Existence of Solutions to a Class of Nonlinear Convergent Chattering-free Sliding Mode Control Systems

Sliding mode control is a nonlinear control technique, which is robust against some classes of uncertainties and disturbances. However, this control produces chattering which can cause instability due to unmodeled dynamics and can also cause damage to actuators or the plant. There are essentially two ways to counter the chattering phenomenon. One way is to use higher order sliding mode, and the other way is to add a boundary layer around the switching surface and use continuous control inside the boundary. The problem with the first method is that the derivative of a certain state variable is not available for measurement, and therefore methods have to be used to observe that variable. In the second method, it is important that the trajectories inside the boundary layer do not try to come outside the boundary after entering the boundary layer. Control laws producing chattering-free sliding mode using a boundary layer have been proposed and the existence of solutions to the system using these control laws are presente

Smooth non linear high gain observers for a class of dynamical systems

High-gain observers are powerful tools for estimating the state of nonlinear systems. However, their design poses several challenges due to the need of dealing with phenomena such as peaking and chattering. To address these issues, we propose a differentiator operator design based on a non linear second order high-gain observer, which is suited to a class of dynamical systems. Our method includes a procedure to determine high gains in order to avoid chattering in the case of noise-free models, and cut-off frequency based gain design in the case of noisy measurements. Complementary, we suggest performing observability analyses to ensure a priori the feasibility of the estimation. The main strengths of our approach are its simplicity and robustness. We demonstrate the performance of the proposed method by applying it to two processes (chemical and biological).Xunta de Galicia | Ref. ED431F 2021/003MCIN/AEI/10.13039/501100011033 | Ref. RYC-2019-027537-

Diseño de controladores continuos convergentes por un tiempo fijo para sistemas dinámicos con incertidumbre

Este documento presenta controladores no lineales que proveen convergencia en tiempo fijo al origen (o a una vecindad del origen) para sistemas dinámicos de alto orden sujetos a incertidumbres (disturbios deterministicos no desvanescentes y disturbios estocásticos desvanescentes dependientes de los estados y el tiempo). Dos de los tres controladores diseñados incluyen un diferenciador convergente en tiempo fijo, un observador de disturbios convergente en tiempo fijo, y un regulador convergente en tiempo fijo. El diferenciador se da en el caso que el ´único estado medible del sistema dinámico es el de mayor grado relativo. El observador de disturbios convergente en tiempo fijo se emplea para estimar variaciones de disturbios no desvanecentes y no acotados. En caso de que las cotas para los disturbios sean desconocidas se incluye un observador adaptable convergente en tiempo fijo caracterizado por no incrementar de manera excesiva las ganancias del controlador. En cuanto a la presencia simultanea de disturbios determinísticos no desvanescentes y disturbios estocásticos desvanescentes dependientes de los estados y el tiempo, se presenta un algoritmo Super-twisting estocástico convergente en tiempo fijo. El problema de estimación del tiempo de convergencia de los controladores se resuelve calculando una cota superior uniforme del tiempo fijo de convergencia. Finalmente, los algoritmos diseñados se verifican en dos casos de estudio: Un motor DC con armadura y un problema de gestión de stocks. Resultados de las simulaciones confirman convergencia en tiempo fijo y robustez de los controladores diseñados

Sliding Mode Control

The main objective of this monograph is to present a broad range of well worked out, recent application studies as well as theoretical contributions in the field of sliding mode control system analysis and design. The contributions presented here include new theoretical developments as well as successful applications of variable structure controllers primarily in the field of power electronics, electric drives and motion steering systems. They enrich the current state of the art, and motivate and encourage new ideas and solutions in the sliding mode control area

An approach to design of digital sliding mode control for DC-DC converters

The primary goal of research in this Ph.D. dissertation is to investigate the possibilities of application of modern control methods in controlling the output voltage of the DC-DC converters (buck, boost) in order to ensure the system robustness to the input voltage and load variations. This dissertation deals with the analysis and application of sliding mode control algorithms in the synthesis of these converters in order to improve the properties of existing converters and to modify them, as well as to adjust and tune the digital sliding mode controls based on the input-output plant model to be applicable in these converters. The design procedure is based on the converter models given in the form of discrete transfer functions. The proposed control for converters is a combination of the digital sliding mode control and (generalized) minimum variance control techniques. The problem caused by an unstable zero of the boost converter, which prevents the direct control of the output voltage of this converter, has been overcome by introducing the generalized minimum variance control. Also, only the output voltage of converter must be measured for the realization of the proposed control, so there is no need for an additional current sensor. This dissertation includes the modification of the developed algorithms with the aim of applying them to low-cost, standard 8- bit microcontrollers. Finally, the efficiency of the proposed solutions is verified by digital simulation and a series of experiments on the laboratory developed prototypes of both converters, as well as by their comparative analysis. The satisfactory experimental results are obtained regarding the typical characteristics of the converters