Browsing by Subject "Linear control systems"

Now showing 1 - 19 of 19

Open Access
Adaptive control design for nonlinear systems via successive approximations
(ASME, 2017) Babaei, N.; Salamcı, M. U.; Karakurt, Ahmet Hakan
The paper presents an approach to the Model Reference Adaptive Control (MRAC) design for nonlinear dynamical systems. A nonlinear reference system is considered such that its response is designed to be stable via Successive Approximation Approach (SAA). Having designed the stable reference model through the SAA, MRAC is then formulated for nonlinear plant dynamics with a new adaptation rule to guarantee the convergence of the nonlinear plant response to that of the response of the nonlinear reference model. The proposed design methodology is illustrated with examples for different case studies.
Open Access
Adaptive robust sampled-data control of a class of systems under structured perturbations
(IEEE, 1993) Yu, R.; Ocali, O; Sezer, E. S.
Robust adaptive sampled-data control of a class of linear systems under structured perturbations is considered. The controller is a time-varying state-feedback law having a fixed structure, containing an adjustable parameter, and operating on sampled values. The sampling period and the controller parameter are adjusted with simple adaption rules. The resulting closed-loop system is shown to be stable for a class of unknown perturbations. The same result is also shown to be applicable to decentralized control of interconnected systems.
Open Access
Cumulant-based parametric multichannel FIR system identification methods
(Elsevier, 1994) Özgen, M. T.; Alshebeili, S. A.; Çetin, A. Enis; Venetsanopoulos, A. N.
In this paper, “least squares” and recursive methods for simultaneous identification of four nonminimum phase linear, time-invariant FIR systems are presented. The methods utilize the second- and fourth-order cumulants of outputs of the four FIR systems of which the common input is an independent, identically distributed (i.i.d.) non-Gaussian process. The new methods can be extended to the general problem of simultaneous identification of three or more FIR systems by choosing the order of the utilized cumulants to be equal to the number of systems. To illustrate the effectiveness of our methods, two simulation examples are included.
Open Access
Decentralized stabilization: characterization of all solutions and genericity aspects
(Taylor & Francis, 1992) Ünyelioğlu, Konur Alp; Özgüler, Arif Bülent
Electrical and The decentralized stabilization problem of multivariable finite-dimensional systems is considered in a fractional set-up. A new synthesis procedure for decentralized stabilizing compensators is proposed. The class of all admissible local compensators that can be applied to a specified channel as an element of a decentralized compensator is identified. The conditions under which the class of admissible local compensators is generic are investigated. The problem of making a multi-channel system stabilizable and detectable from a single channel applying decentralized feedback around the other channels has been shown to be generically solvable for a given set of dynamic compensators if and only if the plant is strongly connected.
Open Access
Decentralized strong stabilization problem
(IEEE, 1992-06) Özgüler, A. Bülent; Ünyelioğlu, Konur A.
In the decentralized strong stabilization problem for linear time-invariant finite-dimensional systems, the objective is to stabilize a given plant using a stable decentralized controller. A solvability condition for this problem is given in terms of a parity interlacing property which is to be satisfied among the real unstable poles and real unstable decentralized blocking zeros of the plant. The problem of synthesizing decentralized stabilizing controllers with minimum number of unstable poles is also solved.
Open Access
Effects of linear filter on stability and performance of human-in-the-loop model reference adaptive control architectures
(ASME, 2017) Yousefi, Ehsan; Demir, Didem Fatma; Sipahi, R.; Yücelen, T.; Yıldız, Yıldıray
Model reference adaptive control (MRAC) can effectively handle various challenges of the real world control problems including exogenous disturbances, system uncertainties, and degraded modes of operations. In human-in-the-loop settings, MRAC may cause unstable system trajectories. Basing on our recent work on the stability of MRAC-human dynamics, here we follow an optimization based computations to design a linear filter and study whether or not this filter inserted between the human model and MRAC could help remove such instabilities, and potentially improve performance. To this end, we present a mathematical approach to study how the error dynamics of MRAC could favorably or detrimentally influence human operator's error dynamics in performing a certain task. An illustrative numerical example concludes the study.
