Protection Method Of Vsc-hvdc Line Based On First And Backup Discrimination

VSC-HVDC systems meets the requirements of grid connected energy consumption and interconnection of different systems,and become one of the important development directions of power system in the future.High speed and reliable protection technology is of great significance to the development and application of VSC-HVDC.At present,the backup protection will be triggered due to the failure,misoperation and misoperation of the main protection.The backup protection work means that the longer time for the protection system to remove the fault,which is not conducive to the stability of the power system.In order to solve this problem,this paper provides the protection scheme based on the line fault of radial VSC-HVDC system.First of all,this paper analyzes the main equipment of VSC-HVDC system,including the basic structure and classification of the voltage source converter,the basic control system of the converter,the classification and basic structure characteristics of the DC circuit breaker.Then,in view of the current situation that the protection is only tested once,this paper proposed the protection idea of synchronous first discrimination and backup discrimination.The first discrimination is sensitive detection fault and backup discrimination confirms fault,which can avoid the main protection from misoperation and misoperation,and reduce the probability of triggering backup protection.In addition,the maximum difference value is put forward for the possible fault misjudgment of voltage change rate criterion in the bipolar system,and a radial network is built on PSCAD / EMTDC to verify the feasibility of the first discrimination,backup discrimination and pole selection criterion.At last,aiming at the problem of bad working condition of DC circuitbreaker when DC line fault occurs,this paper proposed to limit the current synchronously when the protection was started,adopt the state space average method to equivalent the converter,and adopt the proportional integral differential(PID)control to limit the current of the converter capacitor,and use the mechanism method to build the protection model to verify the feasibility of the active control to limit the current in MATLAB.