IEC TS 62786-41:2023

IEC TS 62786-41
®

Edition 1.0 2023-07
TECHNICAL
SPECIFICATION

colour
inside


Distributed energy resources connection with the grid –
Part 41: Requirements for frequency measurement used to control distributed
energy resources (DER) and loads

IEC TS 62786-41:2023-07(en)

---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2023 IEC, Geneva, Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.


IEC Secretariat Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland

About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always have
committee, …). It also gives information on projects, replaced access to up to date content tailored to your needs.
and withdrawn publications.

Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and once
and French, with equivalent terms in 19 additional languages.
a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc

If you wish to give us your feedback on this publication or need
further assistance, please contact the Customer Service
Centre: sales@iec.ch.

---------------------- Page: 2 ----------------------
IEC TS 62786-41

®


Edition 1.0 2023-07




TECHNICAL



SPECIFICATION








colour

inside










Distributed energy resources connection with the grid –

Part 41: Requirements for frequency measurement used to control distributed

energy resources (DER) and loads

























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 91.140.50  ISBN 978-2-8322-7225-1




  Warning! Make sure that you obtained this publication from an authorized distributor.


® Registered trademark of the International Electrotechnical Commission

---------------------- Page: 3 ----------------------
– 2 – IEC TS 62786-41:2023 © IEC 2023
CONTENTS
FOREWORD . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
4 Performance description . 14
4.1 General . 14
4.2 Input energizing quantities . 14
4.3 Delay time . 15
4.3.1 Description . 15
4.3.2 Reporting of delay time declaration . 15
4.4 Effective resolution and accuracy . 15
4.4.1 Description . 15
4.4.2 Effective measurement resolution . 16
4.4.3 Reporting of the frequency and ROCOF accuracy . 16
4.5 Measuring range, operating range, and rejection of interfering signals . 16
4.6 Timing characteristics . 19
4.6.1 Reporting rate. 19
4.6.2 Settling time . 19
5 Summary of typical performances associated with different use cases . 20
6 Description of functional test principles . 22
6.1 General . 22
6.2 Test reference conditions . 24
6.3 Verification of delay time for frequency and ROCOF measurement . 24
6.3.1 Test description . 24
6.3.2 Example determination of delay time . 25
6.4 Verification of effective resolution for frequency and ROCOF measurement . 27
6.4.1 Test description . 27
6.4.2 Example determination of effective resolution . 29
6.5 Verification of measurement and operating ranges . 29
6.5.1 Verification of measurement and operating ranges under steady state
conditions . 29
6.5.2 Measuring and operating ranges under dynamic conditions . 31
6.5.3 Verification of rejection of interfering interharmonics. 33
6.5.4 Verification of rejection of harmonics . 35
6.6 Verification of settling time . 38
6.6.1 Test description . 38
6.6.2 Verification of settling time for frequency measurement . 39
6.6.3 Example of verification of frequency settling time . 39
6.6.4 Verification of settling time for ROCOF measurement . 40
6.6.5 Example of verification of ROCOF settling time . 40
6.7 Type test report . 41
Annex A (informative) Measurement classes . 43
Annex B (informative) Description of frequency or ROCOF measurement use cases . 44
B.1 Use case "PLL in photovoltaic power generating systems" . 44
B.1.1 Technical background of the use case . 44
B.1.2 Resulting requirements for measurement . 45

---------------------- Page: 4 ----------------------
IEC TS 62786-41:2023 © IEC 2023 – 3 –
B.2 Use case "Primary reserve" . 46
B.2.1 Technical background of the use case . 46
B.2.2 Resulting requirements for measurement . 46
B.2.3 Example of "frequency-watt" function in photovoltaic power generating
systems . 47
B.3 Use case "Secondary reserve – frequency measurement used for centralized
control" . 48
B.3.1 Technical background of the use case . 48
B.3.2 Resulting requirements for measurement . 48
B.4 Use case "Fast frequency-active power proportional controller with dead
band" . 49
B.4.1 Technical background of the use case . 49
B.4.2 Resulting requirements for measurement . 50
B.5 Use case "Fast frequency response" . 51
B.5.1 Technical background of the use case . 51
B.5.2 Resulting requirements for measurement . 51
B.6 Use case "Synthetic inertia" . 51
B.6.1 Technical background of the use case . 51
B.6.2 Resulting requirements for measurement . 52
B.7 Use case "Passive anti-islanding detection" . 52
B.7.1 Technical background of the use case . 52
B.7.2 Resulting requirements for measurement . 53
B.8 Use case "Active anti-islanding detection" . 54
B.8.1 Technical background of the use case . 54
B.8.2 Resulting requirements for measurement . 54
B.9 Use case "ROCOF measurement used for centralized control" . 55
B.9.1 Technical background of the use case . 55
B.9.2 Resulting requirements for measurement . 55
B.10 Use case "Load control with active power management" . 55
B.10.1 Technical background of the use case . 55
B.10.2 Resulting requirements for measurement . 55
B.11 Use case "Self-dispatchable loads" (microgrid applications) . 56
B.11.1 Technical background of the use case . 56
B.11.2 Resulting requirements for measurement . 56
B.12 Use case "Under-frequency load shedding" (UFLS) . 57
B.12.1 Technical background of the use case . 57
B.12.2 Resulting requirements for measurement . 57
Annex C (informative) Summary of requirements expressed in standards and grid
codes related to frequency and ROCOF measurements . 58
Annex D (informative) Maximum ROCOF to be considered on power systems in case
of incidents . 65
D.1 General . 65
D.2 UK . 65
D.3 European continent . 65
D.4 Islands . 65
Annex E (informative) Frequency and rotating vectors . 66
Annex F (informative) Synthetizing input signals with sudden frequency change

