Chattering-free Sliding Mode Control Research Articles

Chattering Free Sliding-Mode Controller Design for Underactuated Tower Cranes With Uncertain Disturbance

Tower cranes are widely used in various industrial sites and require a high level of anti-disturbance performance from the crane controller due to the variability of the application environment. Although sliding mode control is a typical anti-disturbance control method, most sliding mode controllers suffer from output chattering and do not reflect well under severe external disturbances. To address these issues from a practical application perspective, a finite time sliding mode control method using the super-twisting algorithm (STA) is proposed for underactuated tower cranes operating in the presence of external disturbances. The proposed method includes a finite-time chattering-free sliding mode controller that eases the output torque chattering problem and a finite-time sliding mode observer based on STA to observe the uncertain disturbances. The observed values are then applied to the controller through feedforward compensation. Experimental results show that the proposed control method effectively weakens output torque chattering, compensates for disturbance quickly, and accurately completes control tasks.

Finite-time $$H_\infty $$ control for USVs subject to DoS attacks: a chattering-free sliding mode control approach

Finite-time $$H_\infty $$ control for USVs subject to DoS attacks: a chattering-free sliding mode control approach

Development and Control of an Innovative Underwater Vehicle Manipulator System

Recently, as humans have become increasingly interested in ocean resources, underwater vehicle-manipulator systems (UVMSs) have played an increasingly important role in ocean exploitation. To realize precise operation in underwater narrow spaces, the fly arm underwater vehicle manipulator system (FAUVMS) is proposed with manipulators as its core. However, this system suffers severe dynamic coupling effects due to the combination of small vehicle and big manipulators. To resolve this issue, we propose a robust adaptive controller that contains two parts. In the first part, the extended Kalman filter (EKF) is designed to estimate the system states and predicts external disturbances to achieve adaptive control. In the second part, a chattering-free sliding mode control (SMC) is designed to converge the tracking errors to zero, thus guaranteeing the robustness of the controller. We constructed the simulation platform based on the geometric model of FAUVMS, and various simulations are carried out under different situations. Compared to the traditional methods, the proposed method has a faster convergent speed, a better robustness and adaptiveness to external disturbances, and the tracking errors of positions of the vehicle and each end-effector are much smaller.

Chattering-free terminal sliding-mode tracking control for uncertain nonlinear systems with disturbance compensation

In this work, an integral-type terminal sliding mode (TSM) controller with an asymptotic disturbance observer is developed. The proposed controller can be applied to a class of uncertain integrator systems with unknown external disturbances. In addition, the chattering phenomenon and the singularity problem in traditional TSM control and the influence of unknown external disturbances on the system are taken into consideration. For unknown external disturbances in practical applications, a disturbance observer with asymptotic estimation performance is constructed. Thus, the control strategy is developed to ensure chattering-free and eliminate the singularity problem. By comparing with the traditional TSM control, we expect to synthesize a more efficient chattering-free sliding mode controller. The integral-type TSM transforms the discontinuous sign function into the continuous smooth function. Furthermore, the proposed control algorithm can accurately compensate for the external unknown disturbance and exhibits better robustness. Finally, the simulation results demonstrate the effectiveness of the controller and the stability of the whole closed-loop system is strictly proved.

Chattering Free Sliding Mode Control and State Dependent Kalman Filter Design for Underground Gasification Energy Conversion Process

The fluctuations in the heating value of an underground coal gasification (UCG) process limit its application in electricity generation, where a desired composition of the combustible gases is required to operate gas turbines efficiently. This shortcoming can be addressed by designing a robust control scheme for the process. In the current research work, a model-based, chattering-free sliding mode control (CFSMC) algorithm is developed to maintain a desired heating value trajectory of the syngas mixture. Besides robustness, CFSMC yields reduced chattering due to continuous control law, and the tracking error also converges in finite time. To estimate the unmeasurable states required for the controller synthesis, a state-dependent Kalman filter (SDKF) based on the quasi-linear decomposition of the nonlinear model is employed. The simulation results demonstrate that despite the external disturbance and measurement noise, the control methodology yields good tracking performance. A comparative analysis is also made between CFSMC, a conventional SMC, and an already designed dynamic integral SMC (DISMC), which shows that CFSMC yields 71.2% and 69.9% improvement in the root mean squared tracking error with respect to SMC and DISMC, respectively. Moreover, CFSMC consumes 97% and 23.2% less control energy as compared to SMC and DISMC, respectively.

