Research On Variable Universe Fuzzy PI Control Of SVC In Weak Receiving System In HVDC

High voltage direct current(HVDC)technology is widely used in the field of longdistance and large-capacity power transmission in my country due to its advantages of small power loss,low power transmission cost and good safety.At the same time,the structural form of "strong direct and weak AC" in the power system is becoming more and more obvious.The inverter station of HVDC needs to be matched with a largecapacity dynamic reactive power compensation device to strengthen the voltage support capability of the weak receiving AC system.In this thesis,the static var compensator(SVC)is used to compensate the reactive power in weak receiving system in HVDC,and the control system is improved according to the problems of SVC in reactive power compensation.Firstly,the structure,mathematical model and control method of HVDC system are introduced.The reactive power balance of HVDC system is analyzed,and the definition and characteristics of the weak receiver HVDC system are introduced,which lays a theoretical foundation for subsequent simulation research.The basic principle and control method of SVC are introduced.Aiming at the problem of voltage instability caused by various faults of the weak receiving AC system,the changes of various electrical quantities before and after the installation of SVC in the inverter station are simulated and studied,and the ability of SVC to support the voltage of the weak receiving AC system,restrain the inverter commutation failure and maintain the active power transmission of the DC system is analyzed.The research shows that when a fault occurs,SVC can reduce the drop amplitude of the voltage of the converter bus and the active power transmitted by HVDC system,and can reduce the influence of commutation failure of the thyristor in the inverter station.Secondly,in view of the shortcomings of the SVC control system,a SVC voltage regulation method based on the variable universe fuzzy Proportional Integral(PI)control is applied.On the basis of conventional PI control and fuzzy theory,this method combines them organically and introduces variable universe technology for further improvement.The application of three control methods,conventional PI,fuzzy PI and variable universe fuzzy PI,in SVC is compared and studied.The research shows that the variable universe fuzzy PI control SVC can adjust the voltage more quickly and flexibly,has a good reactive power compensation ability,and can effectively improve the voltage stability of the power system.Finally,the SVCs controlled by conventional PI,fuzzy PI and variable universe fuzzy PI are respectively installed in weak receiving system in HVDC model for simulation and comparison experiments,the application effect of SVC under three control methods when various faults occur during the operation of the weak receiving AC system are analyzed.It is proved that the SVC based on the variable universe fuzzy PI control can effectively improve the problem of excessive overshoot of the converter bus voltage and DC transmission active power during the fault recovery process.