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.

Local sliding mode inversion algorithms and state observers with space applications

AbstractThe main objective of this work is to propose novel finite‐time algorithms to either invert a time‐varying map or to estimate the state of a time‐varying nonlinear plant. The former goal is pursued by using a sliding mode version of the Newton algorithm, whereas the latter objective is achieved by resorting to the inverse of the Jacobian matrix of the observability map to implement a sliding mode differentiator in the original coordinates. Finally, it is shown how these two techniques can be efficiently used to solve some relevant space applications, such as the estimation of the angular velocity of an axial symmetric satellite, the estimation of the inertia parameters of an orbiting object from measurements of its angular velocities, and the estimation of a Keplerian orbital element given measurements of the other five ones.

Continuous finite-time extended state observer design for electro-hydraulic systems

This paper presents a novel framework towards a time-varying observer design for nonlinear electro-hydraulic actuators. The key idea of this paper is to employ a positive-increasing function associated with the observer objective to improve the estimation performance. An extended state observer is designed to estimate the full state variables and the uncertainties without any knowledge about the upper bounds of the uncertainties and their derivatives. First, without loss of generality, the system model is divided into three parts, and the extended state observers are designed for each part, independently. Then, the time-varying gains of each observer are designed to make the observation errors uniformly bounded. Finally, the simulated performance of the presented framework is compared with two valid approaches including high-order sliding mode and high-gain extended state observers.

Load following control of a pressurized water reactor via finite-time super-twisting sliding mode and extended state observer techniques

The problem of load following of a pressurized water reactor (PWR) has been extensively investigated in the last decades. However, most of the pre-existing controllers proposed in the literature rely on full system state measurements. This paper proposes a finite-time super-twisting sliding mode controller based on an extended state observer (FTSTSMC-ESO) for the load following of the PWR in the presence of compound disturbances, without assuming full system state measurements. First, a description of the PWR system with two-points kinetics equations is given. Then, an ESO that provides exact estimates of the compound disturbances simultaneously with the unmeasured states (relative density of delayed neutron precursor, average fuel temperature, temperature of the coolant, xenon concentration, and iodine concentration) is designed by employing the measurements of the PWR system. With the use of information from the ESO, a FTSTSMC is proposed to improve the load following performance and deal with the estimation errors of the ESO, while at the same time limiting the axial power difference of the PWR core. Theoretical analysis indicates that the stability of the proposed whole load following control system can be guaranteed by means of Lyapunov stability theory. Finally, simulation results reveal that the proposed FTSTSMC-ESO scheme can achieve satisfactory estimation performance and better load following performance in comparison with a proportional-integral-derivative (PID) controller, an active disturbance rejection controller (ADRC), and an extended state observer-based sliding mode controller (ESO-SMC).

Robust fractional‐order super‐twisting sliding mode control to accurately regulate lithium‐battery / super‐capacitor hybrid energy storage system

One of the main challenges in front of the inventors and researchers to compensate the power quality problems is the existence of an efficient and reliable electric energy source for dynamic voltage restorer (DVR). Recent advances in the technologies of lithium-battery (LB) and super-capacitor (SC) have made them possible to be used as hybrid energy storage system (HESS) for DC-power supply of DVR. But then, a robust and efficient controller must be essentially designed to compensate the intricate correlation between system components, unknown nonlinearities, parameter uncertainties related to the HESS. Hence, fractional-order super-twisting sliding mode control (FOSTSMC) is proposed for LB/SC-HESS to smoothly and accurately smoothly track the current reference and control the DC-link voltage of the asymmetric half-cascaded multilevel inverter of DVR during different compensation conditions. As the primary controller, FOSTSMC has compensated the unknown nonlinear parts and parameter uncertainties related to LB/SC-HESS through the real-time disturbance estimation using sliding mode state and disturbance observer (SMSDO). Both the battery current and DC-link voltage due to the physical measurability are chosen to design the control scheme based on the proposed FOSTSMC. The proposed controller has been compared with the proportional integral derivative and the sliding mode control under different probable scenarios to evaluate and validate its observability and controllability. To better present the effects of FOSTSMC, AHCMLI, and HESS-based DVR, they have been quantified as follows: Three real-time stability benchmarks that is, overshoot, undershoot and settling time are respectively attained for FOSTSMC: 0.6, 0.4, and 0.03; for sliding mode control: 1.1, 0.7 and 0.019; for proportional integral derivative: 0.9, 2, and 0.117. That is to say, FOSTSMC can smoothly and accurately track the current reference and control the DC-link voltage during different compensation conditions as compared with other controllers. Asymmetric half-cascaded multilevel inverter can provide 33 steps with consideration of 12 unidirectional switches, whereas binary, trinary, and other multilevel structures can provide less than 27 steps with consideration of 12 switches. The quasi-AC voltage synthesizer-based DVR can completely and accurately compensate the voltage sag and swell with THD of 2.12 and 2.35, respectively. The THD of mal-compensation voltage sag and swell using the conventional DVR are respectively 11.57 and 13.86.

