Sliding Mode State Observer Research Articles

Fixed-time observer-based control of DFIG-based wind energy conversion systems for maximum power extraction

To extract maximum power from the available wind energy, it is necessary that the doubly-fed induction generator (DFIG) based wind energy conversion system (WECS) outputs that maximum power at each instant of time for different wind speeds. This can be achieved by controlling the rotor voltage of the DFIG. To make it possible, a novel maximum power point tracking (MPPT) controller in combination with state and disturbance observers and fixed-time stability notion is proposed in this paper. The sliding mode control (SMC) method is used to design the observer-based controller and ensure the robustness. The sliding mode state observer is designed while only the measurement of the stator reactive power and rotor speed is required. The modelling uncertainties and external disturbances are estimated by the sliding mode disturbance observer without information about their upper bounds in advance. Then, the combinatorial effect of uncertainties and disturbances are fully compensated by the designed controller. The fixed-time convergence issue is addressed where the bound on the settling time is user-defined using design parameters regardless of initial conditions. The elimination of chattering issue is considered in the design of the SMC laws. The stability analysis of the closed-loop system is obtained via the Lyapunov stability theory. The validity and robustness of the proposed method is tested in Simulink/MATLAB for a DFIG under two different scenarios of wind speed modelling. The proposed fixed-time method is also compared with a classical finite-time method. Comparing the results demonstrate that the proposed method outperforms the other method.

Fuzzy-Based Fixed-Time Nonsingular Tracker of Exoskeleton Robots for Disabilities Using Sliding Mode State Observer

In this article, the position tracking control of the wheelchair upper-limb exoskeleton robotic system is investigated with the aim of rehabilitation of disabled people. Hence, the fuzzy nonsingular terminal sliding mode control method by using the state observer with a fixed-time convergence rate is designed in three main parts. In the first part, the fixed-time state observer is proposed for estimation of the states of the system. Secondly, the fixed-time convergence of position tracking error of the upper-limb exoskeleton robot system is examined by using the nonsingular terminal sliding mode control approach. In the third part, with the target of the improvement of the controller performance for removal of the chattering phenomenon which diminishes the controller performance, the fuzzy control method is used. Finally, the efficiency and proficiency of the proposed control method on the upper limb exoskeleton robotic system are demonstrated via the simulation results which are provided by MATLAB/Simulink software. In this part, simulation results are obtained based on different initial conditions in two examples using various desired values. Thus, it can be demonstrated that the proposed method applied to the upper-limb exoskeleton robot system is robust under various initial conditions and desired values.

The stability control for isolated wind‐diesel power system based on the cross coupling effect model

In the isolated wind-diesel hybrid power system, the system voltage and frequency may be affected simultaneously by the fluctuated wind turbine output power and variable load, which can make the system crash in extreme cases without control strategy. Therefore, in order to reduce the voltage and frequency deviation caused by system power fluctuation, both the battery and super twisting algorithm sliding mode state observer (STATCOM) are equipped to adjust the active power and reactive power for load power demand in the isolated small-scale power system. Then, the system mathematical model is established which considers the cross-coupling effect exist in the small-scale power system. In order to improve the control effect of battery and STATCOM, the unified control strategy is designed for battery and STATCOM by using the super twisting sliding mode state observer and the adaptive sliding mode controller according to the constructed cross-coupling effect model. Furthermore, the parameters of controller are further optimized by using the fuzzy method. Finally, the simulation experiments are performed by the real-time digital simulator to validate the effectiveness of the proposed control strategy under different operation points.

English

English

Real-Time Processor-in-Loop Investigation of a Modified Non-Linear State Observer Using Sliding Modes for Speed Sensorless Induction Motor Drive in Electric Vehicles

Tracking performance and stability play a major role in observer design for speed estimation purpose in motor drives used in vehicles. It is all the more prevalent at lower speed ranges. There was a need to have a tradeoff between these parameters ensuring the speed bandwidth remains as wide as possible. This work demonstrates an improved static and dynamic performance of a sliding mode state observer used for speed sensorless 3 phase induction motor drive employed in electric vehicles (EVs). The estimated torque is treated as a model disturbance and integrated into the state observer while the error is constrained in the sliding hyperplane. Two state observers with different disturbance handling mechanisms have been designed. Depending on, how they reject disturbances, based on their structure, their performance is studied and analyzed with respect to speed bandwidth, tracking and disturbance handling capability. The proposed observer with superior disturbance handling capabilities is able to provide a wider speed range, which is a main issue in EV. Here, a new dimension of model based design strategy is employed namely the Processor-in-Loop. The concept is validated in a real-time model based design test bench powered by RT-lab. The plant and the controller are built in a Simulink environment and made compatible with real-time blocksets and the system is executed in real-time targets OP4500/OP5600 (Opal-RT). Additionally, the Processor-in-Loop hardware verification is performed by using two adapters, which are used to loop-back analog and digital input and outputs. It is done to include a real-world signal routing between the plant and the controller thereby, ensuring a real-time interaction between the plant and the controller. Results validated portray better disturbance handling, steady state and a dynamic tracking profile, higher speed bandwidth and lesser torque pulsations compared to the conventional observer.

