This paper investigates the problem of adaptive neural tracking control via output-feedback for a class of switched uncertain nonlinear systems without the measurements of the system states. The unknown control signals are approximated directly by neural networks. A novel adaptive neural control technique for the problem studied is set up by exploiting the average dwell time method and backstepping. A switched filter and different update laws are designed to reduce the conservativeness caused by adoption of a common observer and a common update law for all subsystems. The proposed controllers of subsystems guarantee that all closed-loop signals remain bounded under a class of switching signals with average dwell time, while the output tracking error converges to a small neighborhood of the origin. As an application of the proposed design method, adaptive output feedback neural tracking controllers for a mass-spring-damper system are constructed.

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SUMMARYIn this paper, we investigate the H 1 control problem for uncertain switched nonlinear systems with passive and non-passive subsystems. For any given average dwell time, any given passivity rate and any given disturbance attenuation level, we design feedback controllers of subsystems, which may depend on the pre-given constants, to solve the H 1 control problem for the uncertain switched nonlinear systems for all admissible uncertainties. For linear systems, the exponential small-time norm-observability is shown to be preserved under disturbance. Two examples are provided to demonstrate the effectiveness of the proposed design method.

This paper addresses the state-tracking model reference adaptive control problem for a class of switched systems with parametric uncertainties, where switchings between subsystems and designed adaptive controller are asynchronous. First, we establish a stability criterion for a switched reference model and convert the state-tracking problem into the stability problem of an error switched system. Then, an adaptive law is designed, and the global practical stability of the error switched system is guaranteed under a class of switching signals characterized by a dwell-time condition. An electrohydraulic system is given as an example to demonstrate the feasibility and effectiveness of the proposed design method.nonswitched uncertain systems, a number of types of adaptive control methods have been developed. Among these methods, model reference adaptive control (MRAC) has been extensively applied in engineering systems [16]. Asymptotic state tracking as well as the boundedness of all signals in the closed-loop system can be guaranteed by designing a proper adaptive controller with adjustable parameters under a tuning mechanism [17,18].Obviously, uncertainties exist extensively in switched systems and make the study of switched systems even more complicated. Adaptive control as a powerful tool for uncertain nonswitched systems is also expected to be an effective tool for the study of uncertain switched systems [19][20][21][22]. However, it is worth pointing out that most existing results are based on the assumption that switching between the designed adaptive controllers is exactly the same as that between subsystems. This assumption is often unrealistic in practice [23]. Normally, there is a communication channel to connect the system and the controller, and thus, it might be physically impossible to identify the active subsystem and to apply the corresponding adaptive controller simultaneously. In this case, the controller switches later than the system, which causes asynchronous switching in the closedloop system. Apparently, the mismatched controller may lead to instability of switched systems [24]. Thus, it is of great importance to consider the effects of asynchronous switching. In recent years, there are an increasing number of applications of switched control systems with asynchronous switching, such as power converters [25] and multi-agent systems [26]. In [27], the stabilization problem of switched linear neutral systems with asynchronous switching was studied. In [28], the input-to-state stabilization based on asynchronous switching was investigated. Asynchronously switched control in both continuous-time and discrete-time contexts was discussed in [29]. The synthesis of Markov jump linear systems under asynchronous switching was conducted in [30].It is often inevitable that uncertainties and the asynchronous switching coexist in a switching system in practice. For structural uncertainties, in a class of switched nonlinear systems, robust control problems under asynchronous switching were investigated in [31...