Fault-tolerant control for a class of n-order systems based on fast terminal sliding mode and extended state observer

This paper focuses on fast terminal sliding mode fault-tolerant control for a class of n-order nonlinear systems. Firstly, when the actuator fault occurs, the extended state observer (ESO) is used to estimate the lumped uncertainty and its derivative of the system, so that the fault boundary is not needed to know. The convergence of ESO is proved theoretically. Secondly, a new type of fast terminal sliding surface is designed to achieve global fast convergence, non-singular control law and chattering reduction, and the Lyapunov stability criterion is used to prove that the system states converge to the origin of the sliding mode surface in finite time, which ensures the stability of the closed-loop system. Finally, the effectiveness and superiority of the proposed algorithm are verified by two simulation experiments of different order systems.

Active fault-tolerant control scheme of aerial manipulators with actuator faults

In this paper, an active fault-tolerant control (FTC) strategy of aerial manipulators based on non-singular terminal sliding mode (NTSM) and extended state observer (ESO) is proposed. Firstly, back-stepping technology is adopted as the control framework to ensure the global asymptotic stability of the closed-loop system. Next, the NTSM with estimated parameters of actuator faults is used as main robustness controller to deal with actuator faults. Then, the ESO is utilized to estimate and compensate the complex coupling effects and external disturbances. The Lyapunov stability theory can guarantee the asymptotic stability of aerial manipulators system with actuator faults and external disturbances. The proposed FTC scheme considers both actuator fault and modelling errors, combined with the adaptive law of actuator fault, which has better performance than traditional FTC scheme, such as NTSM. Finally, several comparative simulations are conducted to illustrate the effectiveness of the proposed FTC scheme.

Robust Output Feedback Sliding Mode State and Disturbance Observer-based Controller Design for Nonlinear Systems

This study uses an output feedback disturbance observer-based proportional derivative (PD) controller with variable damping ratios for a class of single-input, single-output nonlinear systems in the presence of unknown disturbances. The proposed sliding mode state and disturbance observer, in which the switching term of the output estimation error is employed to counteract the effect of external disturbance, ensures that the estimation error is finally bounded in a neighborhood and reconstructs simultaneously the system state and unknown disturbance. Herein, the characteristics of the proposed observer are presented in the frequency domain, followed by the corresponding analysis in the time domain. A nonlinear PD controller with a variable damping ratio designed using the estimation state and disturbances should achieve low overshoot and short settling time. Finally, the simulation results demonstrate the validity of the proposed method.

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

Frameworks for double hyperbolic function‐based robust sliding mode differentiator and observer for nonlinear dynamics

AbstractThis paper puts forward contemporary designs of sliding mode differentiator and state observer for evaluation of unknown nonlinear signal derivatives and unknown internal system states, respectively, by the virtue of tangential and inverse sinusoidal hyperbolic functions. The utility of the proposed frameworks is that it bestows smooth and robust estimation without inciting unacceptable oscillations (chattering), unlike high gain discontinuous function‐based preliminary observers/differentiators. Moreover, the employed double hyperbolic functions would drive the various deviations in estimations of signals or states to a very close neighborhood of origin in finite time which is substantiated via Lyapunov's energy function. To demonstrate the efficiency of the introduced techniques, two examples for estimating the derivatives of a nonlinear signal and internal states of motor are also illustrated with time varying uncertainties. At last, the attained simulation outcomes of the proposed differentiator are further compared with formerly formulated designs such as higher‐order sliding mode differentiator (HOSMD) and uniformly convergent differentiator (UCD).

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.

