Research On Reactive Power Compensation Strategy For UHV AC/DC Hybrid Power Grid

The distribution of primary energy in China is seriously uneven,and most of it exists in remote areas.In order to transmit clean energy to load centers over long distances,it is urgent to develop UHV hybrid transmission technology with large transmission capacity and long transmission distance.UHV hybrid transmission project can effectively alleviate the contradiction of uneven energy division by connecting the load center with large energy stations.With the development of UHV hybrid transmission in China,UHV AC/DC hybrid power grid is gradually taking shape.UHVDC transmission has many obvious advantages over AC transmission lines.However,UHVDC transmission system also faces many problems in voltage stability operation.Once bipolar blockade occurs,it will cause a large range of transient voltage rise and wind power disconnection.With the continuous increase of wind power installed and grid-connected capacity,the safe and stable operation of UHVDC system voltage is seriously challenged.How to configure the dynamic reactive power compensation,restrain the transient voltage rise after fault and ensure the stable operation of UHV AC/DC hybrid power grid is an urgent problem to be solved.Firstly,this paper summarizes the research status of UHV grid,especially UHVDC grid,reactive power optimization of high voltage grid and reactive power optimal allocation of high voltage grid.Secondly,the reactive power compensation model of UHV AC/DC hybrid power grid is established.By comparing the characteristics of reactive power compensation device,the phase modulator is selected as the reactive power compensation device,and the simulation model is built in the full digital real-time simulation software ADPSS.The characteristics of reactive power and voltage in UHV AC/DC hybrid power grid are studied,the reactive power characteristics of UHV AC/DC power grid are analyzed,and the transient voltage characteristics of bipolar blocking fault in UHVDC power grid are studied.The reason of transient voltage rise after bipolar blocking is explained.The bipolar blocking fault of UHVDC transmission line is simulated with ADPSS software.The maximum transient voltage rise of converter bus and typical wind farm bus is compared before and after the Synchronous Compensator is installed.Finally,the minimum deviation of AC bus voltage of UHV converter station,bus voltage of a key node of power grid and bus voltage of a grid-connected node of wind farm is taken as the optimization objective.An optimal reactive power allocation model for UHV AC/DC hybrid power grid is proposed.The model is solved by sensitivity method and artificial bee colony method.The optimal reactive power compensation access points are selected by optimizing and comparing multiple reactive power compensation access points.The effectiveness of reactive power optimal allocation strategy is proved by an example.