IEC TS 62898-3-3:2023

Microgrids - Part 3-3: Technical requirements - Self-regulation of dispatchable loads

IEC TS 62898-3-3:2023 deals with frequency and voltage stabilization of AC microgrids by dispatchable loads, which react autonomously on variations of frequency and voltage with a change in active power consumption. Both 50 Hz and 60 Hz electric power systems are covered. This document gives requirements to emulate the self-regulation effect of loads including synthetic inertia.
The loads recommended for this approach are noncritical loads, this means their power modulation will not significantly affect the user as some kind of energy storage is involved which effectively decouples end energy use from the electricity supply by the electric network. The self-regulation of loads is beneficial both in island mode and grid-connected mode. This document gives the details of the self-regulation behaviour but does not stipulate which loads shall participate in this approach as an optional function.
This document covers both continuously controllable loads with droop control and ON/OFF switchable loads with staged settings. The scope of this document is limited to loads connected to the voltage level up to 35 kV. Reactive power for voltage stabilization and DC microgrids are excluded in this document.

General Information

• Status: Published
• Publication Date: 15-Aug-2023
• ICS: 29.240.01 - Power transmission and distribution networks in general
• Technical Committee: SC 8B - Decentralized electrical energy systems
• Drafting Committee: JWG 1 - TC 8/SC 8B/JWG 1
• Current Stage: PPUB - Publication issued
• Start Date: 17-Jul-2023
• Completion Date: 16-Aug-2023

Standards Content (Sample)

IEC TS 62898-3-3
®

Edition 1.0 2023-08
TECHNICAL
SPECIFICATION

colour
inside


Microgrids –
Part 3-3: Technical requirements – Self-regulation of dispatchable loads

IEC TS 62898-3-3:2023-08(en)

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IEC TS 62898-3-3

®


Edition 1.0 2023-08




TECHNICAL



SPECIFICATION








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Microgrids –

Part 3-3: Technical requirements – Self-regulation of dispatchable loads


























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ICS 29.240.01  ISBN 978-2-8322-7336-4




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– 2 – IEC TS 62898-3-3:2023 © IEC 2023
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, abbreviated terms and symbols . 7
3.1 Terms and definitions . 8
3.2 Abbreviated terms and symbols . 16
3.2.1 Abbreviated terms . 16
3.2.2 Symbols . 16
4 Requirements on self-regulation . 17
4.1 General . 17
4.1.1 Operational ranges . 17
4.1.2 Continuous and discrete control . 17
4.1.3 Dead band . 18
4.1.4 Accuracy and resolution . 18
4.1.5 Step response objective . 19
4.1.6 Damping . 20
4.2 Frequency stabilization . 20
4.2.1 General . 20
4.2.2 Continuously controllable loads . 21
4.2.3 Switchable loads. 23
4.2.4 Recommended default values . 24
4.3 Voltage stabilization . 24
4.3.1 General . 24
4.3.2 Continuously controllable loads . 25
4.3.3 Switchable loads. 26
4.3.4 Recommended default values . 27
4.4 Hybrid controls for both voltage and frequency . 28
5 Testing . 28
5.1 General . 28
5.2 Test for frequency response of self-regulated loads . 30
5.2.1 Purpose . 30
5.2.2 Procedure . 30
5.2.3 Criteria . 30
5.2.4 Comments . 30
5.3 Test for voltage response of self-regulated loads . 30
5.3.1 Purpose . 30
5.3.2 Procedure . 30
5.3.3 Criteria . 31
5.3.4 Comments . 31
Annex A (informative) Background information about the self-regulation effect . 32
Annex B (informative) Choice of coefficients k and k . 34
f U
B.1 General . 34
B.2 Expression of coefficient k for self-regulation of frequency . 34
f
B.3 Example of frequency settings in an isolated microgrid . 35
B.4 Example of frequency settings in a large interconnected network . 36

