| The Unified Power Flow Controller (UPFC) is the most important and valuable device in Flexible AC Transmission Systems (FACTS). The configuration of actual UPFC device is consisted with the shunt-wound part and the series-wound part, this universal configuration determines that it has several functions in one device, such as STATCOM, SSSC, TCPS, and combines these functions in a device. UPFC can effectively control the power flow in power system; improve the line transmission ability; ameliorate the transient stability simultaneously and so on. Therefore it has important significance for researching UPFC.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.The model of power distribution systems and UFPC is set up by simulink tools in MATLAB, this model is very important for researching the operational capability . Based on this model, the author analyzes the regulative performance of UPFC in stable and dynamic condition. The simulative results show that UPFC can respond quickly and accurately to the demands of power system. Moreover, with the proposed control, the active and reactive power control can be effectively decoupled and the stability of DC side capacitance voltage are enhanced.
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