JWG 5 - TC 8/SC 8A/JWG 5

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

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.

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.