The Design, Modeling, Simulation Of Nonlinear Controller For FACTS

With deregulation of the electric industry and persistent increase of electric loads more attention is paid to the security of power systems. The Flexible AC Transmission System (FACTS) based on high power electronic elements is becoming the research focus, since they have a lot of advanced characteristics, such as, flexibly and rapidly control power systems, improve transfer capability of transmission networks, strengthen the stability, reliability and security of power systems, make power system higher controllable and so on. At present, various kinds of FACTS have widely been applied in power systems. FACTS devices make the power system more flexible and controllable than before, but add the control difficulties of the system as well. Therefore, the design and research of FACTS are of great significance and urgency.There are many methods for the controller design of the FACTS devices, such as linear optimal control, feedback linearization method of nonlinear system, H∞robust control, ANN control, intelligent control and so on. Recently, the nonlinear control method is widely used in different areas because of its advantages, but it is not easy to use the nonlinear method in the controller design of FACTS while the mathematical models of FACTS are so complicated with multi-input variables.This paper studied the nonlinear controller design of three representative FACTS devices, STATCOM, SSSC and UPFC. At first, the nonlinear mathematic equations of the power system installed with FACTS devices are established, and from the dynamic equations, the steady-state operation point can be deduced. To deal with the nonlinearity, based on the energy conservation, a function is constructed to meet theLyapunov globally asymptotical stability, and combined with the linearization method. The nonlinear control system is also degraded to a simple linear system. Then, through linear feedback control, the input variables can be deduced easily. At last, three controllers are modeled on EMTP/EMTPWorks, and tested in three typical systems with long transmission lines. The simulation results demonstrate the correctness of the proposed controllers. Compared with the PI controller of UPFC, the new proposed controller of UPFC has better stability and dynamic performance. These results also illustrate that the FACTS device with small capacity can offer larger series compensation to the system, and enhance the stability of the system, for example, when a sing-phase to ground fault occurs.