Fernando Lizarralde

Output-feedback model-reference sliding mode control of uncertain multivariable systems

This note considers the robust output tracking problem using a model-reference sliding mode controller for linear multivariable systems of relative degree one. It is shown that the closed loop system is globally exponentially stable and the performance is insensitive to bounded input disturbances and parameter uncertainties. The strategy is based on output-feedback unit vector control to generate sliding mode. The only required a priori information about the plant high frequency gain matrix K/sub p/ is the knowledge of a matrix S/sub p/ such that -K/sub p/S/sub p/ is Hurwitz which relaxes the positive definiteness requirement usually needed by other methods.

Dynamic positioning of remotely operated underwater vehicles

The paper describes an automatic dynamic positioning system for remotely operated underwater vehicles (ROVs) using a mechanical passive arm for position measurement that is suitable for inspection and intervention tasks requiring precise positioning. Good dynamic performance in tracking was also attained, particularly with the variable structure model reference adaptive control strategy.

A variable structure model reference robust control without a prior knowledge of high frequency gain sign

The design of a variable structure model reference robust control without a prior knowledge of high frequency gain sign is presented. Based on an appropriate monitoring function, a switching scheme for some control signals is proposed. It is shown that after a finite number of switching, the tracking error converges to zero at least exponentially for plants with relative degree one or converges exponentially to a small residual set for plants with higher relative degree, and the input disturbance can be completely rejected without affecting the tracking performance.

Multivariable Output-Feedback Sliding Mode Control

This chapter addresses the problem of model-reference sliding mode control of uncertain linear multi-input-multi-output systems by output-feedback. After a brief revision of the main approaches and results available in the literature, a new method to solve the problem is presented using unit vectors as switching functions to induce sliding modes. It is named Unit Vector Model-Reference Adaptive Control (UV-MRAC).

Lyapunov/Passivity-Based Adaptive Control of Relative Degree Two MIMO Systems With an Application to Visual Servoing

This note presents a Lyapunov-based design of model-reference adaptive control (MRAC) for multiple-input-multiple-output (MIMO) systems of uniform relative degree two. It consists of an extension of a well known MRAC Lyapunov-based scheme for single-input-single-output (SISO) plants with relative degree one or two. The case of relative degree one, was completely extended to the MIMO case only recently. The corresponding extension of the relative degree two case remained hitherto unpublished. While MIMO MRAC schemes exist which can deal with arbitrary relative degree, the one presented here has the significant advantage of possessing an explicit Lyapunov function which easily leads to a stability and error convergence proof. It can also be regarded as a passivity-based approach. As a result, it becomes easier to guarantee stability when connecting such adaptive system to other adaptive control systems with similar passivity properties, e.g., in adaptive visual servoing of robot manipulators

Global Exact Tracking for Uncertain Systems Using Output-Feedback Sliding Mode Control

This note presents a solution to the problem of global exact output tracking for uncertain linear plants with arbitrary relative degree using output-feedback sliding mode control. The key idea to overcome the relative degree obstacle is to introduce a hybrid compensator by combining, through switching, a standard lead filter with a robust exact differentiator, based on higher-order sliding modes, achieving uniform global exponential practical stability and asymptotic exact tracking.

Peaking free variable structure control of uncertain linear systems based on a high-gain observer

An output-feedback model-reference variable structure controller based on a high-gain observer (HGO) is proposed and analyzed. For single-input-single-output (SISO) linear plants with relative degree greater than one, the control law is generated using the HGO signals only to drive the sign function of the variable structure control component while the sign function gain, also called modulation, as well as the other components of the control signal are generated using signals from state variable filters which do not require high gain and are free of peaking. This scheme achieves global exponential stability with respect to a small residual set and does not generate peaking in the control signal.

Modeling and feedback control of color-tunable LED lighting systems

This paper presents a color-science-based approach to feedback control design of color-tunable LED lighting systems for smart spaces. The general design problem is posed as the minimization of a cost function consisting of metrics that capture light quality, energy consumption and human comfort. A linear light transport map is used for modeling and identifying the optical fingerprint of the room. The feedback control law is then derived based on the identified model through gradient-based optimization of the cost function. Finally, experimental results are presented to highlight the performance of the feedback control law in terms of (1) energy savings, (2) delivered light quality, (3) adaptivity to external disturbances (such as daylighting) and (4) human comfort.

Wave-to-Wire Model and Energy Storage Analysis of an Ocean Wave Energy Hyperbaric Converter

This paper addresses the dynamic modeling and the energy storage analysis of a wave energy hyperbaric converter, which consists of a set of oscillating bodies (named as pumping modules) linked to hydropneumatic accumulators and an electric generating unit. A mathematical model of the accumulator is presented and a model for the generating unit is proposed, including a nonlinear model of a Pelton turbine. Then, the hydrodynamic, mechanical, and electrical characteristics of the subsystems that compose the converter are discussed. With the proposed model, it is possible to evaluate the dynamic behavior of the entire system. That is, for a given incident ocean wave, it is possible to evaluate all the system state variables and the generated electric power, including the quality (fluctuation, for example) of the generated voltage and frequency for islanded or power-grid-connected operation. Simulation results considering the proposed wave-to-wire model under the action of regular and irregular incident waves are presented to illustrate the performance of the system.

Adaptive visual servoing scheme free of image velocity measurement for uncertain robot manipulators

This work addresses the visual tracking problem of robot manipulators with non-negligible dynamics using a fixed camera, when the camera-robot system parameters are uncertain. An adaptive strategy is developed for visual servoing systems based on the image-based look-and-move structure to allow the tracking of a 2D reference trajectory, without using image velocity measurements. The adaptive visual servoing problem free of image velocity information is formulated as a relative degree two MIMO adaptive control problem. As a solution, we employ a recently proposed Lyapunov/passivity-based adaptive control scheme based on the SDU factorization method. From a cascade control strategy, the resulting online camera calibration scheme is combined with a direct adaptive motion controller for the robot manipulator, which takes into account its uncertain nonlinear dynamics. The overall stability of the adaptive visual servoing system can be proved thanks to the explicit Lyapunov-like functions of both adaptation schemes.