Robust Adaptive Autonomous Braking Control for Intelligent Electric Vehicles*

This paper presents a two-stage autonomous braking control for electric vehicles with preview information acquired by intelligent transportation systems (ITS) or connected and autonomous vehicle (CAV) technologies. The goal of the control method is firstly to plan a speed profile to comply with a target speed and a target residual distance to an upcoming deceleration event and then to track the planned speed profile by generating tracking-driven braking control torques, which maximally employ regenerative braking. Once deceleration circumstances are perceived, the intelligent reference speed planner computes a smooth speed profile by using a current vehicle speed, a target speed, and a target residual distance. For the braking control to robustly track the planned speed profile, a chattering-free sliding mode controller is designed on the interconnected vehicle and braking system model with braking system uncertainties and external disturbances, and a sufficient condition for the sliding mode gain is introduced. Also, adaptive update laws to compensate for the braking system uncertainties provide feed-forward control efforts for the tracking control inputs. To verify the effectiveness of the proposed control approach, the control methods are applied to a real commercial vehicle and the consecutive driving experiments with various deceleration circumstances illustrate a successful tracking-driven cooperative braking performance.

Model-Free Controller Design for Nonlinear Underactuated Systems With Uncertainties and Disturbances by Using Extended State Observer Based Chattering-Free Sliding Mode Control

Most of the control strategies require a mathematical model or reasonable knowledge that is difficult to obtain for complex systems. Model-free control is a good alternative to avoid the difficulties and complex modeling procedures, especially if the knowledge about the system is insufficient. This paper presents a new control scheme completely independent of the system model. The proposed scheme combines sliding mode control (SMC) with intelligent proportional integral derivative (iPID) control based on a local model and extended state observer (ESO). Although the iPID control makes the proposed method model-free, it cannot guarantee that the tracking errors converge to zero asymptotically except the system is in a steady-state regime. Therefore, the SMC is added to the control scheme to ensure the convergence by minimizing the estimation errors of the observer. The proposed iPIDSMC controller is tested in the presence of different parameter variations and external disturbances on an inverted pendulum - cart (IPC), which is a highly unstable underactuated system with nonlinear coupled dynamics. The proposed controller is compared with the PID, iPID and Hierarchical Sliding Mode Control (HSMC) for a clearer evaluation. Simulation results showed that the proposed controller is extremely insensitive to parameter variations, matched and mismatched disturbances and the control signal of the proposed method is chattering-free, even though it is based on a discontinuous control action.

Robust chaos suppression of uncertain unified chaotic systems based on chattering-free sliding mode control

For continuous sliding mode control (SMC) in the unified chaotic systems subjected to matched/unmatched uncertainties, a novel chattering-free SMC design is proposed. First, an augmented state is introduced such that it becomes possible to develop a continuous controller to eliminate the undesired chattering which often appears in the typical SMC. Then by using this chattering-free controller, the chaos behavior in unified chaotic systems with matched uncertainties can be completely suppressed. As for the unmatched uncertainties, every state of controlled systems can be driven and limited to a predictable bound, which is not addressed in the literature. Finally, the effectiveness of the proposed chattering-free controller is verified by the numerical simulations.

Backstepping control for a class of underactuated nonlinear mechanical systems with a novel coordinate transformation in the discrete-time setting

In this technical note, a combined discrete-time controller, consisting of a partial feedback linearization controller and a backstepping controller, is proposed to manage the stabilization for a class of underactuated nonlinear mechanical systems. The traditional backstepping control method is impracticable to directly apply it to underactuated systems since they are generally not in the lower triangular form. First, a feedback controller that partially linearizes the underactuated mechanical systems is derived to facilitate the backstepping controller design. In the design, discrete-time system dynamics obtained utilizing the Euler approximation are considered. Afterward, a novel coordinate transformation is introduced for a class of underactuated systems that transform the mathematical model of the partially linearized underactuated mechanical systems into the strict-feedback form. After these steps, the conventional backstepping approach is structured in discrete-time setting. The stability of the closed-loop system dynamics with the proposed combined discrete-time controller is shown utilizing Lyapunov theory. Several computer-based simulations are executed to depict the performance and the applicability of the proposed method on the Cart–Pole system and the Inertia Wheel Pendulum. Moreover, the effectiveness of the proposed nonlinear controller is verified by numerical simulation results in comparison with a discrete-time chattering-free sliding-mode controller.

