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Ursu L.,Elie Carafoli National Institute for Aerospace Research | Toader A.,Elie Carafoli National Institute for Aerospace Research | Halanay A.,Polytechnic University of Bucharest | Balea S.,Polytechnic University of Bucharest
European Journal of Control | Year: 2013

Some nonlinear control laws for a fifth order mathematical model, representative for an electrohydraulic servomechanism (EHS), are presented in the paper. Intrinsically, the EHS mathematical model has several shortcomings: critical case for stability, relative degree defect, and switching type nonsmooth nonlinearity. First, the control synthesis is approached, in the framework of the so-called Malkin canonical form for a critical case in the stability theory, from the perspective of the two paradigms: the regulator, or stabilization problem, and the tracking problem. In the first part of the paper, the stabilization problem is solved and a stabilizing control law, of geometric type, is designed and then illustrated by numerical simulations. Further on, the solution of the stabilizing control is extended as a geometric control for the EHS tracking problem, but given the extreme difficulty of the problem, the proposed solution works only as a conjecture, well confirmed by numerical simulations. In this context, the importance of the electrohydraulic servovalve dynamic response, defined by the time constant, to ensure a reasonable parametric robustness of the control law, has been established. Leaving apart the geometric control approach, the EHS tracking problem was finally solved by appealing to the backstepping synthesis, also validated by numerical simulations. © 2013 European Control Association. Published by Elsevier Ltd. All rights reserved.


Balea S.,Polytechnic University of Bucharest | Halanay A.,Polytechnic University of Bucharest | Ursu I.,Elie Carafoli National Institute for Aerospace Research
Control Engineering and Applied Informatics | Year: 2010

The main result of the paper is a suffcient condition for existence of controllers that stabilize the zero solution for some switched nonlinear control systems in the critical case of a zero eigenvalue in the spectrum of the Jacobian matrix calculated in zero. The control synthesis is based on a condition on the relative degree in the equilibrium point and subsequent coordinates transformations. An application to a pump controlled electrohydraulic servoactuator is given.


Ursu I.,Elie Carafoli National Institute for Aerospace Research | Toader A.,Elie Carafoli National Institute for Aerospace Research
12th WSEAS International Conference on Mathematical Methods, Computational Techniques and Intelligent Systems, MAMECTIS '10 | Year: 2010

The paper proposes a unitary approach of adaptive output feedback control for non-affine uncertain systems, about which the positive knowledge refers to the relative degree r. Given a reference model, the objective is to design a controller that forces the measured system output to track the reference model output with bounded error. The components of the so called pseudocontrol, thought on a superposition effects principle, are the following: 1) the output of reference model, 2) the output of a Kalman type stabilizing compensator of the pair of systems composed by a) an output dynamics of a set of integrators of order tantamount to the assumed known relative degree r of the controlled system and b) an internal model, of order r - 1, oriented to the tracking error decreasing in the presence of step input signals, and 3) the adaptive control designed to approximately cancel the error of approximate dynamic inversion by virtue of whom the real control is hereby determined from pseudocontrol. A single hidden layer neural network is used to counteract this dynamic inversion error. The common approach of pseudocontrol design based on tracking error dynamics estimation is evaded. A proof of stable working of this intelligent type controller is sketched. The mathematical model for the longitudinal channel of a hovering VTOL-type aircraft is used as framework of synthesis and validation by numerical simulations.


Ursu I.,Elie Carafoli National Institute for Aerospace Research | Toader A.,Elie Carafoli National Institute for Aerospace Research | Tecuceanu G.,Elie Carafoli National Institute for Aerospace Research
Proceedings of the Romanian Academy Series A - Mathematics Physics Technical Sciences Information Science | Year: 2010

The paper proposes a new and unitary approach of adaptive output feedback control for non-affine uncertain systems, about which the positive knowledge refers to the relative degree r. Given a reference model, the objective is to design a controller that forces the measured system output to track the reference model output with bounded error. The components of the so called pseudocontrol, thought on a superposition effects principle, are the following: 1) the output of reference model, 2) the output of a Kalman type stabilizing compensator of the pair of systems composed by a) an output dynamics of a set of integrators of order tantamount to the assumed known relative degree r of the controlled system and b) an internal model, of order r - 1, oriented to the tracking error decreasing in the presence of step input signals, and 3) the adaptive control designed to approximately cancel the error of approximate dynamic inversion by virtue of whom the real control is hereby determined from pseudocontrol. A single hidden layer neural network is used to counteract this dynamic inversion error. The classical approach of pseudocontrol design based on tracking error dynamics estimation is evaded. A proof of stable working of this intelligent type controller is sketched. The mathematical model for the longitudinal dynamics of an experimental helicopter is used as framework of synthesis and validation by numerical simulations.


Toader A.,Elie Carafoli National Institute for Aerospace Research | Ursu I.,Elie Carafoli National Institute for Aerospace Research
Advances in Intelligent Systems and Computing | Year: 2013

In this paper, a study is performed from the perspective of giving a methodology to analyze and predict the emergence of PIO (Pilot-Induced Oscillation) phenomenon. More precisely, a proper procedure of human pilot mathematical model synthesis in order to analyze PIO II type susceptibility of a VTOL-type aircraft, related with the presence of position and rate-limited actuator, is considered. The mathematical tools are those of LQG control synthesis and semi-global stability theory developed in recent works.


Toader A.,Elie Carafoli National Institute for Aerospace Research | Ursu I.,Elie Carafoli National Institute for Aerospace Research
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2014

A review of some human pilot models of the years 1970-1990 - the Kleinman-Baron-Levison optimal control model, the Davidson-Schmidt modified optimal control model, and the Hess optimal control model - has been presented from the perspective of a new model based on the optimal control synthesis of time-delay systems. In the first of the listed models, the 'central nervous' reaction of the pilot is naturally defined as a pure time delay in the measurement equation of the system. In the framework of the optimal control theory, the pilot's behavior is modeled by linear quadratic regulator gain and Kalman-Bucy filter with a linear predictor. Starting from this optimal model of the 1970s, the other two models assumed the Padé approximation of the pure time delay, thus eliminating the linear predictor. In this article, the pure time delay of pilot reaction was reconsidered and divided, for convenience, into two equal parts: for the output measurement equation and for the input control. The pilot model problem has been first defined in the framework of rigorous time-delay synthesis and then solved by making reference to the control separation and duality principles. A closed-form expression of the solution is thereby obtained. The proposed model was then compared by numerical simulations with Kleinman and Hess consacrated models. The analysis of the results shows that this new pilot model is described by a simplified representation, instead denoting similar performance versus previous optimal models - which contains additional insertions as Kleinman-Baron predictor or Padé approximation, respectively. Finally, joint evaluation of the proposed model and Kleinman and Hess models with respect to the well-known Neal-Smith criterion confirms the consistency and viability of the employed strategy as a possible tool for pilot-induced oscillations phenomenon investigation. © IMechE 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.


Ursu I.,Elie Carafoli National Institute for Aerospace Research | Chiroiu V.,Romanian Academy of Sciences | Munteanu L.,Romanian Academy of Sciences
Proceedings of the Romanian Academy Series A - Mathematics Physics Technical Sciences Information Science | Year: 2012

This paper discusses the modeling and feedforward control of hysteresis in a nonlinear five-story system using observed vibration signals. The generalized play operator is analyzed in connection with the system equations. Results show that hysteresis can be reduced to less than 35% when applying the feedforward control.

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