Wind Power Transmission through LCC-HVDC with Wind Turbine Inertial and Primary Frequency Supports

This paper investigates the control design when a wind power base of doubly fed induction generators (DFIGs) is directly connected to line-commutated converter (LCC) HVDC link. Firstly, the positive feedback characteristic of PLL in DFIG is analyzed, which allows DFIG to self-maintain frequency without an available grid voltage reference. Furthermore, in order to avoid the rapid variation of HVDC power flow when some disturbances happened to the local system, it is proposed that the local inertial and primary frequency supports are provided by wind turbines, and the LCC-HVDC link is only responsible for transmitting wind power to the main grid. The dynamic performances of an aggregated DFIG in island operation, and operating with HVDC are demonstrated by the simulation results. Satisfactory responses verify the feasibility and effectiveness of the proposed control strategy.