IEC TR 63401-1:2022

Dynamic characteristics of inverter-based resources in bulk power systems - Part 1: Interconnecting inverter-based resources to low short circuit ratio AC networks

IEC TR 63401-1:2022(E) discusses the challenges of connecting inverter-based resources to low short circuit ratio AC networks, key technical issues and emerging technologies. There are the steady-state stability issue, transient state stability issue, and oscillatory stability issue, which are the most distinct differences compared to inverter-based resources or traditional generators, and accordingly brings new challenges to operation, control, protection, etc. Therefore, technical solutions are needed. The potential solutions will include new technologies, methods and practices, in order to provide more flexibility and improve the efficiency of power systems. It is expected that this document can also provide guidance for further standardization on relevant issues

General Information

• Status: Published
• Publication Date: 24-Nov-2022
• ICS: 29.020 - Electrical engineering in general
• Technical Committee: SC 8A - Grid Integration of Renewable Energy Generation
• Drafting Committee: JWG 5 - TC 8/SC 8A/JWG 5
• Current Stage: PPUB - Publication issued
• Start Date: 03-Jan-2023
• Completion Date: 25-Nov-2022

Standards Content (Sample)

IEC TR 63401-1 ®
Edition 1.0 2022-11
TECHNICAL
REPORT
colour
inside
Dynamic characteristics of inverter-based resources in bulk power systems –
Part 1: Interconnecting inverter-based resources to low short circuit ratio AC
networks
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IEC TR 63401-1 ®
Edition 1.0 2022-11
TECHNICAL
REPORT
colour
inside
Dynamic characteristics of inverter-based resources in bulk power systems –

Part 1: Interconnecting inverter-based resources to low short circuit ratio AC

networks
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.020 ISBN 978-2-8322-6143-9

– 2 – IEC TR 63401-1:2022  IEC 2022
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 10
3 Terms and definitions . 10
4 Characteristics of low short circuit ratio AC networks . 12
4.1 Definition of low short circuit ratio . 12
4.1.1 General . 12
4.1.2 Low SCR in IEEE Std 1204-1997 . 13
4.1.3 Low SCR in CIGRE B4.62 TB671 . 13
4.2 Stability issues posed by inverter-based resources . 15
4.2.1 General . 15
4.2.2 Static voltage control . 16
4.2.3 Fault ride-through . 16
4.2.4 Multi-frequency oscillation . 16
4.3 Summary . 17
5 Identification of low short circuit ratio AC networks . 17
5.1 Problem statement . 17
5.2 Short circuit ratio for a single-connected REPP system . 18
5.2.1 SCR calculation with fault current . 18
5.2.2 SCR calculation with equivalent circuit . 19
5.3 Short circuit ratio for multi grid-connected WPP system . 26
5.3.1 General . 26
5.3.2 Modal decoupling method . 27
5.3.3 Circuit aggregation method . 38
5.4 Summary . 45
6 Steady state voltage stability issue for low short circuit ratio AC networks . 47
6.1 Problem statements . 47
6.2 Steady state stability analysis method . 47
6.2.1 P-V curve . 47
6.2.2 Q-V curve . 48
6.2.3 Voltage sensitivity analysis . 49
6.2.4 Relation to short circuit ratio . 54
6.3 Control strategy for inverter-based resource . 56
6.3.1 Active power and reactive power control . 56
6.3.2 Voltage control . 58
6.4 Case study . 59
6.4.1 Steady state voltage stability problem – China . 59
6.4.2 Low SCR interconnection experience – Vestas . 62
6.5 Summary . 63
7 Transient issue for low short circuit ratio AC networks . 64
7.1 Problem statement . 64
7.2 Transient characteristic modelling and analysis . 65
7.2.1 Transient stability analysis tools and limitations . 65
7.2.2 Electromagnetic transient (EMT) type models . 66
7.2.3 Transient stability analysis model requirements . 67

7.3 Fault ride-through protection and control issue. 67
7.3.1 General . 67
7.3.2 Hardware protection of inverter-based resource during fault . 68
7.3.3 Unbalancing-voltage ride-through issue . 71
7.3.4 Overvoltage ride-through control strategy . 73
7.3.5 Multiple fault ride-through . 75
7.3.6 Under and over -voltage ride-through in time sequence . 78
7.3.7 Active/reactive current support of inverter-based resource during fault . 79
7.4 Operating experiences . 80
7.4.1 Operating experience – China . 80
7.4.2 Operating experience . 81
7.5 Summary . 83
8 Oscillatory instability issue for low short circuit ratio AC networks. 83
8.1 Problem statement . 83
8.2 Modelling and stability analysis . 86
8.2.1 Analysis and modelling of the inverter in the time-domain . 86
8.2.2 Analysis and modelling of the inverter in the frequency-domain . 86
8.3 Mitigation of the oscillation issues by active damping control . 93
8.4 Cases study based on the benchmark model . 94
8.5 Summary . 99
9 Conclusions . 100
Bibliography . 101

Figure 1 – Measured voltage and current curves of sub-synchronous oscillation . 15
Figure 2 – Schematic diagram of a WPP with no static or dynamic reactive support . 19
Figure 3 – Equivalent circuit representation of the WPP shown in Figure 2 . 20
Figure 4 – A typical SIPES . 24
Figure 5 – Changes of system eigenvalues, and the weakest system eigenvalue’s
damping ratio with SCR in a SIPES. 24
Figure 6 – Schematic diagram of a WPP with static reactive support plant (capacitor
banks) . 25
Figure 7 – Equivalent circuit representation of the WPP shown in Figure 6 . 25
Figure 8 – Schematic diagram of a WPP with dynamic reactive support plant
(synchronous condensers) . 26
Figure 9 – Equivalent circuit representation of the WPP shown in Figure 8 . 26
Figure 10 – Mechanism illustration of decoupling a MIPES into a set of equivalent
SIPESs . 28
Figure 11 – A typical MIPES . 29
Figure 12 – A test wind farm system that contains nine wind turbines . 33
Figure 13 – One-line diagram of 5-infeed PES . 35
Figure 14 – Eigenvalue comparison of 5-infeed PES and its 5 equivalent SIPESs . 36
Figure 15 – The 9-converter heterogeneous system with a IEEE 39-bus network
topology . 37
Figure 16 – The dominant eigenvalues and the damping ratios . 38
Figure 17 – Nearby WPP connected to the same region in a power system. 39
Figure 18 – Equivalent representation of multiple windfarms connecting to a power
system with its Z matrix . 40

– 4 – IEC TR 63401-1:2022  IEC 2022
Figure 19 – Equivalent circuit representation of two WPPs connected to the same
connection point-configuration 2 . 41
Figure 20 – Four WPPs integrated into the system with weak connections . 42
Figure 21 – Multiple WPPs connecting to the same HV bus or HV buses in close
proximity . 43
Figure 22 – Equivalent circuit representation of WPPs connecting to the same HV bus . 43
Figure 23 – Approximate equivalent representation assumed for CSCR method . 43
Figure 24 – System topology .
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