This paper addresses the output-tracking control problem for a class of nonlinear sandwich systems with external disturbances and model uncertainties. Sandwich systems are a special class of nonlinear systems in the cascade structure, which are made up of several distinct subsystems while the non-smooth nonlinear functions are sandwiched among their separate subsystems. This paper concentrates on the sandwich systems consisting of two arbitrary-order nonlinear cascaded subsystems, while the saturation nonlinearity is sandwiched between them. The robust control law is designed such that the output of the sandwich system tracks the desired time-varying reference signal despite the saturation occurrence. Due to the characteristics of the saturation function and also the existence of the external disturbances and model uncertainties, the considered problem is facing some serious challenges. To deal with these difficulties, the design procedure is divided into two phases. In the first phase, the second subsystem and the sandwiched saturation nonlinearity are considered. In this phase, by utilizing the backstepping approach, the desired input signal of the saturation function is designed. In the second phase, the control input of the first subsystem is designed based on the sliding mode technique in a way that the output of the first subsystem tracks the desired signal which is obtained in the first phase. Finally, to verify the effectiveness of the proposed method, it is applied to a practical sandwich system.

中文翻译：

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具有夹心饱和非线性的夹心非线性系统的鲁棒时变跟踪控制

本文解决了一类具有外部扰动和模型不确定性的非线性夹心系统的输出跟踪控制问题。夹心系统是一类特殊的级联结构的非线性系统，它由几个不同的子系统组成，而非光滑非线性函数则夹在它们独立的子系统之间。本文重点研究由两个任意阶非线性级联子系统组成的夹心系统，而饱和非线性则夹在它们之间。鲁棒控制律的设计使得夹心系统的输出跟踪所需的时变参考信号，尽管发生饱和。由于饱和函数的特性以及外部扰动和模型不确定性的存在，所考虑的问题正面临一些严峻的挑战。为了解决这些困难，设计过程分为两个阶段。在第一阶段，考虑第二子系统和夹层饱和非线性。在这个阶段，利用反步法设计饱和函数的期望输入信号。在第二阶段，第一子系统的控制输入基于滑模技术设计，使得第一子系统的输出跟踪第一阶段获得的期望信号。最后，为了验证所提出方法的有效性，将其应用于实际的三明治系统。考虑第二子系统和夹层饱和非线性。在这个阶段，利用反步法设计饱和函数的期望输入信号。在第二阶段，第一子系统的控制输入基于滑模技术设计，使得第一子系统的输出跟踪第一阶段获得的期望信号。最后，为了验证所提出方法的有效性，将其应用于实际的三明治系统。考虑第二子系统和夹层饱和非线性。在这个阶段，利用反步法设计饱和函数的期望输入信号。在第二阶段，第一子系统的控制输入基于滑模技术设计，使得第一子系统的输出跟踪第一阶段获得的期望信号。最后，为了验证所提出方法的有效性，将其应用于实际的三明治系统。第一子系统的控制输入基于滑模技术设计，使得第一子系统的输出跟踪在第一阶段获得的期望信号。最后，为了验证所提出方法的有效性，将其应用于实际的三明治系统。第一子系统的控制输入基于滑模技术设计，使得第一子系统的输出跟踪在第一阶段获得的期望信号。最后，为了验证所提出方法的有效性，将其应用于实际的三明治系统。