A Network-Side Assessment Framework and Benchmark System for Weak-Grid PMSG-Based Subsynchronous Oscillations

The increasing integration of Type-4 wind farms (WFs) based on permanent magnet synchronous generators (PMSGs) into weak AC networks has raised stability concerns, particularly subsynchronous oscillations (SSOs), referred to as weak-grid PMSG-SSOs (WG-PMSG-SSOs). Despite their growing relevance, current standards lack explicit screening criteria, and most existing studies rely on simplified single-WF models with limited consideration of network-side factors' effects. This article proposes a simulation-based framework to systematically evaluate WG-PMSG-SSO risk by combining dynamic frequency scanning of PMSG-based WFs with time-domain electromagnetic transient (EMT) simulations. Two key screening indicators are identified: the presence of a negative damping in the WF impedance profile and low grid strength, quantified by short-circuit ratio (SCR) and network Thevenin impedance at the point of common coupling. A regime-based interpretation is further established, distinguishing between disturbance-triggered and self-excited WG-PMSG-SSO conditions as a function of SCR. A benchmark model based on the IEEE 39-bus system is developed to generate over 10 000 realistic WG-PMSG-SSO scenarios, with oscillation frequencies between 36 and 55 Hz and magnitudes up to 37% of the fundamental current. Analysis results demonstrate that network strength and WF location dominate WG-PMSG-SSO severity, while fault type, location, impedance, and clearing time primarily influence oscillation triggering near the stability boundary, with minimal impact on oscillation frequency and severity once excited. Based on these findings, practical planning, and operational guidelines are proposed to reduce WG-PMSG-SSO risk in weak grids, emphasizing network strength reinforcement, key screening metrics, and the identification of worst-case operating conditions.