In this paper, an observer-based controller is designed to control a class of discrete-time switched nonlinear systems with state delay and external disturbances. Based on the passivity concept, the average dwell time method, and auxiliary matrices, less-conservative sufficient conditions are derived to make the closed-loop system finite-time bounded and passive in the presence of disturbances. In contrast to existing papers in this field, this paper deals with discrete-time nonlinear switched systems and especially with an observer-based controller. The developed conditions are presented in the form of linear matrix inequalities. Finally, computer simulations (numerical and practical examples) are provided to illustrate the performance of the proposed controller.
K E Y W O R D Saverage dwell time method, discrete-time switched systems, finite-time boundedness, observer, time-delay
INTRODUCTIONLyapunov stability focuses on infinite-time convergence 1-5 ; however, in many practical systems, the behavior of the system in a finite time is important. 6,7 In other words, the state variables should not exceed a certain threshold in a finite period. 8 For this purpose, the concept of finite-time stability which focuses on the transient behavior of the system has been introduced. 9 Then, due to the importance of the system performance in the presence of external disturbances, this concept has been generalized to finite-time boundedness. 10 It means that the state variables do not exceed a determined threshold over an interval in the presence of external disturbances with a bounded initial condition. 11 On the other hand, switched systems as a class of hybrid systems have attracted the attention of many researchers. 12-16 Switched systems include multi-subsystems and a switching rule specifying the active subsystem at each time instant. Many researchers have investigated finite-time stability or boundedness of switched systems including discrete-time or continuous-time cases. 1,[17][18][19][20] Practically, discrete-time systems are more important when a digital controller should be implemented. Moreover, finite-time control of discrete-time switched systems can be found in the literature for linear, 21-23 singular, 24 nonlinear, 8,25 stochastic, 26 and markovian jump 27 systems.Passivity plays an important role in the controller design for many practical systems, and also switched systems. [28][29][30] The passivity theory has been presented in various fields such as time-delay systems, 31 signal processing, 32 fuzzy control, 33 neural networks systems, 34 and chemical processes. 30 Generally, passivity-based control allows a better closed-loop performance under transient and steady-state operating conditions. 33 In this method, the model of the system is not necessarily passive; the designed controller will make the closed-loop system passive according to the definition that will be introduced later.