Browsing by Subject "Robust control"

Now showing 1 - 20 of 24

Open Access
Adaptive human pilot model for uncertain systems
(IEEE, 2019-06) Tohidi, Shahab; Yıldız, Yıldıray
Inspired by humans' ability to adapt to changing environments, this paper proposes an adaptive human model that mimics the crossover model despite input bandwidth deviations and plant uncertainties. The proposed human pilot model structure is based on the model reference adaptive control, and the adaptive laws are obtained using the Lyapunov-Krasovskii stability criteria applied to the overall closed loop system including the human pilot and the plant. The proposed model can be employed for human-in-the-Ioop stability and performance analyses with different controllers and plant types. A numerical example is used to demonstrate the effectiveness of the presented method.
Open Access
Constructing convex directions for stable polynomials
(IEEE, 2000) Özgüler, A. B.
The constructions of convex directions based on phase-derivative interpretations were obtained for Hurwitz-stable polynomials. The phase-derivative conditions were based on the sensitivity of root-locus associated with the even and odd parts of a polynomial. The phase-growth condition directly established anti-Hurwitz polynomials, polynomials of degree one, even polynomials and odd polynomials for the entire set of Hurwitz polynomials.
Open Access
Decentralised robust flow controller design for networks with multiple bottlenecks
(Taylor & Francis, 2009) Munyas, I.; Yelbaşi, Ö.; Biberovic, E.; İftar, A.; Özbay, Hitay
Decentralised rate-based flow controller design in multi-bottleneck data-communication networks is considered. An H∞ problem is formulated to find decentralised controllers which can be implemented locally at the bottleneck nodes. A suboptimal solution to this problem is found and the implementation of the decentralised controllers is presented. The controllers are robust to time-varying uncertain multiple time-delays in different channels. They also satisfy tracking and weighted fairness requirements. Lower bounds on the actual stability margins are derived and their relation to the design parameters is analysed. A number of simulations are also included to illustrate the time-domain performance of the proposed controllers.
Open Access
Delay margin optimization for systems with ınternal delayed feedback
(Elsevier, 2021-07-16) Özbay, Hitay
In this brief paper, controller design for delay margin optimization is considered for systems with internal feedback delays (systems with delays in the state variables). Similar to existing results on delay margin optimization for finite dimensional systems with I/O delays, it is shown that the problem considered can be solved by using Nevanlinna-Pick interpolation involving non-minimum phase zeros of the plant.
Open Access
Design of a switched robust control scheme for drug delivery in blood pressure regulation
(Elsevier B.V., 2016) Ahmed, S.; Özbay, Hitay
A control algorithm based on switching robust controllers is presented for a Linear Parameter Varying (LPV) time-delay system modeling automatic infusion of vasodilator drug to regulate postsurgical hypertension. The system is scheduled along a measurable signal trajectory. The prospective controllers are robustly designed at various operating points forming a finite set of robust controllers and then a hysteresis switching is performed between neighboring robust controllers for a larger operating range of the LPV system. The stability of the switching LPV system for the entire operating range is ensured by providing a sufficient condition in terms of bound on the scheduling signal variation using the concept of dwell time. Simulation results are provided to verify the performance of the designed control scheme. © 2016
Open Access
Financial stability under model uncertainty
(Elsevier B.V., 2018) Kantur, Z.; Özcan, G.
This paper studies how asset price model misspecification affects the conduct of monetary policy under commitment in a New Keynesian model using robust control techniques. We find that monetary policy reacts aggressively to both asset price and inflation shocks to guard herself against worst-case outcome.
Open Access
Flexible test-bed for unusual behavior detection
(ACM, 2007-07) Petrás I.; Beleznai, C.; Dedeolğu, Yiğithan; Pards, M.; Kovács L.; Szlávik, Z.; Havasi L.; Szirányi, T.; Töreyin, B. Uğur; Güdükbay, Uğur; Çetin, A.hmet Enis; Canton-Ferrer, C.
Visual surveillance and activity analysis is an active research field of computer vision. As a result, there are several different algorithms produced for this purpose. To obtain more robust systems it is desirable to integrate the different algorithms. To help achieve this goal, we propose a flexible, distributed software collaboration framework and present a prototype system for automatic event analysis. Copyright 2007 ACM.
Open Access
H∞ filter design for vehicle tracking under delayed and noisy measurements
(IEEE, 2007-06) Ezercan, Sami; Özbay, Hitay
In many intelligent vehicles applications tracking plays an important role. This paper considers tracking of a vehicle under delayed and noisy measurements. For this purpose we design an H∞ optimal filter for linear systems with time delays in the state and output variables. By using the duality between filtering and control, the problem at hand is transformed to a robust controller design for systems with time delays. The skew Toeplitz method developed earlier for the robust control of infinite dimensional systems is used to solve the H∞ filtering problem. The results are illustrated with simulations and effects of the time delay on the tracking performance are demonstrated. ©2007 IEEE.
