Research On Topology And Control Strategy Of Offshore Wind Farm Based On DC Grid

As an ideal location for wind power generation, offshore sea has gained widespread concerns in recent years. HVDC is the only way to transfer power in a far-sea wind farm set up over75km offshore. Since the traditional VSC-HVDC is not conducive to the setup of offshore wind farm due to its step-up transformer structure, the topological structure of the DC Grid-based offshore wind farm has replaced the original bulky low frequency transformer with the high-voltage and high-capacity DC-DC converter, hence a more simple system. This is at present a popular topic in the research of the setup of offshore wind farms. My analysis and study of the DC Grid-based offshore wind farm are categorized into the following parts:1. Analyze and summarize the recent developments of offshore wind farm and its grid connection methods; elaborate especially on the typological structure of the DC Grid-based offshore wind farm and the DC-DC converter applicable for the wind farm.2. Put forward the control strategy of the DC Grid-based offshore wind farm. Expound every converter’s movement prieiple in the system:including the mathematic model, control strategy and MPPT theory of PMSG-WT. Analyzed the id=0theory of PMSG control strategy. Analyzed two-level and three-level VSC SVPMW theory and conventional DC-DC converter in offshore wind farm.Put forward the control strategy of generator side DC-DC converter and onshore converter.3. Use MATLAB/Simulink to set up a model of DC Grid-based offshore wind farm with52.5MW wind turbines running in parallel, including PMSG-WT model,FB DC-DC model and onshore VSC model.Carry out simulation and verification of the system control strategy of selected topological structure.4. Replace the original two-level VSC in the system with three-level VSC; compare harmonic characteristics when the system is functioning properly.