094 Relationships between changes in time of quality of life and changes in time of the results of cardiopulmonary exercise test and echocardiography at a follow-up of patients with heart failure

PurposeCardiopulmonary exercise testing, echocardiography and plasma NT-proBNP levels assess patients (pts) with heart failure (HF). Quality of life (QoL) in HF is measured by Minnesota Living with Heart Failure Questionnaire (MLHF) and Specific Activity Questionnaire (SAQ). It is not known whether changes in QoL questionnaire scores correlate to changes in the results of the aforementioned laboratory tests during the follow-up of pts with HF.MethodsWe performed repeat measurements after a median of 26 (21 - 34) months in 30 pts with HF.They underwent a cardiopulmonary exercise test, an echocardiography test (LVEF) and a measurement of plasma NT-proBNP. Pts completed MLHF and SAQ. Changes were calculated in all measures between the first and the second measurement (Δ). All the patients were taking b-blockers, 83% ACE/ARBs and 83% diuretics.ResultsNonsignificant increases were found in peak VO2 (21.47±9.3 to 21.9±4.9 ml/kgr/min; ΔpeakVO2= 1.14±3.5; NS), VE/VCO2 slope (34.47±7 to 35.13±5.1; ΔVE/VCO2= 0.66±5.8; NS), LVEF (32.17±6.27 to 32.48±7.6%; ΔLVEF= 0.16±2.7; NS). NT-proBNP levels decreased nonsignificantly from a median value of 375.5 pg/ml to 235 pg/ml; median ΔNT-proBNP=-21 pg/ml; NS. SAQ scores improved significantly (6.86±1 to 7.48±1.15; ΔSAQ= 0.625±1.43; p=0.029) and MLHF scores decreased significantly from 21.5±9.3 to 16.6±13 (ΔMLHF= -4.13±9.5; p=0.033). ΔSAQ correlated with ΔMLHF (r=-0.417, p=0.03) and ΔpeakVO2 (r=0.448, p=0.017). ΔMLHF correlated with ΔLVEF (r=-0.557, p=0.007). ΔVE/VCO2 correlated with ΔpeakVO2 (r=-0.417, p=0.025). ΔNT-proBNP only correlated with ΔpeakVO2 (r=-0.518, p=0.004) and ΔVE/VCO2 (r=0.538, p=0.003), but with neither questionnaire.ConclusionsSignificant changes in quality of life expressed by MLHF scores relate to nonsignificant changes in left ventricular ejection fraction, while significant changes in activity capacity as measured by SAQ relate to nonsignificant changes in peak oxygen consumption

Distributed LQR Design for a Class of Large-Scale Multi-Area Power Systems

Load frequency control (LFC) is one of the most challenging problems in multi-area power systems. In this paper, we consider power system formed of distinct control areas with identical dynamics which are interconnected via weak tie-lines. We then formulate a disturbance rejection problem of power-load step variations for the interconnected network system. We follow a top-down method to approximate a centralized linear quadratic regulator (LQR) optimal controller by a distributed scheme. Overall network stability is guaranteed via a stability test applied to a convex combination of Hurwitz matrices, the validity of which leads to stable network operation for a class of network topologies. The efficiency of the proposed distributed load frequency controller is illustrated via simulation studies involving a six-area power system and three interconnection schemes. In the study, apart from the nominal parameters, significant parametric variations have been considered in each area. The obtained results suggest that the proposed approach can be extended to the non-identical case