Open Access
Local convex directions
(IEEE, 2001) Özgüler, Arif Bülent; Saadaoui, Karim
A proof of a strengthened version of the phase growth condition for Hurwitz stable polynomials is given. Based on this result, a necessary and sufficient condition for a polynomial p(s) to be a local convex direction for a Hurwitz stable polynomial q(s) is obtained. The condition is in terms of polynomials associated with the even and odd parts of p(s) and q(s).
Open Access
Local convex directions for Hurwitz stable polynomials
(IEEE, 2002) Özgüler, A. B.; Saadaoui, K.
A new condition for a polynomial p(s) to be a local convex direction for a Hurwitz stable polynomial q(s) is derived. The condition is in terms of polynomials associated with the even and odd parts of p(s) and q(s), and constitutes a generalization of Rantzer's phase-growth condition for global convex directions. It is used to determine convex directions for certain subsets of Hurwitz stable polynomials.
Open Access
Numerical computation and implementation of H-infinity controllers for retarded and neutral time delay systems
(2017-11) Yeğin, Mustafa Oğuz
Being the most commonly encountered systems in engineering applications, design of robustly stabilizing H∞ controller with maximum performance for timedelay linear time-invariant systems has been an attractive topic in control theory for many decades. A Matlab package called HINFCON is published in 1996. It applies an early solution to the problem, the so-called Toker-Özbay formula. It assumes that the coprime factorization is given, and computes the optimal performance level and the corresponding optimal controller through a manual iteration. The software introduced in this thesis, combines HINFCON with another Matlab package, YALTA, that is being used to do stability analysis for neutral/retarded systems, to perform coprime and inner-outer factorizations of the given infinite dimensional system. Additionally, an iterative algorithm for computation of optimal performance level automatically is implemented to prevent any manual computation. Finally, the Matlab command fitfrd is incorporated into the software that is used for approximation of the optimal controller to obtain a robustly stabilizing suboptimal finite dimensional controller. This thesis also introduces a new structure of the optimal controller which is more reliable and implementable on practical systems. Various examples are solved to compare the suboptimal controllers obtained by using the new structure with direct approximation of plant and optimal controller.
Open Access
Numerical computation of H∞ optimal controllers for time delay systems using YALTA
(Elsevier B.V., 2016) Yeğin, M. O.; Özbay, Hitay
Numerical computation of H∞ controllers for time delay systems has been a challenge since 1980s. Even though significant techniques are developed to obtain direct optimal controllers, application of these methods may require manual computation depending on the plant. In this paper, an alternative computational technique is proposed for direct optimal controllers originally obtained by Toker and Özbay (1995). The new controller expression contains finite dimensional transfer functions and an infinite dimensional term, which is stable. Thus it is suitable for finite dimensional approximations and practical non-fragile implementations. In this method, in order to eliminate manual computation of the plant factorization for neutral and retarded delay systems YALTA (a tool developed at INRIA) is used. The new controller computation is implemented in Matlab, and it is illustrated on an example. © 2016
Open Access
On the discrete adaptive posicast controller
(IFAC, 2015) Abidi, K.; Yıldız, Yıldıray
In this paper, we present the discrete version of the Adaptive Posicast Controller (APC) that deals with parametric uncertainties in systems with input time-delays. The continuous-time APC is based on the Smith Predictor and Finite Spectrum Assignment with time-varying parameters adjusted online. Although the continuous-time APC showed dramatic performance improvements in experimental studies with internal combustion engines, the full benefits could not be realized since the finite integral term in the control law had to be approximated in computer implementation. It is shown in the literature that integral approximation in time-delay compensating controllers degrades the performance if care is not taken. In this work, we present a development of the APC in the discrete-time domain, eliminating the need for approximation. In essence, this paper attempts to present a unified development of the discrete-time APC for systems that are linear with known/unknown input time-delays. Performances of the continuous-time and discrete-time APC, as well as conventional Model Reference Adaptive Controller (MRAC) for linear systems with known time-delay are compared in simulation studies. It is shown that discrete-time APC outperforms its continuoustime counterpart and MRAC. Further simulations studies are also presented to show the performance of the design for systems with uncertain time-delay.
Open Access
On the robust controller design for Hard Disk Drive servo systems with time delays
(IEEE, 2013) Yan, P.; Özbay, Hitay
Due to the existence of various sources of delays, the dynamical model of HDD (Hard Disk Drive) servo systems is actually infinite dimensional, although most of the control algorithms simplified the model with Padé expansions or other finite dimensional approximations. In this paper, a robust loop shaping algorithm is developed for the HDD model with delays by using an h ∞ synthesis approach for infinite dimensional systems. The h∞ controller is derived with a structure of an internal feedback loop including an FIR (Finite Impulse Response) filter and an IIR (Infinite Impulse Response) filter, which facilitates non-fragile implementations. Comparisons to other robust control methods are given and the advantages of this approach are demonstrated in terms of improvement of TMR (track misregistration) and tracking TPI (Track-per-Inch) capability.