without discontinuity in voltage waveform. 68
Annex G (informative) Step test equivalent time sampling technique . 71
G.1 Overview. 71

---------------------- Page: 5 ----------------------
– 4 – IEC TS 62786-41:2023 © IEC 2023
G.2 Equivalent time sampling . 72
G.3 Determination of settling time using instrument errors . 73
Annex H (informative) Voltage and phase angle changes during transmission line
faults related to the type of transformer connection . 75
H.1 Overview. 75
H.2 Power line short circuit fault and protection . 75
H.3 Voltage magnitude and phase angle change at line fault . 77
H.3.1 General . 77
H.3.2 Balanced-three-phase short circuit fault . 77
H.3.3 Line-to-line short circuit fault . 77
H.4 Conclusion . 79
Annex I (informative) Influencing factors and functional tests . 80
I.1 Influencing factors . 80
I.2 Functional tests . 80
I.2.1 General . 80
I.2.2 Phase step change . 80
I.2.3 Magnitude step change . 82
I.2.4 Combined magnitude and phase step change . 85
I.2.5 Voltage magnitude drop and restoration . 89
I.2.6 Noise . 95
I.2.7 Unbalanced input signal magnitude . 97
I.2.8 Linear ramp of frequency . 99
Bibliography . 104

Figure 1 – Measuring range and operating range without interfering signals . 17
Figure 2 – Measuring range and operating range in the presence of interfering signals . 17
Figure 3 – Settling time description with input signal added . 20
Figure 4 – Example of frequency delay time validation: measurement of delay time for
a power frequency of 50 Hz . 26
Figure 5 – Example of cross-correlations of the normalized frequencies and ROCOF . 26
Figure 6 – Example of frequency modulation used to determine frequency effective
resolution . 29
Figure 7 – Example of frequency modulation used to determine ROCOF effective

resolution . 29
Figure 8 – Example of verification of measurement bandwidth under steady state
conditions . 31
Figure 9 – Example of verification of measuring and operating ranges under dynamic
conditions . 33
Figure 10 – Example of verification of rejection of interfering interharmonics . 34
Figure 11 – Waveforms with superimposed harmonics . 36
Figure 12 – Three-phase harmonic test signals, 0° and 180° harmonic phases . 37
Figure 13 – Example of verification of rejection of harmonics . 38
Figure 14 – Example of verification of frequency settling time using positive 1 Hz step

in frequency . 39
Figure 15 – Example of verification of frequency settling time using negative 1 Hz step
in input frequency . 40
Figure 16 – Example of verification of ROCOF settling time using positive 1 Hz/s step
in ROCOF . 41

---------------------- Page: 6 ----------------------
IEC TS 62786-41:2023 © IEC 2023 – 5 –
Figure 17 – Example of verification of ROCOF settling time using negative 1 Hz/s step
in ROCOF . 41
Figure B.1 – Example of a system diagram of a PV system with a three-phase DC to

AC converter . 44
Figure B.2 – Example of system diagram of a three-phase PV system for voltage
control . 45
Figure B.3 – Example of system diagram of PV system with frequency-watt function . 47
Figure B.4 – Application example of frequency-watt function for PV systems . 48
Figure B.5 – Example of fast frequency-active power proportional controller with dead
band (LFSM-O and LFSM-U characteristics from European Grid Code) . 50
Figure E.1 – Phasor representation of a power system signal, which has amplitude (a),

