Research On Flexible Topology Structure And Characteristics Of High Proportion New Energy Transmission Grid

Achieving a large-scale,large-scale,long-distance,and cross-regional delivery of high proportion of new energy is the future development direction of new energy power systems.Increasing the proportion of new energy access,as well as the stability of grid connection and the transmission and delivery capacity of transmission systems are currently Research hotspots.This thesis proposes a flexible topological structure for the coordinated operation of the source-grid network of a new proportion of new energy power systems by studying the delivery characteristics when different proportions of wind power are connected to various transmission grid structures and system failures.The transmission characteristics are studied in depth.Firstly,a mathematical model of DFIG(Double Feedback Inductive Generator),HVDC,UHV AC,and AC-DC hybrid transmission was established.Based on this,the DC power supply system when the transmission end system was a conventional power supply was studied.Outgoing characteristics of transmission and AC-DC hybrid transmission.Aiming at the problem of power flow transfer in the case of DC failure in AC-DC hybrid systems,the main factors affecting the frequency stability of AC and DC hybrid transmission systems with parallel and non-parallel structures are analyzed.Improved the stability evaluation index for long-distance and large-capacity transmission of the hybrid power grid.Secondly,the transmission and dissipation capacity of the AC-DC hybrid transmission system connected to wind power is studied.By connecting different proportions of wind power to the transmission-end system of the AC-DC hybrid power grid,the voltage and power fluctuations of the hybrid system are studied.The method of improving the voltage stability at the sending end of the parallel-connected system by adding dynamic reactive power compensation(SVC)to the sending-end system is proposed,and then the method of improving the out-feeding capacity of the hybridconnected system.Relevant models are established on the PSCAD / EMTDC software platform for verification.Simulation results show that improving the stability of the voltage at the sending end of the hybrid system can not only improve the delivery capacity of the hybrid system,but also improve the system's ability to accept wind power.Operational stability of DC-hybrid grids.Finally,based on the research on the transmission characteristics of various transmission grid technologies,a hybrid flexible AC-DC transmission technology is proposed.Based on the hybrid flexible DC LCC-MMC three-port transmission mode,a high proportion of wind power at the transmission end system is connected.The flexible AC power transmission device SVC(Static Var Compensator)is used for dynamic reactive power compensation to improve the voltage stability of the transmitting end system,which can effectively improve the system's ability to accept wind power,while the receiving end system adopts the MMC structure to solve the problem of conventional DC transmission.Multi-DC feed-in problem,using PSCAD / EMTDC for simulation verification.The results of simulation experiments show that this strategy can not only increase the access ratio of wind power,increase the delivery capacity,but also improve the operating stability of the receiving system,and achieve large-scale wind power Long distance delivery.