Research On The Control Design For Upfc Based On Differential-Algebraic Systems

Unified Power Flow Controller (UPFC), which is one of the most representative one of Flexible AC Transmission System (FACTS)devics, not only can control the voltage, impedance and phase angle of the transmission line effectively, but also can independent regulate the active and reactive power, increase system damping and restrain subsynchronous oscillation. As the milepost of development in FACTS technology,it can effectively improve the static stability and transient stability of power system. Undoubtedly, the control system is the core of UPFC, in this case, the study of control strategy in UPFC is of great theoretical and practical significance. This paper focuses on the application of control theory in UPFC and its effect on improving the stability of power system.First of all, this paper introduces the control theory of differential-algebraic system, discusses the design method of SISO and MIMO control systems, and proposed a new model of UPFC with differential-algebraic equation. Considering the concept of multi-index control design, this paper selects a plurality of target state of linear combination for the output function, such as voltage increment of controlled bus, angle increment of enerator, rotor speed incement of generator, and DC capacitor voltage incement of UPFC ect. After that, the new control strategy of UPFC is derived through the control theory of differential-algebraic control systems. The effects for enhancing dynamic performance of Power system and conrolling bus coltage and line power flow are illustrated by simulation on a one machine infinite bus system.It manifests the validity and significant advantages of the design approach proposed in this paper.Secondly, according to the drawbacks of control performance, a new control law for the UPFC was given, which is based on the Nonlinear Control method with Objective Holographic Feedbacks (NCOHF).Applying the design scheme, all control targets of the nonlinear control system of UPFC were transformed into the linear space, and punished by the performance index. Thus the linear control law have all the feedback informations of control targets. After that, a better controller of UPFC is derived through the control theory of NCOHF and linear optimal.The simulation manifests that there is perfect harmony between the dynamic and the static performances of the UPFC. Obviously, NCOHF improves the output characteristic of the UPFC.Finally, on the basis of the mention above, it combines organically the control theory of differential-algebraic system and the objective holographic feedback.Then a new UPFC is derived through the above control theory, and the simulation results show that the method is effective and practical.