Dynamic characteristics of inverter-based resources in bulk power systems - Part 2: Sub- and Super-synchronous control Interactions

IEC TR 63401-2:2022, which is a technical report, covers the "control interactions" in converter interfaced generators e.g, wind and PV with the frequency of the resulting oscillation below twice the system frequency. SSCI can be categorized into:
1) SSCI in DFIG is caused by the interaction between DFIG wind turbine converter controls and the series compensated network.
2) SSCI involving FSC (both type-4 wind turbine or PV generators) is caused by the interaction between wind turbine or solar PV's FSC controls and weak AC grid.
This technical report is organized into nine clauses. Clause 1 gives a brief introduction and highlights the scope of this document. Clause 4 presents the historical background of various types of subsynchronous oscillation (SSO) and revisits the terminologies, definitions, and classification in the context of classical SSR and emerging SSCI issues to better understand and classify the emerging interaction phenomena. Clause 5 provides the description, mechanism, and characteristics of the SSCI phenomenon in the framework of real-world incidents, including the SSCI events in the ERCOT, Guyuan, and Hami wind power systems. Clause 6 proposes two benchmark models to study the SSCI DFIG and FSC-based wind turbines or PV generators. Clause 7 gives an overview of existing and emerging modeling and stability analysis approaches to investigate the SSCI phenomenon. Clause 8 outlines various techniques to mitigate the SSCI. It discusses various SSCI mitigation schemes, such as bypassing the series capacitor, selective tripping of WTGs, generator, and plant-level damping control schemes. Clause 9 highlights the need for future works towards standardization of terms, definitions, classification, analysis methods, benchmark models, and mitigation methods.

General Information

Status
Published
Publication Date
26-Jun-2022
Current Stage
PPUB - Publication issued
Completion Date
27-Jun-2022
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IEC TR 63401-2
Edition 1.0 2022-06
TECHNICAL
REPORT
colour
inside
Dynamic characteristics of inverter-based resources in bulk power systems –
Part 2: Sub- and super-synchronous control interactions
IEC TR 63401-2:2022-06(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 63401-2
Edition 1.0 2022-06
TECHNICAL
REPORT
colour
inside
Dynamic characteristics of inverter-based resources in bulk power systems –
Part 2: Sub- and super-synchronous control interactions
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160, 27.180, 29.020 ISBN 978-2-8322-3929-2

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

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

FOREWORD ........................................................................................................................... 6

INTRODUCTION ..................................................................................................................... 8

1 Scope ............................................................................................................................ 10

2 Normative references .................................................................................................... 10

3 Terms and definitions .................................................................................................... 10

4 Terms, definitions and classification .............................................................................. 11

4.1 Existing terms, definitions and historical background ............................................ 11

4.1.1 General ......................................................................................................... 11

4.1.2 Subsynchronous resonance (SSR) ................................................................ 12

4.1.3 Device dependent SSO (DDSSO) .................................................................. 13

4.2 Necessity to revisit the terms and classification .................................................... 13

4.3 Revisiting the terms and classification .................................................................. 13

4.3.1 General ......................................................................................................... 13

4.3.2 Torsional interaction ...................................................................................... 14

4.3.3 Network resonance ........................................................................................ 15

4.3.4 Control interaction ......................................................................................... 15

4.4 Clause summary ................................................................................................... 16

5 SSCI incidents in real-world wind power systems .......................................................... 16

5.1 General ................................................................................................................. 16

5.2 SSCI in DFIGs connected to series-compensated networks .................................. 17

5.2.1 ERCOT SSCI incident in 2009 ....................................................................... 17

5.2.2 ERCOT SSCI events in 2017 ......................................................................... 18

5.2.3 SSCI events in Guyuan wind power system ................................................... 20

5.3 SSCI in FSC-based generators connected to weak AC network ............................ 24

5.3.1 SSCI event in Hami wind power system ......................................................... 24

5.4 Clause summary ................................................................................................... 27

6 Modeling and analysis approaches ................................................................................ 28

6.1 Preview ................................................................................................................. 28

6.2 Time-domain modeling and analysis approaches .................................................. 28

6.2.1 General ......................................................................................................... 28