angle (Φ) and angular velocity (ω) . 66
Figure F.1 – Example of voltage waveform without discontinuity at t = 0,02 s . 69
o
Figure F.2 – Example of voltage waveform with discontinuity at t = 0,02 s. 70
o
Figure G.1 – Example of reports during step response . 71
Figure G.2 – Example of reports during step response with higher resolution . 72
Figure G.3 – Example of reports during step response with higher resolution . 73
Figure H.1 – Voltage phase change by transmission line short circuit fault . 76
Figure H.2 – Transmission line protection sequence and line voltage, frequency
change . 76
Figure H.3 – Voltage and phase angle change at three-phase short circuit . 77
Figure H.4 – Relationship of voltage phase angle between Y-connection side and
Δ-connection side . 78
Figure H.5 – Voltage magnitude and phase angle change at two-phase short circuit
fault 78
Figure I.1 – Frequency error response to +0,3 radian phase step followed by −0,3
radian step . 82
Figure I.2 – ROCOF error response to +0,3 radian phase step followed by −0,3 radian
step 82
Figure I.3 – Frequency error response to magnitude step changes . 84
Figure I.4 – ROCOF error response to steps in magnitude . 85
Figure I.5 – Voltage vectors for test case a) . 86
Figure I.6 – Voltage vectors for test case b) . 87
Figure I.7 – Frequency error responses to combined phase and magnitude steps . 88
Figure I.8 – ROCOF error responses to combined phase and magnitude steps . 89
Figure I.9 – Representation of the input energizing quantity (voltage, RMS) injection . 91
Figure I.10 – Frequency response to voltage drop and restoration . 92
Figure I.11 – ROCOF response to voltage drop and restoration . 94
Figure I.12 – Frequency error absolute values from noise test scenarios a) and b) . 96
Figure I.13 – ROCOF error absolute values from noise test scenarios a) and b) . 97
Figure I.14 – Frequency absolute error due to unbalanced input signal magnitude . 98
Figure I.15 – ROCOF absolute error due to unbalanced input signal magnitude . 99
Figure I.16 – Frequency ramp test scenarios . 100
Figure I.17 – Absolute frequency error during linear ramp of frequency test scenarios . 102
Figure I.18 – Absolute ROCOF error during linear ramp of frequency test scenarios . 103

---------------------- Page: 7 ----------------------
– 6 – IEC TS 62786-41:2023 © IEC 2023
Table 1 – Performance characteristics presented in Clause 4 . 14
Table 2 – Example of delay time . 15
Table 3 – Example of measurement resolution and maximum absolute error for
frequency and ROCOF measurements . 16
Table 4 – Example of measuring range and operating range for frequency and ROCOF

measurements (taken from an actual instrument) . 18
Table 5 – Example of reporting of settling time and reporting rate . 19
Table 6 – List of use cases and associated requirements . 21
Table 7 – Input signal harmonic magnitudes . 35
Table A.1 – Measurement classes for frequency measurements . 43
Table A.2 – Measurement classes for ROCOF measurements . 43
Table B.1 – Typical requirements for frequency measurement of PLL in PV systems . 46
Table B.2 – Typical requirements for frequency measurement – use case "Primary
reserve" . 46
Table B.3 – Example of requirements of frequency-Watt function of PV systems. 48
Table B.4 – Typical requirements for use case "Secondary reserve – frequency
measurement used for centralized control" . 49
Table B.5 – Typical requirements for frequency measurement – use case "Fast
frequency-active power proportional controller with dead band" . 51
Table B.6 – Typical requirements for frequency measurement – use case "Fast
frequency response" . 51
Table B.7 – Typcial requirements for ROCOF measurement – use case "Synthetic
inertia" . 52
Table B.8 – Set of typical requirements for frequency measurement – use case
"Passive anti-islanding detection" . 53
Table B.9 – Typical requirements for ROCOF measurement – use case "Passive anti-
islanding detection" . 53
Table B.10 – Typical requirements for frequency measurement – use case "Active anti-
islanding detection" . 54
Table B.11 – Typical requirements for ROCOF measurement – use case "ROCOF
measurement used for centralized control" . 55
Table B.12 – Typical requirements for frequency measurement – use case "Load
control with active power management" . 55
Table B.13 – Typical requirements for frequency measurement – use case "Self-
dispatchable loads" . 56
Table B.14 – Typical requirements for frequency measurement – use case "Under-
frequency load shedding" . 57
Table B.15 – Typical requirements for ROCOF measurement – use case "Under-
frequency load shedding" . 57
Table C.1 – Requirements expressed in standards and grid codes related to frequency
and ROCOF measurements . 59
Table I.1 – Influencing factors of frequency and ROCOF measurements . 80
Table I.2 – Test case a) for combined magnitude and phase step change . 86
Table I.3 – Test case b) for combined magnitude and phase step change . 86
Table I.4 – Magnitudes and phase angles for three phase voltages . 97

---------------------- Page: 8 ----------------------
IEC TS 62786-41:2023 © IEC 2023 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

DISTRIBUTED ENERGY RESOURCES CONNECTION WITH THE GRID –

Part 41: Requirements for frequency measurement used to control
distributed energy resources (DER) and 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
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Repor
...