Converter Controller Design And DC Transmission Capability Research Of VSC-HVDC

In face of the increasing pressure of energy crisis and environmental pollution issues,renewable energy generation technologies including wind power and solar power are expanding rapidly.Voltage source converter based high voltage direct current(VSC-HVDC)technology is considered one of the most desirable technique for massive renewable power integration.For VSC-HVDC system,converter controller is of great importance to dynamic characteristics of converter as well as stability of power system.Power transfer capability of converter station has direct impact on the design,operation and dispatching of the grid.In this thesis,the two essential issues of VSC-HVDC mentioned above are studied.The main works of the thesis are as follows.Firstly,on the basis of inheriting the advantages of traditional dual closed loop decoupling control structure,this thesis takes advantage of linear disturbance rejection control(LADRC)strategy instead of traditional proportional integral(PI)control strategy in converter controller design,which can make full use of LADRC.Compared with traditional PI controller,the LADRC controller designed in this thesis exhibits good qualities such as outstanding dynamic characteristics,good robustness and high disturbance rejection ability.Secondly,this thesis focus on parameter tuning issue of converter LADRC controller designed.In view of frequency domain tuning method is not applicable for converter LADRC controller as there are too many parameters to be tuned,this thesis puts forward a concrete and feasible parameter tuning method.The number of controller parameters to be tuned is simplified through theoretical analysis according to bandwidth method and frequency domain method.On this basis,the controller parameters are tuned from three perspective.Establishing small signal model of AC and DC system and tuning the controller parameters on the perspective of stability of the whole system.Deriving closed loop transfer function of control system of VSC converter and tuning the controller parameters on the perspective of closed loop stability of controller.Establishing two terminal VSC-HVDC equivalent model in which equivalent processing is made to the complicated outer AC system,and tuning the controller parameters on the perspective of stability of VSC-HVDC system.The advantages and disadvantages of the three methods are analyzed through examples and the application of each method is discussed.The study brings inspirations to LADRC parameter tuning and provides theoretical basis for the application of LADRC in VSC-HVDC domain.Lastly,this thesis studied power transmission capability of VSC-HVDC based on LADRC.The small signal model of the AC and DC system is established and power transmission capability is studied on the perspective of stability of the whole system.The method can reflect impact of AC system dynamics and VSC-HVDC stability on power transmission capability sufficiently.The results of small signal analysis are validated through examples and the main factors of power transmission capability connected to strong AC grid are then illustrated.The influence of weak AC grid condition to power transmission capability of VSC-HVDC based on LADRC is discussed through theoretical analysis and specific example.The study provides theoretical foundation for the study of power transmission capability of VSC-HVDC based on LADRC in engineering.