Design and Stability Analysis of a Robust-Adaptive Sliding Mode Control Applied on a Robot Arm with Flexible Links

Modelling errors and robust stabilization/tracking problems under parameter and model uncertainties complicate the control of the flexible underactuated systems. Chattering-free sliding-mode-based input-output control law realizes robustness against the structured and unstructured uncertainties in the system dynamics and avoids the excitation of unmodeled dynamics. The main purpose of this paper was to propose a robust adaptive solution for stabilizing and tracking direct-drive (DD) flexible robot arms under parameter and model uncertainties, as well as external disturbances. A lightweight robot arm subject to external and internal dynamic effects was taken into consideration. The challenges were compensating actuator dynamics with the inverter switching effects and torque ripples, stabilizing the zero dynamics under parameter/model uncertainties and disturbances while precisely tracking the predefined reference position. The precise control of this kind of system demands an accurate system model and knowledge of all sources that excite unmodeled dynamics. For this purpose, equations of motion for a flexible robot arm were derived and formulated for the large motion via Lagrange’s method. The goals were determined to achieve high-speed, precise position control, and satisfied accuracy by compensating the unwanted torque ripple and friction that degrades performance through an adaptive robust control approach. The actuator dynamics and their effect on the torque output were investigated due to the transmitted torque to the load side. The high-performance goals, precision and robustness issues, and stability concerns were satisfied by using robust-adaptive input-output linearization-based control law combining chattering-free sliding mode control (SMC) while avoiding the excitation of unmodeled dynamics. The following highlights are covered: A 2-DOF flexible robot arm considering actuator dynamics was modelled; the theoretical implication of the chattering-free sliding mode-adaptive linearizing algorithm, which ensures robust stabilization and precise tracking control, was designed based on the full system model including actuator dynamics with computer simulations. Stability analysis of the zero dynamics originated from the Lyapunov theorem was performed. The conceptual design necessity of nonlinear observers for the estimation of immeasurable variables and parameters required for the control algorithms was emphasized.

Robust p53 recovery using chattering free sliding mode control and a gain-scheduled modified Utkin observer

p53 protein plays an essential role in protecting the genomic integrity of mammalian cells. A drastic decrease in the amount of p53 protein has been observed in cancerous cells. By using Nutlin-based small molecule drugs, the concentration of p53 can be restored to the desired level. This paper presents the drug-dosage design for p53 pathway, based on a control-oriented nonlinear model. A chattering free sliding mode control (CFSMC) strategy is employed to track the desired trajectory of p53 concentration for both of its dynamic behaviors, i.e., sustained and oscillatory responses. A gain-scheduled modified Utkin observer (GSMUO) is designed for robust state reconstruction and disturbance estimation. The simulation results show that CFSMC and GSMUO exhibit desired robustness and performance properties in the presence of parametric variations, an input disturbance and measurement noise. Moreover, a comprehensive simulation study, along with a detailed quantitative analysis is performed to compare CFSMC-GSMUO with four different techniques: a sliding mode control (SMC) with an equivalent control based sliding mode observer (SMO) and GSMUO, respectively, and a dynamic sliding mode control (DSMC) with SMO and GSMUO, respectively. The analysis demonstrates that the tracking error and utilization of the control energy is the least in the case of CFSMC-GSMUO as compared to its counterparts.

Observer-based discrete-time sliding mode control for systems with unmatched uncertainties

This paper addresses an observer-based sliding mode control (SMC) approach for discrete-time systems with unmatched uncertainties. A modified sliding surface based on disturbance estimation and a sliding mode controller are designed to counteract with the unmatched disturbance. The proposed method exhibits the following three features. First, the hyperplane matrix is designed in a simple way based on the discrete-time Riccati equation. Second, a chattering-free SMC method is utilized. Third, the proposed approach retains the nominal performance of the system. The stability of the overall system is achieved and simulation results are presented to verify the effectiveness of the proposed method.

