IEC TR 63401-4:2022

Dynamic characteristics of inverter-based resources in bulk power systems - Part 4: Behaviour of inverter-based resources in response to bulk grid faults

IEC TR 63401-4:2022 (E), which is a technical report, focuses on the fault behaviour of IBRs and performances of the existing relay protection in grids with large-scale integration of IBRs.
This document includes:
The IBR fault current requirements in present grid codes, including the requirements of active and reactive currents in positive- and negative-sequence systems during symmetrical and unsymmetrical faults.
Fault current behaviour of IBRs, including the current components in transient and fundamental frequency in different IBR topology and control schemes.
Adaptability of existing relay protection with the large-scale integration of IBRs, including the performances of distance protection, phase selector, directional relay and over-current protection.

General Information

• Status: Published
• Publication Date: 26-Jun-2022
• ICS: 29.020 - Electrical engineering in general
• Technical Committee: SC 8A - Grid Integration of Renewable Energy Generation
• Current Stage: PPUB - Publication issued
• Completion Date: 27-Jun-2022

Standards Content (sample)

IEC TR 63401-4
Edition 1.0 2022-06
TECHNICAL
REPORT
colour
inside
Dynamic characteristics of inverter-based resources in bulk power systems –
Part 4: Behaviour of inverter-based resources in response to bulk grid faults
IEC TR 63401-4:2022-06(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 63401-4
Edition 1.0 2022-06
TECHNICAL
REPORT
colour
inside
Dynamic characteristics of inverter-based resources in bulk power systems –
Part 4: Behaviour of inverter-based resources in response to bulk grid faults
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.020 ISBN 978-2-8322-3930-8

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 63401-4:2022  IEC 2022
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms, definitions and abbreviated terms ........................................................................ 8

3.1 Terms and definitions .............................................................................................. 8

3.2 Abbreviated terms ................................................................................................... 9

4 Existing requirements for fault current behaviour of IBRs ................................................. 9

4.1 Review of the present requirements ........................................................................ 9

4.2 Requirements for wind power stations and PV stations by NERC .......................... 12

4.3 Requirements for wind power stations and PV power stations in China ................. 14

4.4 Requirements for wind power stations and PV power stations in Germany ............ 17

4.5 Clause summary ................................................................................................... 19

5 Analysis on the behaviour of fault current ...................................................................... 19

5.1 Fault current needs ............................................................................................... 19

5.2 Fault current characteristics of full-scale-converter based IBRs ............................ 19

5.2.1 General ......................................................................................................... 19

5.2.2 Typical control schemes of FSC-based IBRs ................................................. 20

5.2.3 Fault current characteristics of FSC-based IBR during symmetrical fault........ 22

5.2.4 Fault current characteristics of FSC-based IBR under unsymmetrical

fault ............................................................................................................... 22

5.3 Fault current behaviour of doubly fed induction generator (DFIG) based wind

turbine (WT) .......................................................................................................... 23

5.3.1 General ......................................................................................................... 23

5.3.2 FRT solutions of DFIG-based WT .................................................................. 23

5.3.3 Fault current behaviour of DFIG-based WT during symmetrical faults ............ 26

5.3.4 Fault current behaviour of DFIG-based WT during unsymmetrical faults ........ 27

5.4 Behaviour of large-scale wind farm when outgoing line faults ................................ 27

5.5 Clause summary ................................................................................................... 32

6 Impact of IBRs on relay protection ................................................................................. 33

6.1 Influence factors of IBRs on relay protection ......................................................... 33

6.2 Impact on distance protection ............................................................................... 34

6.2.1 Basic principle of distance protection ............................................................. 34

6.2.2 Power frequency component distance relay ................................................... 36

6.2.3 Time-domain distance relay ........................................................................... 36

6.2.4 Power frequency variation component distance relay ..................................... 36

6.2.5 Phase-comparison distance relay .................................................................. 37

6.2.6 Conclusion .................................................................................................... 39

6.3 Impact on phase selector ...................................................................................... 39

6.3.1 Fault component of phase current difference based phase selector ............... 39

6.3.2 Fault component of sequence current based phase selector .......................... 41

6.3.3 Conclusion .................................................................................................... 42

6.4 Impact on directional relay .................................................................................... 42

6.4.1 Fault component of phase voltage and current based directional relay ........... 42

6.4.2 Fault component of sequence voltage and current based directional

relay .............................................................................................................. 42

6.4.3 Conclusion .................................................................................................... 44

---------------------- Page: 4 ----------------------
IEC TR 63401-4:2022  IEC 2022 – 3 –

6.5 Clause summary ................................................................................................... 45

7 Conclusions and future work .......................................................................................... 45

7.1 Conclusions .......................................................................................................... 45

