Browsing by Subject "Delay control systems"

Now showing 1 - 17 of 17

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
Explicit time-delay compensation in teleoperation: an adaptive control approach
(John Wiley and Sons Ltd, 2016) Abidi K.; Yildiz, Y.; Korpe, B. E.
This paper proposes a control framework that addresses the destabilizing effect of communication time delays and system uncertainties in telerobotics, in the presence of force feedback. Force feedback is necessary to obtain transparency, which is providing the human operator as close a feel as possible of the environment where the slave robot is operating. Achieving stability and providing transparency are conflicting goals. This is the major reason why, currently, a very few, if at all, fully operational force feedback teleoperation devices exist except for research environments. The proposed framework handles system uncertainty with adaptation and communication time delays with explicit delay compensation. The technology that allows this explicit adaptive time-delay compensation is inspired by Massachusetts Institute of Technology (MIT)'s Adaptive Posicast Controller. We provide simulation results that demonstrate stable explicit adaptive delay compensation in a force-reflecting teleoperation set up. Copyright Â© 2016 John Wiley & Sons, Ltd. Copyright Â© 2016 John Wiley & Sons, Ltd.
Open Access
Independent estimation of input and measurement delays for a hybrid vertical spring-mass-damper via harmonic transfer functions
(IFAC, 2015-06) Uyanık, İsmail; Ankaralı, M. M.; Cowan, N. J.; Saranlı, U.; Morgül, Ömer; Özbay, Hitay
System identification of rhythmic locomotor systems is challenging due to the time-varying nature of their dynamics. Even though important aspects of these systems can be captured via explicit mechanics-based models, it is unclear how accurate such models can be while still being analytically tractable. An alternative approach for rhythmic locomotor systems is the use of data-driven system identification in the frequency domain via harmonic transfer functions (HTFs). To this end, the input-output dynamics of a locomotor behavior can be linearized around a stable limit cycle, yielding a linear, time-periodic system. However, few if any model-based or data-driven identification methods for time-periodic systems address the problem of input and measurement delays in the system. In this paper, we focus on data-driven system identification for a simple mechanical system and analyze its dynamics in the presence of input and measurement delays using HTFs. By exploiting the way input delays are modulated by the periodic dynamics, our results enable the separate, independent estimation of input and measurement delays, which would be indistinguishable were the system linear and time invariant. © 2015, IFAG.
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
A numerical method for stability windows and unstable root-locus calculation for linear fractional time-delay systems
(Elsevier, 2012-08-14) Fioravanti, A.R.; Bonnet, C.; Özbay, Hitay; Niculescu, S. I.
This paper aims to provide a numerical algorithm able to locate all unstable poles, and therefore the characterization of the stability as a function of the delay, for a class of linear fractional-order neutral systems with multiple commensurate delays. We start by giving the asymptotic position of the chains of poles and the conditions for their stability for a small delay. When these conditions are met, the root continuity argument and some simple substitutions allow us to determine the locations where some roots cross the imaginary axis, providing therefore the complete characterization of the stability windows. The same method can be extended to provide the position of all unstable poles as a function of the delay.
Open Access
Observer based friction cancellation in mechanical systems
(IEEE, 2014-10) Odabaş, Caner; Morgül, Ömer
An adaptive nonlinear observer based friction compensation for a special time delayed system is presented in this paper. Considering existing delay, an available Coulomb observer is modified and closed loop system is formed by using a Smith predictor based controller as if the process is delay free. Implemented hierarchical feedback system structure provides two-degree of freedom and controls both velocity and position separately. For this purpose, controller parametrization method is used to extend Smith predictor structure to the position control loop for different types of inputs and disturbance attenuation. Simulation results demonstrate that without requiring much information about friction force, the method can significantly improve the performance of a control system in which it is applied. © 2014 Institute of Control, Robotics and Systems (ICROS).
Open Access
On Smith predictor-based controller design for systems with integral action and time delay
(IEEE, 2013-06) Taşdelen, Uğur; Özbay, Hitay
A new Smith predictor based controller is proposed for systems with integral action and flexible modes under input-output time-delay. The design uses controller parametrization and aims to achieve a set of performance and robustness objectives. Compared to existing Smith predictor based designs, disturbance attenuation property is improved, with respect to periodic disturbances at a known frequency. A two-degree of freedom controller structure is shown to be helpful in shaping the transient response under constant reference inputs. Stability robustness properties of this system are also investigated. Simulation results demonstrate the effectiveness of the proposed controller. © 2013 IEEE.
Open Access
On the H∞ controller design for a magnetic suspension system model
(Elsevier, 2013) Karagül, E.; Özbay, Hitay
This paper deals with the H∞ optimal controller design for a magnetic suspension system model derived in Knospe and Zhu [2011], with added input/output delay. The plant is a fractional order system with time delay i.e., the transfer function of the plant involves infinite dimensional terms including a rational function of √/s and e-hs, where h > 0 represents the delay. The H∞ optimal controller is designed by using the recent formulation given in Ozbay [2012] for the mixed sensitivity minimization problem for unstable infinite dimensional plants with low order weights. The effect of time delay on the achievable performance level is illustrated. © 2013 IFAC.
