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This paper addresses an augmented nonlinear lateral vehicle and lane keeping dynamics in the presence of some unknown disturbances. In a geometric basin, considering unobservable spaces, their orthogonal complements, and using control invariant properties, a disturbance decoupling mechanism is designed for the mentioned dynamics. Afterward, a nonlinear tracking controller is designed to steer the vehicle on a reference path. The obtained disturbance decoupling and tracking controllers are implemented on a typical passenger car in a simulation environment to demonstrate the effectiveness and performance of the proposed method. It is shown that the controller decouples both the uniformly distributed and exponentially attenuated disturbances from the output.

International audience; In this paper, we consider the problem of disturbance decoupling for a class of non-minimum phase nonlinear systems. Based on the notion of partially-minimum phaseness, we shall characterize all actions of disturbances which can be decoupled via a static state feedback while preserving stability of the internal residual dynamics. The proposed methodology is then extended to the sampled-data framework via multi-rate design to cope with the rising of the so-called sampling-zero dynamics intrinsically induced by classical single-rate sampling.

In this paper two classical problems of interest in control theory, namely disturbance decoupling and the design of Unknown Input Observers (UIO), are revisited in the context of linear hybrid systems in the presence of state-driven jumps, induced by multi-affine sets. Interestingly, the latter feature renders the overall problem intrinsically nonlinear, hence classical (geometric) conditions cannot be straightforwardly applied. Firstly, it is shown that the definition of the disturbance decoupling control objective needs to be adapted to the hybrid setting, by distinguishing between weak and strong decoupling. In the former, the desired requirement consists in ensuring that the output of the plant is independent of the disturbance on each flow subinterval and across the successive jump, while the latter requires that both the output trajectory and the corresponding time domain, which is potentially perturbed in the uncontrolled case, are not affected by the disturbance. Easily verifiable geometric necessary and sufficient conditions to achieve weak or strong decoupling are presented and discussed. Then, it is shown that the solution to an auxiliary strong decoupling control problem is instrumental for the design of unknown input observers, whose existence conditions mimic and extend those for purely continuous-time systems. The paper is concluded by numerical simulations that corroborate the theoretical analysis.

This study is devoted to robust state estimation and fault detection for nonlinear discrete fractional order systems using a novel fractional order filter algorithm. While noise and disturbance effects can suppress or even disturb the state estimation, the proposed filter can preciously estimate the states of nonlinear fractional order systems. Disturbance decoupling approach is the fundamental basis for the proposed filter to make it robust against unknown inputs. Simulation results illustrate the advantages of the proposed filter for state estimation and fault detection of nonlinear fractional order systems in the presence of both noise and disturbance.

We propose a novel approach to design an integral sliding mode control (ISMC) for a nonlinear system in regular form. The control method is capable to compensate a class of matched and, in particular, unmatched uncertainties with respect to some given output. Conditions for stability and decoupling are presented. For the case of linear nominal dynamics these conditions take a very simple form. A direct comparison to conventional design methods for ISMC is given and the concepts are illustrated using a simulation example.

This paper presents an Attitude Active Fault Tolerant Control for satellite. The proposed fault tolerant controller is constituted by two main parts: a nominal controller, designed assuming that the system is healthy, and a fault diagnosis module which is in charge of detecting, isolating and estimating the fault affecting the system. The fault diagnosis module is designed by using the Non Linear Geometric Approach which allows for the design of detection residuals and estimation filter decoupled from the aerodynamic disturbance which represents the main uncertainty in low Earth orbits. The simulation results show the benefits, in terms of attitude tracking accuracy, arising when adopting the proposed method.

