In this paper, a model reference fault tolerant control strategy based on a reconfiguration of the reference model, with the addition of a virtual actuator block, is presented for uncertain systems affected by disturbances and sensor noise. In particular, this paper (1) extends the reference model approach to the use of interval state observers, by considering an error feedback controller, which uses the estimated bounds for the error between the real state and the reference state, and (2) extends the virtual actuator approach to the use of interval observers, which means that the virtual actuator is added to the control loop to preserve the nonnegativity of the interval estimation errors and the boundedness of the involved signals, in spite of the fault occurrence. In both cases, the conditions to assure the desired operation of the control loop are provided in terms of linear matrix inequalities. An illustrative example is used to show the main characteristics of the proposed approach.
This is the peer reviewed version of the following article: Rotondo D, Cristofaro A, Johansen TA. Fault tolerant control of uncertain dynamical systems using interval virtual actuators. Int J Robust Nonlinear Control. 2018;28:611–624, which has been published in final form at https://doi.org/10.1002/rnc.3888. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
A data-driven methodology that includes the unfalsified control concept in the framework of fault diagnosis and isolation (FDI) and fault-tolerant control (FTC) is presented. The selection of the appropriate controller from a bank of controllers in a switching supervisory control setting is performed by using an adequate FDI outcome. By combining simultaneous online performance assessment of multiple controllers with the fault diagnosis decision from structured hypothesis tests, a diagnosis statement regarding what controller is most suitable to deal with the current (nominal or faulty) mode of the plant is obtained. Switching strategies that use the diagnosis statement are also proposed. This approach is applied to a nonlinear experimentally validated model of the breathing system of a polymer electrolyte membrane fuel cell. The results show the effectiveness of this FDI–fault-tolerant control data-driven methodology
This work considers the control of nonlinear bilateral teleoperators with variable time delays without the need of velocity measurements. The recently proposed Immersion and Invariance observer is used to obtain an exponentially convergent estimate of the unmeasured velocities. Under the classical assumption that the human operator and the environment define passive, velocity to force, maps, it is proved that with this observer and a Proportional plus damping controller, velocities and position error are globally bounded. Finally, in the case that the human operator and the environment do not exert forces on the local and remote manipulators, respectively, global asymptotic convergence of velocities and of position error to zero is achieved. The theoretical results are sustained with simulations using a couple of two degrees-of-freedom nonlinear manipulators.
Aldana, C.; Romero, E.; Nuño, E.; Basañez, L. International journal of robust and nonlinear control Vol. 25, num. 14, p. 2279-2298 DOI: 10.1002/rnc.3200 Data de publicació: 2015-09-25 Article en revista
This paper proposes a novel pose (position and orientation) consensus controller for networks of heterogeneous robots modeled in the operational space. The proposed controller is a distributed proportional plus damping scheme that, with a slight modification, solves both the leader-follower and leaderless consensus problems. A singularity-free representation, unit quaternion, is used to describe the robots orientation, and the network is represented by an undirected and connected interconnection graph. Furthermore, it is shown that the controller is robust to interconnection variable time delays. Experiments with a network of two 6-degrees-of-freedom robots are presented to illustrate the performance of the proposed scheme. Copyright (c) 2014 John Wiley & Sons, Ltd.
Vargas, A.; Acho, L.; Pujol-Vazquez, G.; Costa, E.; Ishihara, J.; João B. R. do Val, J. International journal of robust and nonlinear control DOI: 10.1002/rnc.3393 Data de publicació: 2015-07-30 Article en revista
The note presents an output feedback control strategy for Markov jump linear systems with no mode observation. Based on minimizing a finite-time quadratic cost, we derive an algorithm that generates output feedback gains that satisfy a necessary optimality condition. These gains can be computed off-line relying only on the initial condition of the system. This result expands a previous one from the literature that considered state-feedback only. To illustrate the usefulness of the approach, real-time laboratory experiments were performed to control an automotive electronic throttle valve subject to Markov-driven voltage fluctuations.
