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In this paper, we discuss the speed regulation problem of permanent magnet synchronous motor (PMSM) servo systems. Firstly, a continuous terminal sliding mode control (CTSMC) method is introduced for speed loops to eliminate the chattering phenomenon while still ensuring a strong disturbance rejection ability for the closed-loop system. However, in the presence of strong disturbances, the CTSMC law still needs to select high gain which may result in large steady-state speed fluctuations for the PMSM control system. To this end, an extended state observer (ESO)-based continuous terminal sliding mode control method is proposed. The ESO is employed to estimate system disturbances and the estimation is employed by the speed controller as a feed-forward compensation for disturbances. Compared to the conventional sliding mode control method, the proposed composite sliding control method obtains a faster convergence and better tracking performance. Also, by feed-forward compensating system disturbances and tuning down the gain of the CTSMC law, the fluctuation of steady-state speed of the closed-loop system is reduced while the disturbance rejection capability of the PMSM system is still maintained. Simulation and experimental results are provided to demonstrate the superior properties of the proposed control method.

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This article investigates the finite-time output tracking problem for a class of nonlinear systems with multiple mismatched disturbances. To efficiently estimate the disturbances and their derivatives, a continuous finite-time disturbance observer (CFTDO) design method is developed. Based on the modified adding a power integrator method and CFTDO technique, a composite tracking controller is constructed such that the system output can track the desired reference signal in finite time. Simulation results demonstrate the effectiveness of the proposed control approach. K E Y W O R D S composite control, continuous finite-time disturbance observer, finite-time tracking control, mismatched disturbance, nonlinear system Int J Robust Nonlinear Control. 2020;30:4095-4111.wileyonlinelibrary.com/journal/rnc

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Successful future asteroid landing missions require that the control method provides advanced disturbance rejection performance and strong robustness against parameter uncertainties to give higher accuracy and reliability in the complex space environment. Motivated by the requirement for safe and precise soft landing on asteroids, the finite-time soft-landing problem of an asteroid probe is addressed in this paper via a nonsingular terminal sliding mode (NTSM) control technique. The problem is formulated as a two-point boundary-value constraints control problem, where the initial and terminal requirements of the soft-landing problem are all included in the problem formulations. Then, according to the specific characteristics of the problem, an NTSM control law for soft landing on an asteroid is proposed. Simulation results demonstrate that, compared to the widely used traditional sling mode control method, the proposed method provides a much faster convergence rate, higher accuracies, better disturbance rejection properties and stronger robustness against parameter uncertainties.

In this paper, the global stabilization problem of a class of cascaded systems with upper-triangular structures is considered. On the basis of the forwarding technique, a series of virtual controllers are recursively constructed for the driving subsystem. According to the mild assumption imposed on the driven subsystem, a partial-state feedback controller is obtained for the entire cascaded nonlinear system by developing a delicate design fashion. It is shown that the obtained state feedback controller will render the entire cascaded nonlinear system globally asymptotically stable. Numerical examples are conducted to validate the proposed control scheme. /journal/rnc Int J Robust Nonlinear Control. 2018;28:4330-4344. LAN ET AL. 4331does not necessarily imply the stability of the nonlinear CSs. 1 Therefore, the control problem of nonlinear CSs is more challenging in the control field. Over the last two decades, various control methods have been developed for nonlinear CSs in the literature. * For the stabilization problem of nonlinear CSs, one intuitive idea to deal with this problem is to design full-state feedback controller that makes full use of the states information of the entire cascade systems. On the basis of the feedback passivation approach, a Lyapunov function construction and global controller design method is proposed in the work of Jankovic et al 2 for a class of nonlinear cascade and feedforward systems whose zero dynamics of the driven subsystem are globally stable. Then, this result is generalized in the work of Mazenc et al 15 by replacing the earlier growth conditions with a necessary boundedness condition in the construction of the Lyapunov function. Under the assumption that the zero dynamics of the driven subsystem are globally asymptotically stable and locally exponentially stable, a robust full-state feedback controller is constructed by using backstepping procedure in the work of Lin. 3 For a class of minimum-phase nonlinear CSs with unknown parameters, an adaptive regulation problem is investigated in the work of Lin and Qian 16 by using parameter separation technique and feedback domination approach. Another basic idea is to stabilize CSs by using partial-state feedback control approach, that is, only the driving subsystems' information is involved in the feedback controller design, whereas the driven subsystems' information is used in the stability analysis of the entire cascade system. On the basis of small gain theorem, 17 a stepwise constructive partial-state feedback control methodology is proposed in the work of Jiang and Marcels 4 for a class of nonlinear CSs in the context of input-to-state stability (ISS). 18 The robust global stabilization problem for a class of nonlinear CSs with dynamic uncertainty is considered in the work of Chen and Huang 6 by using Lyapunov's direct method. When the zero dynamics of the driven subsystem are ISS but not exponentially stable, a robust controller is constructed recursively for a class of polynomial CSs. 19 As the driven subsystem satisfies ...

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