Research On Multiport DC Power Flow Controller Based On MMC

The DC grid is an intelligent and stable transmission network with advanced energy management system.It is especially suitable for the centralized grid connected and long-distance transmission of new energy sources.However,the unjustified power flow distribution of the DC power grid will lead to the overload of the line,which leads to the low efficiency of the DC power grid and even brings serious security risks.The DC power flow controller can effectively improve the degree of freedom of complex DC grid,and solve the problem of uncontrollable part of the power flow.It is of great significance for the safety,reliability and economy of DC power grid operation.This paper proposes the topology and control strategy of a multi-port DC power flow controller based on modular multilevel converter.First,summarizethe advantages and disadvantages of the existing DC power flow controller topology and control effect.The topology and working principle of MMC and full bridge submodule are analyzed,and the mathematical model of MMC in a three-phase stationary and two-phase rotating coordinate system is established.Andset upthe three terminal DC power gridin the simulation platform.Secondly,as the basis of the multi-port DC power flow controller,the topology of the dual port DC power flow controller based on MMC is proposed and the working principle is analyzed.The relationship between the voltage of the DC line and the line current is obtained.Designthe mathematical model and control strategy,and the simulation platform is used to verify it.Finally,in view of the fact that the traditional DCPFC is two port,it is unable to adapt to the increasingly complex DC power grid.The topology of the multi-port DC power flow controller is proposed,and the working principle is expounded in detail,and the method of determining the number of ports required according to the DC power grid structure is explained.Taking three port as an example,particularly introduces the working principle,mathematical model and control strategy of the multi-port DC power flow controller.In the simulation platform,the five terminal flexible DC transmission system in Zhoushan withthe three port DC power flow controller is built.The proposed topology and control strategy are simulated and verified.