Open Access
Experimental study of linear closed-loop control of subsonic cavity flow
(2006) Yan P.; Debiasi, M.; Yuan X.; Little J.; Özbay, Hitay; Samimy, M.
A study is presented of the modeling and implementation of different concepts for linear feedback control of a single-mode resonance shallow cavity flow. When a physics-based linear model is used for cavity pressure oscillations-, an H∞ controller was designed and tested experimentally. It significantly reduced the main Rossiter mode for which it was designed, while leading to strong oscillations at other Rossiter modes. Other linear control methods such as Smith predictor controller and proportional integral derivative (PID) controller exhibited similar results. The ineffectiveness of using fixed linear models in the design of controllers for the cavity flows is discussed. A modification of the PID design produced a parallel-proportional with time-delay controller that remedied this problem by placing zeros at the frequencies corresponding to other resonance states. Interestingly, it was observed that introducing the same zero to the H∞ controller can also successfully avoid the strong oscillations at other Rossiter modes otherwise observed in the single-mode-based design. The parallel-proportional with time-delay controller was compared to a very effective open-loop method for reducing cavity resonance and exhibited superior robustness with respect to departure of the Mach number from the design conditions. An interpretation is presented for the physical mechanisms by which the open-loop forcing and the parallel-proportional with time-delay controllers reduce the cavity flow noise. The results support the idea that both controls induce in the system a rapid switching between modes competing for the available energy that can be extracted from the mean flow.
Open Access
Fixed zeros of decentralized control systems
(IEEE, 2000) ÜÜnyelioglu, K. A.; Özgüner, Ü.; Özgüler, A. B.
This paper considers the notion of decentralized fixed zeros for linear, time-invariant, finite-dimensional systems. For an N-channel plant that is free of unstable decentralized fixed modes, an unstable decentralized fixed zero of Channel i (1 ≤ i ≤ N) is defined as an element of the closed right half-plane, which remains as a blocking zero of that channel under the application of every set of N - 1 controllers around the other channels, which make the resulting single-channel system stabilizable and detectable. This paper gives a complete characterization of unstable decentralized fixed zeros in terms of system-invariant zeros.
Open Access
Global stabilization via local stabilizing actions
(Institute of Electrical and Electronics Engineers, 2006) Özgüler, A. B.
Stabilization of a linear, time-invariant system via stabilization of its main diagonal subsytems is the underlying problem in all diagonal dominance techniques for decentralized control. In these techniques as well as all Nyquist-based techniques, sufficient conditions are obtained under the assumption that the collection of the unstable poles of all diagonal subsystems is the same as the unstable poles of the overall system. We show that this assumption is by itself enough to construct a solution to the problem at least in cases where the diagonal subsystems have disjoint poles. © 2006 IEEE.
Open Access
LQ optimal design at finitely many frequencies
(Institute of Electrical and Electronics Engineers, 1998) Köroğlu, H.; Morgül, Ö.
The notion of Linear Quadratic (LQ) optimality at a single frequency is developed in single-input single-output (SISO) linear time-invariant (LTI) system/quasi-stationary signal framework and the optimality condition is given. LQ optimal design at finitely many frequencies is then shown to be reducible to an interpolation problem.
Open Access
A new method for the computation of all stabilizing controllers of a given order
(Taylor & Francis, 2005) Saadaoui, K.; Özgüler, A. B.
A new method is given for computing the set of all stabilizing controllers of a given order for linear, time invariant, scalar plants. The method is based on a generalized Hermite-Biehler theorem and the successive application of a modified constant gain stabilizing algorithm to subsidiary plants. It is applicable to both continuous and discrete time systems.