7.2 Future work ........................................................................................................... 45

Annex A (informative) Expressions of DFIG-based WT's fault current .................................. 46

Bibliography .......................................................................................................................... 48

Figure 1 – Fault-ride-through profile of power-generating modules ........................................ 10

Figure 2 – Category Ⅰ Abnormal voltage ride-through requirement [2] ................................. 12

Figure 3 – Category Ⅱ Abnormal voltage ride-through requirement [2] ................................. 13

Figure 4 – Category Ⅲ Abnormal voltage ride-through requirement as amended in [2] .......... 13

Figure 5 – Under voltage ride through requirements for wind farms in China ......................... 14

Figure 6 – Under voltage ride through requirements for photovoltaic power stations in

China .................................................................................................................................... 15

Figure 7 – Over voltage ride through requirements for photovoltaic power stations in

China .................................................................................................................................... 16

Figure 8 – Voltage ride through requirements for type II power stations according to

VDE-AR-N-4120 ................................................................................................................... 17

Figure 9 – Requirements of the reactive current according to VDE-AR-N 4120 ..................... 18

Figure 10 – Typical topology of a Type-IV WT ....................................................................... 20

Figure 11 – Typical topology of a VSC-based PV inverter ..................................................... 20

Figure 12 – Diagram of basic AC current control strategy of GSC during fault ....................... 20

Figure 13 – Diagram of positive- and negative-sequence AC current control strategy of

GSC for eliminating oscillations during voltage unbalance .................................................... 21

Figure 14 – Diagram of positive- and negative-sequence AC current control strategy of

GSC for complying I1R and I2R injection requirements ......................................................... 22

Figure 15 – Typical topology of a DFIG-based WT ................................................................ 23

Figure 16 – Energy flow and ESEs of a DFIG-based WT in normal operation ........................ 24

Figure 17 – ESEs and vector control scheme of a DFIG-based WT in normal operation ........ 24

Figure 18 – FRT solutions of a DFIG-based WT during grid fault ........................................... 25

Figure 19 – FRT solutions of a DFIG-based WT during grid fault ........................................... 26

Figure 20 – The identified components of fault currents by the analytical expression ............ 26

Figure 21 – The topology of wind farm integrated to power grid in Shanxi Province .............. 28

Figure 22 – The u and i recorded when BG fault occurs at point F1 ............................. 28

OL OL

Figure 23 – The u and i recorded when BG fault occurs at point F1 ................................. 29

D D
Figure 24 – The EPSI, ENSI, EZSI of wind farm including both DFIG and PMSG based

WTs ...................................................................................................................................... 30

Figure 25 – The EPSI, ENSI, EZSI of wind farm including only DFIG based WTs .................. 31

Figure 26 – The u , i and i recorded when ABCG fault occurs at point F2 ................... 32

OL OL D

Figure 27 – General fault characteristics of wind power system ............................................ 34

Figure 28 – Diagrams of wind power integration system for distance protection .................... 35

Figure 29 – Wind power integration system ........................................................................... 37

Figure 30 – Operation performance of distance relays when the BC fault occurs at the

midpoint of DFIG wind power outgoing line ........................................................................... 38

---------------------- Page: 5 ----------------------
– 4 – IEC TR 63401-4:2022  IEC 2022

Figure 31 – Fault component network ................................................................................... 39

Figure 32 – The ratio of positive and negative sequence impedance for DFIG wind farm

when an AG fault occurs ....................................................................................................... 43

Figure 33 – Fault component of phase voltage and current based directional relay ............... 43

Figure 34 – Fault component of line to line voltage and current based directional relay......... 44

Figure 35 – Fault component of sequence voltage and current based directional relay .......... 44

Table 1 – Parameters for Figure 1 for fault-ride-through capability of power-generating

modules ................................................................................................................................ 10

Table 2 – Detailed parameters for Figure 1 for fault-ride-through capability of power-

generating modules in different countries .............................................................................. 11

Table 3 – Simulation results of distance relays when BC faults occur at different

locations of the DFIG wind power outgoing line ..................................................................... 39

Table 4 – Behaviour of traditional phase selectors under different kinds of faults .................. 41

Table 5 – Summary of adaptability of traditional relay protection ........................................... 45

Table A.1 – Fault current expressions of DFIG-based WT during symmetrical voltage

dip ........................................................................................................................................ 46

Table A.2 – Typical values and ranges of parameters in fault current expression .................. 47

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IEC TR 63401-4:2022  IEC 2022 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DYNAMIC CHARACTERISTICS OF INVERTER-BASED
RESOURCES IN BULK POWER SYSTEMS –
Part 4: Behaviour of inverter-based resources
in response to bulk grid faults
FOREWORD

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rights. IEC shall not be held responsible for identifying any or all such patent rights.

