Power Flow Modelling And Frequency Regulation Based On Dynamic Power Flow With DFIG Integrated Through VSC-HVDC

Due to the flexible control of the voltage source converter-high current(VSC-HVDC),it is widely applied to the integration of the doubly-fed induction generator(DFIG).Considering the structure and control characteristic of the DFIG and the VSC-HVDC,the unified power flow model of the DFIG integrated through the VSC-HVDC is established.With the increasing capacity of the integrated DFIG,its integration will affect the voltage and frequency stability of the power system.As for the power system with the DFIG integrated through the VSC-HVDC,the impacts of the wind power fluctuation on the voltage of the point of common coupling,and the coordinated frequency regulation by the DFIG and the VSC-HVDC on the system frequency,are analyzed.The contents of the research in this paper are summarized as below:(1)Considering the detailed model of the DFIG and multiple control modes of the VSC-HVDC,the unified power flow model of the DFIG integrated through the VSC-HVDC or the AC/VSC-HVDC is established.(2)Based on the unified power flow model,the sensitivity of the voltage of the common coupling to the reactive power output of the VSC at the DFIG side is proposed.The accuracy of the proposed sensitivity index is also verified.(3)Based on the virtual inertia control of the DC capacitor and the frquency regulation strategies using the over speed/variable pitch angle control,the dynamic power flow model of the system frequency regulation with the participation of the DFIG integrated through the VSC-HVDC is established.The scheme of the virtual inertia time constant of the DC capacitor,and the dynamic correction algorithm of the inertia time constant of the DFIG during the frequency regulation are proposed.(4)The time delay of the SG output power is further introduced to the dynamic power flow analysis on the frequency regulation.The maximum deviation of the system frequency is analyzed,and for the virtual inertia time constant of the DC capacitor,the selection of the initial value and optimization with correction based on the dynamic power flow analysis are proposed,to maximize the inertia support capability for the system frequency.