Robust networked controlled systems

This research work is concerned with robustness issues arising in Νetworked Cοntrοlled Systems - ("ΝCS"), where the main sources of uncertainty are the time-varying network-induced delays. In this framework the presented results concern robust stability analysis and synthesis of robust controllers. The NCS studied consist of a Linear Time Invariant continuous time plant and a discrete time controller. This configuration includes a time driven (periodic) sampler (taking samples from the sensors with constant sampling period h) and an event–driven controller which transmits the control command via the network to the event–driven actuator. Two modeling approaches for Networked Controlled Systems (NCS) with uncertainly varying bounded transmission delays and static discrete--time control laws are presented. Different models are offered for each case, all linked to the objective of designing robust discrete-time controllers. It is shown how the careful mixing of asynchronous (event--driven) and synchronized (clocked) signals can lead to discrete time uncertain (possibly switched) systems. Two families of sufficient conditions for robust stability are given for each approach and a comparison of the conservation of results is discussed. The first group of robust stability results (one for each of the two discrete-time NCS models) is based on a singular value formulation, which although conservative, is extremely simple and has low computational cost. The second one is derived and expressed via Linear Matrix Inequalities (LMI) and yields less conservative results at the expense of higher computational cost. Regarding the synthesis of Robust controllers, the following four methodologies were developed: 1. Synthesis of Robust Static State feedback 2. Synthesis of Robust Static State feedback via the “Guaranteed Cost Formulation” which combines stability and performance design objectives 3. Synthesis of Constrained Robust feedback controller (with a Piecewise Affine Structure) which respects the constraints on the control effort and the state (or output). 4. The previous result (Constrained Robust feedback controller) is then generalized for set-point tracking and for various types of network-induced delays (small, large and switching delays).Το ερευνητικό αντικείμενο της Διατριβής είναι τα θέματα σθεναρότητας του προκύπτουν στα Δικτυωμένα Συστήματα Ελέγχου (Νetworked Cοntrοlled Systems - εφεξής "ΝCS"), όπου η βασική πηγή αβεβαιότητας είναι οι καθυστερήσεις λόγω δικτύου. Στο πλαίσιο αυτό παρουσιάζονται αποτελέσματα του αφορούν στην ανάλυση σθεναρής ευστάθειας και στην σύνθεση σθεναρών ελεγκτών. Να επισημανθεί ότι στην Διατριβή, ο προσδιορισμός "σθεναρός" αφορά αποκλειστικά σθεναρότητα (ευστάθειας και επιδόσεων) ως προς τις αβέβαιες, χρονικά μεταβαλλόμενες, φραγμένες καθυστερήσεις. Τα μελετώμενα ΝCS απαρτίζονται από την διασύνδεση γραμμικών χρονικά αμετάβλητων συστημάτων συνεχούς χρόνου με ελεγκτές διακριτού χρόνου. Η βασική διάρθρωση των συστημάτων αυτών απαρτίζεται από έναν "οδηγούμενο από χρόνο" (time driven) αισθητήρα/δειγματολήπτη (με σταθερή περίοδο δειγματοληψίας h) που μεταδίδει μέσω του δικτύου τα δείγματα που λαμβάνει από το σύστημα στον "οδηγούμενο από γεγονότα" (event–driven) ελεγκτή. Ακολούθως ο ελεγκτής υπολογίζει την δράση ελέγχου και την μεταδίδει μέσω του δικτύου στον "οδηγούμενο από γεγονότα" (eveτιt–driven) ενεργοποιητή. Οι διαδικασίες της μοντελοποίησης, της ανάλυσης ευστάθειας και της σύνθεσης σθεναρών ελεγκτών (στατικών αλλά και κατά τμήματα γραμμικών) στην εργασία αυτή λαμβάνουν χώρα στο πεδίο του διακριτού χρόνου μετά από διακριτοποίηση του συνολικού συστήματος. Προτείνονται και μελετώνται δύο προσεγγίσεις μοντελοποίησης βασισμένες σε ισάριθμες επιλογές «επηυξημένων» διανυσμάτων κατάστασης και ακολούθως καταδεικνύεται με ποιον τρόπο τα μοντέλα αυτά σχετίζονται με την ανάλυση και την σύνθεση σθεναρών ελεγκτών. Όσον αφορά στην ανάλυση σθεναρής ευστάθειας προτείνονται δύο προσεγγίσεις: 1. η πρώτη, βασιζόμενη σε ανάλυση ιδιαζουσών τιμών, είναι υπολογιστικά ελκυστική αλλά συνήθως δίδει συντηρητικά αποτελέσματα, 2. η δεύτερη, διατυπωμένη σαν ανισότητα πινάκων (LMI), είναι απαιτητική ως προς τον χρόνο υπολογισμού αλλά δίδει αποτελέσματα με μειωμένο συντηρητισμό. Όσον αφορά στην σύνθεση σθεναρών ελεγκτών ανατροφοδότησης κατάστασης μελετώνται οι εξής προσεγγίσεις: 1. Σύνθεση σθεναρής ευσταθειοποιούσας ανατροφοδότησης κατάστασης 2. Σύνθεση σθεναρής ευσταθειοποιούσας ανατροφοδότησης κατάστασης "εγγυημένου κόστους" που απαντάει στην συνδυασμένη απαίτηση ευστάθειας και επίδοσης 3. Σύνθεση σθεναρής ευσταθειοποιούσας ανατροφοδότησης κατάστασης με περιορισμό (Cοnstrained Controller) για ΝCS με "μικρή καθυστέρηση". Επέκταση των αποτελεσμάτων για ΝCS με "μεγάλη καθυστέρηση". Εφαρμογή των παραπάνω αποτελεσμάτων σε προβλήματα παρακολούθησης σταθερής εντολής (set point tracking). 4. Σύνθεση σθεναρής ευσταθειοποιούσας ανατροφοδότησης κατάστασης με περιορισμό (Constrained Controller), για ΝCS με μικρή και διακοπτική καθυστέρηση

