Pitch Angle and Droop-Virtual Inertia Coordinated Control of DFIG in Hybrid AC/DC Grid: Dynamic Frequency Regulation with Stability Guarantees

Under the prospect of dual-carbon goals, China actively promotes the integration of new energy power. Long distance wind power should use flexible DC transmission technology connecting to traditional grid to reduce transmission loss. Its latest common technology is the flexible DC transmission system (MMC-HVDC) function on the use of modular multilevel converter. Nowadays, the most used wind power generator is doubly-fed induction generator (DFIG). Due to its inherent frequency regulation capability, it's unable to participate in frequency regulation, which will lead to the decline of the stability of the power system. Therefore, the impact from high proportion wind turbine integration on the stability of the grid cannot be ignored. In this paper, the information of flexible DC transmission and doubly fed wind turbine is summarized, including its background and research status. A simulated system is set up in MATLAB/simulink to study its negative impact from wind turbines connected to the AC/DC hybrid grid on the frequency stability of the power system and then coordinated control strategy combining frequency modulation control to the DFIG for its participation in frequency control. The results verify two key findings that wind turbine connected to the power system, the frequency stability of its grid can be reduced and if wind turbine adjunct with an additional frequency stability control, the frequency stability of the grid will be improved.