Mixed Kalman-Fuzzy Sliding Mode State Observer in Disturbance Rejection Control of a Vibrating Smart Structure

In the controllers that are synthesized on a nominal model of a nonlinear plant, the parametric matched uncertainties and nonlinear/unmodelled dynamics of the high order nature can significantly affect the performance of the closed-loop system. On this note, owing to the robust characteristic of the sliding mode observer against modelling perturbations, measurement noise, and unknown disturbances and due to the non-fragile behaviour of the Kalman filter against process noise, a mixed Kalman sliding mode state-observer is proposed and later enhanced by the addition of an intelligent fuzzy agent. In light of the proposed technique, the chattering phenomena and the conservative boundary neighboring layer of the high gain sliding mode observer are addressed. Then, a robust active disturbance rejection controller is developed by using the static feedback of the estimated states using a~direct Lyapunov quadratic stability theorem. The reduced order plant for control design purposes is subjected to some simulated square-integrable disturbances and is assumed to have mismatched uncertainties in the system matrices. Finally, the robust performance of the closed-loop scheme with respect to the mentioned perturbation signals and modelling imperfections is tested by implementing the control system on a mechanical vibrating smart cantilever beam.

Mass and heat transfer control in the GMAW process utilizing feedback linearization and sliding mode observer

Controlling the gas metal arc welding (GMAW) process is investigated utilizing feedback linearization with heat input, detaching droplet diameter and melting rate as controlled variables while accounting for actuator saturation. The control algorithm is employed using a state space model with eight dynamic states. Stability and internal dynamics of the process are studied thoroughly. Sliding mode state observers are implemented to determine the arc current and contact tip to work piece distance as well as the stick out length (which constitute the internal states of the system). Several simulation reports are provided to demonstrate successful regulation and tracking of detaching droplet diameter, heat input rate and melting rate. Finally, simulations indicate that the method is capable of overcoming parametric uncertainty.

Design of infinite sliding mode state observer with application to CO2 absorption system of space station

The CO2 absorption system plays the important roles in controlling the partial pressure of CO2 and providing the condensed CO2 for Sabatier reduction device. This paper deals with the design of the state observer of the CO2 absorption system in the environment control and life support system of the space station. The main design difficulty is that the dynamic model of the CO2 absorption system is described by the partial differential equation, which causes to the traditional state observer based on ordinary differential equation is no longer applicable. In order to solve this problem, an infinite dimensional slide mode observer algorithm is proposed. This algorithm firstly uses a new projection approximation method to transform the partial differential equation to ordinary differential equation, and then estimates the system state by using sliding mode observer with better robustness to the model approximation error and external disturbance. Compared with the traditional algorithm, the proposed method not only applies to the more general case, e.g. the case of non-orthogonal basis, but also effectively reduces the influence of approximation error and disturbances. Next, the detail realization procedure is illustrated by using a simulation example. The simulation results show that the new algorithm can effectively estimate the state of the CO2 absorption system and further guarantee robust to the model error and external disturbances.

Sensorless Vector Control of Permanent Magnet Synchronous Linear Motor Based on Self-Adaptive Super-Twisting Sliding Mode Controller

Due to its own structural characteristics, permanent magnet synchronous linear motors (PMSLMs) have unstable motor parameters during operation due to the end effect and the inherent magnetic circuit instability. At the same time, linear motors have the characteristics of reciprocating switching motion and high-speed positioning motion in industrial applications, thus placing high demands on the controller. In order to improve the performance of the PMSLM, this paper firstly studies the linear motor structure, the distribution characteristics of its air gap magnetic field are obtained, and the simulation analysis for the back electromotive force (EMF) of PMSLM of its running process is carried out. Then, a state observer based on the sliding mode state observer (SMO) is built to replace the traditional speed sensor and a super-twisting sliding mode controller is designed. The double-closed loop control of the speed and the use of high-order sliding mode control features effectively reduce the chattering of the system and reduce the impact of the observation error brought by the observer on the system. The adaptive sliding mode control strategy is used to effectively suppress the influence of the boundaryless uncertainty interference on the system and reduce the influence of the observation error brought by the observer on the system. This paper also combines the linear motor experimental platform to further verify the control scheme based on the super-twisting sliding mode non-sensing linear motor. The simulation and experimental results show that SMO has accurate speed and position tracking performance, the system's chattering is significantly reduced, the control precision is excellent, and the introduction of adaptive sliding mode controller enhances the robustness of the system.

