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Summary: The problem of practical predefined‐time tracking control is con sidered for high‐order strict‐feedback nonlinear systems subject to unknown mismatched disturbances. The exact bound of the mismatched disturbances is unknown in this study. A novel adaptive predefined‐time tracking control strategy based on backstepping is proposed by applying a predefined time stability theory. Using the designed tracking controller, all signals are bounded, and a user‐defined bound on the tracking error is ensured in a predefined interval, independent of initial states. The estimation parameters associated with the upper bound of the disturbances are updated adaptively, making the system robust to the disturbances. Simulation studies are conducted to illustrate the performance of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Summary: In this article, we consider the event‐triggered cascade high‐gain observer (ETCHGO) for a class of nonlinear systems. By cascading lower dimensional observers, we design a cascade high‐gain observer together with a Zeno‐free event‐triggered mechanism to estimate the state of the plant. We show that the ETCHGO has the same steady‐state performance as the continuous‐time cascade high‐gain observer, that is, there is a finite time after which the estimation error will not exceed the given threshold, and moreover, the finite time and the threshold can be made sufficiently small by adjusting some design parameters. We also investigate an ETCHGO with saturation, which will reduce the peaking value while maintaining the steady‐state estimation performance. Furthermore, we use the ETCHGO with saturation to solve the output feedback stabilization problem for a class of nonlinear systems. An example is given to illustrate our results. [ABSTRACT FROM AUTHOR]

Summary: In this paper, we study the event‐triggered global robust practical output regulation problem for a class of nonlinear systems in output feedback form with any relative degree. Our approach consists of the following three steps. First, we design an internal model and an observer to form the so‐called extended augmented system. Second, we convert the original problem into the event‐triggered global robust practical stabilization problem of the extended augmented system. Third, we design an output‐based event‐triggered control law and a Zeno‐free output‐based event‐triggered mechanism to solve the stabilization problem, which, in turn, leads to the solvability of the original problem. Finally, we apply our result to the controlled hyperchaotic Lorenz systems. [ABSTRACT FROM AUTHOR]

The global robust output regulation problem of nonlinear systems in output feedback form has been studied via a linear internal model. In this paper, we study the same problem using a class of nonlinear internal models. An advantage of nonlinear internal models is that it exists even when the system contains nonpolynomial nonlinearity and the exosystem is nonlinear. Thus, the result of this paper applies to a larger class of nonlinear systems and a larger class of exosystems. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The surface-mounted permanent-magnet synchronous motor is a two-input, two-output nonlinear system. The multi-input, multi-output nature of the system has posed some specific challenges to various control methods. Recently, the robust output regulation problem of the system subject to a known neutrally stable exosystem was studied. The problem came down to a global robust stabilization problem of an augmented system composed of the original plant and an internal model. In this paper, we will further study the robust output regulation problem of the system subject to an unknown neutrally stable exosystem. Like in the case where the exosystem is known, the current problem can be solved by globally stabilizing an augmented system. But unlike in the case where the exosystem is known, the augmented system takes a much more complicated form because of uncertainty in the exosystem than the case where the exosystem is known. In particular, the dynamic uncertainty in the current augmented system contains linearly parameterized uncertainty, and hence is not input-to-state stable. By utilizing some dynamic coordinate transformation technique, and combining some robust control and adaptive control techniques, we will solve the problem via a recursive approach. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The cooperative global adaptive output regulation of nonlinear multi-agent systems with unity relative degree was studied recently for the case where the inverse dynamics of the follower subsystems are input-to-state stable (ISS). In this paper, we present a further result by relaxing the ISS assumption to the integral ISS (iISS) assumption. As the iISS condition is strictly weaker than the ISS condition, our result applies to a larger class of nonlinear multi-agent systems. [ABSTRACT FROM AUTHOR]

SUMMARY The asymptotic rejection of spacecraft systems under multi-tone sinusoidal disturbances has been studied recently for the case where the frequencies of the disturbance are known. In this paper, we further consider the case where the frequencies of the disturbance are unknown. We show that this case can be solved by an adaptive regulation technique. We also present some analysis on the convergence issue of the estimated frequencies to unknown frequencies. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, we study the global robust output regulation problem for a class of multivariable nonlinear systems. The problem is first converted into a stabilization problem of an augmented system composed of the original plant and an internal model. The augmented system is a multi-input system containing both dynamic uncertainty and time-varying static uncertainty. By decomposing the multi-input control problem into several single-input control problems, we will solve the problem by solving several single-input control problems via a recursive approach utilizing the changing supply function technique. The theoretical result is applied to the speed tracking control and load torque disturbance rejection problem of a surface-mounted permanent magnet synchronous motor. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]