Open Access
On the structure and implementation of the optimal Q-Parameter in the one-block H-infinity control problem
(2020-11) Taştekin, Çetin
In the robust control theory, H∞ methods are carried out to procure solutions to sensitivity minimization (nominal performance) and robust stability problems in general. These one – block control problems can be analyzed separately or in a combined fashion. In the general sense, the design of the robust controller is made to achieve stability and performance objectives for a plant, whose nominal model and uncertainty bounds can be determined from the experimental data. This study aims to present a solution to infinite dimensional one – block H∞ control problem and provide a general structural result for Q – Parameter. The methods like Nevanlinna – Pick interpolation will not work for infinite dimensional control problems whereas Sarason’s Theorem provides solution to infinite dimensional control problems. In this thesis, Sarason’s Theorem is analyzed and examined extensively and applied on infinite dimensional one – block H∞ control problem. The detailed structural analysis of the resulting Q – Parameter is made as the main contribution of the thesis. Various examples are given to illustrate the computational issues. In this analysis, stability status of Q – Parameter is demonstrated by examining stable terms and FIR part of its sub – blocks.
Open Access
An operator theoretic approach to robust control of infinite dimensional systems
(Applied Mathematics Scientific Research Institute, 2013) Özbay, Hitay
The purpose of this paper is to give an overview of the skew Toeplitz approach to H∞ control of a class of infinite dimensional systems. Numerical steps involved in the computations of optimal and suboptimal controllers are demonstrated with different examples, including flexible beam models and systems with time delays.
Open Access
Reactive planning and control of planar spring-mass running on rough terrain
(Institute of Electrical and Electronics Engineers, 2012) Arslan, Ö.; Saranlı, U.
An important motivation for work on legged robots has always been their potential for high-performance locomotion on rough terrain. Nevertheless, most existing control algorithms for such robots either make rigid assumptions about their environments or rely on kinematic planning at low speeds. Moreover, the traditional separation of planning from control often has negative impact on the robustness of the system. In this paper, we introduce a new method for dynamic, fully reactive footstep planning for a planar spring-mass hopper, based on a careful characterization of the model dynamics and the design of an associated deadbeat controller, used within a sequential composition framework. This yields a purely reactive controller with a large domain of attraction that requires no explicit replanning during execution. We show in simulation that plans constructed for a simplified dynamic model can successfully control locomotion of a more complete model across rough terrain. We also characterize the performance of the planner over rough terrain and show that it is robust against both model uncertainty and measurement noise without replanning. © 2012 IEEE.
Open Access
Remarks on H ∞ controller design for SISO plants with time delays
(2006-07) Gümüşsoy, Suat; Özbay, Hitay
The skew Toeplitz approach is one of the well developed methods to design H ∞ controllers for infinite dimensional systems. In order to be able to use this method the plant needs to be factorized in some special manner. This paper investigates the largest class of SISO time delay systems for which the special factorizations required by the skew Toeplitz approach can be done. Reliable implementation of the optimal controller is also discussed. It is shown that the finite impulse response (FIR) block structure appears in these controllers not only for plants with I/O delays, but also for general time-delay plants.
Open Access
Robust adaptive sampled-data control of a class of systems under structured nonlinear perturbations
(Institute of Electrical and Electronics Engineers, 1997-04) Ocah, O.; Sezer, M. E.
A robust adaptive sampled-data feedback stabilization scheme is presented for a class of systems with nonlinear additive perturbations. The proposed controller generates a control input by using high-gain static or dynamic feedback from nonuniform sampled values of the output. A simple adaptation rule adjusts the gain and the sampling period of the controller.
Open Access
Robust flow control in data-communication networks with multiple time-delays
(WILEY, 2009-11-20) Ünal, H. U.; Ataşlar-Ayyildiz, B.; Iftar, A.; Özbay, Hitay
Robust controller design for a flow control problem where uncertain multiple time-varying time-delays exist is considered. Although primarily data-communication networks are considered, the presented approach can also be applied to other flow control problems and can even be extended to other control problems where uncertain multiple time-varying time-delays exist. Besides robustness, tracking and fairness requirements are also considered. To solve this problem, an H∞ optimization problem is set up and solved. Unlike previous approaches, where only a suboptimal solution could be found, the present approach allows to design an optimal controller. Simulation studies are carried out in order to illustrate the time-domain performance of the designed controllers. The obtained results are also compared to the results of a suboptimal controller obtained by an earlier approach.