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IEC TS 62898-3-3:2023 © IEC 2023 – 3 –
B.5 Expression of coefficient k for self-regulation of voltage. 37
U
B.6 Example of voltage settings in an isolated microgrid . 38
Annex C (informative) Prioritization of loads . 40
Annex D (informative) Damping measure in electric power systems . 44
Annex E (informative) Formula development on the relation of power and torque . 46
Annex F (informative) Examples for desynchronisation strategies . 47
F.1 General . 47
F.2 Heterogeneous load types . 47
F.3 Fuzzy or randomized control logic . 47
F.4 Emulating continuously controllable loads . 47
Bibliography . 48

Figure 1 – Hysteresis curve of a switchable load . 10
Figure 2 – Typical step response of a system . 12
Figure 3 – Example of P(f) self-regulation before and after activating the dead band . 18
Figure 4 – Bode diagram of a typical differential loop . 21
Figure 5 – Time domain response of first order low-pass filter . 22
Figure 6 – Functional diagram of a combined frequency control function for
continuously controllable dispatchable loads . 22
Figure 7 – Example of a hysteresis controller to control the temperature of a freezer in
response to variations in grid frequency . 23
Figure 8 – Functional diagram of a combined voltage control function for continuously
controllable dispatchable loads . 26
Figure 9 – Schematic diagram for the test environment of a self-regulated load . 28
Figure A.1 – Frequency development after a disturbance . 32
Figure A.2 – Particle model of switchable loads . 33
Figure B.1 – Example of P(f) self-regulation in an isolated microgrid . 36
Figure B.2 – Example of P(f) self-regulation in a large interconnected network . 37
Figure B.3 – Example of P(U) self-regulation in an isolated microgrid . 39
Figure C.1 – Frequency distribution of the power frequency of a 50 Hz network . 40
Figure C.2 – Four different droop curves according to prioritization . 41
Figure C.3 – Schematic representation of voltage probability distribution . 42
Figure D.1 – Typical location for desired eigenvalues . 44

Table 1 – Declared frequency measurement accuracy levels . 18
Table 2 – Declared voltage measurement accuracy levels . 19
Table 3 – Time quality levels . 19
Table 4 – Performance quality levels . 20
Table B.1 – Relationship between k and droop for self-regulation of frequency . 35
f
Table B.2 – Relationship between k and droop for self-regulation of voltage . 38
U
Table C.1 – Frequency domain (example for 50 Hz systems) . 41
Table C.2 – Frequency domain (example for 60 Hz systems) . 41
Table C.3 – Voltage domain (example) . 43

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– 4 – IEC TS 62898-3-3:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

MICROGRIDS –

Part 3-3: Technical requirements –
Self-regulation of dispatchable loads

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
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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.
IEC TS 62898-3-3 has been prepared by subcommittee SC 8B: Decentralized electrical energy
systems, of IEC technical committee TC 8: System aspects of electrical energy supply. It is a
Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
8B/155/DTS 8B/172/RVDTS

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 Specification is English.

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IEC TS 62898-3-3:2023 © IEC 2023 – 5 –
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/standardsdev/publications.
A list of all parts in the IEC 62898 series, published under the general title Microgrids, can be
found on the IEC website.
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,
• replaced by a revised edition, or
• amended.

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– 6 – IEC TS 62898-3-3:2023 © IEC 2023
INTRODUCTION
Self-regulation of loads is a phenomenon known very well to transmission system operators,
see Annex A. This effect historically emerged from the dynamic behaviour of electric motors
that were used to directly power mechanical drivetrains, for example for pumps or air blowers.
The higher the rotational speed of the drive, the more active power is used and vice versa. This
effect automatically contributes to frequency stabilization without a supervisory control.
There is also a self-regulation effect on the voltage due to resistive loads. At higher voltages,
the current through a resistive load increases and therefore the active power consumption
increases as well. This increased current also flows through the impedance of the upstream
supply network, resulting in a voltage reduction at the load’s point of connection and vice versa.
This effect helps to stabilise the voltage and is also used indirectly with power system stabilisers
(PSS). Modulated system voltage at transmission level is translated to corresponding changes
of active power consumption of loads at distribution level which dampen low frequency power
oscillations.
This document intends to emulate the above explained beneficial behaviours with dispatchable
loads, which do not affect the functionality with regard to the end user, and to make this effect
available for frequency and voltage stabilization in microgrids. Dispatchable loads can modify
the active power consumption while maintaining their functionality by keeping system
parameters within acceptable ranges. This is usually achieved by the use of an internal energy
storage, for example thermal energy storage in refrigerators, freezers, air conditioners, water
heaters, or electrical energy storage units such as batteries. As the loads respond to the
frequency and voltage they experience, no communication channels or complex control systems
are necessary to include small loads in the common task of keeping the electric system stable.

