Large-Signal Stability Analysis of Grid-Forming Wind Turbine Connected to DRU-HVDC

This paper investigates the large-signal stability of the grid-forming wind turbines connected to diode-rectifier-unit based high voltage direct current system. The nonlinear differential equation model of the system incorporating current limitation dynamic is analytically developed. Based on the model, theoretical analysis is carried out to prove the existence and uniqueness of the equilibrium point under the symmetrical voltage drop, highlighting the superiority of the q-axis priority current limitation and phase locked loop-based frequency control. Furthermore, the large-signal stability region (LSSR) is defined and constructed based on the domain of attraction estimated using Takagi-Sugeno method. The LSSR provides an intuitive control parameter range that ensures large-signal stability, considering the combined effects of various control parameters. Simulations carried out in PSCAD/EMTDC validate the effectiveness of the large-signal stability analysis.