Robust control design for UPFC to improve damping of oscillation in distribution system by H2 method
Tech. Eng. Dept., Univ. of Sci. & Technol., Tehran, IranConference: Electrical Power Distribution Networks (EPDC), 2011 16th Conference on
Source: IEEE Xplore
An industrial plant, such as power systems, always contains parametric uncertainties. In the design of a controller the uncertainties have to be considered. Otherwise, if the real plant differs from the assumed plant model, a controller designed based on classical controller design approaches may not ensure the stability of the overall system. In this paper design of robust control for the UPFC controllers including power - flow and DC voltage regulator, using a H2 design is presented. As an example, we have designed a case for the system to compare the proposed method with a conventional method (classical P-I controller). AS the results of the simulations, the validity of the proposed method has been confirmed.
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ABSTRACT: Unified power flow controller (UPFC) is one of the most versatile and complex flexible AC transmission system devices to have emerged with a proven capability of instantaneous control of transmission line parameters. This study presents an approach based on the direct Lyapunov stability theory with finite-time convergence and chattering free characteristics to improve the power flow control in transmission lines using a UPFC. A state variable control strategy is derived and implemented to tackle the problems of reference tracking, robustness against parameter uncertainty and external disturbances. The main goal of the presented control system is power flow control with finite-time convergence of system states’. The chattering phenomena and discontinuity of the controller that is common in finite-time controllers are also removed to obtain a continuous and smooth controller. Simulation results are given to illustrate the effectiveness of the proposed algorithm. It is shown that the settling time of the system enhanced with the proposed controller is significantly less than the conventional non-linear controllers. As the most simply measurable states of the system are used in the suggested controller, there is no need to design a state space variable observer system. The proposed controller is investigated on the UPFC connected to a twobus power system.
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ABSTRACT: The unified power flow controller (UPFC) integrates properties of both shunt and series compensations, and can effectively alter power system parameters in such a way that increases power transfer capability and enhances system stability. In practice, simple proportional-integral (PI) controllers are used to control the UPFC. However, the PI control parameters are usually tuned based on classical or trial-and-error approaches and as such, they are incapable of obtaining good dynamic performance for a wide range of operating conditions and various loads in power systems. Hence, in this article robust control approaches are proposed based on the quantitative feedback theory (QFT), H-infinity and mu-synthesis, to design UPFC controllers (power-flow and DC-voltage regulator). The three mentioned methods are compared with each other and a supplementary damping controller is developed to improve damping power system oscillations. Here, a single-machine infinite-bus (SMIB) power system, installed with a UPFC (with system parametric uncertainties) is considered as a case study. The system parametric uncertainties are obtained following 40% simultaneous alterations in parameters and load from their typical values. The simulation results indicate satisfactory verifications of the robust control methods in dealing with the uncertainties considered. When the above three methods and the PI controller are compared in performance in several time-domain simulation tests, the results show clear superiority of the three methods over the PI controller, with the QFT presenting the best performance amongst the three robust control.
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