Research On Characteristics Of Transient Voltage Oscillation At The Moment Of DC Side Short-Circuit Fault Of VSC-HVDC System

At the moment of a short-circuit fault on the DC side of the VSC-HVDC system,high-frequency transient voltage oscillations will appear at the smoothing reactor and converter valve,which are possible installation positions of the DC circuit breaker.Under the background that DC circuit breakers are gradually put into engineering applications,this transient voltage oscillation will cause severe disturbances in the potential of the circuit breaker platform in a short period of time,posing a potential threat to its normal operation.Therefore,it is necessary to conduct in-depth research on the transient voltage oscillation at the moment of short-circuit fault on the DC side of VSC-HVDC system to master its generation mechanism and characteristic law.This thesis focuses on the transient voltage oscillation at the moment of a short-circuit fault on the DC side of a VSC-HVDC system.From both analytical calculations and modeling simulations,relevant researches are carried out on its generation mechanism and characteristic laws and suppression techniques are proposed.First,according to the system topology of the Dinghai converter station of the Zhoushan VSC-HVDC Project and the working status and action characteristics of the main equipment of the converter station during the DC side fault transient process,an electromagnetic transient model suitable for simulation and an equivalent simplified model suitable for analytical calculation are established respectively,and the overall electromagnetic transient simulation model and simplified equivalent model of the commutation system are further built.Then,based on the simplified equivalent model of the commutation system,two calculation methods are used to calculate the transient voltage under the conditions of bipolar short circuit and unipolar short circuit on the DC side.The oscillations are calculated analytically,and the mechanism of them is analyzed.The actual measured voltage data of the artificial short circuit test is compared with the analytical calculation and simulation results of transient voltage oscillation,which verifies the accuracy of the analytical calculation and the simulation model.Finally,the characteristics of transient voltage oscillations in cables and overhead lines VSC-HVDC systems are both studied.Relying on the electromagnetic transient simulation model of the VSC-HVDC commutation system,the influencing factors and characteristic laws of voltage oscillation are simulated and analyzed,and the difference in transient voltage oscillation characteristics between the cable and the overhead line VSC-HVDC system is compared and analyzed.According to the changing law of oscillation characteristics,the suppression techniques for transient voltage oscillations are proposed.In this thesis,through theoretical analysis and simulation modeling,the transient voltage oscillation at the moment of DC side fault of VSC-HVDC system is deeply studied,combined with the actual measurement results of the artificial short-circuit test,and the generation mechanism of the voltage oscillation is clarified,and its characteristic law is established.The research in this thesis can provide a reference for the construction of the follow-up VSC-HVDC project.