A (informative) Application of power electronic reactive power shunt
compensators . 20
A.1 SVC application . 20
A.1.1 General . 20
A.1.2 SVC in Ethiopia . 20
A.1.3 SVC in Norway . 22
A.1.4 SVC in France . 23
A.2 STATCOM application . 24
A.2.1 General . 24
A.2.2 STATCOM in China . 24
A.2.3 STATCOM in Chile . 26
A.2.4 STATCOM in England . 27
A.2.5 STATCOM in Germany . 29
Bibliography . 31

Figure 1 – Example configuration of an SVC . 6
Figure 2 – Example configuration of an STATCOM . 7
Figure 3 – A typical configuration example of static var system . 7
Figure 4 – A typical configuration example of shunt compensators for integration of a
power plant and industry plant . 8
Figure 5 – Definition of response and settling time . 10
Figure 6 – Basic block diagram of STATCOM system terminal voltage regulation . 12
Figure 7 – Power system overvoltage range . 14
Figure 8 – Power system undervoltage range . 14
Figure 9 – Structure of the sub-synchronous damping controller of SVC . 17
Figure 10 – Structure of the sub-synchronous damping controller of STATCOM . 17
Figure 11 – Example of the POD controller . 18
Figure A.1 – The SLD of 900 Mvar SVC in Ethiopia . 20
Figure A.2 – The site view of 900 Mvar SVC in Ethiopia . 21
Figure A.3 – The SLD of ±250 Mvar SVC . 22
Figure A.4 – The site view of ±250 Mvar SVC in Norway . 22
Figure A.5 – The SLD of ±250 Mvar SVC in France . 23
Figure A.6 – The site view of ±250 Mvar SVC in France . 24
Figure A.7 – The SLD of ± 300 Mvar STATCOM in China . 25
Figure A.8 – The SLD of 140 Mvar STATCOM in Chile . 26
Figure A.9 – The site view of 140 Mvar STATCOM in Chile . 27
Figure A.10 – The SLD of ±300 Mvar STATCOM in England . 28
Figure A.11 – The site view of 225 Mvar STATCOM in England . 29
Figure A.12 – The SLD of ±300 Mvar STATCOM in Germany . 30

Table A.1 – The characteristics of the SVC in Ethiopia . 21
Table A.2 – The characteristics of ±250 Mvar SVC in Norway . 23
Table A.3 – The characteristics of ±250 Mvar SVC in France . 24
Table A.4 – The characteristics of the STATCOM in China . 25
Table A.5 – The characteristics of the STATCOM in Chile. 27
Table A.6 – The characteristics of the STATCOM in England . 29
Table A.7 – The characteristics of the STATCOM in Germany . 30

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Performance of power electronic reactive power shunt compensators in
high voltage alternating current (HVAC) systems

FOREWORD
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IEC TR 65535 has been prepared by subcommittee 22F: Power electronics for electrical
transmission and distribution systems, of IEC technical committee 22: Power electronic systems
and equipment. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
22F/823/DTR 22F/829/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
1 Scope
This document provides general guidelines on the performance of power electronic reactive
power shunt compensators in high voltage alternating current systems. It includes terms,
definitions, symbols and abbreviated terms, introduction, applications and performance.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1
point of common coupling
PCC
point of a power supply network, electrically nearest to a particular load, at which other loads
are, or may be, connected
[SOURCE: IEC 60050-614:2016, 614-01-12, modified – "in an electric power system" replaced
with "of a power supply network", Note 1 to entry removed]
3.2
voltage-sourced converter
VSC
electronic AC/DC converter having an essentially smooth DC voltage provided by e.g. a
common DC link capacitor or distributed DC capacitors within the converter arms
[SOURCE: IEC 62747:2014, 5.3]
3.3
static synchronous compensator
STATCOM
shunt connected reactive compensation equipment which is capable of generating and/or
absorbing reactive power based on voltage sourced converter (VSC), whose capacitive or
inductive output current can be controlled independently of the AC system voltage
[SOURCE: IEC 62927:2017, 3.4.1, modified – "based on voltage sourced converter (VSC)"
added, Note 1 to entry removed]
3.4
step response time
for a step response the duration of the time interval between the instant of the step change of
an input variable and the instant when the output variable reaches for the first time a specified
percentage of the difference between the final and the initial steady-state value
