Research On Commutation Failure Suppression Method For UHVDC Transmission System

UHVDC transmission can effectively improve the power transmission capacity,realize the long-distance and large-capacity power transmission of large energy base,so as to meet the needs of China’s economic and social development.After more than ten years of rapid development,China has become a large country of UHVDC transmission project.However,UHVDC transmission also brings many new technical problems.Commutation failure is one of them.Supported by the key project,"The construction of the physical simulation platform for the UHVDC power transmission and the study on commutation failure mechanism and its suppression measures for the Jiu-Hu Project".In the paper,a commutation failure suppression method based on fixed minimum turn-off area control is proposed,and the method is tested by simulation.At the same time,the suppression effect of t wo reactive power compensation devices,STATCOM and synchronous condenser,on commutation failure is simulated and compared.The main contents and innovations in this paper are as follows:(1)The equivalent model of three-phase commutation circuit of inverting station is established,the commutation process of inverting station is analyzed,and the calculation formula of turn-off angle is deduced.According to the formula,the influence of various factors on turn-off angle is analyzed,and the influence characteristics of AC side faults on turn-off angle of valves are emphatically quantitatively analyzed.(2)According to the influence of single-phase fault on the voltage amplitude and phase angle of the commutation line,the parameters are selected.Then,a commutation failure suppression method based on fixed minimum cross-section area control is proposed.The proposed method consists of two parts: improved fixed minimum turn-off area control and DC current suppression.It can adjust the setting value of turn-off angle when voltage drop occurs,make the turn-off angle recover quickly,and also limit the rapid rise of DC current,so as to mitigate the impact of DC current change on subsequent commutation failure,so as to effectively suppress the occurrence of continuous commutation failure.(3)CIGRE is established in PSCAD/EMTDC environment,and the proposed suppression method is verified by simulation.The simulation results show that th e proposed method can effectively suppress the occurrence of continuous commutation failure under the condition of grounding fault.At the same time,it will not affect the normal operation of the system.(4)The working principle of STATCOM and synchronous camera is analyzed.In the environment of PSCAD/EMTDC,a simulation platform is built according to the operation parameters of Jiuhu HVDC transmission project.The suppression effect of STATCOM and synchronous camera on commutation failure is simulated a nd compared.The simulation results show that both STATCOM and synchronous camera can suppress commutation failure when AC side is short-circuited and setting bus voltage drop to critical value,but STATCOM has faster response speed and better voltage support effect.