Hybrid Simulation And Key Technologies Of Blocking Cascading Failures For AC/DC Hybrid Power System

With the successive application and commissioning of large-capacity and long-distance DC transmission projects,our country’s power grid has changed from an AC interconnected large grid to a ‘strong direct current(DC)systems connect to weak alternating current(AC)systems’ hybrid AC/DC grid.The coupling between AC and DC systems is becoming increasingly tighter,and improper handling of a single AC fault may cause cascading failures in the AC/DC hybrid power grid.Modeling the AC/DC hybrid power grid is the basis for analyzing the coupling characteristics and stable operation of the AC/DC power grid.Suppressing DC commutation failures and identifying vulnerable lines are key technologies to block cascading failures of AC/DC hybrid power grids and ensure stable operation.In view of this,it is urgent to carry out research on hybrid simulation and key technologies of blocking cascading failures for AC/DC hybrid power system.This paper first builds an electromechanical-electromagnetic transient hybrid simulation model of AC/DC hybrid power grid after the ultra high voltage direct current(UHVDC)hierarchical access to accurately simulate its operation and control characteristics.Then the research on key technologies of blocking cascading failures is carried out from two aspects of subsequent commutation failure suppression and vulnerable lines identification.The main progresses are as follows:(1)Based on the Yazhong-Jiangxi hierarchical UHVDC transmission system in planning and construction,the hybrid simulation model construction process of the AC/DC hybrid power grid is introduced combining with the electromechanical-electromagnetic transient hybrid simulation software platform ADPSS in detail.Taking Jiangxi Power Grid as an example,the advantages and effectiveness of the built model are verified through simulation comparison.(2)In order to suppress the subsequent commutation failure of the DC transmission system,on the basis of detailed analysis of the influencing factors and mechanism of subsequent commutation failure,an adaptive firing angle compensation control method for suppressing the subsequent commutation failure of the DC is proposed.The effectiveness of the proposed method in suppressing subsequent commutation failures and improving the fault recovery characteristics of the HVDC system is verified by simulation.(3)A vulnerable lines identification method suitable for AC/DC hybrid power grids is proposed.This method uses the branch power flow model to model the AC/DC system.The steady-state security margin of the system after disconnection is calculated combined with the analysis principle of static security domain.Simulation results show the effectiveness of the proposed identification method.