Alexandru Codrean

Issues of Identifying, Estimating and Using Delay Times in Telecontrol Systems Based on TCP/IP Networks

Abstract Todays performant equipment and high speed connections make network control systems a reality. For a series of teleoperation applications like the ones from network control systems domain it is essential to estimate the time delay between the acquisition moment of primary data that needs to be sent and the moment it is available for the receivers use. This paper presents a methodology for estimating the time delay from experimental measurements, while also taking into account the information loss during transmission. A series of unwanted exceptions that may occur in signal transmission are identified and solution methods are proposed. Based on the above study, three real scenarios were designed for three TCP/IP network types. These scenarios were implemented through simulations for a telecontrol system that uses adaptive PD compensators for the time-varying delays. Finally, the improvement in the systems performances with the PD compensators were validated using real life scenarios.

Averaged modeling of the cardiovascular system

In approximating nonlinear systems, averaging theory provides very useful tools, especially for periodic/quasi-periodic systems. In the case of complex dynamical systems (e.g. biological systems), such an approach leads to consistent simplifications of the encountered mathematical models. The current paper addresses the problem of deriving a simple averaged model of the cardiovascular system, which is shown to be part of the class of pulse-frequency modulated switched systems. Because conventional averaging methods lead to frequency independent averaged models, the paper proposes a weighted averaging approach, which leads to a frequency dependent averaged model (simpler than the original one).

Time delay and information loss compensation in a network control system for a DC motor

Due to their high reliability and low cost, network control systems are becoming key players in the future of control systems. However, their usage requires handling issues like time delays and information loss. This paper presents a method for dealing with these issues through a control structure based on the usage of a proportional-derivative type adaptive compensator. Finally the experimental case study attests the feasibility of the proposed method.

Design, analysis and validation of an observer-based delay compensation structure for a Network Control System

A pressing issue of Network Control Systems is the time-varying delay which alters the systems performance. The current study designs and analysis a control structure based on a communication disturbance observer for delay compensation for second order linear processes. The proposed networked control system is tested through simulations and experiments, using a new network model recently proposed by the authors, for a scenario involving random delay variation and packets loss during network transmissions.

Up to Date Issues on Modeling the Nervous Control of the Cardiovascular System on Short-Term

Abstract Physiological control mechanisms are receiving an increasing amount of attention due to their primary role in homeostasis, while systems theory is becoming an indispensable tool for understanding the dynamic behaviors that emerge. In this context, a topic that has been intensively studied is the nervous control of the cardiovascular system on short term. This paper tries to develop a common framework for future efforts in modeling the nervous control of the cardiovascular system in orthostatic stress, through a systemic analyze of the roles and interactions of the regulatory mechanisms identified in the literature.

Dead time compensation for interpolative-type, control systems

Signal transmission in control structures is usually characterized by propagation processes, i.e. existence of time delays. For the interpolative-type control structures the problem is often disregarded, especially in the design step. Undoubtedly, the effect consists in worse real performances that those designed. In this context, the present paper proposes and presents a solution able to compensate, via a discrete-time PD compensator, the effect of the dead times appeared on the feedback channels for both a fuzzy and an interpolative control structure. For systems with variable time delays an adaptive-interpolative type PD compensator is suited. Experimental results, obtained through simulation on a second order positioning system, validate the proposed solution. Finally, the paper discusses the issue of the accuracy of simulation. It is emphasized the manner in which the simulation can be done using initial segment generators for the elementary dead time transfer elements.

A network control structure with a switched PD delay compensator and a nonlinear network model

The current study proposes a novel network control structure based on local and remote placed control elements, together with a nonlinear network transmission model recently proposed by the authors. For rejecting the disturbance effect of the network, a switched PD compensator is proposed. The control design methodology encompasses both analytical and numerical methods, so that both the stabilization and the tracking control objectives are met. The stability is assessed by considering the overall system as a switched linear system. Finally, the results are validated on a numerical example.

Stability analysis and control synthesis for a network control system using a nonlinear network transmission model - A switched system approach

The stability analysis of network control systems still poses a challenge due to the nonlinear behavior induced by network transmissions. The current paper addresses the stability problem for a network control system which includes a nonlinear network transmission model. The network transmission model embeds the main characteristics of real TCP/IP network transmissions like time varying delays, packet loss and irregular situations. The closed-loop network control system is recasted as a switched linear system with multiple switching signals. The stability is investigated under arbitrary switching, by adopting a switched quadratic Lyapunov candidate function. Linear matrix inequality based conditions are derived for stability and controller design. Finally, an appropriate example illustrates how the approach is used.

Modeling the Vestibular Nucleus

In recent years the vestibular-sympathetic reflex has received an increasing amount of attention due to the role it could play in the human organism in different types of scenarios. Despite this, quantitative models of this reflex mechanism are still lacking. In this context, the current paper aims at taking a first step towards the modeling of the vestibular-sympathetic reflex by developing a model of the Vestibular Nucleus – the central part of the vestibular-sympathetic reflex. After a careful analysis of the limitations and uncertainties of the available experimental data from the literature, a three step modeling methodology for the Vestibular Nucleus is presented. After a description of the operations involved in each step, in the end, some preliminary results are shown.

The influence of omitting the prehistory on the accuracy of modelling dead time systems

The paper covers the problem involving the consequences of omitting to model the prehistory of dead time elements in control system modelling. It is shown that this omission is equivalent to the action of disturbances that can cause different effects, ranged from simple calculus differences to loss of stability. For this purpose three case studies are presented: a linear control system, a state feedback control system with limited control domain and a fuzzy control system affected by propagation delay.