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In this paper, we study H∞ performance of interval systems. We show that, for an interval system, the maximal H∞ norm of its sensitivity function is achieved at twelve (out of sixteen) Kharitonov vertices. Furthermore, we study robustness of multivariable systems with parametric uncertainties, and establish a multivariable version of Edge Theorem. An illustrative example is presented.
The effect of the uncertainty in time-delay on the performance and robustness of a two-degree-of-freedom control system is discussed. The result shows that this delay mismatch strongly influences the reachable closed-loop performance and viceversa. Acceptable robustness and robustness sensitivity can only be reached for less demanding performance requirements.
A new monotonic companding function is proposed for non-uniform lookup table (LUT) indexation used in digital predistortion (PD) of Radio Frequency (RF) power amplifiers (PA) under wideband signals. This function, designed to be robust to the input signal statistics variations, overcomes the disadvantages of optimal indexation which depends on the input back-off (IBO) operation point of the PA. Simulations...
A framework for identification oriented robust controller design is developed. The model is identified from open-loop ilo-data and contains parametric uncertainties as well as an additive and norm-bounded error. The set of all robustly stabilising controllers, that additionally guarantee robust performance is characterised by a system of second order cones, which can be efficiently solved by interior...
This paper deals with the Boyd-Barratt paradigm for feedback controller design. This approach combines the Youla parameterization with convex optimization. In this paper, this paradigm is accepted in its entirety, but a completely different numerical approach is adopted. We propose replacing the descent methods of Boyd and Barratt by an algorithm due to Akilov and Rubinov. This alternative approach...
Iterative Feedback Tuning (IFT) is a direct tuning method using closed loop experimental data. The method is based on numerical optimization and in each iteration an unbiased gradient estimate is used. In this contribution we show how to use IFT to do robust loopshaping. One method, based on the approach suggested by Glover and McFarlane [1], uses an approximate H∞ cost function and alternates between...
In this paper the robustness of the Smith predictor is discussed. An extension of the time delay tolerance is given for systems presenting an open-loop frequency response with multiple unity gain crossover frequencies. A two-degree-of-freedom decoupling scheme is proposed to independently adjust set point and load disturbance responses. Classical design tools (PI, PID) can be used to design the feedback...
This paper presents an integrated methodology for feedback control of active vibration attenuation systems. The basic steps of the methodology are: open loop identification of the secondary path, design of a robust digital controller, identification in closed loop of a ”control oriented” model, redesign of the controller based on the closed loop identified model and controller reduction. The feasability...
The problem of eigenvalue assignment with minimum sensitivity in multivariable descriptor linear systems via state feedback is considered. Based on the perturbation theory of generalized eigenvalues of matrix pairs, the sensitivity measures of the closed-loop finite eigenvalues are established in terms of the closed-loop normalized right and left eigenvectors. By combining these measures with a recently...
The aim of this paper is to identify an LFT model of a rigid aircraft. The highly structured aerodynamic model is first put under a standard LFT form, in which the uncertain parameters are gathered inside a full real block A. Time domain measurements are then translated into frequency domain ones, using a classical FFT technique. Under a rank condition which is satisfied in our aircraft application,...
Robust steering control is used here for improving the yaw dynamics of a passenger car. A specific two degree of freedom control structure is adapted to the vehicle yaw dynamics problem and shown to robustly improve performance. The design study is based on six operating conditions for vehicle speed and the coefficient of friction between the tires and the road representing the operating domain of...
The significance of certain basic stability concepts for feedback systems are discussed in the light of the recent interest in non-fragile controller design. It is shown that certain standard controller representations can have vanishing stability margins against controller coefficient perturbations for control problems defined on the doubly-infinite time axis. Furthermore, it is demonstrated via...
New synthesis techniques for the design of Robust Fault Detection and Isolation (RFDI) filters are developed. The approach provides techniques for designing filters that maximise sensitivity, in some sense, to the effects of faults on the residual signal, while guaranteeing the robustness to noise, disturbances and modelling errors. The design procedure is iterative and is based on robust H∞ estimation...
An experimental application of a state-space predictive controller is presented. The controller is used for low-level control of a gas conditioning unit, an integrating process with two inputs and two outputs, in a real-life environment. An original approach to the tuning of the controller's feedback action for efficient disturbance rejection performance and robustness is introduced. Feedback action...
This paper considers robust control with a stable controller using proportional-integral-plus control techniques. A formulation of robust PIP controllers is proposed on the basis of parametric pole assignment. The robustness function in the frequency domain is minimised using the freedom provided by parametric pole assignment. It shows how to combine time-domain performance specifications provided...
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).
This paper deals with the so-called robust disturbance attenuation problem. This problem is to find the controller which robustly minimizes the infinity norm of the weighted sensitivity function. So this is a robust performance problem. This problem has not been solved at an analytical level. However, one can try to approach the optimum using, for instance, μ-synthesis or the convex optimization paradigm...
This paper's aim is to present a tuning approach for full Two-Degree-of-Freedom (2-DOF) PID controllers for Second-Order-Plus-Dead-Time (SOPDT) controlled processes. The tuning relations provide the value of the typical parameters for a PID controller plus the set-point weighting factor, being these relations driven by just one single design parameter to be selected by the user. This fact makes the...
Dynamic observer provides more freedom to meet the diversified specifications in contrast with static observer. However, little attention is paid on its application for fault detection purpose. In this work, we propose an innovative dynamic observer based fault detection method for linear time invariant (LTI) systems subjected to unknown disturbance and possible faults with the aid of the generalized...
This paper presents a H∞ loop-shaping controller for regulating the switching signal of the inverter connected with a single-phase photovoltaic (PV) system. To facilitate the control design, the system is represented in terms of state space realization with uncertainties. The controller design involves achieving proper loop shapes through the choice of the proper weighting functions. A H∞ synthesis...
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