Bifurcation and synchronization stability analysis for PMSG-based wind farm with VSC-HVDC system

A nonlinear model is developed to describe the sophisticated dynamic behavior of PMSG based wind farm with VSC-HVDC for studying the synchronization characteristics of sending-end interconnected system, which includes the grid-side converter (GSC) of wind farm and the wind farm-side VSC (WFVSC). The proposed model retains the full nonlinearity of aforementioned interconnected system, unlike conventional small-signal methods, thus revealing how WFVSC control dynamics govern the synchronization characteristics of system. It is shown that two feedback loops incorporating sine and cosine functions may exist for the PLL of GSC, owing to the presence of PLL phase-locking errors. And those feedback loops are closely correlated with the control dynamics of WFVSC, indicating that the control dynamics of WFVSC directly affect the synchronization stability of interconnected system. Theoretical analysis results demonstrate that the interconnected system exhibits two types of bifurcations: saddle-node bifurcation (SNB) and Hopf bifurcation, due to the existence of sine and cosine nonlinear terms. Furthermore, participation factors of bifurcations are identified, and the influence law of key control parameters on bifurcation characteristics is summarized. Finally, simulation results are provided to verify the correctness of theoretical analysis.