Research On Multi-time Scale Model Of Distributed Power Flow Controller Based On Modular Multilevel Converter

At present,the research of Distributed Power Flow Controller(DPFC)is based on topology of two-level or three-level voltage converter.And the Modular Multilevel Converter(MMC)has advantages of low harmonic content of AC output,easy to be modularized and easy to be expanded system capacity and put into industrialized production and high reliability,compared with traditional two-level or three-level voltage converter,it has obvious advantages in practical engineering application field of high voltage,large capacity flexible AC and DC transmission.Therefore,for the high voltage and large capacity transmission field,the MMC is introduced into the parallel side of the DPFC,and the topological structure of the DPFC based on the MMC(MMC-DPFC)is proposed.On the basis of summarizing the work carried out by predecessors,this paper studies the new flexible AC transmission technology called MMC-DPFC starting from various references.According to the topological characteristics of the device,the paper studies in two aspects which are the equivalent mathematical model and the multi time scale mathematical model,and carries out the following tasks:(1)On the basis of summarizing the current research situation of DPFC and MMC-DPFC at home and abroad,this paper introduces the mathematical model,detailed model and control method of the MMC-DPFC in detail.Then the topological structure and basic working principle of the device are introduced,and the power flow control ability of the system is analyzed.(2)Based on the topological structure and basic working principle of MMC-DPFC,this paper uses the MMC average model and the equivalent voltage source to establish an equivalent mathematical model of the device.Then the appropriate control strategy is designed according to the control target of the device.Finally,the equivalent mathematical model of the device is modeled on the ADPSS simulation platform,the dynamic and static characteristics of the device are reflected and the control function of the system flow is verified by the simulation test,and the validity and correctness of the equivalent mathematical model are validated.(3)Based on the singular perturbation theory,this paper introduces the method of establishing multi time scale model of MMC-DPFC.According to the topology structure of the device,by introducing the concept of cycle by cylcle switch average model of MMC and switching function,a five-order dynamic mathematical model of parallel and series side converters is established.Then,a multi time scale model of MMC-DPFC is established by analyzing the dynamic mathematical model of the device and determining the fast state variable and the slow state variable in the system.Finally,the control strategy is designed with the fixed slow variable dc voltage equation,only from the angle of the fast variable AC side dynamic current equation design controller.(4)Based on the PSCAD/EMTDC simulation platform,a simulation test system with multi time scale model of MMC-DPFC is established,and the simulation analysis is carried out from two aspects of steady state and transient state of the system.The simulation test verifies the validity and correctness of the multi time scale model of MMC-DPFC and its control strategy.