| HVDC based on voltage source converter(VSC-HVDC) is one of the important fields of research and construction in power electronics and power systems recently,and it has great advantages in solving the long-distance transmission, sea-crossing cable, in interconnecting asynchronous power grid of ac system, in protecting the environment and so on. A new cascade multilevel converter, the modular multilevel converter MMC with its unique advantages has received the widespread research and application in the field of high voltage power.The modulation method and control strategy of applying MMC to HVDC based on voltage source converter through analyzing the working characteristic of HVDC based on voltage source converter and the new cascade multilevel converter MMC,and by building the mathematical model to design the control system has been presented. Finally, the simulation example is employed to illustrate the validity of the applied modulation method, mathematical model and control strategy. To be specific, the main contents of this dissertation are as follows:Working principle and control strategy of VSC-HVDC system, and deduced the mathematical model of VSC-HVDC are introduced in detail;MMC in new cascade multilevel converter is analyzed the basic structure and operation mechanism, and established the mathematical model of MMC converter;MMC converter control strategy is discussed and the modulation method, sub modules of capacitance voltage equilibrium problem is studied, and on this basis, construct the MMC converter control structure as a whole;Finally through the building up of the simulation model MMC converter and VSC-HVDC system in Matlab/Simulink, respectively, inverter and rectifier simulation test was carried out on the MMC converter, and the normal and fault simulation experiment of the VSC-HVDC system based on MMC converter control was carried out. |
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