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Summary: This paper explores regulation theory for the design of robust precision attitude tracking of an uncertain rigid spacecraft with external disturbances. Focusing on the attitude system in terms of unit quaternions with an unknown inertia matrix and unmodeled input disturbances, we first introduce specific nonlinear logic such that the resultant error‐quaternion system has an input‐to‐state stability property. Then, we establish an attitude deviation system with an output feedback normal form that has a strict vector relative degree of unity. This enables us to achieve robust output regulation based on an internal model. In particular, we can construct a high‐gain stabilizer for the relevant augmented system. As a major consequence, our study achieves not only precision attitude tracking with exponential convergence but also the input‐to‐state stability disturbance attenuation for the closed‐loop system. Finally, we show extensive simulation and experimental results to illustrate the approach. [ABSTRACT FROM AUTHOR]

Summary: This paper is to suggest a novel design for ship tracking control of the benchmark Norrbin nonlinear ship model under relaxed conditions. The challenges of the problem under investigation include the uncertain or absent information of the model time constant, the uncertain reference course, and the intrinsic environmental disturbances. We formulate the ship tracking control problem in terms of a nonlinear output regulation problem with unknown control direction and uncertain exosystems. To solve the problem, we first adopt a novel internal model candidate to convert the output regulation problem into a stabilization problem for an augmented system. Then, a Nussbaum‐gain‐based stabilizer is developed for the augmented system to complete the design. Simulation results are presented to show the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper presents a Nussbaum function-based universal cooperative output regulation design for a class of nonlinear multiagent systems with both an unknown exosystem and nonidentical unknown control directions. The major challenges include the nonidentical unknown control directions in a directed communication graph and the concurrence of the unknown parameters in both the plant and the exosystem. To handle the nonidentical unknown control directions, we propose a dynamic compensator-based distributed controller such that the Nussbaum gain technique can be successfully implemented under directed communication graphs. Moreover, to deal with the unknown exosystem, we integrate the distributed controller with a novel internal model candidate. The resulting distributed controller is a universal regulator in the sense that it does not require the unknown parameters to be in known compact sets. Furthermore, the proposed controller is more flexible compared with those in the existing works as any existing Nussbaum gains can be adopted in the controller design and the adopted Nussbaum gains can be nonidentical for each agent. [ABSTRACT FROM AUTHOR]

This paper concerns global robust output regulation of a class of nonlinear lower triangular systems with an unknown high-frequency gain as well as an unknown exosystem. A novel class of internal model candidates is integrated with the output regulation framework. As a result, stabilization of the augmented system can be performed without parameter estimators. However, the new internal models bring challenges to the stabilization of the augmented system. To overcome these challenges, we propose a new recursive controller design procedure and use it to develop a Nussbaum-gain-based controller. This work extends the existing results on nonlinear output regulation of lower triangular systems to the case where both the high-frequency gain sign and the exosystem are unknown. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]