The Research On The Control Strategy Of Unified Power Flow Controller

Nowadays,the Unified Power Flow Controller(UPFC) is the most powerful device in the FACTS family, which have the ability of controlling kings of power system’s fundamental parameters. The paper primarily do some studies on operation mechanism, model and control strategy of UPFC for getting deep insight into the impacts of UPFC on power system performance.Firstly, the UPFC’s current research situation and working principle is introduced. The simple two machines model is adopted to explain UPFC’s working principle. The basic structure of UPFC is described and the UPFC’s parallel and series parts’operation mechanism are respectively analyzed. We have introduced kinds of UPFC’s working modes.We do some introduction of PSAT (Power System Analysis Toolbox) software and its simulation principle and simulation models.The PAST software is adopted to set up multi-machine systems with UPFC model,which include WSCC three machines nine nodes system and four machine two area system. The WSCC three machines nine nodes system including UPFC is simulated to analyze its steady state performance.We have simulated four machine two area system including UPFC in the short-circuit fault and have preliminary conclusions that UPFC can improve the steady state and transient performance of the system and multiple UPFCs will promote power system’s stability.Then the paper describes the unified power flow controller’s system parameters and the definition of the UPFC capacity. And we should notice some key factors when UPFC DC’s and transformer’s capacitors are selected. The paper adopted UPFC’s series part and parallel part models and decoupled control strategy to designe two parts controllers.Then we have simulated parallel part and verifed that the control strategy is feasible for the systems. In orde to compare fuzzy control strategy and PI (Proportional-Integral) control strategy, the PI control is adopted to design the series and parallel part controllers in the whole UPFC model.The UPFC model is set up by PSCAD software,which is simulated to analysis the steady-state and transient-state performance. Through large numbers of simulation,we get the good PI parameters and find that UPFC with PI control is able to imrove the the steady-state and transient-state performanceFinally, the Fuzzy control is applied to UPFC controllers. Firstly,we have introduced the concept of Fuzzy control and designed UPFC’s series part with Fuzzy-PI control.The active and reactive power difference are the fuzzy control input.We have introduced the Fuzzy-PI control design process and the selection of parameters in detail.The simulation shows that the Fuzzy-PI control have improved response time and overshoot and improve steady state and transient state performance of UPFC than the conventional PI control.