Browsing by Subject "Control system analysis"

Now showing 1 - 16 of 16

Open Access
Associative memory design using overlapping decompositions
(Pergamon Press, 2001) Akar, M.; Sezer, M. E.
This paper discusses the use of decomposition techniques in the design of associative memories via artificial neural networks. In particular, a disjoint decomposition which allows an independent design of lower-dimensional subnetworks and an overlapping decomposition which allows subnetworks to share common parts, are analyzed. It is shown by a simple example that overlapping decompositions may help in certain cases where design by disjoint decompositions fails. With this motivation, an algorithm is provided to synthesize neural networks using the concept of overlapping decompositions. Applications of the proposed design procedure to a benchmark example from the literature and to a pattern recognition problem indicate that it may improve the effectiveness of the existing methods.
Open Access
A controllable spin prism
(IOP Institute of Physics Publishing, 2009) Hakiolu, T.
Based on Khodas et al (2004 Phys. Rev. Lett. 92 086602), we propose a device acting like a controllable prism for an incident spin. The device is a large quantum well where Rashba and Dresselhaus spin-orbit interactions are present and controlled by the plunger gate potential, the electric field and the barrier height. A totally destructive interference can be manipulated externally between the Rashba and Dresselhaus couplings. The spin-dependent transmission/reflection amplitudes are calculated as the control parameters are changed. The device operates as a spin prism/converter/filter in different regimes and may stimulate research in promising directions in spintronics in analogy with linear optics. © 2009 IOP Publishing Ltd.
Open Access
Decentralized blocking zeros and the decentralized strong stabilization problem
(IEEE, 1995) Ünyelioğlu, K. A.; Özgüler, A. B.; Özgüner, Ü.
This paper is concerned with a new system theoretic concept, decentralized blocking zeros, and its applications in the design of decentralized controllers for linear time-invariant finite-dimensional systems. The concept of decentralized blocking zeros is a generalization of its centralized counterpart to multichannel systems under decentralized control. Decentralized blocking zeros are defined as the common blocking zeros of the main diagonal transfer matrices and various complementary transfer matrices of a given plant. As an application of this concept, we consider the decentralized strong stabilization problem (DSSP) where the objective is to stabilize a plant using a stable decentralized controller. It is shown that a parity interlacing property should be satisfied among the real unstable poles and real unstable decentralized blocking zeros of the plant for the DSSP to be solvable. That parity interlacing property is also sufficient for the solution of the DSSP for a large class of plants satisfying a certain connectivity condition. The DSSP is exploited in the solution of a special decentralized simultaneous stabilization problem, called the decentralized concurrent stabilization problem (DCSP). Various applications of the DCSP in the design of controllers for large-scale systems are also discussed.
Open Access
Decentralized control and periodic feedback
(IEEE, 1994) Khargonekar P. P.; Özgüler, A. B.
The decentralized stabilization problem for linear, discretetime, periodically time-varying plants using periodic controllers is considered. The main tool used is the technique of lifting a periodic system to a time-invariant one via extensions of the input and output spaces. It is shown that a periodically time-varying system of fundamental period N can be stabilized by a decentralized periodic controller if and only if: 1) the system is stabilizable and detectable, and 2) the N-lifting of each complementary subsystem of identically zero input-output map is free of unstable input-output decoupling zeros. In the special case of N = 1, this yields and clarifies all the major existing results on decentralized stabilization of time-invariant plants by periodically time-varying controllers. © 1994 IEEE
Open Access
Discrete-time LQ optimal repetitive control
(IEEE, 1999) Köroğlu, Hakan; Morgül, Ömer
LQ optimal repetitive control is developed in single-input single-output discrete-time signal/system framework. For a given plant and a stabilizing controller, the LQ optimal repetitive control system can be obtained by the addition of a plug-in unit to the existing control system. The overall behaviour (stochastic behaviour, stability robustness etc.) of the new system can be improved by the appropriate choice/tuning of the design parameters.
Open Access
A dynamic control law for the wave equation
(Elsevier, 1994) Morgül, Ö.
We consider a system described by the one-dimensional linear wave equation in a bounded domain with appropriate boundary conditions. To stabilize the system, we propose a dynamic boundary controller applied at the free end of the system. The transfer function of the proposed controller is restricted to be a positive real function which could be strictly proper. We then show that, if the transfer function of the controller is strictly proper, then the resulting closed-loop system is asymptotically stable, and if proper but not strictly proper, then the resulting closed-loop system is exponentially stable.
Open Access
Observer based control of chaos
(IEEE, 1997-08) Solak, Ercan; Morgül, Ömer; Ersoy, Umut
In this work we consider the control of forced chaotic oscillators. To obtain any desirable behavior, the system parameters are effectively modified using state feedback. The system states used in the feedback are estimated through a nonlinear observer. The application of the proposed method is illustrated for Duffing and Van der Pol oscillators.
Open Access
On algebraic properties of general proper decentralized systems
(Elsevier, 1993) Yu, R.; Sezer, M. E.; Gao, W.
