Research On Operating Characteristic And Control Strategy For Unified Power Flow Controller

Modern power system becoming increasingly huger and more complex,flexible AC transmission systems(FACTS)has been widespreadly focused around the world.Since the unified Power Flow Controller(UPFC)is able to concurrently or selectively control the transmission voltage,impedance and angle,how to flexibly adjust the power flow in the transmission line by UPFC is becoming the heated research home and abroad.At present,there are a lot of papers based on UPFC control strategies,but there are also some problems to be solved.Therefore,based on the results of previous researches,this thesis is focused on the control strategy of UPFC in Transmission Line.The details of this paper are as follows:At first,this paper gives a brief introduction to the basic structure of UPFC and analyzes its operating principle and working pattern from the aspects of serial-shunt parts respectively.Then,the basic parameters which UPFC controls the power flow in transmission line is calculated.Based on the previous formulas,UPFC's working ranges are listed in paper and the mathematical models of shunt-serial parts through topology model will be established.The cross-decoupled control strategy will be adopted in shunt part and the cross-coupled control strategy in series part.Based on the reactive power balance analysis,the output real power of serial parts is considered as a feedback to shunt part directly in the paper.By this way,the advanced strategy can achieve a coordination control between shunt part and serial part.It will also make the DC-link voltage more insensitive when the transmission line changes.In order to raise the reacting speed of series part,an advanced proposal is put forward based on fuzzy PI control,Detailed design of fuzzy PI controller is also given in the thesis.In this thesis,the simulation model of UPFC is set up by Matlab / Simulink.Different models of UPFC are tested on the condition of steady-state operation and three-phase fault in Matlab/ Simulink.The simulation indicates that When transmission line happens to mutate,the advanced UPFC contorller's DC-link voltage fluctuation become relatively smaller.Compare to the traditional PI controller,the reacting speed of fuzzy PI controller is faster,more precise and more robuster.