A High Precision Compound Control Scheme Based on Non-singular Terminal Sliding Mode and Extended State Observer for an Aerial Inertially Stabilized Platform

This paper presents a high precision compound control scheme based on non-singular terminal sliding mode and extended state observer (ESO) for an aerial inertially stabilized platform (ISP) to suppress the effects of multi-source disturbances on the control performance of the ISP. Firstly, a non-singular terminal sliding mode controller is proposed to achieve high disturbance rejection ability, by which the multi-source disturbances are integrally suppressed as an aggregate disturbance. And then, to restrain the chattering effect of the sliding mode control, a disturbance compensation scheme based on the extended state observer is proposed. By the ESO, the disturbances are observed and compensated in real time and hence the chattering effect is significantly alleviated. Meanwhile, a parameter configuration method is proposed to simplify the ESO design. To verify the method, simulations and experiments are conducted. The results show that the proposed compound control scheme has excellent ability in both disturbance rejection and chattering reduction, by which the stabilization precision of the ISP is improved significantly.

Finite-Time Control Algorithm Based on Modal State Observer for Flexible Satellite Attitude Tracking

An attitude controller with finite time convergence rate for satellite attitude tracking issue considering the flexible dynamic based on a finite time modal state observer is proposed in this article. The deformation of flexible appendages is taken into consideration and a finite-time state observer with auxiliary state to offset the initial error is proposed to get the flexible vibration estimation. The modal state and its derivative could be estimated by a full dimensional feedback observer. A finite time sliding mode based on the fraction order feedback of MRP is constructed and the finite time controller is proposed. The modal estimation is implied in controller design hence the counteraction of flexible system could be offset. System global finite-time stability is proved by Lyapunov method and the superiority is demonstrated by simulation results.

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.

Robust tracking control for vehicle electronic throttle using adaptive dynamic sliding mode and extended state observer

• The mathematical modelling of automotive engine electronic throttle (EET) system is obtained by considering the nominal model and parameter uncertainty component and all the system uncertainties are detailedly analyzed, then a modified extended state observer (ESO) is adopted to estimate the lumped uncertainty online. • An adaptive dynamic sliding mode (ADSM) feedback control scheme with ESO techniques is designed to achieve a robust closed-loop tracking performance. By adopting the ESO and designing the dynamic secondary sliding surface (DSSS), the chattering phenomenon of the conventional sliding mode can be significantly alleviated. • The additional dynamics introduced in the sliding mode can improve the system stability. A detailed theoretical stability analysis for the whole closed-loop EET control system is presented by innovatively combining the observer dynamics with the feedback control system. • The real-time experimental results from the DSP-based EET experimental platform are given with performance comparisons with other controllers, and both the excellent performance and robustness of the proposed control are achieved. • The robust adaptive dynamic sliding mode control scheme for EET systems will provide the automotive engineers with a good candidate of robust EET controller in practical applications. The proposed control technique can also be applied to other automotive systems for achieving excellent control performance. This article proposes an extended state observer (ESO)-based robust adaptive dynamic sliding mode (ADSM) tracking control for an automobile engine electronic throttle (EET) system. The newly developed control scheme exhibits the following three attractive characteristics. First, a modified ESO is adopted to estimate the lumped uncertainty online. Second, an ADSM feedback control is then designed to achieve a robust closed-loop tracking performance. Third, the switching gain is adaptively updated by the adaptive law to eliminate the need of the uncertainty information. The stability proof combining the observer with the feedback control is presented in detail. High tracking precision and robustness of the proposed control are verified by extensive experimental results with comparison of existing adaptive sliding mode control and conventional robust controllers.

Fault detection in rotating machinery by using the modal state observer approach

The existence of cracks in rotating shafts can lead to failures, which imply economic losses and security issues. In the last decades, attention has been devoted to this subject leading to the development of vibration-based structural health monitoring techniques. In this paper, a fault detection methodology based on the so-called modal state observer is applied for detecting transversal cracks in a horizontal rotating shaft. A rotor composed by a flexible horizontal shaft, two rigid discs, and two self-aligning ball bearings is used. The Luenberger state observer is formulated in the modal domain to estimate the rotor vibration responses described in the modal domain. Consequently, the most affected vibration modes due to the crack existence can be determined. The kernel density estimator is applied to quantify the influence of a crack over the dynamic behavior of the rotor. The time domain vibration responses measured directly on the rotating machine are used for comparison purposes. Numerical and experimental investigations are presented by considering both breathing and open cracks. The breathing behavior of the crack is simulated according to the Mayes model, in which the crack transition from fully open to fully closed is described by a cosine function. The additional flexibility introduced in the shaft by the crack is determined by using the linear fracture mechanics theory. The obtained results demonstrated that the methodology conveyed represents a good alternative technique to detect faults in rotating machines.

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.