Transient Compensation of Asymmetrical Line Faults in Multigrid-Forming VSG Systems

Abstract

Grid-forming virtual synchronous generators (VSGs) operate by aligning their phase angle with that of the main grid to facilitate power transmission. The effectiveness of grid-forming control is influenced by the line impedance angle. Asymmetrical line faults (ALFs) are a common challenge in power systems, leading to significant fluctuations in power angle and voltage within VSG formations, which could potentially result in grid collapse. To address these issues, this study proposes transient compensation techniques designed to enhance resilience in ALF scenarios. First, we present an incremental power angle compensation (IPAC) method to enhance traditional VSG configurations, specifically addressing power angle instability during ALFs. Furthermore, we propose a three-phase synchronous rotating coordinate transformation to develop positive sequence transient current compensation (PSTCC) and offset transient current compensation (OTCC), which together help mitigate excessive transient currents during ALFs. Experimental validation conducted through hardware-in-the-loop simulations with three parallel VSGs demonstrated a significant improvement in active power response times (from 83.3% to 87.5%) and a notable reduction in short-circuit transient currents (ranging from 31.7% to 95%), effectively preventing power oscillations following fault recovery. Additionally, a prototype tested in single-phase grounding experiments further highlights the effectiveness of the proposed enhancements.