6.2.2 Nonlinear time-domain EMT simulation .......................................................... 28

6.2.3 Controller hardware-in-the-loop simulation ..................................................... 28

6.2.4 Linearized state-space modeling and modal analysis ..................................... 29

6.2.5 Discussions on time-domain approaches for SSCI studies ............................. 30

6.3 Frequency-domain modeling and analysis approaches .......................................... 30

6.3.1 Frequency scanning ...................................................................................... 30

6.3.2 Complex torque coefficient method ................................................................ 31

6.3.3 Impedance-based modeling and analysis ....................................................... 33

6.4 Guidelines on the approaches to SSCI studies ...................................................... 39

6.5 Clause summary ................................................................................................... 40

7 Proposed benchmark models ......................................................................................... 40

7.1 Overview............................................................................................................... 40

7.2 Benchmark model based on Guyuan wind power system ...................................... 40

7.2.1 General ......................................................................................................... 40

7.2.2 Configuration and parameters of the WTGs and Guyuan substation ............... 41

7.2.3 Parameters of the DFIG's converter control ................................................... 41

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IEC TR 63401-2:2022  IEC 2022 – 3 –

7.2.4 Series-compensated electrical network .......................................................... 41

7.2.5 Case study .................................................................................................... 41

7.3 Benchmark model based on Hami wind power system .......................................... 42

7.3.1 General ......................................................................................................... 42

7.3.2 Configuration and parameters of FSCs .......................................................... 43

7.3.3 Configuration and parameters of LCC-HVDC ................................................. 43

7.3.4 Synchronous generators ................................................................................ 45

7.3.5 Electrical network .......................................................................................... 45

7.3.6 Case studies .................................................................................................. 45

7.4 Clause summary ................................................................................................... 46

8 Mitigation methods ........................................................................................................ 46

8.1 General ................................................................................................................. 46

8.2 Bypassing the series capacitor .............................................................................. 47

8.3 Selective tripping of WTGs .................................................................................... 47

8.4 Network/Grid-side subsynchronous damping controller (GSDC) ............................ 48

8.5 Generation-side subsynchronous mitigation schemes ........................................... 50

8.5.1 Adjusting the wind turbine converter control parameters ................................ 50

8.5.2 Adding an SSDC in the RSC control loop ....................................................... 51

8.5.3 Adding an SSDC in the GSC control loop ...................................................... 53

8.6 Protection schemes .............................................................................................. 54

8.7 Clause summary ................................................................................................... 54

9 Future work ................................................................................................................... 54

Annex A (Informative) ........................................................................................................... 56

Bibliography .......................................................................................................................... 60

Figure 1 – Multi-frequency oscillations in the modern power system with high-share of

renewables and power electronic converters ......................................................................... 10

Figure 2 – Timeline of the historical developments of SSO terms, definitions and

classification [12] .................................................................................................................. 11

Figure 3 – Terms and classification of SSR by IEEE [13] ...................................................... 12

Figure 4 – Classification of subsynchronous interaction based on the origin [12]................... 14

Figure 5 – Reclassification of subsynchronous interactions based on the interaction

mechanism ........................................................................................................................... 14

Figure 6 – Timeline of SSCI events reported around the world .............................................. 16

Figure 7 – Structure of the ERCOT wind power system in 2009 [16]...................................... 17

Figure 8 – Oscilloscope record of the 2009 SSCI event in the ERCOT system [19] ............... 18

Figure 9 – Structure of the ERCOT wind power system in 2017 [24]...................................... 18

Figure 10 – Event#1 August 24, 2017: current, voltage and frequency spectrum of the

current during the SSCI event and after bypassing the series capacitor [24] ......................... 19

Figure 11 – Event#2 September 27, 2017: current, voltage and frequency spectrum of

the current during the SSCI event [24] .................................................................................. 20

Figure 12 – Event#3 October 27, 2017: current, voltage and frequency spectrum of the

current during the SSCI event [24] ........................................................................................ 20

Figure 13 – Geographical layout of the Guyuan wind power system, Hebei Province,

China .................................................................................................................................... 21

Figure 14 – Power flow measured at the 200 kV side of the Guyuan step-up

transformer ........................................................................................................................... 22

