| As an important technology means, the flexible AC transmission systems(FACTS) can implement the power system security, economic running, and comprehensive control. The features of response rapidity and control stability, FACTS devices can solve problems of flow control and stability in the traditional AC transmission systems. Unified Power Flow Controller(UPFC) is a type of FACTS devices with the extremely flexible, powerful performance. By adjusting the basic power system parameters such as the voltage, phase angle and line impedance, UPFC not only realizes accurately real and reactive power regulation of the system, but also provides a variety of compensation to increase transmission capacity of power lines. Moreover, UPFC also can effectively suppress power-angle oscillations and improve transient stability of power systems.The function of the power flow regulation is mainly completed by the series side of UPFC. So, in this paper, the influences of the UPFC series-side injecting voltage components of the d axis and q axis to the active and reactive power are analyzed under the 2-phase rotating d-q coordinate system. The analysis indicates that, in the synchronous rotating d-q frame, UPFC mathematical model reveals a nonlinear system with features of a multi-variable, strong coupling, and more interference. In view of these system characteristics, the paper presents a nonlinear cross decoupled strategy with better stability and dynamic performance for UPFC control. The nonlinear cross decoupling control model is established in the d-q coordinate system. The d-axis and q-axis utilizes current cross decoupling control respectively, so as to realize the active and reactive power independent control, and the coordinated control between series side and shunt side of the UPFC, and finally, to improve the dynamic performance of the system as well as keeping the voltage stability of shunt side of UPFC. For the function of the series converter in power flow control of UPFC, we try to using the fuzzy combining neural network control in control system of UPFC after the analysis to the fuzzy combining neural network control method. The intelligent control method can improve the respond speed of system and make the power flow regulate time shorter.In order to verify the control strategy performance, the simulative experiments to the cross decoupling control are carried out under the platform of MATLAB. Simulation results show that the proposed control strategy can quickly and accurately respond to the needs of the power system, and realize real power and reactive power decoupling control effectively. |
