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SUMMARYIn this brief, we extend the existing results on fault tolerant control via virtual actuator approach to a class of systems with Lipschitz nonlinearities to maintain the closed‐loop stability after actuator faults. This generalization is established by relying on the input‐to‐state stability properties of cascaded systems. The virtual actuator block, placed between faulty plant and nominal controller, generates useful input signals for faulty plant by using output signals of the nominal controller to guarantee the closed‐loop stability in the presence of actuator faults. This design problem is reduced to a matrix inequality that can be turned to an LMI by fixing a variable to a constant value and solving the resulting LMI feasibility problem. The proposed fault tolerant control method is successfully evaluated using a nonlinear system. Copyright © 2013 John Wiley & Sons, Ltd.

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We extend existing theory on robust nonlinear observer design to the class of nonlinear Lipschitz systems where the systems are subject to sensor faults and disturbances. The designed observer is used for robust reconstruction of fault signals. Allowing bounded unknown disturbances to model system uncertainties, it is shown that by adjusting a design parameter we can trade off between fault reconstruction and disturbance attenuation. An LMI procedure solvable using commercially available softwares is presented. Two examples are presented to illustrate the application of the results.

This article presents novel robust adaptive fault tolerant control strategies for the class of nonlinear Lipschitz systems in the presence of bounded matched or unmatched disturbances and actuator faults (failure, loss of effectiveness, and stuck). Two constructive algorithms, based on linear matrix inequalities with creatively using Lyapunov stability theory, are developed for online tuning of adaptive and fixed state feedback gains to stabilize the closed-loop control system asymptotically, to compensate actuator faults, and to attenuate disturbance effects. The resultant control schemes have simpler and constructive structures as compared with most existing methods. The merits of the proposed schemes have been verified by the simulation on an unstable nonlinear process subjected to actuator faults.

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In this paper, the trajectory tracking problem for a wheeled mobile robot in the presence of kinematic and dynamic uncertainties has been addressed. Uncertainties are modeled as lumped disturbances. A kinematic controller based on feedback linearization approach and a dynamic controller based on model reference adaptive control are designed in the presence of disturbances. In order to ensure both robustness and implementability of the controllers, the disturbances are estimated by a generalized linear matrix inequality-based disturbance observer. Simulation results show the effectiveness of the proposed method.

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