A Discontinuous Adaptive Sliding-Mode Observer for a Class of Uncertain Nonlinear Systems

In this paper the problem of simultaneous state and parameter estimation is studied for a class of uncertain nonlinear systems. A discontinuous adaptive sliding-mode observer is proposed based on a discontinuous nonlinear parameter estimation algorithm. It is shown that such an algorithm provides a rate of convergence faster than exponential. Then, the proposed discontinuous parameter estimation algorithm is included in the structure of a sliding-mode state observer providing an ultimate bound for the full estimation error. Some simulation results illustrate the feasibility of the proposed adaptive sliding-mode observer.

Trajectory Tracking Control of XY Table Using Sliding Mode Adaptive Control Based on Fast Double Power Reaching Law

AbstractCurrently, high velocity and precision are the main developing directions of the XY table. However, the nonlinear effects of friction at low speed deteriorate the precision of the XY table servo system. As a result, it is very important to design a control method to carry out friction compensation and trajectory tracking. In this paper, dual sliding mode state observers are used to estimate these immeasurable parameters in the dynamic LuGre model, and the Lyapunov function is used to design the adaptive update law. In addition, fast double power reaching law has the advantage of improving the global asymptotic convergence rate and overcoming these disadvantages where traditional sliding mode control reaching law causes severe chattering. Simulation results that compare the proposed method with exponent sliding mode control and PID control, demonstrate that the fast double power sliding mode control guarantees position and speed signals, tracking the desired references asymptotically.

A Modified Disturbance Rejection Mechanism in Sliding Mode State Observer for Sensorless Induction Motor Drive

This paper presents a modified sliding mode state observer for sensorless vector-controlled induction motor drive. The objective is to improve the dynamic performance of the sensorless drive subjected to parameter uncertainty, fault and disturbances. The sensorless drive along with the proposed observer is modeled and built in Simulink, and the dynamic behavior is obtained for different test cases such as flux-weakening region, variations in commanded speed and torque, low-speed operation and under faulty operation mode subjected to an electrical fault in the inverter. The conventional disturbance rejection mechanism is modified by constraining the estimated disturbance along with the stator current error in the sliding surface, thereby increasing the ability of the observer to reject the effect of the external load on the tracking performance. Extensive simulation results prove that the modified observer has a wide speed bandwidth compared to the conventional observer along with superior tracking, disturbance rejection characteristics and torque holding capability.

Control of a hydraulic hexapod for a Hardware-in-the-Loop axle test rig

Abstract The present paper describes the controller design for a hydraulic hexapod which is used as an excitation unit for a Hardware-in-the-Loop axle test rig. This includes a description of the plant model, the subordinate drive controllers, the sliding mode state observer as well as the position control of the free hexapod. Measurements show the high dynamics of the position-controlled hexapod. The concept is extended to a hybrid position/force control to be used during axle test maneuvers. Its functionality is demonstrated by a measurement used for the identification of the axle kinematics.

Observer-Based Adaptive Neural Network Trajectory Tracking Control for Remotely Operated Vehicle.

This paper focuses on the adaptive trajectory tracking control for a remotely operated vehicle (ROV) with an unknown dynamic model and the unmeasured states. Unlike most previous trajectory tracking control approaches, in this paper, the velocity states and the angular velocity states in the body-fixed frame are unmeasured, and the thrust model is inaccurate. Obviously, it is more in line with the actual ROV systems. Since the dynamic model is unknown, a new local recurrent neural network (local RNN) structure with fast learning speed is proposed for online identification. To estimate the unmeasured states, an adaptive terminal sliding-mode state observer based on the local RNN is proposed, so that the finite-time convergence of the trajectory tracking error can be guaranteed. Considering the problem of inaccurate thrust model, an adaptive scale factor is introduced into thrust model, and the thruster control signal is considered as the input of the trajectory tracking system directly. Based on the local RNN output, the adaptive scale factor, and the state estimation values, an adaptive trajectory tracking control law is constructed. The stability of the trajectory tracking control system is analyzed by the Lyapunov theorem. The effectiveness of the proposed control scheme is illustrated by simulations.

