The paper studies sliding mode (SM) features in systems characterized by the presence of unmatched disturbances. Although it is possible to establish a SM in such systems, the unmatched part of disturbances has impact on the SM dynamics. Under these circumstances system trajectory does not converge to the origin but wanders in its neighborhood along the sliding manifold. This paper offers a sliding hyperplane design method to minimize the effects of the unmatched disturbances upon the SM dynamics, for a class of linear systems. The optimization criterion is minimization of the steady state vector norm. The suggested approach has been demonstrated on a numerical example.

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.

This paper considers the application of extrapolation techniques in finding approximate solutions of some optimization problems with constraints defined by the Robin boundary problem for the Laplace equation. When applied extrapolation techniques produce very accurate solutions of the boundary problems on relatively coarse meshes, but this paper demonstrates that this is not a real restriction when dealing with optimization problems. Producing a solution of continuous problem by polynomial extrapolation based on the low-order discrete problem solutions significantly reduces both computational time and memory. The present paper illustrates this approach using finite-difference and finite-element methods, and finally makes a brief remark about some tacit engineering assumptions regarding numerical solutions of conductive media problems by construction of equivalent resistor networks.

This paper presents a novel payload analysis method. Consecutive bytes are separated by boundary symbols and defined as words. The frequencies of word appearance and word to word transitions are used to build a model of normal behavior. A simple anomaly score calculation is designed for fast attack detection. The method was tested using real traffic and recent attacks to demonstrate that it can be used in IDS. Tolerance to small number of attack in training data is shown.

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.

This paper describes a new method, proposed for the control of objects with a stable finite zero, using sliding mode control strategies. The method is a combination of the conventional linear control and the sliding mode approach with an observer structure. The proposed structure looks like a reference model control system. The object control signal has two components: the first one is integral of the sliding mode controller output signal, and the second is a linear combination of observer error signal and its derivative. Such a control signal has not switching nature, i.e. the process control is chattering-free. The stability of the proposed control structure is analyzed and some recommendations for controller synthesis are given. The effectiveness of the proposed control strategy is demonstrated by simulation on an example.

This paper investigates the effects of signal quantization and velocity estimation on the quality of the discrete-time sliding mode (DSM) in a positional servo-system. Velocity estimation is based on a simple backward finite difference method using the measured quantizied discrete-time position samples. It is shown that such introduced and amplified measurement noise degrades sliding motion into the quasi-sliding mode and threatens to provoke chattering. Furthermore, a DSM control algorithm is proposed, which provides satisfactory performance under these conditions. To avoid chattering, system trajectories are slowed down near the sliding surface by dividing the state space into the fast and slow convergence zones. In the slow zone an additional integral action is employed to secure convergence under action of disturbances. The proposed DSM controller has been experimentally tested in an induction motor position control.

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.

This paper considers the design of robust servo system for accurate tracking of complex referent signals in the presence of internal and external disturbances. Discrete-time sliding mode tracking controller is employed in servo-system design. In order to improve tracking accuracy, application of active disturbance estimator is suggested. The same sliding mode controller, designed for reference tracking of nominal system, is identically implemented in the control subsystem within the estimator. The overall servo-system exhibits high tracking accuracy under action of parameter uncertainties and external disturbances. Experimental results confirm the effectiveness of the proposed servo-system structure

The paper deals with the design of digital sliding mode controllers using only input and output sequences of plant. Two approaches are considered. The first one is based on the sliding mode based generalized minimum variance control implemented on the linearized plant model, whereas the second one utilizes the similar idea from the previous method modified for and applied on the discrete-time nonlinear model of the plant. The proposed algorithms are presented and tested by digital simulation on an example of inverted pendulum control

This paper proposes a simple extension of the well-known Ziegler-Nichols’ (ZN) method. As in the standard ZN method, the experiment may be performed using the controller only, without any extra equipment. But, in opposite to the ZN method, the experiment may be performed using damped oscillations. Also, the proposed method allows more complex models of the plant, so a better tuning may be obtained.

The problem of how to assess the probability distribution function (PDF) of the propagation delay for different adder types in order to compare their sensitivities to stochastic changes of gate delays is addressed. An original methodology that solves the problem for combinational circuits of arbitrary topology (without loops) is introduced. Its capabilities are demonstrated through the modeling and analysis of propagation delays in GaAs adders. This methodology is directly applicable to a number of analogous problems in other fields. >