Research On Improving The Operating Characteristics Of Transient And Steady State Of HVDC With STATCOM

HVDC transmission has been developing rapidly in China.With the increase of HVDC transmission project and the upgrading of voltage level and transmission capacity,HVDC failure is becoming more serious.It is becoming more and more important to improve the resistance to the commutation failure and improve the recovery characteristics of the system in the actual project.Meanwhile,the voltage fluctuation and switching loss caused by reactive power group switching in steady state are becoming more important.STATCOM has good reactive power response ability.It can effectively improve the operation characteristics and support the AC bus voltage dynamically when connected to the AC bus of inverter side.The existing literature has many points for studying the influence of STATCOM on the operation characteristics of HVDC on simple models.Almost no practical parameters and control strategies are used.And the conclusion of the study is not convincing.This paper is based on the science and technology project of State Grid Economic and Technological Research Institute--The study on the strategy of coordinated control and simulation of STATCOM in converter station.It is closely integrated with Jiuquan-Hunan HVDC.It is deeply studied that improving the running characteristics of HVDC with STATCOM.The main research contents are as follows.First,based on the actual engineering parameters and control strategies of Jiuquan Hunan DC project,the simulation and modeling of HVDC and H bridge cascaded STATCOM are carried out on PSCAD/EMTDC.And the effectiveness of the HVDC model is verified by simulation of transient and steady state characteristics.The H bridge cascaded STATCOM is connected to the HVDC bus on the AC bus of inverter side.And the constant AC voltage control and constant reactive power control of STATCOM is simulated and verified.Based on the actual engineering of the model,commutation failure immunity factor is used as the index to analyze the ability of STATCOM to HVDC system to resist commutation failure.And commutation failure duration and power recovery time are used as the index to analyze the ability of improving the recovery of the fault system.The simulation results show that STATCOM can enhance the system's ability to resist commutation failure.Although STATCOM can also shorten commutation failure duration and power recovery time.But the effect is not obvious when the capacity of STATCOM is small.And compared with the first commutation failure and continuous commutation failure under severe faults,the effect of STATCOM on the improvement of recovery characteristics under less serious faults is relatively obvious.In order to further suppress commutation failure and improve the recovery performance,the additional fuzzy control of STATCOM is proposed.The maximum value of the turn-off angle deviation of the HVDC inverter side is taken as the input.And the PI parameters of the STATCOM outer ring are optimized based on the fuzzy control.It can be used to improve the dynamic response characteristics and control precision.The results show that the additional fuzzy control can significantly improve the system's ability to resist the first commutation failure under the fault of the inverter side.And it also can improve the system's recovery performance.In order to improve the overall performance of the system,considering the different operating conditions,a detailed coordinated control strategy of STATCOM and HVDC reactive groups is proposed,which is close to the actual project.The results show that the strategy can reduce the number of switching in steady state conditions and the fluctuation of voltage.It can also improve the system transient performance and enhance the speed of recovery system.