Stability, positive invariance and design of constrained regulators for networked control systems

In this article, the stability analysis, the positive invariance of polyhedral sets and the design of state-feedback regulators for networked control systems (NCS) with bounded transmission delays, constant and unknown or time-varying, are investigated. The dynamics of the NCS is described by autoregressive-moving-average (ARMA) models. Contrary to former approaches based on quadratic Lyapunov functions, in this article polyhedral Lyapunov functions are used for both stability and positive invariance analysis and state-feedback synthesis. Then, based on the property that the exponential of a matrix can be expressed as a weighted sum of its constituent matrices, it is proven that the problems of determination of stability margins or the design of stabilising controllers can be reduced to linear programming optimisation problems. The use of ARMA models allows the development of methods for the design of state-feedback controllers satisfying state constraints or convergence rate specifications defined on the NCS state space and not on the state of an augmented state space representation

Combined networked switching output feedback control with D-region stability for performance improvement

In this article, a combined networked switching output feedback control scheme, with a (Formula presented.)-region stability performance improvement module is presented. The network induced time delays, that are considered to be time varying and integer multiples of the sampling period, are being embedded in the system model, by state augmentation. The resulting model of the overall networked closed-loop system is switching, with the current measured round-trip time delay acting as the switching rule. Based on this modelling approach, a Linear Matrix Inequality (LMI) tuned switching output feedback controller is designed. The proposed approach establishes robustness against time delays and is able to guarantee the overall stability of the switching closed-loop system. Integrated in the controlled synthesis phase, an LMI tuned performance improvement module is being introduced, based on (Formula presented.)-region stability. Multiple simulation results are being presented that prove the efficacy of the proposed scheme.Validerad; 2014; 20140317 (johsod

Set-theoretic detection of data corruption attacks on cyber physical power systems

Abstract This paper addresses a set-theoretic method for the detection of data corruption cyber-attacks on the load frequency control loop of a networked power system. The system consists of several interconnected control areas forming a power grid. Based on the overall discrete-time network dynamics, a convex and compact polyhedral robust invariant set is extracted and is used as a set-induced anomaly detector. If the state vector exits the invariant set, then an alarm will be activated, and the potential threat is considered disclosed. The attack scenario used to assess the efficiency of the proposed anomaly detector concerns corrupted frequency sensor measurements transmitted to the automatic generation control unit of a compromised control area. Simulation studies highlight the ability of a set-theoretic approach to disclose persistent and intermittent attack patterns even when they occur at the same time with changes in the power load demand