Figure 15 – Field recorded line current and frequency spectrum ........................................... 22

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– 4 – IEC TR 63401-2:2022  IEC 2022

Figure 16 – Field recorded voltage and frequency spectrum ................................................. 23

Figure 17 – Hami wind power system, Xinjiang, China [27] ................................................... 24

Figure 18 – Current (upper plot) and active power (lower plot) .............................................. 25

Figure 19 – Frequency spectrum of the current (upper plot) and active power (lower

plot) ...................................................................................................................................... 25

Figure 20 – Field measured active power of a wind farm (a) From 09:46 to 09:47 (b)

From 11:52 to 11:53.............................................................................................................. 26

Figure 21 – Torsional modes and frequency variation of the unstable oscillation ................... 26

Figure 22 – Torsional speed of modes 1 to 3 of unit #2 in Plant M ........................................ 27

Figure 23 – Configuration of CHIL simulation ........................................................................ 29

Figure 24 – Three-phase subsystem represented in the dq domain using equivalent

small-signal impedance......................................................................................................... 34

Figure 25 – Three-phase subsystem represented in the sequence domain using

equivalent small-signal impedance ........................................................................................ 34

Figure 26 – Impedance measurement in a simple system ..................................................... 36

Figure 27 – A simple system in the impedance model, consisting of two separable

components: source and load ............................................................................................... 38

Figure 28 – Impedance model with voltage and current as input and output of the

source and load sides; system stability is determined by the two transfer function

matrices, Z (s) and Z (s) ....................................................................................................... 38

s l

Figure 29 – The unified dq-frame INM of a typical power system ........................................... 38

Figure 30 – Recommended guidelines for the SSCI stability analysis of a real-world

wind power system ............................................................................................................... 40

Figure 31 – One-line diagram of the proposed benchmark model adopted from the

Guyuan wind power system .................................................................................................. 41

Figure 32 – Simulation results of benchmark model (a) phase A current (b) frequency

spectrum of the current (c) subsynchronous current component ............................................ 42

Figure 33 – One-line diagram of the proposed benchmark model adopted from the

Hami wind power system ...................................................................................................... 42

Figure 34 – The structure of the LCC HVDC system ............................................................. 43

Figure 35 – AC filters and reactive power compensations ..................................................... 44

Figure 36 – Three tuned DC filtersTT12/24/45 ...................................................................... 44

Figure 37 – The common electrical network .......................................................................... 45

Figure 38 – SSO in the second benchmark model (a) the SG rotor speed (b)

subsynchronous frequency component in the speed (c) time-frequency analysis of the

rotor speed ........................................................................................................................... 46

Figure 39 – A system-wide SSCI mitigation scheme based on selective tripping of

WTGs ................................................................................................................................... 48

Figure 40 – (a) A series-compensated wind power system with GSDC (b) design and

configuration of GSDC including SSDC and SCG .................................................................. 49

Figure 41 – CHIL test results of GSDC (a) active power (b) subsynchronous current ............ 50

Figure 42 – SSCI mitigation by increasing the K of the inner controllers of the GSC

(a) voltage at PCC (b) current phase-A (c) active and reactive power ................................... 51

Figure 43 – SSCI mitigation by reducing the PLL bandwidth (a) voltage at PCC (b)

current phase-A (c) active and reactive power ...................................................................... 51

Figure 44 – Control diagram of the virtual resistor for DFIG's RSC controllers ...................... 52

Figure 45 – The SSCI damped out when the virtual resistor is enabled at 2 seconds in

simulation (a) voltage at PCC (b) current phase-A (c) active and reactive power ................... 52

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IEC TR 63401-2:2022  IEC 2022 – 5 –

Figure 46 – Control diagram of GSC of a typical FSC wind turbine ........................................ 53

Figure 47 – The SSCI mitigated after the virtual resistor is switched-on (a) voltage at

PCC (b) current phase-A (c) active and reactive power ......................................................... 53

Table 1 – Comparison of the characteristics of real-world SSCI events ................................. 27

Table 2 – Main Features of time-domain approaches for SSCI studies .................................. 30

Table A.1 – Number of DFIGs in the wind farms of Guyuan system ....................................... 56