Open Access
On the stabilization and stability robustness against small delays of some damped wave equations
(IEEE, 1995) Morgül, O.
In this note we consider a system which can be modeled by two different one-dimensional damped wave equations in a bounded domain, both parameterized by a nonnegative damping constant. We assume that the system is fixed at one end and is controlled by a boundary controller at the other end. We consider two problems, namely the stabilization and the stability robustness of the closed-loop system against arbitrary small time delays in the feedback loop. We propose a class of dynamic boundary controllers and show that these controllers solve the stabilization problem when the damping coefficient is nonnegative and stability robustness problem when the damping coefficient is strictly positive.
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 posicast controller
(IFAC, 2015) Yıldız, Yıldıray; Annaswamy, A.
Adaptive Posicast Controller that is robust to delay-mismatch is introduced in this paper. Inspired from a recent result on guaranteed delay margins in adaptive control, the original adaptive laws of the above mentioned controller are modified using projection to compensate the uncertainty in the input delay. It is conjectured and shown in simulations that even though the assumed upper bound for the delay value is exceeded, Adaptive Posicast Controller with projection algorithm keeps all the system signals bounded.
Open Access
A secant condition for cyclic systems with time delays and its application to Gene Regulatory Networks
(IFAC, 2015) Ahsen, M. E.; Özbay, Hitay; Niculescu, S. -I.
A stability condition is derived for cyclic systems with time delayed negative feedback. The result is an extension of the so-called secant condition, which is originally developed for systems without time delays. This extension of the secant condition gives a new local stability condition for a model of GRNs (Gene Regulatory Networks) under negative feedback. Stability robustness of homogenous networks is also investigated.
Open Access
Sensitivity minimization by stable controllers: an interpolation approach for suboptimal solutions
(IEEE, 2007) Gümüşsoy, S.; Özbay, Hitay
Weighted sensitivity minimization is studied within the framework of strongly stabilizing (stable)H∞controller design for a class of infinite dimensional systems. This problem has been solved by Ganesh and Pearson, [8], for finite dimensional plants using Nevanlinna-Pick interpolation. We extend their technique to a class of unstable time delay systems. Moreover, we illustrate suboptimal solutions, and their robust implementation.
Open Access
Stability analysis of human–adaptive controller interactions
(American Institute of Aeronautics and Astronautics (AIAA), 2017) Yücelen, T.; Yıldız, Yıldıray; Sipahi, R.; Yousefi, Ehsan; Nguyen, N.
In this paper, stability of human in the loop model reference adaptive control architectures is analyzed. For a general class of linear human models with time-delay, a fundamental stability limit of these architectures is established, which depends on the parameters of this human model as well as the reference model parameters of the adaptive controller. It is shown that when the given set of human model and reference model parameters satisfy this stability limit, the closed-loop system trajectories are guaranteed to be stable. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
Open Access
Stability analysis of switched time-delay systems
(IEEE, 2008-12) Yan, P.; Özbay, Hitay
This paper addresses the asymptotic stability of switched time delay systems with heterogenous time invariant time delays. Piecewise Lyapunov-Razumikhin functions are introduced for the switching candidate systems to investigate the stability in the presence of infinite number of switchings. We provide sufficient conditions in terms of the minimum dwell time to guarantee asymptotic stability under the assumptions that each switching candidate is delay-independently or delaydependently stable. Conservatism analysis is also provided by comparing with the dwell time conditions for switched delay free systems. © 2008 IEEE.
Open Access
Stability windows and unstable root-loci for linear fractional time-delay systems
(Elsevier, 2011) Fioravanti, A.R.; Bonnet, C.; Özbay, Hitay; Niculescu, S.-I.
The main point of this paper is on the formulation of a numerical algorithm to find the location of all unstable poles, and therefore the characterization of the stability as a function of the delay, for a class of linear fractional-order neutral systems with multiple commensurate delays. We start by the asymptotic position of the chains of poles and conditions for their stability, for a small delay. When these conditions are met, we continue by means of the root continuity argument, and using a simple substitution, we can find all the locations where roots cross the imaginary axis. We can extend the method to provide the location of all unstable poles as a function of the delay. Before concluding, some examples are presented. © 2011 IFAC.
Open Access
A switching control approach to stabilization of parameter varying time delay systems
(IEEE, 2009) Yan, P.; Özbay, Hitay; Şansal, M.
Robust stabilization problem is considered for time varying time delay systems, where the system parameters are scheduled along a measurable signal trajectory. A switching control approach is proposed for a class of parameter varying systems, where candidate controllers are designed for robust stabilization at certain operating regions. A dwell time based hysteresis switching logic is proposed to guarantee the stability of the switched parameter varying time delay system in the whole operating range. It is shown that if the parameter variation is slow enough (upper bound of the time derivative is determined in terms the dwell time for the switched delay system), then the system is stable with the proposed switched controllers.