Virtual Synchronous Machine Testing and System Split Resilience: A Comparative Analysis with Grid-Following PV Inverters

The increasing penetration of converter-interfaced generation raises critical concerns for power system stability, especially during rapid transients and system split events that are not yet adequately addressed in current grid code compliance tests. This paper assesses the resilience of a Virtual Synchronous Machine (VSM) compared with a grid-following photovoltaic (PV) inverter using a combined framework of standardized benchmark tests and realistic system-split scenarios. In benchmark testing, the VSM provided synthetic inertia by delivering a transient power burst from 0.30 p.u. to 0.545 p.u. under a -0.4 Hz/s frequency ramp, corresponding to an equivalent inertia constant of approximately 15s. With the Limited Frequency Sensitive Mode-Underfrequency (LFSM-U) function enabled, it sustained additional active power up to 0.61 p.u. once the frequency fell below 49.8Hz. The PV inverter, by contrast, demonstrated compliance with conventional grid requirements: it curtailed power through LFSM-O during overfrequency conditions. It injected 0.25 p.u. of reactive current during a fault ride-through (FRT) event at 1.129 p.u. voltage. In system-split tests, the VSM absorbed surplus PV generation, stabilizing frequency after a transient rise to 52.8 Hz and preventing voltage excursions exceeding 1.2 p.u. During imbalance stress, it absorbed 1.266 MW against its 1.0~MW rating, corresponding to a 26.6 % overload. These results demonstrate that while the PV inverter contributes valuable voltage support, only the grid-forming VSM maintains frequency stability and ensures secure islanded operation. The novelty of this study lies in integrating standardized compliance tests with system-split scenarios, thereby providing a comprehensive framework for evaluating grid-forming controls from both regulatory and resilience-oriented perspectives and informing the evolution of future grid codes.