Research On Wind Power Connected To Power Grid By Fractional Frequency Transmission System

Wind power, solar power and other new environmental protection and renewable energy has become a new power system development trend. With the gradual expansion of wind power installed capacity, grid-connected wind farm has become the main form of wind power utility. Besides, wind energy resources are always away from load centers. So the transmission and grid connecting of large-capacity and long-distance wind power is of great importance and difficulty for wind power development.The thesis analyzes the problem of existing offshore wind power's transmission and grid connected model, as well as the characteristic of various wind turbines, and discusses the application of new fractional frequency transmission technology in offshore wind power. And then the offshore wind power flexible fractional frequency transmission system model:"Direct-drive Permanent Magnet synchronous wind turbine Generator (DPMG)+Fractional Frequency Transmission System (FFTS) based on matrix converter," is proposed in this thesis.In traditional design, the terminal needs Frequency Multiplication Transformer (FMT) to convert low frequency power to 50Hz power. But a lot of researches and tests indicate that there are many problems in the designing and working of FMT. Therefore a scheme based on FFTS using matrix converter, instead of FMT, which is called Flexible Fractional Frequency Transmission System (FFFTS) is studied in this thesis. A simulation model of matrix converter based on MATLAB/Simulink software package is constructed. And then the simulation model of offshore wind power flexible fractional frequency transmission system is constructed too.Based on the above model, the steady-state operation mode, especially harmonics, transmission capacity, transmission efficiency, reactive power compensation etc. are studied.The analyses in this thesis show that the FFTS based on matrix converter is a flexible and efficient combination of fractional frequency transmission technology and power electronics. This technology provides a highly potential method of transmission and grid connecting for offshore wind power with large capacity and long distance.