Disturbance Observer-based Control Research Articles

Disturbance Observer-based Neural Network Integral Sliding Mode Control for a Constrained Flexible Joint Robotic Manipulator

Disturbance Observer-based Neural Network Integral Sliding Mode Control for a Constrained Flexible Joint Robotic Manipulator

Disturbance Observer-Based Repetitive Control System With Nonminimal State-Space Realization and Experimental Evaluation

This brief develops a disturbance observer-based repetitive control system using a non-minimal state-space (NMSS) realization where all state variables correspond to the system’s input and output variables and past values. Tracking a periodic reference signal or rejection of a periodic disturbance signal is achieved by including a disturbance observer to estimate an input disturbance containing the same frequency characteristics. This new approach differs from previously published designs because it separates the design procedure into two tasks: first, stabilization via state feedback control; second, independent incorporation of the periodic modes via estimation of the disturbance. Moreover, the new design naturally contains an anti-windup mechanism when the control signal reaches its maximum or minimum value. Results from the experimental evaluation are given, including a comparison against a design that constructs a minimal state controller using an observer. These results demonstrate that the new method can deliver significant performance improvement, with excellent disturbance rejection and reference tracking.

Anti-disturbance control of a piezo-driven micromanipulator with a non-minimum phase

In precision micromanipulation tasks, operation accuracy and anti-disturbance performance of micromanipulators are critical. This paper presents anti-disturbance control for a piezo-driven micromanipulator with a non-minimum phase. The micromanipulator is constructed by mounting a flexible manipulator on a parallel positioning stage. The micromotion and dynamic behavior of the micromanipulator are analyzed. Then, an anti-disturbance control strategy combining H-infinity feedback control and disturbance observer-based control for a non-minimum phase is designed to reduce disturbances and ensure control accuracy. Finally, the experimental measurement and control system is built. The observed phenomena show that sinusoidal disturbances are almost eliminated and the overshoot of step disturbances is significantly reduced. In addition, the time for suppressing the step disturbance is shortened from 0.9 to 0.3 s. Experiments verify the viability of the anti-disturbance control strategy.

Disturbance observer-based adaptive neural guidance and control of an aircraft using composite learning

An adaptive neural guidance and control system is proposed in this paper for a generic fixed-wing aerial robot. Unlike most of the existing low-level control systems, which utilize a non-adaptive guidance loop, in this work both the guidance and control loops are trained using an efficient adaptive neural algorithm. A feedforward neural network is employed in each loop to identify uncertain dynamics, while an adaptive disturbance observer allows to compensate for both the external disturbances and estimation error of the neural network. This would lead to a resilient flight control system, and thus, the asymptotic stability of both the guidance and control loops can be theoretically ensured for a generic aerial robot subject to different types of nonparametric internal and external disturbances. Besides, to enhance the learning efficiency, a composite learning method is adopted in which the neural network and the disturbance observer are trained using a composite error function consisting of the tracking error and the estimation error of an introduced adaptive state observer. To the best of the authors’ knowledge, this is the first completely adaptive integrated guidance and control system with guaranteed stability under parametric and nonparametric internal and external disturbances. The introduced control system is then applied to a simulation model of an electric aircraft that has been validated on the basis of real data and flight experiments. The obtained results indicate that the proposed approach could be considered a reliable guidance and control system for a generic fixed-wing aerial vehicle in the presence of actuator faults, unmodeled dynamics, external disturbances, and measurement noises.

Disturbance Observer-based Adaptive Fuzzy Fault-tolerant Tracking Control for Uncertain Nonlinear Systems with Input Delay and Actuator Faults

Disturbance Observer-based Adaptive Fuzzy Fault-tolerant Tracking Control for Uncertain Nonlinear Systems with Input Delay and Actuator Faults

Disturbance Observer-based Anti-unwinding Control for Flexible Spacecrafts

Disturbance Observer-based Anti-unwinding Control for Flexible Spacecrafts

Decoupled Control Design of Aerial Manipulation Systems for Vegetation Sampling Application