The paper presents a robust fault estimation approach for a class of nonlinear discrete-time systems. In particular, two sources of uncertainty are present in the considered class of systems, that is, an unknown input and an exogenous external disturbance. Thus, apart from simultaneous state and fault estimation, the objective is to decouple the effect of an unknown input while minimizing the influence of the exogenous external disturbance within the inline image framework. The resulting design procedure guarantees that a prescribed disturbance attenuation level is achieved with respect to the state and fault estimation error while assuring the convergence of the observer. The core advantage of the proposed approach is its simplicity by reducing the fault estimation problem to matrix inequalities formulation. In addition, the design conditions ensure the convergence of the observer with guaranteed inline image performance. The effectiveness of the proposed approach is demonstrated by its application to a twin rotor multiple-input multiple-output system
In this paper, a model reference fault tolerant control (FTC) strategy based on a reconfiguration of the reference model, with the addition of a virtual actuator block, is presented for linear parameter varying (LPV) systems. The advantage of the proposed FTC method is that the control system is reconfigured in such a way that the nominal controller is used without the need of retuning it. Moreover, the presence of saturations is taken into account through their incorporation in the reference model, and the introduction of additional varying parameters, such that the system exhibits some graceful performance degradation when the system could not achieve the desired state because of the actuator limits. The design of the control scheme is based on linear matrix inequalities (LMIs) and polytopic LPV techniques. In order to implement the proposed active FTC strategy, a fault estimation is required. In this paper, the fault estimation is formulated as a parameter estimation problem, which is solved using a set-membership approach. An aeronautical application is used to assess the performance of the proposed approach.
Montes de Oca, S.; Tornil-Sin, S.; Puig, V.; Theilliol, D. International journal of robust and nonlinear control Vol. 24, num. 14, p. 1969-1988 DOI: 10.1002/rnc.3185 Data de publicació: 2014-09-25 Article en revista
In this paper, a fault-tolerant control (FTC) design method based on linear parameter varying (LPV) gain-scheduling theory is proposed. The main contribution is the design of a fault-tolerant state-feedback observer-based controller based on a polytopic LPV representation where faults are considered in the same way that those parameters that vary with the operating point. Within this framework, the ranges of fault magnitudes that are wanted to be tolerated can be specified as design parameters. Control specifications are defined in terms of H-infinity or H-2 performance in combination with regional pole placement, as traditionally carried out in conventional LPV control. Passive and active FTC formulations are developed, the latter assuming the availability of online fault estimations. In both cases, the associated controller synthesis methods are based on the well-established LPV-LMI framework. Additionally, a fault estimation procedure is provided to allow the implementation of the active formulation. Finally, the use of the proposed method is illustrated by applying it to the FTC of a two-degree-of-freedom helicopter. Copyright (C) 2014 John Wiley & Sons, Ltd.
di Bernardo, M.; Montanaro, U.; Olm, Josep M.; Santini, S. International journal of robust and nonlinear control Vol. 23, num. 7, p. 709-730 DOI: 10.1002/rnc.2786 Data de publicació: 2013-06-01 Article en revista
This article presents a switched model reference adaptive controller for discrete-time piecewise linear systems.
In the spirit of the work by Landau in the late seventies, proof of asymptotic stability of the closed-loop error system is obtained, recasting its dynamics as a feedback system and showing the feedforward and the feedback paths are both passive. The challenge is that both paths can be piecewise linear. Numerical results
show excellent performance of the proposed controller even in the face of sudden variations of the plant parameters.
A robust linear parameter varying (LPV) identification/invalidation method is presented. Starting from a given initial model, the proposed method modifies it and produces an LPV model consistent with the assumed uncertainty/noise bounds and the experimental information. This procedure may complement existing nominal LPV identification algorithms, by adding the uncertainty and noise bounds which produces a set of models consistent with the experimental evidence. Unlike standard invalidation results, the proposed method allows the computation of the necessary changes to the initial model in order to place it within the consistency set. Similar to previous LPV identification procedures, the initial parameter dependency is fixed in advance, but here a methodology to modify this dependency is presented. In addition, all calculations are made on state-space matrices which simplifies further controller design computations. The application of the proposed method to the identification of nonlinear systems is also discussed.
Luo, N.; Sen, M.; Rodellar, J. International journal of robust and nonlinear control Vol. 7, num. 1, p. 59-74 DOI: 10.1002/(SICI)1099-1239(199701)7:1<59::AID-RNC205>3.0.CO;2-X Data de publicació: 1997-01 Article en revista
This paper addresses the problem of robust stabilization of a class of uncertain systems subject to internal (i.e., in the state) point delays, external (i.e., in the input) point delays and nonlinear disturbances by using sliding mode control. Methods for the design of sliding mode controllers based on state feedback, static output feedback and dynamic output feedback, respectively, are proposed. Sufficient conditions for the asymptotic stability and robustnesss of the closed–loop systems are given under a wide class of admissible nonlinear disturbances