Analysis of Short Circuit Ratio Stability Domain of Direct-Drive Wind Farm with Hybrid-Synchronous Control Under Different Input Proportional Coefficients

With the yearly increase in wind power installation capacity, optimizing the grid-integrated converter control strategies for wind farms has emerged as an effective approach to enhance power system stability. Currently, grid-integrated converter control strategies for renewable energy can be generally divided into two categories: Grid-Following (GFL) and Grid-Forming (GFM), each facing instability risks in weak and strong grids respectively. In order to address this issue, the voltage synchronization loop of GFL is firstly combined with the power synchronization loop of GFM, considering the input proportional coefficients of the synchronization loops, to form a Hybrid-Synchronous Control (HSC) scheme for wind farm grid-integrated converters. Secondly, by comparing the mathematical model of HSC with the swing equation, it is identified that the dynamic characteristics of HSC have similarities with the operating mechanism of synchronous generator damping windings. In addition, the coupling effect is found between its inertia coefficient and damping coefficient. Subsequently, a small-signal model of HSC-based Direct-Drive Wind Farm (DDWF) is established, accounting for the input proportional coefficients. Based on the root locus analysis, the Short Circuit Ratio (SCR) stability domain of DDWF under different input proportional coefficients is studied, analyzing the dominant synchronization components that cause system instability under different SCR conditions. Finally, instability verification is conducted on the established small-signal model and stability domain results, providing theoretical guidance for ensuring the stable operation of wind farm grid-integrated converters.