The new concepts of the decentralized output feedback variable polynomial, the decentralized output feedback cycle index of general proper systems, and the geometric multiplicities of decentralized fixed modes are introduced. Their computational methods and some algebraic properties are presented. It is shown that the decentralized output feedback cycle index of a general proper system is equal to one when the system has no fixed modes or equal to the maximum of the geometric multiplicities of its decentralized fixed modes. It is also shown that almost all decentralized output feedback can be used to make the zeros of the decentralized variable polynomial distinct, and disjoint from any given finite set of points on the complex plane.
Open Access
On switching H ∞ controllers for a class of LPV systems
(IEEE, 2003) Yan, P.; Özbay, Hitay
We consider switching H ∞ controllers for a class of LPV systems scheduled along a measurable parameter trajectory. The candidate controllers are selected from a given controller set according to the switching rules based on the scheduling variable. We provide sufficient conditions to guarantee the stability of the switching LPV systems in terms of the dwell time and the average dwell time. Our results are illustrated with an example, where switching between two robust controllers is performed for an LPV system.
Open Access
Robust stability of discrete-time systems under parametric perturbations
(IEEE, 1994-05) Karan, M.; Sezer, M. E.; Ocali, O.
Stability robustness analysis of a system under parametric perturbations is concerned with characterizing a region in the parameter space in which the system remains stable. In this paper, two methods are presented to estimate the stability robustness region of a linear, time-invariant, discrete-time system under multiparameter additive perturbations. An inherent difficulty, which originates from the nonlinear appearance of the perturbation parameters in the inequalities defining the robustness region, is resolved by transforming the problem to stability of a higher order continuous-time system. This allows for application of the available results on stability robustness of continuous-time systems to discrete-time systems. The results are also applied to stability analysis of discrete-time interconnected systems, where the interconnections are treated as perturbations on decoupled stable subsystems.
Open Access
Sensitivity minimization by stable controllers for a class of unstable time-delay systems
(IEEE, 2006) Gümüşsoy, S.; Özbay, Hitay
In this paper sensitivity minimization problem is considered for a class of unstable time delay systems. Our goal is to find a stable controller stabilizing the feedback system and giving rise to smallest H∞ norm for the sensitivity function. This problem has been solved by Ganesh and Pearson (1986) for finite dimensional plants using Nevanlinna-Pick interpolation. We extend their technique to include possibly unstable time delay systems. Moreover, we illustrate suboptimal solutions, and their robust implementation.
Open Access
Sensitivity reduction by stable controllers for mIMO infinite dimensional systems via the tangential nevanlinna-Pick interpolation
(IEEE, 2014) Wakaiki, M.; Yamamoto, Y.; Özbay, Hitay
We study the problem of finding a stable stabilizing controller that satisfies a desired sensitivity level for an MIMO infinite dimensional system. The systems we consider have finitely many simple transmission zeros in C +, but they are allowed to possess infinitely many poles in C +. We compute both upper and lower bounds of the minimum sensitivity achievable by a stable controller via the tangential Nevanlinna-Pick interpolation. We also obtain stable controllers attaining such an upper bound. To illustrate the results, we discuss a repetitive control system as an application of the proposed method.
Open Access
Stability of delayed feedback controllers for discrete time systems
(IEEE, 2003) Morgül, Ömer
We consider the delayed feedback control (DFC) scheme for one dimensional discrete time systems. To analyze the stability, we construct a map whose fixed points correspond to the periodic orbits of the system to be controlled. Then the stability of the DFC is equivalent to the stability of the corresponding equilibrium point of the constructed map.
Open Access
Stabilization and disturbance rejection for the wave equation
(IEEE, 1994) Morgül, Ömer
We consider a system described by the one dimensional linear wave equation in a bounded domain with appropriate boundary conditions. To stabilize the system, we propose a dynamic boundary controller applied at the free end of the system. We also consider the case where the output of the controller is corrupted by a disturbance and show that it may be possible to attenuate the effect of the disturbance at the output if we choose the controller transfer function appropriately.
Open Access
Stable controllers for robust stabilization of systems with infinitely many unstable poles
(Elsevier, 2013) Wakaiki, M.; Yamamoto, Y.; Özbay, Hitay
This paper studies the problem of robust stabilization by a stable controller for a linear time-invariant single-input single-output infinite dimensional system. We consider a class of plants having finitely many simple unstable zeros but possibly infinitely many unstable poles. First we show that the problem can be reduced to an interpolation-minimization by a unit element. Next, by the modified Nevanlinna-Pick interpolation, we obtain both lower and upper bounds on the multiplicative perturbation under which the plant can be stabilized by a stable controller. In addition, we find stable controllers to provide robust stability. We also present a numerical example to illustrate the results and apply the proposed method to a repetitive control system.
Open Access
Tangential Nevanlinna-Pick interpolation for strong stabilization of MIMO distributed parameter systems
(IEEE, 2012-12) Wakaiki, M.; Yamamoto, Y.; Özbay, Hitay
We study the problem of finding stable controllers that stabilize a multi-input multi-output distributed parameter system while simultaneously reducing the sensitivity of the system. The plants we consider have finitely many unstable transmission zeros, but they can possess infinitely many unstable poles. Using the tangential Nevanlinna-Pick interpolation with boundary conditions, we obtain both upper and lower bounds of the minimum sensitivity that can be achieved by stable controllers. We also derive a method to find stable controllers for sensitivity reduction. In addition, we apply the proposed method to a repetitive control system. © 2012 IEEE.