Seamless Transitions between Grid-Following and Grid-Forming Control for Wind Turbines: A Novel Switching Metric and Smooth Control Strategy

Abstract

As the proportion of wind power within the energy grid increases, the grid's strength diminishes, thereby exacerbating the stability challenges faced by conventional grid-following (GFL) wind turbines (WTs). Research has demonstrated that grid-forming (GFM) control offers superior stability in weak grid environments. Consequently, it is crucial to explore a switching control strategy for GFL/GFM WTs to enhance their adaptability to varying grid strengths. However, the switching process can induce overvoltage and overcurrent issues, potentially causing irreversible damage to hardware components. In response, this paper proposes a seamless switching control strategy to enhance the system's stability and safety in complex environments. Initially, the study employs eigenvalue analysis to examine the grid-integrated characteristics of GFL and GFM units. Based on the analysis, a novel switching metric is defined. Additionally, a smooth switching control strategy is introduced to mitigate the overcurrent phenomenon during the transition by compensating for voltage and frequency through a consistency algorithm. Experimental results indicate that the proposed switching metric and smoothing control strategy more accurately assess the switching requirements of WTs across different operational modes, significantly reducing switching time compared to traditional methods. Furthermore, the new switching metric and smoothing control strategy markedly enhance the system's switching performance indices.

Keywords: Grid-forming control, Grid-following control, Smooth switching control, Switching metrics, Event triggering mechanism, Consistency algorithm