[SOURCE: IEC 60050-351:2013, 351-45-36]
3.5
settling time
for a step response the duration of the time interval between the instant of the step change of
an input variable and the instant, when the difference between the step response and their
steady-state value remains smaller than the transient value tolerance
[SOURCE: IEC 60050-351:2013, 351-45-37]
3.6
slope
percentage of the voltage change to the current change at the defined controlled range of the
shunt connected reactive compensation equipment counting
4 Overview of reactive power shunt compensators
Power electronic reactive power shunt compensators are applied to solve a variety of problems,
namely, to achieve effective voltage control, to provide/absorb reactive power, to eliminate
high-order current harmonics, and to balance electrical loads. Several types of power electronic
reactive power shunt compensators are available. Examples of the application of power
electronic reactive power shunt compensators are given in Annex A.
Static var compensators (SVC) can output reactive power continuously and rapidly, and
thyristors are the main power switches used in SVC. SVC branches come in four types: thyristor
controlled reactors (TCR), thyristor switched capacitors (TSC), thyristor switched reactors (TSR)
and filters. A single SVC system typically includes at least two types of these branches (see
Figure 1).
Figure 1 – Example configuration of an SVC
STATCOM can adjust the consumption or absorption of reactive power faster than SVC,
because the semiconductor device used as the main switch is fully controllable, in contrast to
a thyristor (see Figure 2).
Figure 2 – Example configuration of an STATCOM
Static var system is a type of hybrid dynamic reactive compensator with the combination of SVC
and STATCOM (see Figure 3).
Figure 3 – A typical configuration example of static var system
5 Applications
5.1 General
The basic operating principle of shunt connected reactive power compensators is illustrated in
Figure 4. It consists of a power supply that provides current i , a reactive power compensator
sup
that draws current i and a feeder for a load which draws current i . The primary purpose

comp load
of the reactive power compensator is to provide dynamic reactive support to help control the
voltage at the connection point, supply or absorb reactive power, eliminate high-order current
harmonics and balance three-phase loads.
Figure 4 – A typical configuration example of shunt compensators
for integration of a power plant and industry plant
Power electronic reactive power shunt compensator with characteristics and controls can have
different utilization for different applications, as shown in 5.2, 5.3 and 5.4.
5.2 Power generation plant
Reactive power compensation equipment can either supply reactive power or absorb reactive
power. Power plants can be categorized into traditional and renewable energy types, and the
former are mainly based on synchronous generators electrically connected directly to the grid
and mechanically coupled to a prime mover (such as a steam, gas or hydro turbine), while the
latter are interfaced to the grid via power electronic converters. In power generation plants,
reactive power compensation equipment has several applications, such as:
– To facilitate integration of renewable generation;
– To improve fault recovery;
– To damp sub-synchronous oscillations;
– To regulate power factor, e.g. increase the power factor to fulfil the requirements of PCC
especially in the renewable energy scenario.
5.3 Transmission network
In the transmission network of power grids, reactive power compensation equipment is also
important for application such as:
– To achieve effective voltage control in steady state;
– To provide/absorb reactive power;
– To increase the active power transfer capacity of both existing and new transmission
systems;
– To increase transient stability margins;
– To increase dynamic reactive reserve margins;
– To improve fault recovery;
– To reduce temporary overvoltage;
– To increase transmission limits;
– To damp sub-synchronous oscillations;
– To increase damping of power oscillations;
NOTE 1 If the reactive power compensation equipment has the power oscillation damping (POD) function, it
would mitigate active power oscillations in a lower frequency to keep the transmission network stable.
