Study On Transient Voltage Stability Of HVDC Integration To Receiving-end AC Grid

DC system has been widely basedon the obvious advantages in large-capacity and long-distance transmission.However,when the local power supply is insufficient,commutation failure and DC blockade will leads to unbalanced power flow in the regional power grid after DC fault occurs,which results in more serious voltage drops.In this paper,the problem of transient voltage stability at the receiving-end of AC/DC power grid is studied in depth focusing on the influencing factors,the impact mechanism,measures to improve..Firstly,PSD-BPA power system simulation software is used establish to a typical AC/DC power grid model.The dynamic response characteristics of induction motors during and after fault removal are analyzed,and the transient voltage instability mechanism based on the combined load of induction motors is clarified.When the load power demand exceeds the transmission limit,the power shortage and voltage drop form a positive feedback process,which causes voltage instability.The critical clearance slip and the critical clearance time of the fault considering the transient process of the rotor voltage are further calculated.The results are verified by simulation examples,which can be used as the basis for judging the transient voltage instability after the fault.Then the external characteristics of reactive power and voltage of DC receiving terminal are studied and analyzed.The inherent dynamic characteristics of reactive power and the influence of DC control on the dynamic characteristics of reactive power of DC system are analyzed.The source-load conversion characteristics of reactive power of DC system under commutation failure are revealed.Considering the interaction between reactive power characteristics of DC system and load reactive power of induction motor,the reactive power dynamic characteristics of DC system under critical transient voltage stability are quantitatively analyzed,and the critical cut-off slip of induction motor considering reactive power recovery characteristics of DC is calculated.The simulation results are verified by numerical examples,and the voltage stability mechanism based on AC/DC mutual feed characteristics of receiving end is obtained.Based on the planning data of Zhejiang Power Grid in 2018,the potential voltage stability problems caused by Lingshao DC feeding into Zhejiang Power Grid are studied and analyzed by using simulation software.The influence of DC fault on the stability of AC power grid is analyzed under full DC feeding.The load characteristics of induction motor and the characteristics of DC system are analyzed comprehensively.The effects of different VDCOL parameters on voltage stability are analyzed.