Levent Ucun

Receding horizon H ∞ control of time-delay systems

This paper deals with the disturbance rejection problem for discrete-time linear systems having time-varying state delays and control constraints. The study proposes a novel receding horizon H∞ control method utilizing a linear matrix inequality based optimization algorithm which is solved in each step of run-time. The proposed controller attenuates disturbances having bounded energies on controlled output and ensures the closed-loop stability and dissipation while meeting the physical control input constraints. The originality of the work lies on the extension of the idea of the well-known H∞ receding horizon control technique developed for linear discrete-time systems to interval time-delay systems having time-varying delays. The efficiency of the proposed method is illustrated through simulation studies that are carried out on a couple of benchmark problems.

Internal model controller design via H∞ dynamic output feedback

This paper deals with internal model controller design via H ∞ dynamic output feedback for linear perturbed systems. The study proposes an internal model controller within the perspective of H ∞ dynamic output feedback, utilizing a linear matrix inequality based optimization algorithm. This proposed method is a synthesis of an internal model controller design that has different application fields, as reported in the literature, and an H ∞ dynamic output feedback controller, which has proven its success in several studies. The proposed controller attenuates disturbances, having bounded energies on controlled output. The originality of the work lies in the combination of two different approaches to obtain an optimal controller design algorithm. The liability and performance of the proposed method are illustrated via simulations, which are applied to a couple of benchmark problems.

Robust delay-dependent feedforward control of neutral time-delay systems via dynamic IQCs

This paper studies the design problem of delay-dependent based robust and optimal feedforward controller design for a class of time-delay control systems having state, control and neutral type delays which are subject to norm-bounded uncertainties and type measurable or observable disturbance signals. Two independent loops which include state-feedback and dynamic feedforward controller form the basis of the proposed control scheme in this study. State-feedback controller is generally used in stabilisation of the nominal delay-free system, whereas the feedforward controller is used for improving disturbance attenuation performance of the overall system. In order to obtain less conservative results, the delay and parametric uncertainty effects are treated in operator view point and represented by frequency-dependent (dynamic) integral quadratic constraints (IQCs). Moreover, sufficient delay-dependent criterion is developed in terms of linear matrix inequalities (LMIs) such that the time-delay system having parametric uncertainties is guaranteed to be asymptotically stable with minimum achievable disturbance attenuation level. Plenty of numerical examples are provided at the end, in order to illustrate the efficiency of the proposed technique. The achieved results on minimum achievable disturbance attenuation level and maximum allowable delay bounds are exhibited to be less conservative in comparison to those of controllers having only feedback loop.

Delay-Dependent Feedforward Control of Uncertain Neutral Time-Delay Systems via Dynamic IQCs

Abstract This paper deals with the design problem of a delay-dependent ℋ ∞ based robust optimal feedforward controller for a class of time-delay control systems having state delays, control delays and neutral delays when the system is subject to norm bounded uncertainties. The proposed scheme in this study is formed by two independent loops which include state-feedback and dynamic feedforward controller. The delay and parametric uncertainty effects are represented by dynamic Integral Quadratic Constraints (IQCs). Furthermore, sufficient delay-dependent criteria is developed in terms of Linear Matrix Inequalities (LMIs) such that the time-delay system with parametric uncertainty is guaranteed to be asymptotically stable with a minimum disturbance attenuation level. The achieved results on the minimum allowable disturbance attenuation level in the provided numerical examples are exhibited to be less conservative in comparison to those of controllers having only feedback loop.

LPV control active suspension system

The ℒ2 gain control problem for disturbance attenuation in Linear Parameter Varying (LPV) Systems with saturating actuators has been addressed in this paper. The active suspension system which is used as a benchmark control problem is subjected to ℒ2 disturbances and actuator saturation. Actuator saturation nonlinearity is reformalized in terms of some convex hull of linear feedback. This point of view allows us to construct ℒ2 control problem having actuator saturation nonlinearities as a convex optimization problem. Nested ellipsoids have been used to measure the stability and disturbance rejection capabilities of the control system. At this point, the inner ellipsoid covers the initial conditions of states whereas the outer ellipsoid designates the ℒ2 gain of the system. Finally, the proposed method has been applied to an active suspension system having linear time-varying parameter such as suspension spring constant. The results have been verified on a real experimental system. Experimental results demonstrate the efficiency of the proposed method.