A key challenge in the use of drones for an aerial manipulation task such as cutting tree branches is the control problem, especially in the presence of an unpredictable and nonlinear environment. While prior work focused on simplifying the problem by modeling a simple interaction with branches and controlling the system with nonlinear and non-robust control schemes, the current work deals with the problem by designing novel robust nonlinear controllers for aerial manipulation systems that are appropriate for vegetation sampling. In this regard, two different potential control schemes are proposed: nonlinear disturbance observer-based control (NDOBC) and adaptive sliding mode control (ASMC). Each considers the external disturbances and unknown parameters in controller design. The proposed control scheme in both methods employs a decoupled architecture that treats the unmanned aerial vehicle and the manipulator arm of the sampler payload as separate units. In the proposed control structures, controllers are designed after comprehensively investigating the dynamics of both the aerial vehicle and the robotic arm. Each system is then controlled independently in the presence of external disturbances, unknown parameter changes, and the nonlinear coupling between the aerial vehicle and robotic arm. In addition, fully actuated and underactuated aerial platforms are examined, and their stability and controllability are compared so as to choose the most practical framework. Finally, the simulation findings verify and compare the performance and effectiveness of the proposed control strategies for a custom aerial manipulation system that has been designed and developed for field trials.

Fast fixed-time nonsingular terminal sliding-mode formation control for autonomous underwater vehicles based on a disturbance observer

In this paper, a novel disturbance observer-based fixed-time formation control method is proposed for autonomous underwater vehicles with actuator faults, model uncertainties and unknown disturbances. Firstly, a fast fixed-time stable system is improved, which has a faster convergence rate than existing stable system. Then, the leader-follower formation control strategy is combined with the path planning strategy based on the artificial potential field to obtain a collision-free formation configuration. Besides, a fast fixed-time disturbance observer is designed to compensate for unknown composite disturbances, which enhances the robustness of the system. Further, based on the disturbance estimation information and the improved nonsingular fast fixed-time terminal sliding-mode surface, a robust fast fixed-time formation control method is presented, which achieves the desired formation configuration. Finally, simulation and comparison results show the effectiveness of the proposed control strategy.

Disturbance Rejection Control for Active Vibration Suppression of Overhead Hoist Transport Vehicles in Semiconductor Fabs

In modern semiconductor fabrication plants, automated overhead hoist transport (OHT) vehicles transport wafers in front opening unified pods (FOUPs). Even in a cleanroom environment, small particles excited by the mechanical vibration of the FOUP can still damage the chips if such particles land on the critical area of the wafers. To minimize the vibration excitation force transferred to the FOUP, this research focuses on controlling the vibration displacement level of an OHT hand unit interface between the OHT vehicle and the FOUP. However, since the OHT vehicle and the FOUP keep traveling, the target system is floating and there exists no external anchoring point for a controlling force source. In addition, no sensor attachments are permitted on mass-production FOUPs, which makes this vibration level suppression problem more challenging. In this research, a custom testbed is designed to replicate the acceleration profile of the OHT vehicle under its travel motion. Then, system modeling and identification is conducted using simulation and experiment to verify the fabricated testbed design. Finally, a disturbance observer-based controller (DOBC) is developed and implemented on a custom active vibration suppression actuator with inertia force-based counterbalancing to reduce peak vibration amplitude from 870 μm to 230 μm.

Adaptive sliding mode fault-tolerant attitude control for flexible satellites based on T-S fuzzy disturbance modeling.

This paper investigates the fault tolerance problem of flexible satellites subject to actuator faults and multiple disturbances. An adaptive sliding mode fault tolerant control (ASMFTC) approach based on Takagi-Sugeno (T-S) fuzzy disturbance observer (TSFDO) is presented for attitude control system (ACS) under loss of actuator effectiveness, environmental disturbance torque and elastic modal generated by flexible appendages. Compared with the traditional disturbance observer based control (DOBC) methods, the T-S fuzzy technology is applied to estimate the unknown nonlinear elastic modal. Then, the energy bounded disturbance is eliminated by designing an adaptive sliding mode controller. The proposed ASMFTC design can guarantee the sliding surface to approach zero. Finally, the effectiveness of the control method proposed in this paper is further verified by comparative simulation.

