Improvement Of Control And Protection Of Flexible DC Transmission System Based On MMC

The modular multi-level converter is more widely used because of its modular design,no need to configure the filter device,good waveform quality,low switching loss,etc.,but study modular multi-level commutation The flexible DC transmission is still in its infancy.Therefore,this text is based on practical principles and deeply studies the protection strategies and control strategies of the system.First,it mainly studies and analyzes the topology and working principle of MMC,and specifically analyzes the working principle of three-phase modular multilevel converter,different working states of submodules,and modular multilevel converter.The type of neutron module.Secondly,the main structure of the system is studied,and the functions of the control system and the control systems of each layer and the structure of the controller are studied in detail.Focus on the pre-charging strategy and modulation strategy,and build the simulation model of the two-end system in the simulation software to simulate and analyze the operating characteristics of the system during steady-state operation.Thirdly,the causes of the fluctuation of the capacitor voltage and the circulation are studied in detail.The principle of the MMC loop suppression controller and the capacitor voltage equalization control are analyzed in depth.Fourthly,the steady-state operation of the system is taken as the corresponding basis,and the single-phase ground fault,the phase-to-phase short-circuit fault,the sub-module fault,and the DC ground short-circuit fault occur in the system.Therefore,on this basis,the protection control strategy is designed for the corresponding faults and the simulation is verified.