IEC TR 63401-4 has been prepared by subcommittee SC 8A: Grid Integration of renewable

energy generation, of IEC technical committee TC 8: Systems aspects of electrical energy

supply. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft TR Report on voting
8A/100/DTR 8A/104/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.
---------------------- Page: 7 ----------------------
– 6 – IEC TR 63401-4:2022  IEC 2022

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 63401 series, published under the general title Dynamic

characteristics of inverter-based resources in bulk power systems, 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.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it

contains colours which are considered to be useful for the correct understanding of its

contents. Users should therefore print this document using a colour printer.
---------------------- Page: 8 ----------------------
IEC TR 63401-4:2022  IEC 2022 – 7 –
INTRODUCTION

Wind turbines and photovoltaic based power sources employ power electronic converters. Their

controllable characteristics significantly change the behaviour of the power system to bulk grid

faults, which brings new challenges to the reliability and safety of the modern power systems.

Relay protection plays a key role in safe and stable operation of power systems for identifying

and isolating faults quickly and reliably.

Relay protection operates on electrical characteristics when a fault occurs. Legacy protection

principles are generally based on the fault characteristics of the synchronous machine. With

the large-scale integration of these inverter-based resources (IBRs) into power systems, the

diversity in IBR topologies and control strategies makes the fault behaviour turn to complex,

and the electrical characteristics in the faulted power systems are significantly changed from

the traditional. Legacy relay protections could be negatively affected.

Considering these challenges, this technical report aims at presenting the fault behaviour of

IBRs in different topologies and control strategies, and then evaluating the adaptability of

existing relay protection principles in IBR scenarios. In this report, IBRs are generally classified

as full-scale converter based IBR (including Type-IV wind turbine and PV inverter) and Type-III

wind turbine (also referred to as doubly-fed induction generator based wind turbine).

---------------------- Page: 9 ----------------------
– 8 – IEC TR 63401-4:2022  IEC 2022
DYNAMIC CHARACTERISTICS OF INVERTER-BASED
RESOURCES IN BULK POWER SYSTEMS –
Part 4: Behaviour of inverter-based resources
in response to bulk grid faults
1 Scope

This part of IEC 63401, which is a technical report, mainly focuses on the fault behaviour of

IBRs and performances of the existing relay protection in grids with large-scale integration of

IBRs.
This document mainly includes:

• The IBR fault current requirements in present grid codes, including the requirements of

active and reactive currents in positive- and negative-sequence systems during symmetrical

and unsymmetrical faults.

• Fault current behaviour of IBRs, including the current components in transient and

fundamental frequency in different IBR topology and control schemes.

Adaptability of existing relay protection with the large-scale integration of IBRs, including the

performances of distance protection, phase selector, directional relay and over-current

protection.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
---------------------- Page: 10 ----------------------
IEC TR 63401-4:2022  IEC 2022 – 9 –
3.2 Abbreviated terms
Abbreviated term Description
DER Distributed Energy Resource(s)
DFIG Doubly Fed Induction Generator
EMF Electromotive Force
ENSI Equivalent Negative-Sequence Impedance
EPS Electrical Power System
EPSI Equivalent Positive-Sequence Impedance
ESE Energy Storage Element
EZSI Equivalent Zero Sequence Impedance
FRT Fault Ride Through
FSC Full-Scale Converter
GSC Grid-Side Converter
IBR Inverter-Based Resource
I1A Positive-Sequence Active Current
I1R Positive-Sequence Reactive Current
I2A Negative-Sequence Active Current
I2R Negative -Sequence Reactive Current
MSC Machine-Side Converter
PMSG Permanent Magnet Synchronous Generator
PCC Point of Common Coupling
RCI Reactive Current Injection
RSC Rotor Side Converter
SG Synchronous Generator
WT Wind Turbine
4 Existing requirements for fault current behaviour of IBRs
4.1 Review of the present requirements

Considering the influence of IBRs during the fault, the technical requirements for connecting

IBRs to power system have been established in many countries around the world. Taking the

network code on requirements for grid connection of generators in EU as an example, the

power-generating modules must be capable of remaining connected to the network and

continuing to operate stably when a symmetrical voltage drop occurs at the point of common

coupling (PCC), unless the protection scheme for internal electrical faults requires the

disconnection of the power-generating modules from the network. The fault-ride-through

capabilities in case of asymmetrical faults must be specified [1]

Table 1 shows the parameters for Figure 1 for fault-ride-through capability of power-generating

modules and the detailed parameters in some countries are given in Table 2.
__________
Numbers in square brackets refer to the bibliography.
---------------------- Page: 11 ----------------------
– 10 – IEC TR 63401-4:2022  IEC 2022
Figure 1 – Fault-ride-through profile of power-generating modules