This paper presents new results regarding the development of a fault detection and isolation scheme for a nonlinear satellite model. The main issue concerns the handling of frequency faults affecting the reaction wheels of a spacecraft attitude control system, i.e. how to detect and isolate faults, and lastly how to determine the different frequencies characterising these faults through spectral analysis. As the study focusses on a general satellite nonlinear model, where aerodynamic and gravitational disturbances, as well as measurement errors are present, the robustness of the suggested strategy is achieved by exploiting an explicit disturbance decoupling method via a nonlinear geometric approach. In order to achieve accurate fault diagnosis, aerodynamic disturbance decoupling represents a key point, since the aerodynamic model is often uncertain. Moreover, an improvement of the nonlinear geometric approach is presented, in order to realise an aerodynamic decoupled fault diagnosis with normalized fault sensitivity. To the best authors? knowledge, this is the first works presenting a methodology for frequency fault diagnosis which is based on the nonlinear geometric approach for the fault and disturbance decoupling. The obtained results demonstrate that the proposed methodology can achieve better performances with respect to traditional fault detection and isolation schemes.

We tackle here, for nonlinear systems, an important problem in the context of deterministic observer-based fault detection and isolation theory: the Fundamental Problem of Residual Generation. By analyzing its solution in the linear case, a formulation of the problem for the nonlinear input-affine case is proposed and conditions for solving it are stated by exploiting the theory of linearization up to input/output injection.

This work shows how to use a differential geometry tool to design a novel nonlinear active fault tolerant flight control system for aircraft. The proposed control scheme consists of two main subsystems: a controller, which is designed for the nominal plant, and a fault detection and diagnosis module, which provides fault estimation. A further feedback loop exploits the fault estimation to accommodate faults affecting the system. The estimate convergence and the stability of the active fault tolerant flight controller are theoretically proved. Finally, high fidelity simulations show the effectiveness of the scheme.

This paper presents a scheme for accommodating faults in the blade pitch, rotor speed and generator torque control sensors of a wind turbine nonlinear system. These measured values are important both for the controller performance as well as the supervisory module of the wind turbine. The proposed control accommodation scheme is based on identified nonlinear filters, which can be also exploited to diagnose these faults. In particular, a nonlinear dynamic system estimation scheme is proposed to obtain these disturbance decoupled nonlinear filters, which provide the on-line estimate of the fault signals. The scheme is tested on a high-fidelity wind turbine simulator, in the presence of disturbance and measurement errors, along nominal operating conditions, including also different realistic fault situations. Tests on this simulated model show the the reliability features of the proposed active fault tolerant control scheme.

In this paper, we consider disturbance decoupling problems for switched linear systems. We will provide necessary and sufficient conditions for three different versions of disturbance decoupling, which differ based on which signals are considered to be the disturbance. In the first version, the exogenous input is considered as the disturbance, in the second, the switching signal and in the third both of them are considered as disturbances. All three versions of disturbance decoupling have direct counterparts for linear parameter-varying (LPV) systems, while the latter instance of the problem is relevant for disturbance decoupling of piecewise linear systems, as we will show. The solutions of the three disturbance decoupling problems will be based on geometric control theory for switched linear systems and will entail both mode-dependent and mode-independent static state feedback.

The L2-gain almost disturbance decoupling problem for SISO nonlinear systems is formulated. Sufficient conditions are identified for the existence of a parametrized state feedback controller such that the L2-gain from disturbances to output can be made arbitrarily small by increasing its gain. The controller is explicitly constructed using a Lyapunov-based recursive scheme. Sufficient conditions for the solvability of the H∞ almost disturbance decoupling problem and the explicit construction of the controller are given for a more restrictive class of nonlinear systems.

A control design approach is presented for active steering of front wheel steered vehicles. The approach consists of the application of disturbance decoupling via state-derivative feedback. Simulations with the resulting controller show that the use of state-derivative information may considerably enhance vehicle safety, in particular under adverse operating conditions such as icy roads.

In this note, we present two worked examples of disturbance decoupling for nonlinear systems, using the concept of controlled invariance, which was recently generalized to nonlinear systems. In the first example, we explicitly construct a feedback which decouples a disturbance from the vertical components of the axes of a rotating rigid body, while the second example deals with a particle in a potential field subject to a disturbance.