Simulation Analysis And Fault Location Research Of Control Strategy Based On MMC-HVDC

Modular multilevel converter(MMC)has drawn more and more attention and application.It has advantages of a good quality of waveform,no need to configure the filter device,the switching loss is low,the device is simple,it can easily achieve multi-module and multi-level design,it can be realized for the independence decoupling control of active and reactive power,supplying power to the passive system.Although MMC has become one of the hotspot technologies,but MMC's research is still in its infancy.In this paper,the control strategy of the MMC-HVDC system and fault location of the monopolar grounding fault in DC side are studied.The structure of this paper as follows:Firstly,the topology and working principle of MMC and the corresponding working state of each sub-module are described.The operating principle and the type of three-phase modular multilevel converter is analyzed.Secondly,the structure of the MMC-HVDC system and the topology of the main circuit are introduced.The equivalent circuit diagram of the system is obtained from the main circuit topology.The transient mathematical model of MMC system is analyzed.The structure of the MMC-HVDC control system are analyzed,the function of the control system and the structure of the controller are studied.The model of MMC-HVDC with two sides was realized by PSCAD/EMTDC.Other physical quantity response characteristics are analyzed when the system in the steady state,the active power have changed,the voltage have changedThirdly,the causes of the fluctuation of the capacitor voltage and the mechanism of circulating current are analyzed.The principle of the MMC's capacitor voltage balancing and the culating current suppressing controller is introduced.The universal circulation suppressor is analyzed and the simulation model is used to verify that the controller can minimize the distortiond degree of the arm current.Finally,the boundary conditions of the MMC-HVDC system and the propagation characteristics of the traveling wave are studied.The influence of the different fault resistance and the different fault distance on the traveling wave characteristics is simulated and analyzed.The traveling wave fault location is used to study the monopolar grounding fault in DC side.