Research On Fault Calculation Of AC Power Grid With HVDC Connection Applied For Setting Calculation

HVDC has been extensively used in long distance and huge capacity transmission and regional system interconnection because of its large transmission capacity,long transmission distance,highly controllable and flexible operation.Among them,the traditional HVDC technology based on thyristor has the advantages of larger transmission capacity and lower equipment construction cost,which is widely used in power grid.However,when the AC power grid fault occurs,the fault transient characteristics of HVDC system are different from that of AC power grid.Under the complex interaction between AC and HVDC,it will bring new characteristics to the fault characteristics of the AC power grid,which is bound to affect the AC protection setting calculation.In this context,it is of great theoretical and practical value to carry out the research on the fault calculation of AC power grid with HVDC connection applied for setting calculation.In chapter Ⅱ,the fault characteristics of HVDC system under AC power grid fault are analyzed.The topological structure and basic operation principle of HVDC system are summarized.From the angle of AC protection setting calculation,the fault characteristics of HVDC system under different AC fault conditions are analyzed.Then the influence factors of HVDC system fault characteristics are studied.Finally,the fault characteristics and influencing factors are verified by simulation.This chapter provides the theoretical basis for the follow-up study of equivalent modeling of HVDC system.In chapter Ⅲ,an equivalent model of HVDC system applied for AC power grid fault calculation is proposed.The improved switch function model for asymmetric fault is introduced and the calculation method of DC side electric quantity under HVDC control mode is given.By combining the calculation method with the improved switch function model,the equivalent model of HVDC system considering HVDC control effect is established.Finally,the proposed equivalent model is compared and verified.This chapter lays the foundation for the follow-up study on the fault calculation method of AC power grid with HVDC connection.In chapter Ⅳ,a fault calculation method of AC power grid with HVDC connection is proposed.The existing fault calculation methods of AC power grid are studied,and the characteristics of different methods are compared and analyzed from different angles.Based on the equivalent model of HVDC system,the dynamic phasor model is established by combining the dynamic phasor method.Then a fault calculation method of AC power grid with HVDC connection is proposed.Finally,the correctness of the method is verified by simulation.