Cedomir Milosavljevic

Robust discrete-time chattering free sliding mode control

A new control algorithm based on discrete-time variable structure systems theory is proposed. The basic feature of this algorithm is that trajectories reach the sliding manifold in finite time, without chattering. Apart from stability, the robustness of the algorithm with respect to parameter uncertainties, as well as external disturbances is considered. It is demonstrated that the robustness is improved by decreasing the sampling period. The theory is illustrated on a DC servo-position system.

High-Performance Position Control of Induction Motor Using Discrete-Time Sliding-Mode Control

A new way of induction-motor position control for high-performance applications is developed in this paper using discrete-time sliding-mode (DSM) control. In addition to the main DSM position controller, the proposed control structure includes an active disturbance estimator (ADE), in which a passive filter is replaced by another DSM-controlled subsystem, in order to improve system robustness and accuracy. Furthermore, the application of an ADE makes possible the design of both controllers using the knowledge of the nominal system only. Experiments have verified high efficiency of the proposed servo system under the influence of large parameter perturbations and external disturbances in the presence of unmodeled dynamics.

Improved Discrete-Time Sliding-Mode Position Control Using Euler Velocity Estimation

This paper presents a design of digitally controlled positional systems with Euler velocity estimation within the framework of the discrete-time sliding mode (DSM). The effects of quantization and simple velocity estimation on DSM quality are analyzed. It is shown that the introduced and amplified quantization noise degrades sliding motion into the quasi-sliding mode and threatens to provoke chattering. Furthermore, a new DSM control algorithm is proposed, featuring a two-scale reaching law and a supplemental integral action. This algorithm avoids chattering and provides excellent performance. The developed DSM controller has been experimentally tested in an induction motor position control.

Sampled Data Quasi-Sliding Mode Control Strategies

Sampled-data (SD) variable structure control systems (VSCS) with quasi-sliding mode (QSM) are treated in this paper as a logical extension of VSCS with ideal sliding mode (SM). The most of well-known SD QSM control algorithms are derived by starting from reaching law approach. The problems of robustness to uncertainties, loads and unmodeled inertial dynamics are considered and some methods to solve these problems are presented. An example that illustrates SD QSM VSCS properties is given.

Discrete-Time Velocity Servo System Design Using Sliding Mode Control Approach With Disturbance Compensation

This work presents a new approach to high performance velocity servo system design. The approach is based on a discrete-time sliding mode (DSM) control with disturbance compensation. For the purpose of design, the controlled plant is approximated by first-order model. The traditional, as well as the integral type of DSM control is considered. The disturbance compensator is based on the fact that the matched disturbances are directly reflected in the previous value of the switching function. In this paper, slow varying disturbances are estimated by a parallel connection of first- and second-order estimators. The integral type of DSM velocity servo system with such combined compensator can track references and significantly reject bounded disturbances, both up to cubic parabola type. The proposed control system is chattering-free. Theoretically obtained results are verified by simulations and experiments.

Influence of tube wall material type and tube temperature on the recombination processes of nitrogen ions and atoms in afterglow

The recombination of positive ions and atoms during an afterglow period, created during previous electrical breakdown and gas discharge, at the molybdenum glass and copper is investigated using the time delay method. It has been shown that the recombination of the positive ions at the copper wall, while the atoms at the molybdenum wall, at room temperature, is more intensive. The temperature influence on the recombination of these particles at copper has also been monitored by the same method, showing that the positive ion recombination rate increases and atom recombination rate decreases with temperature.

Electrical system for measurement of breakdown voltage of vacuum and gas-filled tubes using a dynamic method

This article describes an electrical system aimed at measuring and data acquisition of breakdown voltages of vacuum and gas-filled tubes. The measurements were performed using a nitrogen-filled tube at 4 mbar pressure. Based on the measured breakdown voltage data as a function of the applied voltage increase rate, a static breakdown voltage is estimated for the applied voltage gradient ranging from 0.1 to 1 V s−1 and from 1 to 10 V s−1. The histograms of breakdown voltages versus applied voltage increase rates from 0.1 and 0.5 V s−1 are approximated by the probability density functions using a fitting procedure.

Disturbance compensation in digital sliding mode

This paper proposes a new approach for slow and matched disturbance suppression in digital sliding mode. The previous value of disturbance is extracted from switching function and used to make disturbance estimation, and later used in control to cancel disturbance effects. The control function is linear in state and in disturbance estimate. It may be considered chattering free since its value is zero in equilibrium if there are no disturbances.

Variable structure systems for control of redundant robot

Abstract A combination of one class of kinematic control of redundant robot and Variable Structure Systems (VSS) in manipulating tasks that require large accelerations or decelerations is the main issue of this paper. The inverse kinematic problem will, on a tactical control level, be solved through Distributed Positioning (DP) concept, while the solution of the executive control level will be solved by using a combination of two common VS control algorithms with PI controller. A complete synthesis of VS local regulators for the redundancy, along with stability analysis, will be given. Comparison of VS with PD controller tracking characteristics will be studied on a suitable SCARA robot with redundancy performing one typical pick-and-place movement.

Comprehensive Approach to Sliding Mode Design and Analysis in Linear Systems

This chapter considers the design of reduced and integral sliding mode (SM) dynamics for state space systems. The prescribed sliding mode dynamics are selected to have either a desired spectrum or optimal behavior in the linear quadratic regulator (LQR) sense. Due to the operator representation of the system equations, separate treatment of the discrete time (DT) and the continuous time (CT) cases is not needed. Fully decentralized design of the control used to satisfy the reachability problem is possible using the obtained sliding subspaces. For the sake of straightforward analysis of the SM dynamics, a new way to obtain the SM equation, based on singular value decomposition (SVD), is also provided. Algorithms are implemented in MATLAB. Simulations illustrating the usefulness of the developed design method conclude the chapter.