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IEC TS 62898-3-3:2023 © IEC 2023 – 7 –
MICROGRIDS –

Part 3-3: Technical requirements –
Self-regulation of dispatchable loads



1 Scope
This part of IEC 62898 deals with frequency and voltage stabilization of AC microgrids by
dispatchable loads, which react autonomously on variations of frequency and voltage with a
change in active power consumption. Both 50 Hz and 60 Hz electric power systems are covered.
This document gives requirements to emulate the self-regulation effect of loads including
synthetic inertia.
The loads recommended for this approach are noncritical loads, this means their power
modulation will not significantly affect the user as some kind of energy storage is involved which
effectively decouples end energy use from the electricity supply by the electric network. The
self-regulation of loads is beneficial both in island mode and grid-connected mode. This
document gives the details of the self-regulation behaviour but does not stipulate which loads
shall participate in this approach as an optional function.
This document covers both continuously controllable loads with droop control and
ON/OFF-switchable loads with staged settings. The scope of this document is limited to loads
connected to the voltage level up to 35 kV. Reactive power for voltage stabilization and DC
microgrids are excluded in this document.
NOTE 1 If agreed between system operator and grid user, the self-regulating principles outlined in this document
can also be applied to loads in other electricity networks, see IEC/ISO Directives, Part 1:2023, C.4.3.2, Example 1.
NOTE 2 According to 3.1.7, critical loads with an electrical energy storage system such as an uninterruptable power
supply are considered as noncritical and therefore dispatchable.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms, definitions, abbreviated terms and symbols
For the purposes of this document, the following terms, definitions and abbreviated 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

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– 8 – IEC TS 62898-3-3:2023 © IEC 2023
3.1 Terms and definitions
3.1.1
accuracy
quality which characterizes the ability of a measuring instrument
to provide an indicated value close to a true value of the measurand
Note 1 to entry: This term is used in the "true value" approach. An updated term using the "uncertainty" approach
is in preparation for edition 2 of this document.
Note 2 to entry: Accuracy is all the better when the indicated value is closer to the corresponding true value.
[SOURCE: IEC 60050-311:2001, 311-06-08, modified – Note 1 to entry has been expanded.]
3.1.2
closed-loop control
process whereby one variable quantity, namely the controlled variable is continuously or
sequentially measured, compared with another variable quantity, namely the reference variable,
and influenced in such a manner as to adjust to the reference variable
Note 1 to entry: Characteristic for closed-loop control is the closed action in which the controlled variable
continuously or sequentially influences itself in the action path of the closed loop.
[SOURCE: IEC 60050-351:2013, 351-47-01, modified – Note 2 to entry has been deleted.]
3.1.3
control loop
set of elements or systems incorporated in the closed action of a closed-loop control
[SOURCE: IEC 60050-351:2013, 351-47-11, modified – Note 1 to entry has been deleted.]
3.1.4
damping coefficient
δ
-δt
positive quantity δ in the expression A e f(x) of an exponentially damped oscillation, where f(x)
0
is a periodic function
[SOURCE: IEC 60050-103:2009, 103-05-24]
3.1.5
damping ratio
for a linear time-invariant system described by the second order differential equation
2
ddxx
2
+ 20⋅ϑ⋅ω ⋅ +ω ⋅x=
00
2
dt
dt
the value of the coefficient ϑ,
where
t is the time;
x is a state variable of the system;
ω is the characteristic angular frequency of the system
0
2
1−ϑ
Note 1 to entry: When ϑ<1, ω = ω ∙ is the eigen angular frequency of the system.
d 0
[SOURCE: IEC 60050-351:2013, 351-45-19, modified – Note 2 to entry has been deleted.]