– Improvement of HVDC transmission based on line-commutated converter (LCC) technology.
NOTE 2 Due to their inherent high speed of response, shunt compensators with adequate reactive power
generation and absorption capability, represent an effective method in controlling such disturbances. The
installation of a shunt compensators as part of the converter complex would enable:
a) better control of AC voltage by reducing the effect of reactive power variations due to changes in converter
demand and / or switching of filter banks;
b) reduce the dynamic and temporary overvoltage due to converter blocking;
c) assist in recovery of the AC system from faults.
5.4 Distribution network and industry plant
The reactive power compensation equipment can provide the reactive power required by the
electrical equipment to improve the power factor of the PCC, and support the system voltage.
It also improves equipment production efficiency, as many devices cannot exert their rated
power under low voltage, which reduces production efficiency. In general, the important function
of reactive power compensation equipment is to improve the power quality of load access points.
– To regulate power factor
– To reduce harmonic voltage and current
NOTE 1 Reactive power compensation equipment can filter or compensate harmonics current, such as
configuring filter branches and designing appropriate tuning points to filter out various harmonic currents
generated by the load and reduce the flow into the power grid. The harmonic current of PCC can be reduced by
providing a reverse harmonic current, or by adding an active filter function, to achieve the purpose of harmonic
compensation. STATCOM also can provide active filtering to enhance the harmonic performance.
– To mitigate voltage fluctuation and flicker
NOTE 2 By compensating for the instantaneous reactive power, the voltage fluctuation would be suppressed
to reduce flicker.
– To balance loading of individual phases
NOTE 3 Through the Steinmetz algorithm, the unbalance loading can be balanced by adjusting the output of
the three-phase reactive power, the three-phase unbalance would be mitigated at the PCC point, and negative
sequence suppression would be also achieved.
The above is the application of reactive power compensation equipment in general. For specific
application cases of SVC and STATCOM, refer to Annex A.
6 Performance
6.1 Step response
The dynamic characteristic of the shunt compensator control system is the response to a step
change in the system voltage, so that the shunt compensation system remains within its
controllable range. The step response defines the speed of the control system (controller,
system, and measuring circuit).
Many factors affect the step response time of a shunt compensator, in particular, the gain, slope
setting, system impedance, and the number of shunt compensator connected to the busbar.
Increasing system impedance (that is, the system becomes weaker) leads to a faster response
and, ultimately, instability.
The definition of step response time can also be based on other measured quantities, i.e,
susceptance or output reactive current to verify the dynamic characteristic.
In Figure 5, the process including a step change of the input of the control reference signal and
the following swing of the output is demonstrated.
where
t is the time when the input signal reference step starts.
t is the time when the output starts to change, where the output has reached a specified percentage, e.g. 5 %, of
the desired total change.
t the time when the change of the output reaches 90 % of the desired total change.
t is the time after which the output could be within specified tolerance limit of the final value.
Figure 5 – Definition of response and settling time
Therefore:
Dead time is the time interval between t and t , when the output starts to change.
0 1
Step response time is the time interval between t and t , when the output reaches 90 % of the
0 2
desired total change without any overshoot.
Settling time is the time interval between t and t , when the output is within specified tolerance
0 3
limit of the final value.
Maximum overshoot is measured by percentage to final value or total change.
The validation of response time can be performed on a real time simulator. Several responses
can be demonstrated at different gains, slopes, operating points, and short circuit levels. A
small step can be injected into the control system as a test (small disturbance).
Once at site and in the commissioning process, some of these step tests can be re-performed
to verify the response performance with real system. External element switch tests could be
done additionally if needed.
NOTE 1 The step response defined in Figure 6 has the aim to define the speed of the control system (controller,
system, and measuring circuit). By specifying the response and settling time the performance of the control system
will be defined. In the case where the step is not only performed by linear control devices (TCR or VSC) and a
switched branch (TSC or TSR) is switched in during a step response, the result of overshoot and settling time cannot
be used to evaluate the control system performance.
