Abstract
Fractional frequency transmission system (FFTS) is a relatively new transmission technology that can be used to deliver the energy from remote offshore wind farms, and it can increase the transmission capacity through the reduced transmission frequency. However, the dynamic performance of a FFTS with the wind farm may be different from that of a traditional ac transmission with the wind farm. In this paper, a doubly fed induction generator (DFIG)-based wind farm is connected to the main grid via the FFTS. The detailed dynamic model of the FFTS with wind farm is established first, and then the eigenvalue analysis is carried out to evaluate the system dynamic damping performance. To verify the results of eigenvalue analysis, dynamic simulations are carried out on a single machine infinite bus and a multimachine system. Both eigenvalue analysis and simulations demonstrate that the FFTS will have a negative influence on the damping of the DFIG-based wind farm in comparison to that of the wind farm with the traditional ac transmission system. However, with the control of cycloconverter, this problem can be easily overcome, and the damping performance of wind farm with FFTS can be even better.
Highlights
W IND energy is considered to be one of the widely used renewable energy sources
Ids iq s idg iq g where Vs ∠φ1 is the voltage angle of the doubly fed induction generator (DFIG); Vl ∠φ2 is the voltage angle at the low frequency side of the cycloconverter; XT L is the combined reactance of the transmission line and the transformer; RT L is the combined resistance of the transmission line and the transformer
This paper has applied the Fractional frequency transmission system (FFTS) to deliver the power generated by a DFIG-based offshore wind farm to the main transmission grid
Summary
The delivery of energy from remote offshore wind farms to the transmission grid becomes a big challenge. To cope with this challenge, a few transmission system schemes have been proposed, such as high voltage alternating current system (HVAC), high voltage direct current system (HVDC) and fractional frequency transmission system (FFTS). The FFTS is chosen to deliver the remote offshore wind energy to the main grid.
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