Analysis And Research On The Control Strategy Of Unified Power Flow Controller

At present, the development direction of electric power system of all countries is that more and more transmission-line systems of electric power system is connected each other. UPFC is a kind of powerful and flexible power flow controller of FACTS. UPFC can control the active and reactive power flow in the line, and it can adjust the bus voltage. In addition, the UPFC device has a significant effect on the enhancing stability of the power system network and optimizing operation of electric power system. So it has very important theoretical and practical significance for researching on UPFC in the modern electric power system. This thesis anysises and resaerches two aspects of synchronous phase-locked technology and control strategy of series parallel sides converters based on UPFC device.Synchronous phase lock link is extremely important in the whole UPFC system, it is the control foundation of implementing all the control functions. This thesis presents two novel software phase-locked technologies (SPLL) which can accurately track frequency and phase of the grid system and precisely detect symmetrical component of the grid voltage. So that they can provide the accurate reference phase for generating a variety of control pulses and successfully accomplishing all control functions of the UPFC control system.This thesis allows the internal model control principle to re-bond with cross decoupling method on the foundation of summarizing current control strategies of series and parallel converters in the UPFC system, according to the weak robustness of cross decoupling method in the series and parallel converters. This new control method can have good tracking performance and fast response, and it can achieve strong robustness and eliminate steady-state error. Thus, the UPFC system has a better power flow control function.This thesis establishes the UPFC simulation model in the Matlab/Simulink platform. This simulation software tests the control strategy of UPFC system proposed in this thesis. The simulation results show that the two synchronization phase-locked technologies can overcome the shortcoming of the existing literatures, the SPLL technologies can provide accurate reference phase for generating these trigger pluses and successfully accomplishing all control functions of UPFC device, the design method of UPFC converters based on the internal model control can achieve the totally decoupling control of d axis and q axis controlled variables when the parameters of the control system are disturbed. The UPFC control system has the fast tracking performance and strong robustness, it can better achieve the control purpose of power flow control in the transmission-line systems of electric power system.