Grid integration of DFIG-based offshore wind farms with hybrid HVDC connection

This paper proposes a new HVDC (High-Voltage dc) transmission topology, its modeling and control method, used for large Doubly-fed Induction Generator (DFIG)-based offshore wind farms. The sending end is a Line Commutated Converter (LCC) with a STATCOM (Static Compensator) while the receiving end is a Current Source Inverter (CSI) using IGBTs. The STATCOM provides stator voltage support for DFIGs, as well as commutation voltage for the LCC. The LCC regulates the active power produced by DFIG wind farms, and transmits it to the onshore inverter through HVDC link. Working in constant voltage control mode, the inverter then feeds the active power into the main ac grid. Simulations verify that, as a combination of existing LCC-HVDC and VSC (Voltage Source Converter)-HVDC technologies, the proposed system not only has the black start capability, possesses fast active power dynamics, but also can provide independent reactive support to the grid.