Ensuring Resilience in Grid-Forming Photovoltaic Systems: Modeling and Mitigation of Temporary Overvoltages

This paper presents a comprehensive modeling and simulation framework for evaluating temporary overvoltage (TOV) risks in photovoltaic (PV) systems utilizing grid-forming inverters (GFM). A significant research gap exists in understanding TOV behavior in GFM plants, particularly in relation to the integration of transformer grounding, inverter control types, and system conditions. This study systematically analyzes the three primary sources of TOV: ground faults, load rejection, and hybrid scenarios under multiple GFM control modes, including virtual synchronous machine (VSM), droop, dispatchable virtual oscillator control (dVOC), and synchronized reference frame phase locked loop (SRF-PLL). Using detailed electromagnetic transient simulations, this work quantifies the distinct overvoltage responses and stability margins of each control strategy during these critical events. The study further explores the critical influence of the main power transformer (MPT) grounding configurations, demonstrating the inherent trade-off between the magnitude of the fault current and the severity of the overvoltage. Based on these findings, the paper proposes and evaluates practical, system-level mitigation strategies, such as optimized impedance grounding and mechanically interlocked grounding switches, to suppress overvoltages without compromising system stability. The results provide crucial insights for system design, highlighting that while GFM inverters enhance grid support, their fault response diverges from synchronous machines and demands tailored protection and grounding designs. This work bridges the gap between theoretical GFM control and real-world power system resilience, offering actionable guidance for the secure integration of inverter-based resources.