Integrating Offshore Wind Power Via Fractional Frequency Transmission System

A novel solution to integrating offshore wind power via the fractional frequency transmission system (FFTS) is introduced in this paper. The basic idea of FFTS is to improve the technical and economic performance of ac transmission systems by lowering the grid frequency. FFTS is especially suitable for transmitting offshore wind power because the low frequency dramatically reduces the charging current in the cable. In addition, as a novel ac transmission system, FFTS performs much better than HVDC in constructing a multiterminal (MT) grid. The basic structures and characteristics of a typical PMSG-based FFTS offshore wind power system and a MT-FFTS offshore grid are described first. Then two offshore wind power cases are used to compare the technical and economical pros and cons of the FFTS solution with the conventional solutions: HVAC and HVDC. The feasibility studies show that the performance of FFTS offshore wind power system is superior to that of HVAC and HVDC in both point-to-point (PP) and multiterminal cases. The uniform annual value of PP-FFTS and MT-FFTS is 5.01% and 5.07% cheaper than PP-HVDC and MT-HVDC. Therefore, FFTS is a promising solution to offshore wind power integration and building offshore grids.