Study On The Transient Overvoltage Mechanism And Its Suppression Method In HVDC Start-up Process

For the AC-HVDC mixed power grid,the HVDC system abnormal latching will cause the flow to shift to the regional interconnected AC line,if the power flow is too heavy,it may cause the AC-HVDC system's power angle and voltage instability.Therefore,in 2016,Yunnan power grid was split from the main network,asynchronous networking through HVDC.After asynchronous networking,due to the small body volume of Yunnan power grid and the weak construction of the grid frame,its ability to resist the system active and reactive power impact has decreased.When HVDC is unlocked or the power is abnormally latched,the feed end generates a certain amount of overvoltage,threatening the safe operation of the system.At present,the academic circles have matured in the study of the mechanism,quantitative estimation,influencing factors and the inhibitory measures caused by HVDC power latching.However,there is a lack of attention to the HVDC feed overvoltage problem caused by HVDC start-up,and there is a certain difference in the mechanism of production and the suppression measures between the two situations.The former is difficult to predict subjectively,so its inhibition means more passive inhibition.The overvoltage problem in the HVDC start-up process can be subjectively predicted and calculated,and some active suppression measures can be taken,such as the adding near-zone generator.Therefore,it is necessary to develop a reasonable suppression scheme for the overvoltage problem in the HVDC start-up process,which is of great significance for maintaining the transient stability and power supply reliability of the terminal power grid.This paper first introduces the generation mechanism of transient overvoltage in the AC bus of the rectifier station in the HVDC start-up process,gives the quantitative calculation method of transient overvoltage in the process,and analyzes the factors such as short circuit ratio and excess reactive capacity.Then,the suppression effect,advantages and disadvantages of several measures are discussed for the mechanism of overvoltage generation in this process,namely,the low resistance compensation for the input of the transfer station or substation,the reactive power adjustment through the generator of the HVDC feed-end power plant and the power failure of some lines of the local power grid of the HVDC feed end(subject to the stability boundary of the power grid),etc.,The simulation results of the simple grid model under BPA environment are verified.Then,taking Yunnan power grid as an example,in the smallest way of southern power grid in BPA,according to the actual operation of the power grid,corresponding measures are taken to simulate the overvoltage suppression problem in the HVDC start-up process of Yunnan power grid,and compare with the simulation results inother ways,so as to verify the validity of the simulation method and the correctness of the simulation conclusion.