Power Control of Offshore Grid by Frequency Matching for a Dfig Wind Power Farm Connected Hvdc System Under Voltage Fluctuations

The offshore wind farm is one of the green energy technologies for power production in remote areas. The effective medium of power transmission from the offshore to the far away shore grid of more than 50 Km is feasible only with the help of the HVDC link for economical purposes. This paper proposes a novel power control technique of an offshore DFIG wind power farm (ODWPF) by injection of mitigating current at the shore VSC station of an HVDC link along with constant voltage/frequency (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V} / \mathrm{f}$</tex>) operation at the auxiliary grid. The HVDC link connected offshore wind farm is equipped with a line commutated converter (LCC) at the sending end and a voltage source converter (VSC) at the end terminal. The offshore substation is operated at variable frequency and voltage, which allows the ODWPF to be operated at constant V/f operation. The speed of each turbine varies with respect to other turbines. The DFIG wind turbine can adjust the small variations in the wind speed, and thus the frequency at the offshore auxiliary grid can be controlled according to the HVDC system voltage and frequency. The complete system is simulated in the PSCAD/EMTDC environment.