Research On Overvoltage Control Strategy Of AC Power Grid In Near Area Caused By DC Fault

With the ultra-long-distance and large-capacity delivery of hydroelectric bases in southwest China,it will inevitably lead to the formation of a multi-infeed HVDC transmission in the eastern end of the country.When DC is blocked due to consecutive commutation failures,etc.,there will be abundant electromagnetic transient characteristics in the DC near-end of the delivery end,and over-voltage of the near-zone AC system will be caused.During the commutation failure or line fault restart of the HVDC transmission project,the reactive power consumed by the converter is significantly reduced.Before the AC side filter is removed,a large amount of redundant reactive power in the system will invade the near area AC system,causing the AC bus to overvoltage.To solve this problem,this paper will focus on the mechanism and suppression methods of generating overvoltage in the near-field AC system when the DC system is faulty.This paper first applies PSCAD electromagnetic transient simulation software to develop a quasi-steady-state model of HVDC transmission and interaction model of AC/DC system,and analyzes the mutual influence of AC/DC system and the possible overvoltage in AC/DC system.Utilizing the equivalent circuit of the near-area power grid of the DC converter station,the relationship between the over-voltage of the AC bus and the excess reactive power of the system and the strength of the AC system was introduced through the power flow calculation method.For a weak AC system with high equivalent impedance,after the DC fault occurs,the AC bus voltage is higher.By comparing the simulation software and the required model requirements,a± 800 KV bipolar DC transmission system model and an AC-loop system with a direct-current transmission end and a stand-alone infinity system are constructed in PSCAD.The simulation verifies the results.Model accuracy.Analyzes and contrasts the control characteristics and coordination logic of each control section of the DC inverter.The over-voltage in the AC-DC system caused by typical faults is simulated and related influencing factors of the over-voltage amplitude are studied.The use of the highly controllable and rapidly adjustable features of the HVDC transmission system and the study of the operating characteristics of the generator.An over-voltage suppression scheme for reactive power regulation through the DCsystem and generator phase depth adjustment is proposed.The overvoltage suppression strategy of reactive power control is applied to the model of HVDC transmission system.When the system is under the condition of single-pole locking,the turn-off angle of the DC inverter-side converter is briefly raised,and it is found that the DC is highly reactive power consumption.A substantial increase in the amount,effectively inhibits the AC bus overvoltage.The same DC blocking condition was set in the AC/DC system,and the overvoltage suppression strategy was briefly applied to increase the shut-off angle,generator phase-advance depth adjustment,and hybrid adjustment of the two modes.The simulation verified that each link can effectively suppress AC.Bus overvoltage.Through the comparison of the inhibitory effects,it was found that the mixed suppressing strategy of briefly increasing the shut-off angle and the generator phase depth adjustment had the best inhibitory effect on the AC bus overvoltage.