Design of a Memristor-based Chattering Free Sliding Mode Controller and Speed Control of the BLDC Motor

Design of a Memristor-based Chattering Free Sliding Mode Controller and Speed Control of the BLDC Motor

Robust cascade control of electrical drives using discrete-time chattering-free sliding mode controllers with output saturation

The paper considers electrical drives control having a hierarchical cascaded structure. This structure has an inner current control loop and outer loops for speed and position control. The design of the control is performed using a discrete-time model of electrical drive. In all the loops, the discrete-time quasi sliding mode control is used for controller design because of its robustness to external and parametric matched disturbances (inherent to electrical drives) and the capability to ensure the desired dynamics. To enhance the robustness to disturbances, a nonlinear disturbance compensator is also implemented. The chattering in sliding mode is eliminated by using a new modified discrete-time super twisting control. The current and the speed controllers are designed for linear discrete-time first-order models, while the position controller is designed for a linear second-order discrete-time model. The axis position is measured by a mechanical sensor (encoder). The speed is estimated from the position measurements using Euler derivative approximation. Alternatively, it can be obtained by an observer. The proposed design is straightforward and results in high-performance, robust control with strong disturbance rejection capability and negligible overshoots. All theoretically obtained claims are demonstrated by experiments on an induction motor drive with a rotor field-oriented control structure.

Online High Performance Genetic Algorithm Based Sliding Mode Control for Controllable Pitch Propeller

During the voyage of a ship, the performance of a controllable pitch propeller (CPP) is severely affected by the changing load demand and ever-present disturbance from ocean waves, which will also result in model uncertainty. In order to improve the performance of the CPP system, an online high-performance genetic algorithm (HPGA)-based sliding mode control (SMC) strategy is proposed. Firstly, the model of the CPP system is obtained according to the manufacturer’s instructions. Then, a chattering-free sliding mode controller (CF-SMC) is designed for the CPP system, after which the parameters in the CF-SMC are optimized with the HPGA method. Finally, the optimized CF-SMC is applied to an experimental setup of a prototype CPP system. In order to validate the effectiveness of the proposed method, it is compared with a proportional-integral-derivative (PID) controller, which is typically applied on real CPP-systems, with results indicating the superiority of the proposed method.

Adaptive chattering-free terminal sliding-mode control for full-order nonlinear system with unknown disturbances and model uncertainties

This study investigates an adaptive chattering-free sliding-mode control method for n-order nonlinear systems with unknown external disturbances and uncertain models. The proposed method takes the advantage of finite-time fast convergence to avoid singularity problem and ensure its robustness against system uncertainty and unknown disturbance. To achieve fast convergence from any initial condition to system origin, a full-order terminal sliding-mode controller containing differential terms is proposed based on the property of n-order nonlinear systems. Then the continuous and smooth actual control law is obtained by integrating the differential control law containing the discontinuous sign function to realize chattering free. Meanwhile, instead of evaluating the fixed upper bound of system uncertainty and interference in practical implementations, an adaptive method is utilized for its unknown upper bound estimation. The convergence of the adaptive terminal sliding-mode controller in finite time is verified based on Lyapunov stability theory. Finally, two simulation results demonstrate the effectiveness of the proposed control method.

Chattering Free Sliding Mode Control with Observer Based Adaptive Radial Basis Function Neural Network for Temperature Tracking in a Fixed Bed Reactor

