Research On The Control Method Using SVC And TCSC To Improve The Stability Of The AC/DC Parallel Transmission System

Recently, in the world the high voltage direct current transmission has been applied increasingly in big power system, only in our country more than one AC/DC parallel transmission lines has been built. The direct current transmission has many advantages, but the operating characteristics of the AC/DC parallel transmission system and which mutually affects each other are quite complex, so it brings new problems to the system stability.The direct current system convertor station needs to consume massive reactive power in the operation, which causes the voltage stability problem of the both sides alternating-current system become more and more severely; when quite serious disturbance or breakdown appears, the system stability also faces stern test. Therefore, the research on the methods and measures improving the stability of the AC/DC parallel transmission system is one of important subjects in the current power system.Flexible AC Transmission System (FACTS) will be widely used in power system, which is one of the frontal subjects of power system in recent years. Static Var Compensator (SVC) and Thyristor Controlled Series Compensator (TCSC) are the important elements of FACTS family and useful tools to improve the power system stability. Therefore, the research on using SVC and TCSC to the AC/DC parallel transmission system has significant theoretical meaning and practical value.In this dissertation, the mutual affecting characteristic of the AC/DC parallel system is analyzed according to the system operating characteristic and the problems of the system and the directions to the problems are pointed out. Based on the working principle and mathematic model of SVC and TCSC, then control methods of using SVC and TCSC to the system are researched.SVC is an important var compensation equipment in power system, when using only voltage nonlineral control it has rapid response speed and stronger adjusting ability and can issue or absorb reactive power according to the change of reactive power in the system operation, which improves the voltage stability.TCSC is an important series compensation equipment in power system, which gets up many kinds of stable control action according to the differences of control modes. In the AC/DC parallel transmission system. TCSC can increase the delivery capacity of the line and enhance merit angle and the voltage stability of the system by using the appropriate control strategy and changing flexibly the effective reactance value of it.In this dissertation the typical simulation model of AC/DC parallel transmission system is established, and two kinds of different intensive systems are setup, then the dynamic response is simulated when large disturbances occur in system such as load increasing severely, DC blocking, AC circuit breaking and so on. In view of each kind of big disturbances, the change situation of the voltage and frequency of the system and so on is simulated and analyzed separately to only using SVC or TCSC which uses fixed compensation with different compensativity or other compensation way, and simultaneously using SVC and TCSC, finally the validity and feasibility of the SVC and TCSC to the system stable control is approved.