Simulation Modeling And Control Strategy Research Of Photovoltaic Station Integration System With MMC-HVDC Technology

VSC-HVDC(Voltage Source Converter based High Voltage Direct Current system)is able to control active and reactive power rapidly,independently and accurately.Given the advantages of flexible control and reliable operation,VSC-HVDC is regarded as an effective method to solve the problem of renewable energy consumption in China.Modular Multilevel Converter(MMC)is one of the typical equipment in VSC-HVDC system,which has gained research focus recently.Taking PhtotVoltaic(PV)station as an example,the modeling method and control strategy of PV integration system with MMC-HVDC technology are investigated in this dissertation.The detail work is listed as follows.(1)The development and typical projects of DC transmission system are introduced.The technical characteristic of classical and flexible HVDC system is compared.The trend of VSC-HVDC system is also explained.(2)The operating characteristic of MMC and three kinds of sub-module’s structure are analyzed.Based on the above work,the control strategy to achieve stable operation of MMC is investigated.As the speed of simulation with the detailed model of MMC is very slow,the average value modeling method is adopted to replace power electronic devices in the arm of MMC with a controlled voltage source.Two terminal MMC-HVDC system is built to test the proposed control strategy.(3)The output characteristic and modeling method of PV station are analyzed.The maximum power point tracking is achieved with incremental conductance method.The configuration of PV integration system with MMC-HVDC is designed.A system level coordinated control strategy is proposed and verified with simulation.(4)The broadly used control strategies in multi-terminal HVDC system are presented.To solve the problem of power fluctuation in converter brought by renewable energy,an improved droop control strategy considering transmission loss and renewable energy fluctuation is proposed and verified with simulation.This research is conducted from equipment-level to system-level about the control strategy of PV integration system with MMC-HVDC technology.The achievement serves as a positive reference to solve the problem of renewable energy consumption.