Ioan Ursu

Backstepping design for controlling electrohydraulic servos

Abstract The backstepping technique is one of the tools which provides control Lyapunov functions (CLFs) and, therefore, control laws for automatic systems. In this paper, the backstepping design for position and force nonlinear electrohydraulic servos is investigated. Three control laws ensuring the asymptotic stability of references tracking are obtained by constructing CLFs on the errors concerning the state variables and theirs desired values. The possibility of converting a position servo into a force servo, with only minimal hard modification, is proved. An approach based on partitioning the state system into two subsystems—a first one stable, and a second one taken as framework of control synthesis by backstepping technique—was developed and used. Using as reference point a flight controls hydromechanical servo, numerical simulations were reported from viewpoint of servo time constant performance. Certain conjectures, concerning the behaviour of systems mathematical models, in connection with mathematical methodologies of control synthesis operating on them, are finally stressed.

H ∞ Control with μ-analysis of a Piezoelectric Actuated Plate

This paper presents the development of a multimodal H∞controller for piezoelectric actuated plates designed to simultaneously suppress vibrational components of the first two modes. The controller is developed for a reduced structural model. The closed-loop control scheme is subject to both uncertainties due to control and observation spillover in the unmodeled residual modes and to parametric errors in the structural model. The closed-loop stability and performance robustness is analyzed using μ-analysis, and numerical investigations indicate that the controller tolerates uncertainties of significant size.

Neuro‐fuzzy synthesis of flight control electrohydraulic servo

Presents a switching type neuro‐fuzzy control synthesis. The control algorithm supposes as a component part a neurocontrol designed to optimize a performance index. Whenever the neurocontrol saturates or a certain performance parameter of the system decreases, the scheme of control switches to a feasible and reliable fuzzy logic control. Describes the procedure of return to the optimizing neurocontrol which is essential. This methodology of control synthesis ensures antisaturating, antichattering and robustness properties of the controlling system, as illustrated by numerical simulation in the case of a primary flight controls electrohydraulic servo actuator

From robust control to antiwindup compensation of electrohydraulic servo actuators

A method of designing the controller to solve the robust servomechanism problem is applied in the case of an electrohydraulic servo actuating primary flight control. This method is based on the well‐known solution consisting of two separate devices: a servocompensator, in fact an internal model of the exogenous dynamics, including the reference commands and disturbance signals; and a stabilizing compensator. The proof is made involving the servocompensator structure which is close to the one designed for step signals. The stabilizing compensator is assured by way of a linear quadratic optimal procedure. An antiwindup compensation is added to deal with the adverse effects caused by actuator saturation.

New Results in Control Synthesis for Electrohydraulic Servos

Abstract This survey presents some recent results of the authors in the field of the control synthesis for electrohydraulic servos. Three are the methodologies of control theory herein considered. Firstly, an integrated methodology of robust control synthesis with antiwindup feedback compensation for linear model of electrohydraulic servo is developed. Secondly, in a strongly nonlinear framework, an integrated fuzzy supervised neurocontrol is proposed. This represents a control strategy which is in fact independent of mathematical model of the systems, thus achieving certain robustness and reducing complexity. At last, the backstepping is used for obtaining of control laws for asymptotic tracking of position or force references in the case of a certain model of an electrohydraulic servo. Conclusive numerical simulations are provided to verify the behaviour of the controlled systems by the proposed control laws.

Towards spacecraft applications of structural health monitoring

The first part of the paper presents recent developments in the field of structural health monitoring (SHM) with special attention on the piezoelectric wafer active sensors (PWAS) technologies utilizing guided waves (GW) as propagating waves (pitch-catch, pulse-echo), standing wave (electromechanical impedance), and phased arrays. The second part of the paper describes the challenges of extending the PWAS GW SHM approach to in-space applications. Three major issues are identified, (a) cryogenic temperatures; (b) high temperatures; and (c) space radiation exposure. Preliminary results in which these three issues were address in a series of carefully conducted experiments are presented and discussed. The third part of the paper discusses a new project that is about to start in collaboration between three Romanian institutes to address the issues and challenging of developing space SHM technologies based on PWAS concepts. The paper finishes with conclusions and suggestions for further work.

Intelligent control of HVAC systems. Part II: perceptron performance analysis

This is the second part of a paper on intelligent type control of Heating, Ventilating, and Air-Conditioning (HVAC) systems. The whole study proposes a unified approach in the design of intelligent control for such systems, to ensure high energy efficiency and air quality improving. In the first part of the study it is considered as benchmark system a single thermal space HVAC system, for which it is assigned a mathematical model of the controlled system and a mathematical model (algorithm) of intelligent control synthesis. The conception of the intelligent control is of switching type, between a simple neural network, a perceptron, which aims to decrease (optimize) a cost index, and a fuzzy logic component, having supervisory antisaturating role for neuro-control. Based on numerical simulations, this Part II focuses on the analysis of system operation in the presence only of the neural control component. Working of the entire neuro-fuzzy system will be reported in a third part of the study.

Towards a PIO II Criterion: Improving the Pilot Modeling

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.

PIO I-II tendencies. Part 2. Improving the pilot modeling

The study is conceived in two parts and aims to get some contributions to the problem of PIO aircraft susceptibility analysis. Part I, previously published in this journal, highlighted the main steps of deriving a complex model of human pilot. The current Part II of the paper considers a proper procedure of the human pilot mathematical model synthesis in order to analyze PIO II type susceptibility of a VTOL-type aircraft, related to the presence of position and rate-limited actuator. The mathematical tools are those of semi global stability theory developed in recent works.

Dealing with mathematical modeling in applied control

The first part of the paper presents some conjectures deduced from o long practice of systems mathematical modeling. So, it is underlined the over-emphasis developed in the sixty years history of classical control on the mathematical model. Two lessons derived from the conservativeness-versatility dualism of the mathematical models versus the mathematical theories in providing the classical control law are advanced. A third reflection concerns the spectacular decreasing of the mathematical model importance in the intelligent control. The second part of the paper shows our arguments in favor of proposed conjectures and intends especially to highlight the new intelligent control paradigm.