Open Access
On the set of all stabilizing first-order controllers
(IEEE, 2003) Saadaoui, Karim; Özgüler, Arif Bülent
A computational method is given for determining the set of all stabilizing proper first-order controllers for finite dimensional, linear, time invariant, scalar plants. The method is based on a generalized Hermite-Biehler theorem.
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
On the stabilization of a cable with a tip mass
(IEEE, 1994) Morgül, Ö.; Rao, B. P.; Conrad, F.
In this note, we consider a vertical cable which is pinched at the upper end. A mass is attached at the lower end where a control force is also applied. We show that this hybrid system is uniformly stabilized by choosing a suitable control law for the control force depending on the velocity and angular velocity at the free end. Moreover for specific values of the feedback coefficients, we obtain the rate of decay of the energy of the system.
Open Access
PI and low-order controllers for two-channel decentralized systems
(IEEE, 2003-06) Gündeş, A.N.; Özgüler, A. Bülent
A systematic design method is proposed for simple loworder decentralized controllers in the cascaded form of proportional-integral and first-order blocks. The plant is linear, time-invariant and has two channels, each with a single-input and single-output; there may be any number of poles in the region of stability, but the unstable poles can only occur at the origin.
Open Access
Plant Order Reduction for Controller Design
(IEEE, 2003-06) Özgüler, A. Bülent; Gündeş, A. N.
Two dual methods of plant order reduction for controller design are proposed for linear, time-invariant, multi-input multi-output systems. The model reduction methods are tailored towards closed-loop stability and performance and they yield estimates for the stability robustness and performance of the final design. They can be considered as formalizations of two classical heuristic model reduction techniques: One method neglects a plant-pole sufficiently far to the left of dominant poles and the other cancels a sufficiently small stable plant-zero with a pole at the origin.
Open Access
Reduced-order model-based feedback controller design for subsonic cavity flows
(American Institute of Aeronautics and Astronautics, 2005-01) Yuan, X.; Caraballo, E.; Yan, P.; Özbay, Hitay; Serrani, A.; DeBonis, J.; Myatt, J. H.; Samimy, M.
This paper explores feedback controller design for cavity flows based on reduced-order models derived using Proper Orthogonal Decomposition (POD) along with Galerkin projection method. Our preliminary analysis shows that the equilibrium of the POD model is unstable and a static output feedback controller cannot stabilize it. We develop Linear Quadratic (LQ) optimal state feedback controllers and LQ optimal observers for the linearized models. The linear controllers and observers are applied to the nonlinear system using simulations. The controller robustness is numerically tested with respect to different POD models generated at different forcing frequencies. An estimation for the region of attraction of the linear controllers is also provided.
Open Access
Robust LQ control for harmonic reference/disturbance signals
(IEEE, 2000) Köroğlu, Hakan; Morgül, Ömer
Linear Quadratic (LQ) controller design is considered for continuous-time systems with harmonic signals of known frequencies and it is shown that the design is reducible to an interpolation problem. All LQ optimal loops are parametrized by a particular solution of this interpolation problem and a (free) stable/proper transfer function. The appropriate choice of this free parameter for optimal stability robustness is formulated as a multiobjective design problem and reduced to a Nevanlinna-Pick interpolation problem with some interpolation points on the boundary of the stability domain. Using a related result from the literature, it is finally shown that, if there is sufficient penalization on the power of the control input, the level of optimum stability robustness achievable with LQ optimal controllers is the same as the level of optimum stability robustness achievable by arbitrary stabilizing controllers.
Open Access
Tracking and regulation control of a 2-DOF robot arm with unbalance
(IEEE, 2012-08) Güler, Samet; Özgüler, A. Bülent
Servomechanism synthesis for a two degree-of-freedom robot arm assembled on a vessel and affected from sea disturbances is considered. Dynamic equations of the robot arm with unbalance and of an approximate base disturbance model are derived. Direct linear controller synthesis based on a linearized model is then studied. It is shown that, although the plant model is nonlinear, linear controller that is synthesized based on the "internal model principle" provide good performance and perform better than the commonly used PID controllers. © 2012 IEEE.