Table A.2 – DFIG and step-up transformer parameters (Base capacity = 1,5 MW) ................ 56

Table A.3 – GSC control parameters ..................................................................................... 56

Table A.4 – RSC control parameters ..................................................................................... 57

Table A.5 – Transmission lines and their parameters in Guyuan wind power system ............. 57

Table A.6 – Electrical parameters of the VSC ....................................................................... 57

Table A.7 – Specific parameters of the converter transformer ............................................... 57

Table A.8 – Parameters of AC filters on the rectifier side (800 MW) ...................................... 58

Table A.9 – Parameters of AC filters on the inverter side (800 MW) ...................................... 58

Table A.10 – The control parameters of the LCC-HVDC system ............................................ 58

Table A.11 – The rated parameters and electrical parameters of the synchronous

generator .............................................................................................................................. 59

Table A.12 – 660 MW steam turbine shafting equivalent lumped parameters ........................ 59

Table A.13 – The common electrical network parameters (500 kV transmission line) ............ 59

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– 6 – IEC TR 63401-2:2022  IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DYNAMIC CHARACTERISTICS OF INVERTER-BASED
RESOURCES IN BULK POWER SYSTEMS –
Part 2: Sub- and super-synchronous control interactions
FOREWORD

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IEC TR 63401-2 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/99/DTR 8A/103/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: 8 ----------------------
IEC TR 63401-2:2022  IEC 2022 – 7 –

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.

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---------------------- Page: 9 ----------------------
– 8 – IEC TR 63401-2:2022  IEC 2022
INTRODUCTION

Advancements in power electronic converters have led to an increased proportion of converter

based renewable power generators in modern electric power systems. Power electronic

converters use multi-time scale converter control structures to achieve smooth grid connection.

Such control interactions cause oscillation with the frequency ranging from a few hertz to

several kilohertz, which can interact with other converter-based devices or system components

such as static compensators (STATCOM), series capacitors and weak AC grids. The

interactions of converter control with series-compensated or weak AC grid cause oscillation in

the subsynchronous and its complementary supper synchronous frequency ranges, named as

sub- and super-synchronous control interaction or simply sub-synchronous control interaction

(SSCI).

In the past decade, several incidents have been reported where wind turbine and photovoltaic

(PV) converter controls interacted with series-compensated or weak AC grids at

subsynchronous and/or supersynchronous frequencies. Post-event investigations have shown

that the converter controls actively participate in these interactions. Unlike classical sub-

synchronous resonance (SSR), SSCI is a system-wide phenomenon rather than a localized

converter control issue. The mechanism and characteristics of SSCI are greatly influenced by

converter control structures and parameters, generation resource intermittency, network

topology change, grid strength, etc. Such factors distinguish the converter control participated

interactions in converter-based generators from the classic SSR phenomenon associated with

the conventional power generators. The oscillation caused by SSCI seriously threatens the

stable and reliable operation of wind power systems.

Power systems with high-penetration of power electronic converters face a variety of oscillatory

stability issues. Power electronic converter-based components such as converter-based wind

turbine generators (WTGs), photovoltaic (PV), flexible AC transmission system (FACTS) and

high voltage DC (HVDC) can interact with each other and/or with the series-compensated or

weak AC networks. As a result of such interactions, oscillation from a few hertz to tens or

hundreds of hertz could be triggered, as illustrated in Figure 1.

The interaction between doubly-fed induction generators (DFIGs) and series compensated

transmission lines was first reported in the electric reliability council of Texas (ERCOT) wind

power system in 2009. The frequency of triggered oscillation was 20 Hz to 30 Hz. Later on, from

2010 to 2016, frequent oscillation events were reported between DFIG and series-compensated

network in the Guyuan system located in Hebei, China. In 2015, a new type of interaction was

reported in the Hami wind power system in Western China. Post-event investigations showed

that the full-scale converter (FSC) interacted with the weak AC grid causing strong sub- and

super-synchronous oscillation. The frequency of oscillation originating from the FSC wind

turbines matched with the shafts' natural frequencies of the nearby steam turbine generators,

which resulted in intense torsional vibrations. In 2019, a power out
...

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