Continuous-time Sliding Mode Control Research Articles

Experimental Validation of the Non-Singular Terminal Sliding Mode Controller for a Process Control System

This paper presents the design of a non-singular terminal sliding mode control (NTSMC) algorithm to process a tank system which ensures high robustness, non-singularity, and finite-time convergence. The proposed control method and modified sliding manifold remove the problems associated with singularity and value complexity. The stability of the proposed strategy is proven via Lyapunov analysis, which explores the conditions for a sliding surface and error convergency in finite time to an equilibrium point or origin.
 The control performance of the proposed method is comparable with classical terminal sliding mode control (TSMC) and typical continuous-time sliding mode control (SMC). The simulation and experimental results reveal the efficacy of NTSMC for estimating parameters, set-point changes from one level to another, and external disturbances. The comparison shows better process speed, settling time, rise time, non-overshoot response, and reduced chattering.

A Nonlinear Discrete-Time Sliding Mode Controller for Autonomous Navigation of an Aerial Vehicle Using Hector SLAM

In this paper, a discrete-time sliding mode controller (DTSMC) is designed for full position and attitude control of a quadrotor UAV. The aim of this study is to design a controller suitable for practical implementation on an autonomous quadrotor for remote sensing in the hostile nuclear environments. A nested DTSMC is developed and compared against two continuous-time sliding mode control methods; classical SMC as well as a chattering-free SMC (CFSMC) studied in the previous works. The performance of the controllers are evaluated in combination with the Hector SLAM algorithm for localisation in GPS denied environments. For this purpose, MATLAB in combination with the Robotic Operating System (ROS) are used to develop the controllers. Control signals are sent from MATLAB to the Gazebo simulation environment in ROS, which simulates the quadrotor and runs the Hector SLAM algorithm.

Linear Feedback Dead-Beat Control for Modular Multilevel Converters: Validation Under Faults Grid Operation Mode

The cascaded control approach is widely used to control the modular multilevel converter (MMC). Such approach allows to manage all MMC state variables in a decoupling manner based on modes separation. This separation introduces conditions related to control objectives response time resulting in slow dynamics. This will limit the use of the potential of MMC energy that is considered as a freedom for ac and dc grids ancillary services. On another side, robustness properties for a given control are also of a great interest when considering unmodeled uncertainties and disturbances. Starting from these requirements, a linear feedback dead-beat control is proposed in this article to accelerate the inner loops and consequently the outer ones (control objectives). The proposed control, based on exact discrete-time model of the MMC in which the sampling period is considered a priory in the control design, is synthetized by taking into account the control outputs saturation. The stability proof of the control and the robustness analysis as well as experimental results under fault grid operations highlighted on small-scale MMC will be presented in this article. The comparison with a continuous-time sliding mode control shows the advantage of the proposed control regarding the response time and undesired oscillation reduction.

Real-time laser beam stabilization by sliding mode controllers

This paper reports a series of real-time experiments for stabilization of a laser beam (LBS) employing a set of continuous-time sliding mode controllers. An asymptotic sliding mode controller, as a first strategy, is designed to maintain the laser light in a fixed position; the results of such experiment is detailed in a table where the mean square error shows performance of the algorithm. An integral term added in the control law design demonstrates an improvement in its performance. The well-known super-twisting algorithm, the second controller, is then designed and implemented in the laser beam stabilization experiment. In both cases, a Lyapunov analysis is developed to ensure convergence of the given algorithms, by a suitable selection of the parameters of the algorithms, such a systematic approach to tune the controllers for the laser stabilization ensures the reproducibility of the experiment once parameters in control laws are selected accordingly.

Sliding mode control design via reduced order model approach

This paper presents a design of continuous-time sliding mode control for the higher order systems via reduced order model. It is shown that a continuous-time sliding mode control designed for the reduced order model gives similar performance for the higher order system. The method is illustrated by numerical examples. The paper also introduces a technique for design of a sliding surface such that the system satisfies a cost-optimality condition when on the sliding surface.

Digital Implementation of Continuous-Time Sliding Mode Control

This paper deals with the case that an algorithm of continuous-time sliding mode control in which feedback gain coefficients are switched is digitally implemented in a digital computer. Since these coefficients are changed only at sampling instants, the system trajectory cannot be perfectly confined on a sliding hyperplane. As a results, the performance deterioration occurs. In this paper, the range is shown in which the switching control input guarantees to drive the state trajectory toward the sliding hyperplane and the swtching control algorithm is modified to be effective in it. A control algorithm is also proposed to keep the system trajectory in the narrowest neighborhood of the sliding hyperplane after the trajectory moving outside the range. The same discussion is further done for output tracking systems using sliding mode control. Finally, a numerical example is given for demonstrating the validity of the theoretical results.

Discrete time sliding mode, continuous time sliding mode and vector control of induction motors

Three control strategies are implemented and compared in this paper: vector control, continuous time sliding mode control and discrete time sliding mode control of an induction motor. The induction motor model used for control takes into account magnetizing inductance saturation and rotor resistance variation. While the magnetizing inductance is mapped to the operating conditions, the rotor resistance is estimated on-line. The motor is controlled with optimal efficiency flux. Flux weakening is employed above rated speed. Experimental results are drawn to show the advantages and disadvantages of the control methods.

Adaptive switching gain for a discrete-time sliding mode controller

Sliding mode control is a well-known technique capable of making the closed loop system robust with respect to certain kinds of parameter variations and unmodelled dynamics. The sliding mode control law consists of a continuous component which is based on the model knowledge and discontinuous component which is based on the model uncertainty. This paper extends two known adaption laws for the switching gain for continuous-time sliding mode controllers to the multiple input case. Because these adaption laws have some fundamental problems in discrete-time, we introduce a new adaption law specifically designed for discrete-time sliding mode controllers.

On Robust Adaptive Control of MIMO Linear Plants Using Discrete-Time Sliding Modes

The discrete-time version of the continuous-time sliding mode control approach requires the redefinition of the sliding mode concept. In previous papers the authors have introduced an alternative definition of discrete-time 'equivalent control' as the control signal causing the dead-beat zeroing of the distance from the sliding manifold. Within this paper, the problem of discrete-time zero dynamics is expressly addressed, and what is shown is that with the proposed approach, as long as the sampling interval is small, non minimum phase behaviours cannot occur.