Transient Stability Analysis and Enhancement of Grid-Forming and Grid-Following Converters
Authors: Chenhang Xu; Zhixiang Zou; Jiajun Yang; Zheng Wang; Wu Chen; Giampaolo Buticchi
Extended Abstract:
The increasing integration of grid-following (GFL) converters in modern power systems has sparked concerns regarding transient stability, particularly due to the risk of loss of synchronization (LOS). In contrast, grid-forming (GFM) converters are gaining traction as a means to bolster system stability. However, the majority of existing research primarily focuses on individual converter analysis, with hybrid systems that integrate both GFL and GFM converters remaining largely unexplored. To address this research gap, this study introduces an aggregated swing equation model tailored for heterogeneous converter systems. This model provides insights into their transient dynamics and interaction mechanisms.
Through the aggregated model, the study reveals two distinct types of LOS in GFL converters: accelerating-type and decelerating-type, which are contingent upon their current injection commands. Furthermore, it elucidates the stabilizing influence of incorporating GFM converters into the system. A systematic investigation into the impact of parameters and power commands on stability reveals that, during accelerating-type LOS scenarios, augmenting the active power absorption by GFM converters effectively alleviates system power imbalance. Conversely, in decelerating-type LOS scenarios, boosting active power injection from GFM converters notably enhances transient stability margins.
Moreover, this study analytically derives an equivalent stability criterion that governs the interactions between heterogeneous converters. Leveraging these insights, an adaptive power control strategy for GFM converters is proposed. This communication-free approach facilitates precise and rapid stabilization across diverse operating conditions by adaptively compensating for the power imbalances of GFL-renewable energy source (RES) converters with GFM-energy storage system (ESS) converters. Consequently, this strategy augments the transient stability metrics of the system, achieving a remarkable 110% increase in the system stability margin, as validated through rigorous hardware-in-loop experiments.
