Design Of Unified Power Flow Controller Based On Modular Multilevel

With the continuous development of the power grid,a safe and reliable power grid not only plays an important role in energy security,but also provides an important guarantee for the stable development of society.my country has a vast territory,complex terrain,uneven distribution of energy,and uneven distribution of electricity demand.Therefore,there are higher requirements for the load and scale of the power grid.Unified Power Flow Controller(UPFC),as the most advanced and universal flexible AC transmission equipment in today’s society,combines the advantages of parallel and series flexible AC transmission devices,especially the multi-level module(The gradual development of Modular Multilevel Converter(MMC)type voltage source converter has made the MMC type UPFC a research and academic hotspot,and it has become a unified power flow controller with the most development potential.The MMC circuit is highly modular,and can meet the requirements of different power and voltage levels by increasing or decreasing the number of sub-modules connected to the converter,which facilitates the realization of integrated design,shortens the project cycle,and saves costs.This article mainly takes MMC-UPFC as the research object to study its device-level control strategy,including:1.Based on the structure of MMC-UPFC,analyze the basic principles of MMC-UPFC,introduce the controller and topology of UPFC,and then understand the control functions and operating characteristics of series and parallel connections.It analyzes in detail the working characteristics of MMC and the law of on-off of MMC,as well as the generation principle and suppression strategy of circulating current under this structure.2.Analyze the mathematical model of the parallel side of the UPFC,establish the vector controller of the parallel side converter,and carry out simulation on the basis of simplification,and add intelligent algorithms to optimize the PI controller,which is compatible with traditional PI control.By comparison,verify whether the controller is reasonable and whether the new algorithm can be added to optimize the system.3.Established the detailed mathematical model of the UPFC series converter,established the vector controller of the series-side converter,and verified whether the controller is reasonable,can accurately control the power flow control,and can quickly and accurately control the output voltage to suppress The effect of the line current on the device.4.Use MATLAB/Simulink software to build UPFC simulation,and analyze the dynamic characteristics of UPFC and coordinate the dynamic process.Grid-connected analysis,active power adjustment analysis,reactive power adjustment analysis are carried out on the simulation,and finally a summary is made to analyze the advantages and disadvantages of UPFC.