Study On Multi-terminal HVDC Transmission For Offshore Wind Power Generation Based On Reduced Matrix Converter

Offshore wind power generation with abundant resources, less environmentalpollution, steady wind, low turbulence, small wind shear and other advantages, inrecent years, it has become the focus of the renewable energy development. Forlong-distance transmission of offshore wind energy, the use of high-voltage directcurrent transmission is more economical, more reliable and more stable than Highvoltage AC, Offshore wind power generation and high voltage direct current (HVDC)will be an important development trend in energy transmission.With an installedcapacity of offshore wind farms continue to increase, Affected by the transmissiondistance, maintenance costs and other factors, coupled with wind turbine sitingdifficulties, limited installation space, in addition, considering the complexity ofmarine environment,offshore wind power HVDC transmission Made high demandsto the inverter’s weight, volume and dependability.Reduced matrix converter is a new energy converter and called RMC for short.with compact construction, Easy to control, excellent input/output performance.converter constituted by RMC with high power density, less conversion stages andhigher reliability, possess great application value in offshore wind-HVDC system. Inrecent years, scholars studied its modulation strategies、commutation technology、loss analysis and application on offshore wind-HVDC systems， has made someprogress. But based on RMC offshore wind-HVDC system with a focus on dual-porttopology，For its control strategy studies have only one port for research (sea RMCinverter port or shore grid inverter port). No making in-depth study on thecoordinated control of RMC-HVDC system under the variety of conditions and gridfault.This article describes the RMC inverter topology and working principle,comparing their own characteristics of the voltage source RMC inverter and currentsource RMC inverter, analysis the bi-polar voltage space vector pulse-widthmodulation， established based on RMC offshore wind power HVDC transmissionsystem， proposed control strategy based on RMC offshore wind-HVDC system.achieve the maximum wind energy capture of wind turbines, HVDC grid inverteractive/reactive power decoupling control. when grid voltage drop caused HVDC transmission system active power imbalance, Using super capacitor the rapidcharge-discharge capacity, Proposed super capacitor energy storage port bi-directionalDC-DC converter control strategy. DC-DC converter charge to super capacitoraccording to the DC voltage change in real time. HVDC transmission system achievepower dynamic balance, Strengthen the ability of low voltage ride through, andenhance the reliability and stability of the system. Simulation experimentationdemonstrates its accuracy and feasibility.