Renato A. Borges

H ∞ LPV Filtering for Linear Systems with Arbitrarily Time-varying Parameters in Polytopic Domains

In this paper, the problem of H∞ filtering for linear systems affected by arbitrarily time-varying parameters in polytopic domains is investigated. A linear parameter-varying filter which minimizes an upper bound to the H∞ estimation error performance is determined for both continuous and discrete-time cases. Different from other strategies in the literature, the filter design is accomplished by means of a convex optimization procedure and the time-varying parameters are supposed to affect all systems matrices. The LPV filter is obtained from the optimal solution of a convex linear matrix inequality problem formulated only in terms of the vertices of the polytope. There is no use of exhaustive gridding in the parameter space. Numerical examples illustrate the efficiency of the proposed approach

A new condition for finite time boundedness analysis

Abstract In this paper, a new condition for finite time boundedness analysis is presented. Firstly, a brief discussion of the available conditions found in the literature and comparisons between them regarding computational efficiency and conservatism are presented. Then, a new condition expressed in terms of linear matrix inequalities (LMIs) is derived using Finsler׳s lemma. The proposed condition is proved to be less conservative than LMI conditions previously presented in the literature, and its efficiency is illustrated with numerical examples.

Robust PID Design for Second-Order Processes with Time-Delay and Structured Uncertainties

Abstract This paper deals with the problem of PID design for continuous-time systems with time delays. The system is assumed to be free of parametric disturbances and affected by a time-invariant discrete delay of known magnitude. The robustness of the PID control with respect to structured uncertainties is investigated with the small-gain theorem and better performance is sought through the minimization of an upper bound to the closed-loop system ℋ ∞ norm. A Lyapunov-Krasovskii type functional is used yielding delay-dependent design conditions. The controller design is accomplished by means of a convex optimization procedure formulated using linear matrix inequalities (LMIs). Numerical experiments are provided to illustrate the main characteristics of the proposed design method. The particular case of a recycle process controller is addressed.

H ∞ filtering of networked systems with time-varying sampling rates

In this paper, the problem of robust filter design for networked systems with time-varying sampling rate is investigated. The design conditions are obtained by using the Lyapunov theory and the Finslers Lemma. A robust filter, that minimizes an upper bound to the H∞ performance of the estimation error, is obtained as the solution of an optimization problem. A path-dependent Lyapunov function is used in order to obtain less conservative design conditions. Robust filters based on affine parameter-dependent Lyapunov functions can be obtained as a particular case of the proposed method. Numerical examples illustrate the results.

Robust PI and PID design for first-and second-order processes with zeros, time-delay and structured uncertainties

ABSTRACT The use of robust design techniques such as the one based on and for tuning proportional integral (PI) and proportional integral derivative (PID) controllers have been limited to address a small set of processes. This work addresses the problem by considering a wide set of possible plants, both first- and second-order continuous-time systems with time delays and zeros, leading to PI and PID controllers. The use of structured uncertainties to handle neglected dynamics allows to expand the range of processes to be considered. The proposed approach takes into account the robustness of the controller with respect to these structured uncertainties by using the small-gain theorem. In addition, improved performance is sought through the minimisation of an upper bound to the closed-loop system norm. A Lyapunov–Krasovskii-type functional is used to obtain delay-dependent design conditions. The controller design is accomplished by means of a convex optimisation procedure formulated using linear matrix inequalities. In order to illustrate the flexibility of the approach, several examples considering recycle compensation, reduced-order controller design and a practical implementation are addressed. Numerical experiments are provided in each case to highlight the main characteristics of the proposed design method.

Development of a meteorology and remote sensing experimental platform: The LAICAnSat-1

This work presents the first advanced level CanSat developed by the University of Brasilia, the LAICAnSat-1. The main objective is to design, build and launch an experimental high altitude balloon CanSat withmeteorology and remote sensing applications. Both the scientific need for a self retrievable radiosonde, with precise and high quality sensors, and a high altitude low-cost remote sensing experimental platform inspired the team on the concept of LAICAnSat-1. This platform has a broad sensor suite that provides information about temperature, pressure, humidity and UV light level. It also has a modular design, based on stacks, allowing other sensors to be easily embedded to the main module. The remote sensing sensor is a small high performance camera, constantly imaging the Earth surface. Those images can be used for several applications, including emergency and quick solutions for monitoring the Amazon forest, Pantanal, and other important biomes, supporting and complementing research projects on remote areas. The control system has four sensors to determine the payload attitude and position. Furthermore, this platform could potentially be exploited by the industry, representing a safe and inexpensive way to test components and circuits in high altitudes, as for instance to certify Commercial Off-The-Shelf electronic components with respect to their behavior under low temperature and pressure. The LAICAnSat-1 represents a preliminary step in the development of complex aerospace projects and is also an important first experience for engineering students.

Improved conditions for reduced-order 𠄋 ∞ filter design as a static output feedback problem

In this paper, the problem of reduced order H∞ filter design for time-invariant discrete-time linear systems is investigated. The filtering problem is rewritten as a static output feedback control problem and the elimination lemma is applied to derive the design conditions for both precisely known and uncertain linear systems. An algorithm is proposed to solve the problem in two stages involving only linear matrix inequalities. A robust filter of arbitrary order is obtained by solving an optimization problem that minimizes an upper bound to the H∞ performance of the estimation error dynamics. Numerical examples are presented to illustrate the advantages of the approach when compared to other techniques.

H ∞ robust memory controllers for networked control systems: uncertain sampling rates and time delays in polytopic domains

In this paper, the problem of controller design for networked control systems with time-varying sampling rates and time delays is investigated. By using a memory at the feedback loop, a digital robust controller that minimizes an upper bound to the Hinfin performance of the closed loop system is determined. The design conditions are obtained from the Finslers Lemma combined with the Lyapunov theory and expressed in terms of bilinear matrix inequalities. Extra variables introduced by the Finslers Lemma are explored in order to provide a better system behavior. The time-varying uncertainties are modelled using polytopic domains. The controller is obtained by the solution of an optimization problem formulated only in terms of the vertices of the polytope, avoiding grids in the parametric space. Numerical examples illustrate the efficiency of the proposed approach.

Joint Optimal Design of Digital Filters and State-Space Realizations

In this brief, a procedure for digital filters design is presented. The main purpose is to show that a digital filter and its realization can be simultaneously determined such as to minimize an upper bound of the H2 norm of the estimation error and impose a certain degree of robustness against practical uncertainties as for instance, finite word length implementation, roundoff errors, and numerical precision. The optimal filter and its state-space realization are jointly determined from the solution of a convex programming problem expressed in terms of linear matrix inequalities. A simple illustrative example is presented for comparison purposes making clear the advantages of the reported results

A high precision attitude determination and control system for the UYS-1 nanosatellite

This paper presents the design of a high precision attitude determination and control system for the UYS-1 Ukrainian nanosatellite. Its main task is the 3-axis stabilization with less than 0.5° angle errors, so the satellite may take high precision photos of Earths surface. To accomplish this task, this system comprises a star tracker and three reaction wheels. To avoid external disturbances and actuators faults, a PD-type and a PID-type robust controllers are simulated and the results are compared to an empirically adjusted PD controller.