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This paper deals with the problem of controller design for normal nonlinear switched systems with unknown dynamics. The situation assumes that the nonlinear component of the system dynamics is unknown and there are extra uncertain terms and external perturbations affecting the system responses. Unlike previous methods that usually apply artificial neural networks to obtain an approximate model for an unknown dynamics, we use simple adaptive laws to surmount such fluctuations as well as to circumvent the steady state errors in the approaches provided by neural networks or fuzzy logics. No information on the bounds and parameters of the uncertain parts is needed. We design a twofold sliding mode control methodology to stabilize the whole switched system with arbitrary switching signals. To handle the consequences of the inherent chattering, a smooth integral type control signal is constructed. It is proved that once the system states attain the developed sliding manifold, the system becomes insensitive to both the lumped uncertainties and the dynamics of the switched system. The common assumption of a known Lyapunov functions for the subsystems is relaxed and the derived adaptive approach provides nonconservative circumstances for guaranteeing the global stability of the equilibrium state. The theoretical results of this paper are generalized for the canonical nonlinear systems with mismatched uncertainties and a novel adaptive sliding manifold is proposed to suppress the effects of the system mismatching uncertain parts. A comparative computer simulation is developed to examine the effective performance of the introduced controllers. [ABSTRACT FROM AUTHOR]

Unified power flow controller (UPFC) is one of the most versatile and complex flexible AC transmission system (FACTS) devices. It is 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 damping of power oscillations using UPFC. A state‐variable control strategy is derived and implemented to tackle the problem of finite‐time convergence of system states. In the suggested method, the chattering phenomena and discontinuity of the controller, that is common in finite‐time controllers, are removed to obtain a continuous and smooth controller. The suggested controller is simple and clear than the conventional famous finite‐time controllers for double‐integrator systems. Simulation results are given to illustrate the effectiveness and robustness against parameter uncertainty and external disturbances 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. The proposed controller is investigated on UPFC connected to a two‐bus power system. [ABSTRACT FROM AUTHOR]