Ibone Lizarraga

Stability verification of microwave circuits through Floquet multiplier analysis

This work presents a procedure to verify the stability of periodic regimes of microwave circuits that are simulated with harmonic-balance algorithms. The technique is based on computing the Floquet multipliers associated to the system linearization around the periodic regime. The proposed procedure has been applied to a C-band GaAs prescaler. Stability analysis results provide an estimation of the circuit input sensitivity curve that is in good agreement with measurement results.

Control of a Lightweight Flexible Robotic Arm Using Sliding Modes

This paper presents a robust control scheme for flexible link robotic manipulators, which is based on considering the flexible mechanical structure as a system with slow (rigid) and fast (flexible) modes that can be controlled separately. The rigid dynamics is controlled by means of a robust sliding-mode approach with well-established stability properties while an LQR optimal design is adopted for the flexible dynamics. Experimental results show that this composite approach achieves good closed loop tracking properties both for the rigid and the flexible dynamics.

Systematic Approach to the Stabilization of Multitransistor Circuits

This paper proposes a systematic approach for the elimination of spurious oscillations in circuits with multiple active elements. The procedure is based on detecting the sensitive parts (nodes or branches) of the complex circuit at which we can have a strong control of the dynamics responsible for the instability. To do so, stability analyses based on pole-zero identification are performed at multiple observation ports. Once sensitive locations are detected, stabilization is achieved by adding series or shunt stabilization networks at the suitable node or branch. Standard techniques from linear control theory (pole placement strategies) are used to automatically calculate the values of the stabilization elements ensuring circuit stability. Here, the methodology is applied to the stabilization of a two-stage Ku-band high-power amplifier for active antenna space applications.

CONTROL OF SINGULARLY PERTURBED SYSTEMS UNDER ACTUATOR SATURATION

Abstract This paper addresses the stabilization problem of singularly perturbed systems subject to actuator saturation. A solution in terms of linear matrix inequalities is proposed. The saturation is represented by means of a modified sector nonlinearity. The numerical problems due to the ill conditioning of the system model are avoided using a non-decoupling strategy. Some numerical results are also included for testing the proposed methods.

COMBINED PD-H∞ APPROACH TO CONTROL OF FLEXIBLE LINK MANIPULATORS USING ONLY DIRECTLY MEASURABLE VARIABLES

A control scheme for flexible link manipulators, which makes use only of directly measurable variables and thus is well suited for practical implementations, is presented. The scheme is based on a combined PD-H X design that takes into account the actual coupling between the rigid and flexible dynamics of these kinds of manipulators and needs feedback only from directly available sensor readings. This contrasts with other approaches reported in the literature that require full-state feedback or even feedback of the rigid unperturbed variables, which simply cannot be measured. It is shown that the proposed design, in spite of its ease of implementation, maintains good closed-loop tracking properties.

Stability Analysis of Nonlinear Circuits Driven With Modulated Signals

Existing methods for the large-signal stability analysis of microwave circuits assume a periodic excitation, usually consisting of a single tone. However, practical circuits such as power amplifiers will generally be driven by modulated signals or multiple input tones. This paper presents a procedure for the stability analysis of linear time-varying systems, applicable to circuits excited with nonperiodic input signals. The procedure is based on the determination of the time-varying poles associated to an input-output representation of the system. Under modulated signals, this representation is obtained by linearizing the envelope-transient system that rules the circuit behavior. The formulation and methodology have been applied to a simple nonlinear circuit with arbitrary excitation and a practical power-combined amplifier at 3 GHz with very good agreement in comparison with independent simulations and experimental results.

SLIDING-MODE ADAPTIVE CONTROL FOR FLEXIBLE-LINK MANIPULATORS USING A COMPOSITE DESIGN

ABSTRACT A robust adaptive control scheme for flexible link robotic manipulators is presented. The design is based on considering the flexible mechanical structure as a singular perturbed system, which allows us to assume the existence of slow (rigid) and fast (flexible) modes that separately can be controlled. The rigid dynamics are controlled by means of a robust sliding adaptive approach with well-established stability properties. The flexible dynamics can be controlled using H ∞ or optimal designs, which successfully handle the actual interaction between the slow and fast subsystems. This composite approach achieves good closed-loop tracking properties, both in simulation and experimental results on a laboratory-flexible arm.

Real-time experimental control of a flexible robotic manipulator using a composite approach

This work presents an experimental study of a robust control scheme for flexible link robotic manipulators, which is based on considering the flexible mechanical structure as a system with slow (rigid) and fast (flexible) modes that can be controlled separately. Two experimental approaches are considered. In a first test an LQR optimal design strategy is used. Then a second design based on a sliding-mode scheme is adopted. Experimental results show that this composite approach achieves good closed loop tracking properties for both design philosophies, which compare favorably with conventional rigid robot control schemes.

Nonlinear analysis of an AMB system using harmonic domain LTV models

Although the AMB technology has important advantages mainly due to the lack of mechanical friction, its nonlinear nature complicates the design and control of such systems. In this work, the nonlinear analysis of an AMB system, the MBC500 Rotor Dynamics from Launchpoint Technologies, is presented. This analysis is based on the harmonic domain linearization of the AMB system around a nonlinear stationary solution, leading to a LTV model for each rotating speed. The nonlinear nature of the response appears at high speeds, due to the large oscillations introduced by the shaft unbalance. Using the presented methodology, low frequency gain loss is detected when increasing the rotating speed. This phenomenon causes the instability of the system, leading to destructive crashes

Modelización, Análisis y Control de Sistemas de Cojinetes Magnéticos Activos

In this study the modeling, control design, robustness analysis and vibration active suppression procedure of a system, based on a rotor hovered by active magnetic levitation, are presented. Firstly, the model obtaining and its main characteristics are described. Utilizing this model and taking advantage of its symmetry properties, a stabilizing controller is designed. Then, it is tuned by means of a robustness study, according to the standard ISO 14839-3. Finally, a reduction of the vibrations produced in rotation is performed, using adaptive control. The designed controller has been experimentally implemented successfully.