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IEC TS 62898-3-3:2023 © IEC 2023 – 9 –
3.1.6
dead band
dead zone
finite range of values of the input variable within which a variation of the input variable does not
produce any measurable change in the output variable
Note 1 to entry: When this type of characteristic is intentional, it is sometimes called neutral zone.
[SOURCE: IEC 60050-351:2013, 351-45-15, modified – Note 2 to entry has been deleted.]
3.1.7
dispatchable load
noncritical load
load for which the active power consumption can be modified while maintaining the functionality
of that load within an acceptable range of parameters
Note 1 to entry: Maintaining the load’s functionality is often achieved by use of an internal energy storage.
Note 2 to entry: The use of dispatchability depends on an agreement between grid user and grid operator.
Note 3 to entry: The feature of dispatchability can be made accessible either by self-regulation or remote control.
Note 4 to entry: The reference point for the conformity assessment is the terminal of the load.
3.1.8
droop control
control loop to control dispatchable loads in such a way that the active
power consumption is a function of system frequency, voltage, or both
3.1.9
(electric) island
part of an electric power system that is electrically disconnected from the remainder of the
interconnected electric power system but remains energized from the local electric power
sources
Note 1 to entry: An electric island can be either the result of the action of automatic protections or the result of a
deliberate action.
Note 2 to entry: An electric island can be stable or unstable.
Note 3 to entry: Electric islands can be nested.
[SOURCE: IEC 60050-692:2017, 692-02-11, modified – Note 3 to entry has been added.]
3.1.10
fault ride through
FRT
ability of a load to stay connected during specified faults in the electric power system
3.1.11
(frequency) droop
ratio of the per-unit changes in frequency (Δf)/f (where f is the nominal frequency) to the per-
n n
unit change in power (ΔP)/P (where P is the reference active power):
ref ref
σ = (Δf/f ) / (ΔP/P )
n ref
Note 1 to entry: Frequency droop is f-by-P, whereas the often used characteristic curve is P(f).
Note 2 to entry: The reference active power P is either the nominal active power or the present active power.
ref
Note 3 to entry: The same principle can be applied for a voltage droop.

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– 10 – IEC TS 62898-3-3:2023 © IEC 2023
Note 4 to entry: The frequency gradient of a characteristic curve, which describes the power response to frequency,
is the active power change per frequency change. In a 50 Hz system, a droop of σ % can be transformed into a
gradient g % (in P /Hz) by the formula g = 200/σ; in a 60 Hz system g = 166,7/σ.
n
[SOURCE: IEC 60050-603:1986, 603-04-08, modified – The notes have been added, the
nominal power has been replaced with reference power, and the specific use has
been deleted in the term.]
3.1.12
frequency response
for a linear time-invariant system with a sinusoidal input variable in steady state of the output
variable the ratio of the phasor of the output variable to the phasor of the corresponding input
variable, represented as a function of the angular frequency ω
Note 1 to entry: The frequency response coincides with the transfer function taken on the imaginary axis of the
complex plane.
[SOURCE: IEC 60050-351:2013, 351-45-41, modified – Figure 9, Figure 10 and Note 2 to entry
have been deleted.]
3.1.13
functional diagram
symbolic representation of the actions in a system by functional blocks, summing points and
branching points linked by action lines
Note 1 to entry: The action lines do not necessarily represent physical connections, like electrical wires.
Note 2 to entry: Functional blocks, action lines, summing points, and branching points are elements of the functional
diagram.
[SOURCE: IEC 60050-351:2013, 351-44-01, modified – Figure 1, Figure 2 and Note 3 to entry
have been deleted.]
3.1.14
hysteresis
phenomenon represented by a characteristic curve which has a branch, called ascending
branch, for increasing values of the input variable, and
...