Reliability Improvement of GFM Inverters: Diagnosing DC‐Side Instability Mechanisms and Overvoltage Faults Induced by PV and ESS

ABSTRACT

Integration of the grid‐forming inverter is critical for the stability of future power grids, but their stability in the presence of large disturbance remains a challenge. Most of the existing stability analyses neglect or simplify the DC‐side dynamics, even though this may be one of the main sources of instability of the whole system. Given this gap, the understanding of the limits of the system can often be incomplete and may obscure some important failure risks. This paper addresses the transient stability of GFM inverters deeply, considering the contribution of the DC side to the system. The authors presented a comprehensive model that integrates electrical AC side behaviour with the physical dynamics of an energy storage system and a photovoltaic source. This new framework addresses these previously overlooked issues and reveals how instability problems can originate from the DC side. Results from this study show that reducing the capacity of the ESS actually enhances stability, owing to the fact that it helps to dampen the oscillations resulting from an aggressive control strategy. It also points out one risk: high PV generation could actually threaten stability. A large surplus of DC power during an AC fault could result in overvoltage on the DC link, possibly leading to loss of synchrony and inability to recover by the system. Thus, this research provides a more precise way to assess the stability of GFM inverters. The findings are supported by detailed simulations and are further validated by experiments showing the existence of such DC‐driven instability risks.