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
Current Stage
PPUB - Publication issued
Start Date
17-Jul-2023
Completion Date
16-Aug-2023
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IEC TS 62898-3-3:2023 - Microgrids - Part 3-3: Technical requirements - Self-regulation of dispatchable loads Released:8/16/2023
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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

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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

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.01  ISBN 978-2-8322-7336-4

– 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

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

– 4 – IEC TS 62898-3-3:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MICROGRIDS –
Part 3-3: Technical requirements –
Self-regulation of dispatchable loads

FOREWORD
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