Mouhacine Benosman

Passive Actuators' Fault-Tolerant Control for Affine Nonlinear Systems

In this brief, the problem of passive fault-tolerant control (FTC) for nonlinear affine systems with actuator faults is considered. Two types of faults, additive and loss-of-effectiveness faults, are treated. In each case, a Lyapunov-based feedback controller is proposed, which ensures the local uniform asymptotic (exponential) stability of the faulty system, if the safe nominal system is locally uniformly asymptotically (exponentially) stable. The effectiveness of the FT controllers is shown on the autonomous helicopter numerical example.

Stable inversion of SISO nonminimum phase linear systems through output planning: an experimental application to the one-link flexible manipulator

In this paper, we introduce a new technique that allows for causal stable inversion of linear nonminimum phase systems. This approach is presented through its application to a flexible arm robot. In contrast with the available techniques, which amounts to finding a particular initial value for the inverse system to have bounded state trajectories, the presented scheme starts from any free initial conditions of the inverse dynamics, and searches for proper output trajectories with a polynomial form. Those output trajectories are computed such that the effect of the unstable zeros are completely cancelled. Furthermore, the scheme deals equally with hyperbolic as well as nonhyperbolic systems. The stable inverse is then incorporated into an output tracking controller, using a classical static state feedback. This global controller permits an exact tracking of the planned output. Experiments for a one-link flexible arm show good end-effector tracking results.

A Survey of Some Recent Results on Nonlinear Fault Tolerant Control

Fault tolerant control (FTC) is the branch of control theory, dealing with the control of systems that become faulty during their operating life. Following the systems classification, as linear and nonlinear models, FTC can be classified in two different groups, linear FTC (LFTC) dealing with linear models, and the one of interest to us in this paper, nonlinear FTC (NFTC), which deals with nonlinear models. We present in this paper a survey of some of the results obtained in these last years on NFTC.

Online References Reshaping and Control Reallocation for Nonlinear Fault Tolerant Control

In this paper, we consider the problem of graceful performance degradation, for affine nonlinear systems. The method is an optimization based scheme, that gives a constructive way to reshape online the output reference for the post-fault system, and explicitly take into account the actuators and states saturations. The online output reference reshaping is associated with an online, model predictive control (MPC)-based, controller reconfiguration, that forces the post-fault system to track the new output reference. The effect of fault detection and diagnosis (FDD) uncertainties on the online controller reconfiguration stability are studied, to ensure at least boundedness of the closed-loop systems states. The reshaping and reconfiguration schemes are applied to the Caltech ducted fan numerical example, which is described by a non-minimum phase nonlinear model.

Nonlinear Control Allocation for Non-Minimum Phase Systems

In this brief, we propose a control allocation method for a particular class of uncertain over-actuated affine nonlinear systems, with unstable internal dynamics. Dynamic inversion technique is used for the commanded output to track a smooth output reference trajectory. The corresponding control allocation law has to guarantee the boundedness of the states, including the internal dynamics, and satisfy control constraints. The proposed method is based on a Lyapunov design approach with finite-time convergence to a given invariant set. The derived control allocation is in the form of a dynamic update law which, together with a sliding mode control law, guarantees boundedness of the output tracking error as well as of the internal dynamics. The effectiveness of the control law is tested on a numerical model of the non-minimum phase planar vertical take-off and landing (PVTOL) system.

Constrained Nonlinear Finite-Time Control Allocation

This paper proposed an optimal control allocation method for a general class of overactuated nonlinear systems with internal dynamics. Dynamic inversion technique is used for the commanded subsystem to track a stable model reference control law. The corresponding control allocation law has to guarantee the stability of the internal dynamics and satisfy control constraints. The proposed method is based on a Lyapunov design approach with finite-time convergence to optimality. The derived control allocation is in the form of a dynamic update law, which, together with the stable model reference control law, guarantees the stability of the closed-loop nonlinear system.

Output trajectory tracking for a switched nonlinear non-minimum phase system: The VSTOL aircraft

This work concerns output trajectory tracking for the McDonnell Dougglas YAV68B Harrier VSTOL aircraft. This system can perform three distinct flight modes, and is modelled with a Lagrangian nonlinear hybrid non-minimum phase dynamics. Output tracking is solved using classical input/output linearization scheme associated to an internal dynamics stable inversion for each flight mode dynamics. The performance of the global switched control law is discussed and validated through simulation tests.

Model inversion for a particular class of nonlinear non-minimum phase systems: an application to the two-link flexible manipulator

Concerns the output trajectory tracking for a class of nonlinear nonminimum-phase systems, namely, systems described by Lagrange equations of motion. In the nonminimum-phase case, the direct application of classical input-output inversion procedure fails, due to the unacceptable nature of internal dynamics. The paper concerns the inversion of those internal dynamics. Inversion yielding a bounded state permits then to achieve exact output tracking (or asymptotic tracking), without control saturation. The inversion scheme deals equally with systems having hyperbolic or nonhyperbolic equilibrium points of zero dynamic. This is a consequence of a different formulation of the stable inversion problem. The nonlinear internal dynamics are inverted, without any noncausal computation and are fully based on nonlinear terms, without local dynamic linearization. The performance is demonstrated through application to the tip trajectory tracking for a two-link flexible manipulator.

Accurate Trajectory Tracking of Flexible Arm End-Point

Abstract This paper discusses the design of an open-loop control law for a flexible one-link robot. The obtained torque permits to track with low errors any smooth end-effector trajectory. This feedforward control torque is obtained using a new control approach, based on the parameterization of differential operators, which gave good results on the articular tracking (Benosman and Le Vey, 20006). We present a feedback extension of the obtained nominal torque and test the robustness of the closed-loop law with respect to unstructured uncertainties, parametric errors and measurement noises.

Adaptive nonlinear control allocation of non-minimum phase uncertain systems

This paper presents an adaptive nonlinear control allocation method for a general class of non-minimum phase uncertain systems. Indirect adaptive approach and Lyapunov design approach are applied to the design of adaptive control allocation. The derived adaptive control allocation law, together with a stable model reference control, guarantees that the closed-loop nonlinear system is input-to-state stable.