Study On Modeling And Simulation For UPFC

As a typical Flexible AC Transmission System(FACTS) device, a Unified Power Flow Controller can provide many function. It can control transmission line impedence, voltage magnitude and phase angle either selectively or simultaneously in appropriate combinations and can also control independently the real and reactive power flow in transmission circuit. It is the most creative and flexible controller of FACTS family.The system configuration and work principium of UPFC are introduced in the paper firstly, and then this thesis builds up the model of UPFC in the abc three-phase system and synchronous dq frame by performing a Park-transformation, in which the dynamic performance of the DC link coupling two parts of the UPFC with transmission line is considered. The nonlinear decoupling control of the active power and reactive power of UPFC is discussed in this paper. As a step closer to a practical application of UPFC, the control method is based on the accuracy mathematic model of UPFC in the dq rotation frame, it can quickly and accurately follow the given power of system, moreover, the decoupling effect between the active and reactive power is evaluated. The current feedback control on the capacitor voltage is introduced, which improve the dynamic of UPFC.Sencondly, this thesis set up a Simulink model of UPFC after analyze its principle. And then, this model was applied into a three-phase system to observe its influences to power quality. At first, this paper researched the ability of UPFC to stabilize active and reactive power after a three-phase fault in transmission line. The characteristics of damp power pulse when a new equipment switch into a stable system is also analyzed. At last, whether UPFC could compensate system's voltage is reaerached. As a result, it's obvious that UPFC could keep system voltage in sine wave when in three-phase fault. On the other hand, it was found that UPFC has no negative influence to voltage of stable system.