| With the continuous increase of transmission projects,especially the operation of UHVDC with larger capacity and the centralized feeding of multiple HVDC,the risk of serious fault and cascading fault in power grid increases.On the other hand,the construction of UHV AC project is relatively lagging behind,and the EHV backbone grid does not match the UHV DC transmission power in terms of undertaking DC power transfer,providing voltage support and bearing capacity of power shortage,therefore,the security and stability of the power grid is facing greater challenges.The current situation of power grid is called “strong DC and weak AC”,and the problem of power grid security and stability caused by it is called “strong DC and weak AC”problem.Under the condition of strong DC and weak AC power grid,the relationship between AC and DC systems has evolved from the traditional master-slave relationship to the interdependent relationship,and the dynamic coupling and disturbed behavior are more complex.Aiming at the threat to AC-DC hybrid power grid brought by the pattern of strong DC and weak AC power grid,this project analyzes the AC-DC coupling characteristics under strong dc weak AC power grid,the method to improve the safe and stable operation level of large-scale power grid is put forward.In order to improve the safe and stable operation characteristics of hybrid power grid under the background of strong DC and weak AC,the manifestation of AC-DC coupling is studied firstly,and the mechanism of AC-DC interaction is analyzed from the perspective of converter bus voltage and AC-DC power exchange.The analysis results show that the various forms of AC-DC coupling are cause and effect each other,and the mechanism is complex.It is necessary to build an appropriate time-domain simulation model of power grid to further master the AC-DC coupling characteristics.Therefore,this project builds the ADPSS electromechanical electromagnetic transient simulation model of AC / DC hybrid power grid to meet the needs of accurate and fast simulation of large power grid;using the model,the simulation inversion is carried out for the engineering examples related to AC / DC coupling in the actual project,verify the correctness of the simulation model,and illustrates that the simulation model can solve the problem of AC / DC coupling in the actual project The application prospect of flow coupling problem.Based on the AC-DC coupling analysis,this paper studies the DC emergency power control method to improve the carrying capacity of the receiving end AC power grid.Firstly,the DC emergency power control method to suppress the power swing back of AC tie line and the DC emergency power control method to suppress the power swing peak of AC tie line are proposed based on the emergency power support capability of UHVDC,and the power oscillation of UHV AC Changnan line is suppressed.Secondly,when the DC impact is too strong,the coordinated load shedding method of AC and DC is proposed to improve the ability of the receiving end AC system to resist strong impact,which provides theoretical guidance and application methods for improving the safe and stable operation level of AC / DC hybrid power grid under strong DC and weak AC. |