The diagram represents the lower limit of a voltage-against-time profile of the voltage at the

PCC, expressed as the ratio of its actual value to its reference 1 p.u. value before, during and

after the fault, U is the retained voltage at the PCC during the fault, t is the instant after

ret clear

the fault is cleared, U is the instantaneous voltage after the fault is cleared, U , U ,

clear rec1 rec2

t , t and t specify certain points of the lower limit of voltage recovery after the fault is

rec1 rec2 rec3
cleared.
Table 1 – Parameters for Figure 1 for fault-ride-through capability
of power-generating modules
Voltage parameters (p.u.) Time parameters (seconds)
U t
0-0.2 0,15-0,625
ret clear
U U + ΔU t t + Δt
clear ret 1 rec1 clear 1
U U + ΔU t t + Δt
rec1 clear 2 rec2 rec1 2
U t
U + ΔU t + Δt
rec2 rec3
rec1 3 rec2 3
---------------------- Page: 12 ----------------------
IEC TR 63401-4:2022  IEC 2022 – 11 –
Table 2 – Detailed parameters for Figure 1 for fault-ride-through capability
of power-generating modules in different countries
Requirements
Requirements for Requirements Requirements Requirements
Requirements for for wind power
wind power in for PV power in for wind power for wind power
different countries and PV power in
China China in Denmark in USA
Germany
Symmetrical
fault,
U = 0
ret
Symmetrical
fault,
U = 0,2pu U = 0 t = 150 ms U = 0,15pu
ret ret clear ret
Duration of under
U = 0
voltage ride-through ret
t = 625 ms t = 150 ms Asymmetrical t = 625 ms
clear clear clear
fault,
t = 250 ms
clear
U = 0
ret
t = 220 ms
clear
U = 1,30pu U = 1,30pu
pcc pcc
t = 500 ms t = 100 ms
uni uni
Duration of over
None None None
voltage ride-through
U = 1,20pu U = 1,24pu
pcc pcc
t = 10s t = 60s
uni uni
Symmetrical
fault,
U = 0,85pu
rec2
Symmetrical
fault,
U = 0,9pu U = 0,9pu t = 3s U = 0,9pu
rec2 rec2 rec3 rec2
Fault voltage
U = 0,9pu
recovery time rec2
t = 2s t = 2s two-phase short- t = 3s
rec3 rec3 rec3
circuit fault
t = 10s
rec3
U = 0,85pu
rec2
t = 5s
rec3
Active power
At least 30 % At least 20 % At least 10 % At least 10 %
recovery
At least 10 % P /s
P /s P /s P /s P /s
n n n n
Rate
t ≤ 60ms
res
t ≤ 150ms
adj
η<20 %
t ≤ 75ms,
res
I ≥K ×
T 1
t ≥550 ms
dur
t ≤30ms
(0,9-U )I
res
pcc n
Dynamic reactive
I ≥I
None
I ≥1,5 × T n
(U <0,9,
power capability T
pcc
t ≤60ms
ste
(0,9-U )I
1,5≤K ≤2,5)
pcc n
(0,2≤U ≤0,9)
I ≥K ×
pcc
T 2
(1,1-U )I
pcc N
(U >1,1,
pcc
0≤K ≤1,5)
UU−
1 1min
∆=u
Requirements for
positive-sequence
∆u =
and negative- None None U None None
sequence reactive
current
∆i ku⋅∆
∆i ku⋅∆
2 2
---------------------- Page: 13 ----------------------
– 12 – IEC TR 63401-4:2022  IEC 2022

where U is the voltage at the PCC in p.u., P is the rated active power output of power-

pcc n

generating modules, I is the rated current of power-generating modules, I is the reactive

n T

output current of power-generating modules, t is the uninterrupted operation time of power-

uni

generating modules, t is the response time of dynamic reactive current, t is the adjustment

res adj

time of dynamic reactive current, η is the maximum overshoot of dynamic reactive current, t

dur

is the duration time of dynamic reactive current, t is the steady time of dynamic reactive

ste
is the rated line voltage at the PCC, U is the average line voltage at the PCC
current, U
n 1min

within one minute, U is the positive-sequence voltage during the short-circuit fault, U is the

1 2

negative-sequence voltage during the short-circuit fault, Δu is the ratio of the difference

positive-sequence voltage between average line voltage to rated line voltage during the

short-circuit fault, Δu is the ratio of negative-sequence voltage to rated line voltage during the

short-circuit fault, Δi is the positive-sequence reactive current during the short-circuit fault and

Δi is the negative-sequence reactive current during the short-circuit fault, and k is the scale

factor.
Taking the technical requirements for connecting IBRs to power system
...