Research On The Influence And Optimization Of Cascade Power Stations’ External Transmission Based On VSC-HVDC Grid Connection

In recent years,with the development of Voltage Source Converter Based HVDC(VSCHVDC)technology has become increasingly mature,the application of VSC-HVDC in power systems has become increasingly widespread.However,the grid-connected VSC-HVDC is often accompanied by the reinforcement project of the nearby AC power grid,which involves a wide range of related power grids and has a greater impact on the system characteristics of the AC power grid.As a result,the structure of the nearby AC power grid and the system’s operating characteristics have changed.Therefore,the operation mode of the unit group connected to the nearby power grid needs to be adjusted accordingly.At present,most of the research content of VSC-HVDC grid connection focuses on the optimization of converter control topology and device performance.Few analyses of the impact of VSC-HVDC grid connection on the operation of the connected unit group of the nearby receiving end grid.Most of the associated unit groups are cascade hydropower stations.At present,most researches on the operation and scheduling of cascade power stations consider water conservancy factors such as weather,incoming water and load changes,and less consider factors such as the limit of external transmission section of the nearby power grid and reactive power balance.Based on this,this paper conducts an in-depth study on the operation impact and optimization of cascade power stations based on VSC-HVDC grid connection.The main research contents and research results are as follows:(1)This article briefly describes the research status of VSC-HVDC technology and cascade hydropower station optimization scheduling,and analyzes the existing research results.A research strategy for the operation characteristics of cascade power stations based on the gridconnected VSC-HVDC is proposed,and the influence of the control mode and transmission power of the VSC-HVDC converter is fully considered,and the analysis method of the reactive power balance and the external transmission section limit of the nearby grid of the cascade power station is proposed.Provide theoretical support for later research.(2)Using the Power System Analysis and Synthesis Program(PSASP),take the national key power transmission and transformation project Chongqing-Hubei back-to-back VSCHVDC project and the Qing River cascade power station connected to the DC receiving end grid as examples.The system stability characteristics of the 500 k V AC grid in the vicinity of the Qing River cascade power station were studied when the Chongqing-Hubei back-to-back VSC-HVDC project was put into production.(3)An optimization model of cascade hydropower station based on VSC-HVDC gridconnected is established in Matlab,which aims at the comprehensive optimization of both the economy of cascade power station and the safety of near-area power grid.Combining the constraints and coping strategies under the new boundary conditions proposed in the previous article,the particle swarm-genetic algorithm is used to optimize the model,and one year of real power grid operation data is used for simulation verification,and the operation strategy of Qing River units is obtained.The results prove that the optimization model proposed in this paper can take into account the safety margin of power grid operation and the economic benefits of cascade power stations,guarantee the safe,economic and stable operation of power grids and cascade power stations,and can be used as an important reference for guiding the dispatching of cascade reservoirs.(4)The research content and results of this article are summarized and prospected,and the content and direction for further research are briefly described.