B. Castillo-Toledo

A globally convergent estimator for n-frequencies

In this paper, we propose a solution to the well-known problem of ensuring a simultaneous globally convergent online estimation of the state and the frequencies of a sinusoidal signal composed of n sinusoidal terms. We present an estimator which guarantees global boundedness and convergence of both the state estimation and the frequency estimation for all initial conditions and frequency values.

Robust block second order sliding mode control for a quadrotor

Abstract This paper presents the design of a controller based on the block control technique combined with the super twisting control algorithm for trajectory tracking of a quadrotor helicopter. A first order exact differentiator is used in order to estimate the virtual control inputs, which simplifies the control law design. In addition, the wind parameter resulting from the aerodynamic forces is also estimated in order to ensure robustness against these unmatched perturbations. The stability and finite time convergence of the exact differentiator have been recently proved by means of Lyapunov functions, and therefore the stability analysis of the proposed controller has been carried out along the same lines. The performance and effectiveness of the proposed controller are tested in a simulation study taking into account external disturbances.

Hybrid Control of Induction Motors via Sampled Closed Representations

In this paper, a controller for induction motors is proposed. A continuous feedback is first applied to obtain a discrete-time model in closed form. Then, on the basis of these exact sampled dynamics, a discrete-time controller ensuring speed and flux modulus reference tracking is determined, making use of the sliding mode technique. The resulting controller is hence hybrid, in the sense that it contains both continuous and discrete-time terms. It is shown how to implement such a hybrid controller using the so-called exponential holder, which is the only device to be implemented analogically, together with an analog integrator. Moreover, a discrete-time reduced-order observer is designed for rotor fluxes and load torque estimation. The performance of the proposed controller is finally studied by simulation and experimental tests.

Discrete time sliding mode control with application to induction motors

This work deals with a sliding mode control scheme for discrete time nonlinear systems. The control law synthesis problem is subdivided into a finite number of subproblems of lower complexity, which can be solved independently. The sliding mode controller is designed to force the system to track a desired reference and to eliminate unwanted disturbances, compensating at the same time matched and unmatched parameter variations. Then, an observer is designed to eliminate the need of the state in the controller implementation. This design technique is illustrated determining a dynamic discrete time controller for induction motors.

Discrete-Time Neural Sliding-Mode Block Control for a DC Motor With Controlled Flux

An adaptive discrete-time tracking controller for a direct current motor with controlled excitation flux is presented. A recurrent neural network is used to identify the plant model; this neural identifier is trained with an extended Kalman filter algorithm. Then, the discrete-time block-control and sliding-mode techniques are used to develop the trajectory tracking. This paper also includes the respective stability analysis for the whole closed-loop system. The effectiveness of the proposed control scheme is verified via real-time implementation.

A Structurally Stable Globally Adaptive Internal Model Regulator for MIMO Linear Systems

The problem of compensating an uncertain disturbance and/or tracking some reference signals for a general linear MIMO system is studied in this work using the robust regulation theory frame. The disturbances are assumed to be composed by a known number of distinct sinusoidal signals with unknown phases, amplitude and frequencies. Under suitable assumptions, an exponentially convergent estimator of the unknown disturbance parameters is proposed and introduced into the classical robust regulator design to obtain an adaptive controller. This controller guarantees that the closed-loop robust regulation is attained in some neighborhood of the nominal values of the parameters of system. A simulated example shows the validity of the proposed approach.

Exact Output Regulation for Nonlinear Systems Described by Takagi–Sugeno Fuzzy Models

The exact output regulation for Takagi-Sugeno (T-S) fuzzy models depends on two conditions: 1) The local steady-state zero-error manifolds have to be the same for every local subsystem, and 2) the local input matrices have to be the same for every local subsystem included in the T-S fuzzy model. These conditions are difficult to satisfy in general. In this paper, those conditions are relaxed by solving the fuzzy regulation problem directly on the overall T-S fuzzy model, instead of constructing the fuzzy regulator on the basis of linear local controllers. By considering the fuzzy model as a special class of linear time-varying systems, existence conditions are rigorously derived. These new conditions, which can be solved by means of any mathematical software, depend on the solution of a set of symbolic simultaneous linear equations depending on the membership values of the plant and/or the exosystem. Two examples are given to illustrate the construction of the proposed regulator and to validate the improvement that is achieved with the proposed approach.

An algorithm for on-line detection of high frequency oscillations related to epilepsy

Recent studies suggest that the appearance of signals with high frequency oscillations components in specific regions of the brain is related to the incidence of epilepsy. These oscillations are in general small in amplitude and short in duration, making them difficult to identify. The analysis of these oscillations are particularly important in epilepsy and their study could lead to the development of better medical treatments. Therefore, the development of algorithms for detection of these high frequency oscillations is of great importance. In this work, a new algorithm for automatic detection of high frequency oscillations is presented. This algorithm uses approximate entropy and artificial neural networks to extract features in order to detect and classify high frequency components in electrophysiological signals. In contrast to the existing algorithms, the one proposed here is fast and accurate, and can be implemented on-line, thus reducing the time employed to analyze the experimental electrophysiological signals.

The fuzzy discrete-time robust regulation problem: an LMI approach

This paper is concerned with the design of a robust regulator capable of achieving trajectory tracking for discrete-time nonlinear systems under parameter uncertainty. By assuming that the behavior of the nonlinear system is described, at least locally, by a Takagi-Sugeno dynamic fuzzy model, an approach based in the combination of this fuzzy modeling and the regulator theory is presented. Conditions for the existence of a robust regulator under this approach are then derived and extended to include the use of the linear matrix inequality (LMI) technique.

On the observer design problem for continuous-time switched linear systems with unknown switchings

Abstract The observer design problem for Switched Linear Systems ( SLS ) subject to an unknown switching signal is addressed in this work. Based on known observability results for SLS , an appropriate SLS observer is proposed and its convergence is analysed showing that the corresponding estimates converge in finite-time to the SLS state. More precisely, the observers of the continuous state evolution and the observers of the switching signal are investigated and their convergence studied separately. The main tool to analyse the observability is the well-known geometric concept of ( A , B )-invariant subspaces. The developed SLS observers are then applied to construct synchronized chaotic generators based on the SLS with chaotic behavior. Finally, an example of a non-trivial chaotic SLS and its detailed analysis are presented to illustrate the achieved results.