Design of finite-time high-order sliding mode state observer: A practical insight to PEM fuel cell system

This paper presents a scheme of designing finite-time high-order sliding mode (HOSM) observer which provides some essential requirements to be used in a sensorless control. The observer design technique is proposed to estimate some key states in a Multi-Input Multi-Output (MIMO) proton exchange membrane fuel cell (PEMFC) in a finite-time. Since variation of the load current deeply affects the life time of the cell, estimation and control of oxygen excess ratio (λO2) is suggested to detect and prevent the damage. As a practical application, the observer reconstructs oxygen excess ratio using measurable variables, such as the compressor angular speed, the supply, the return manifold pressures and the load current. The estimation is performed to keep stability without need of any transformation to a canonical form in a finite time. The designed finite-time observer is shown with some increases in the response time indices, improves the accuracy whilst guarantees a fast convergence with respect to using flow sensors. Simulation results verify the achievements whilst signify the fast response as well as robust against uncertainties and disturbances.

State of Charge Estimation of Power Lithium-Ion Battery Based on Sliding Mode Observer

The study of the application of the sliding mode observer method that estimates the state of charge. Based on the state space model of battery established on the model of improved EMF equivalent circuit, a sliding mode state observer is designed to help improve the jitter problem. Considering the nonlinear terms in the model for the analysis of the stability of the observer and the characteristics of the industry under its derivative, and using Lagrange mean value theory to guarantee the convergence conditions of the observer, the design parameters of the observer can thus be determined .Then, this thesis compares the simulation of this method under Matlab environment with the extended Kalman filter method. The results show that the method has higher estimation accuracy in the case of the same battery modeling errors. Therefore, the SOC estimation of the sliding mode observer can effectively reduce the state of charge estimation error introduced by the model error.

Fault Detection in Nuclear Systems Using Sliding Mode Observers

The use of sliding mode observers as a model-based method is proposed for robust fault detection and isolation in linear and nonlinear nuclear systems. A sliding mode output observer and a sliding mode state observer are designed and applied to a U-tube steam generator model, a coupled nonlinear reactor model, and a pressurizer model to detect additive and multiplicative faults in the presence of uncertainties and measurement noise. Numerical results for both steady-state and transient responses of the example systems are presented to illustrate the effectiveness of the proposed method.

Parameter Identification and Synchronization of Uncertain Chaotic Systems Based on Sliding Mode Observer

The synchronization of nonlinear uncertain chaotic systems is investigated. We propose a sliding mode state observer scheme which combines the sliding mode control with observer theory and apply it into the uncertain chaotic system with unknown parameters and bounded interference. Based on Lyapunov stability theory, the constraints of synchronization and proof are given. This method not only can realize the synchronization of chaotic systems, but also identify the unknown parameters and obtain the correct parameter estimation. Otherwise, the synchronization of chaotic systems with unknown parameters and bounded external disturbances is robust by the design of the sliding surface. Finally, numerical simulations on Liu chaotic system with unknown parameters and disturbances are carried out. Simulation results show that this synchronization and parameter identification has been totally achieved and the effectiveness is verified very well.

Micro-/Nanopositioning Using Model Predictive Output Integral Discrete Sliding Mode Control

A piezo-driven micro-/nanopositioning system requires an appropriate controller to suppress the inherent nonlinearity and disturbances. In this paper, we propose a new control scheme called model predictive output integral discrete-time sliding mode control (MPOISMC) to achieve a precise positioning using a piezostage. The proposed controller is featured by an integral type of sliding function based on output error along with a sliding mode state observer. The major advantage of the scheme lies in that it is very easy to implement since it only requires a low-order linear model, whereas neither the bounds on system uncertainties nor the hysteresis model is needed. The model predictive control methodology and the integral item are used to eliminate chattering phenomenon, and a low tracking error is achieved. The feasibility and effectiveness of the proposed MPOISMC approach are verified by experimental studies performed on a micro-/nanopositioning piezostage. Results show that a real-time precise positioning is realized and the performance of the controller is superior to the conventional PID control for motion tracking tasks. Owing to a simple structure, the control strategy can be easily extended to other types of micro-/nanopositioning systems as well.

Fault Reconstruction Based on Sliding Mode Observer for Nonlinear Systems

This paper presents a precision fault reconstruction scheme for a class of nonlinear systems involving unknown input disturbances. First, using the coordinate transformation algorithm, the disturbances and faults of the system are fully decoupled. Therefore, it is possible to eliminate the influence of disturbances to the system, namely, better disturbances robustness. On this basis, the design of a sliding mode state observer makes the most genuine reconstruction realizable, instead of estimation of faults. Furthermore, with the equivalent principle of sliding mode variable structure, the precision reconstruction of arbitrary nonlinear faults is achieved. Finally, the applications of fault reconstruction in a third‐order nonlinear theoretical model with disturbances and in a single‐link robot system, respectively, have demonstrated the validity of the proposed scheme.