NOTE 2 With grid-forming controllers utilizing virtual impedance, a STATCOM can be designed to avoid enhancing
oscillations, and can also provide positive damping. Therefore, a reduction in the gain of the outer voltage control
loop is acceptable. Achieving step-response requirements described in 6.1 would thus not be relevant.
6.2 Operation on weak system
Typically, the load flow study that can derive the strength of the system under different operating
modes is done by the user as part of the specification for the reactive power shunt
compensators. Weak or strong system conditions will affect the operating characteristics of the
power electronic reactive power shunt compensators in HVAC systems and put forward different
control requirements.
Short-circuit capacity refers to the apparent power of the system at the short-circuit point in the
specified operating mode. It is a characteristic parameter of the power supply capacity of the
system that is equal to the product of the short-circuit current and the rated voltage.
S 3×UI× (1)
sc
where
S is the short-circuit capacity, expressed in MVA;
sc
U is the rated voltage of short-circuit point, expressed in kV;
I is the short-circuit current of short-circuit point, expressed in kA.
The short circuit ratio (SCR) is the ratio of the short-circuit capacity at the PCC and the rated
capacity of the power electronic reactive power shunt compensators. A larger short circuit ratio
means a stronger system.
In very weak systems, e.g. SCR < 3:1, voltage regulation stability issues can arise, especially
if the capacitive rating of the reactive power shunt compensators is high in comparison to
system strength. However, other technical challenging issues for weak systems would also be
considered for power electronic reactive compensators including high transient overvoltage,
harmonic resonance, capacitor switching, transient recovery voltage, transformer inrush, motor
starting etc.
As the system impedance X varies (which can happen due to line switching, generator outages
s
etc.), the compensator and its control system will remain stable only if the overall loop gain is
less than unity for the maximum system impedance (weakest system) at the frequency for which
the phase angle reaches −180°, see Figure 7. This is usually achieved by setting the time
constant of the main error amplifier or changing the slope value in the voltage controller to be
appropriately large. However these methods would increase the response time.
=
Figure 6 – Basic block diagram of STATCOM system terminal voltage regulation
A normal range of short circuit ratio down to 3:1 would be handled by appropriate choice of the
slope to have a reasonable response time, e.g. a response time of 50 ms. Below that, i.e. for a
much weaker grid, the gain is reduced and a response time extends, e.g. a response time of
100 ms.
To make the power electronic reactive power shunt compensators adapt to the different short
circuit ratio, the solutions that can be used are as follows:
– Manual gain switching: This method involves predetermining the optimal regulator gains for
different system-operating conditions and allowing the operating personnel to manually
switch the gains according to the existing network states based on breaker-status signals.
– Nonlinear gain: This gain function introduces an enhanced gain to provide a fast response
in case of large voltage fluctuations.
– Bang-bang control: This is a limiting case of the nonlinear gain in which the TCR and/ or
the TSCs switch between their off and on states.
– Automatic gain control: This is an automatic gain-control scheme that provides a control of
the regulator gain over a wide range of system-operating conditions, ensuring a consistently
stable response in all situations.
– Grid forming control of STATCOM: This method maintains an internal voltage phasor without
following the power system phasor, and the STATCOM with grid forming control could
operate stable in the very weak system.
The primary objective of grid forming control functionality is to maintain stable operation of the
STATCOM at low SCR levels, i.e. in weak grids. In the most severe cases, where the SCR level
is extremely low, a grid forming STATCOM can positively contribute to the restoration process
of the grid.
The grid forming STATCOM maintain an internal voltage phasor that is constant or nearly
constant in the sub-transient to transient time frame. This allows the STATCOM with grid
forming control to immediately respond to changes in the external system and maintain
STATCOM control stability during challenging network conditions. Therefore, the grid forming
inherently counteracts changes in the grid voltage, both magnitude and phase.
...