AbstractIn this paper, a Chattering Free Sliding Mode Control (CFSMC) with observer based adaptive Radial Basis Function Neural Network (RBFNN) has been designed for first-order transfer function model of temperature trajectory in a fixed bed reactor. The steady-state behavior and effect of different operating parameters such as feed velocity and temperature on the operation of the fixed bed reactor have been discussed. Due to RBFNN’s capability to map the nonlinear dynamics online through self-learning ability, it is combined with CFSMC to reduce the chattering behavior. The adaptive RBFNN has been used to approximate the nonlinear dynamic behavior of the fixed bed reactor. To predict the states of the system, high gain observer based on adaptive RBFNN has been used. Design parameter of the observer has been estimated using Hurwitz polynomial. The effect of neuron number on the mapping error and the effect of space discretization step on modeling error have also been discussed. To decrease the chattering generated by the Sliding Mode Controller (SMC) in the temperature trajectory tracking, an equivalent control term is neglected from the final controller. It has two main advantages: one is the reduction in chattering behavior which is the main drawback of SMC and the second is the reduction of the high gain requirement. The SMC is used to overcome against external disturbance, load variation, variation in key parameters and model mismatch. To make the simulation realistic, constraints have been applied to control input and input rate. For guaranteeing the system stability, Lyapunov theorem has been applied. To show the suitability of the hybrid controller, a comparison has been carried out between the hybrid and PID controller. To quantify the performance, Integral Time Weighted Absolute Error (ITAE) has been estimated. Under the condition of existing model errors and external disturbances, simulation study of the control of the fixed bed reactor shows that the hybrid control algorithm consisting of sliding mode control and observer-based adaptive RBFNN performs well both for tracking the temperature trajectory and reducing the chattering.

Adaptive Chattering-Free Sliding Mode Control of Chaotic Systems with Unknown Input Nonlinearity via Smooth Hyperbolic Tangent Function

The design of adaptive chattering-free sliding mode controller (SMC) for chaotic systems with unknown input nonlinearities is studied in this paper. A smooth hyperbolic tangent function is utilized to replace the discontinuous sign function; therefore, the proposed adaptive SMC ensures that not only the chaos phenomenon can be suppressed effectively but also the chattering often appearing in the traditional discontinuous SMC with sign function is eliminated, even when the unknown input nonlinearity is present. A sufficient condition for stability of closed-loop system is acquired by Lyapunov theory. The numerical simulation results are illustrated to verify the proposed adaptive sliding mode control method.

Sliding mode control of linear structures and a Duffing system using active tendons

In this paper, the sliding mode control (SMC) method, one of the most efficient algorithms in the mitigation of excessive vibrations, was designed to reduce the dynamic responses of dynamical systems. Direct implementation of the switching-type control law in the proposed algorithm leads to a highly undesirable characteristic of the SMC called chattering and thereafter carries on by unwanted dynamics in the practical implementation of the SMC method. Thereafter, the control law is smoothed by replacing its chattering-generating part with a saturation function. The resultant method is called the chattering-free SMC. In this study, to examine the validity of the proposed method, a linear multi-degree-of-freedom building structure and a non-linear single-degree-of-freedom Duffing system were simulated under external excitations. The linear system was equipped with the active tendon mechanism to mitigate seismic-induced excitations on the floors. The first bifurcation length of the Duffing system was obtained by approximate methods to illustrate the instability. Thereafter, the system was modelled using Caughy's linearisation method and controlled under a harmonic excitation. The results of the numerical simulation indicate the satisfactory performance of the chattering-free SMC method in reducing the dynamic responses of both systems to an acceptable level while removing the chattering and the bifurcation phenomenon.

A Robust Adaptive Chattering-Free Sliding Mode Control Strategy for Automotive Electronic Throttle System via Genetic Algorithm

A robust adaptive chattering-free sliding mode (ACFSM) control method for electronic throttle (ET) system is proposed in this paper. It is well known that nonlinearities in the throttle system including friction, return-spring, limp-home (LH) and gear backlash affect the control accuracy of the throttle valve. Compared with the traditional sliding mode control methods, the ACFSM control not only overcomes the influence of nonlinearities and parameter uncertainties in the ET system, but also eliminates chattering in nature such that excellent throttle tracking performance and robustness are maintained. The proposed ACFSM control method is superior to the traditional sliding mode control in the following two aspects: 1) The chattering-free sliding mode control method is able to attenuate the control chattering without weakening the output tracking performance and robustness. 2) The upper bounds of the uncertainty and disturbance are not required any more in control design. They are online estimated by the adaptive law in the sense of Lyapunov. Moreover, due to the difficulty in selecting proper control parameters, the genetic algorithm (GA) is introduced to optimate the control parameters for the ACFSM controller prior to practical implementation. The comparative experimental results are given to demonstrate the excellent control performance of the proposed ACFSM control.