Experimental assessment of an unknown-input estimator for a nonlinear wave energy converter

In the wave energy field, one of the main challenges towards commercialisation of wave energy devices is the development of suitable control laws, able to maximise the absorbed energy while guaranteeing effective satisfaction of any required physical constraint. However, one of the main characteristics of this optimal control problem is that the system behaviour is strongly influenced by the external (uncontrollable) input arising from the wave source, i.e. the wave excitation, which is often unmeasurable. As such, computation of optimal control solutions for WEC systems requires availability of instantaneous knowledge of the wave excitation, and hence input-unknown estimators are developed within the control loop. State-of-the-art estimation strategies are based on the knowledge of control-oriented linearized models of the system, often neglecting the influence of nonlinear phenomena within the system description. We propose, in this paper, an approach inspired by disturbance observer-based control, able to accommodate well-known hydrodynamic nonlinear effects in the process of estimating the unknown excitation force acting on the device. This strategy, which in contrast to the usually applied estimators does not require an implicit/explicit model of the wave excitation force, is tested on a hardware-in-the-loop facility in different sea state conditions, to realistically assess its performance in terms of estimation error and delay. The experimental appraisal show satisfactory results in terms of normalized root mean square error and average delay, which, together with the simplicity of the method, positions the proposed strategy as a promising candidate for hardware implementations in real environments.

An Output Feedback Stabilizer for Uncertain MIMO Nonlinear Systems: Nonlinear Nominal Input Gain Function

This article presents a robust output feedback stabilizer for multi-input–multi-output nonlinear systems subject to external disturbances and system uncertainties. We assume that the system has a well-defined vector relative degree and the zero dynamics is input-to-state stable. Based on the assumption that there exists a state feedback controller that makes the origin of the nominal closed-loop system asymptotically stable, we present an output feedback stabilizer that recovers the stability of the nominal closed-loop system in the practical sense. We allow that the nominal system can have a nonlinear input gain matrix that is a function of system state, and this is done by modifying the structure of the disturbance observer-based robust outputfeedback controller. Simulation results on a practical system are included to validate the proposed controller.

Disturbance Observer-Based Sliding Mode Controller for Regulating Pantograph–Catenary Contact Force

For most electrified railways, pantographs play a vital role in transmitting energy from overhead line to vehicles, and therefore a stable and continuous contact behavior is required. This paper proposes a disturbance observer-based sliding mode controller (DO-SMC) for the problem of pantograph–catenary contact force regulation. The simulation results show that the DO-SMC with a chattering alleviation approach can effectively reduce contact force fluctuation through a reasonable control input.

Multivariable Disturbance Observer-Based Finite-Time Sliding Mode Attitude Control for Fixed-Wing UAVs Under Matched and Mismatched Disturbances

In this letter, we propose a multivariable disturbance observer-based finite-time sliding mode attitude control (MDOB-FT-SM-AC) for fixed-wing UAVs in the presence of both matched and mismatched disturbances. Compared with existing sliding mode attitude controllers, the significant improvements of the proposed MDOB-FT-SM-AC are the multivariable control structure, strong robustness, and high precision performance with continuous control input signal. In the proposed MDOB-FT-SM-AC, we first develop multivariable finite-time disturbance observers such that the precise estimation of both matched and mismatched disturbances is ensured. Next, a nonsingular terminal sliding manifold is designed such that the fixed-wing UAV is driven to track its desired attitude command in finite time. We finally present a multivariable super-twisting reaching law such that the finite-time convergence of the sliding variable and its derivative to zero is guaranteed. Attentive finite-time convergence analysis is derived based on the Lyapunov and homogeneity theories. Simulation results are given to illustrate the superiority of the proposed MDOB-FT-SM-AC.

Disturbance Observers for Robust Safety-Critical Control With Control Barrier Functions

This letter provides formal safety guarantees for control systems with disturbance. A disturbance observer-based robust safety-critical controller is proposed, that estimates the effect of the disturbance on safety and utilizes this estimate with control barrier functions to attain provably safe dynamic behavior. The observer error bound – which consists of transient and steady-state parts – is quantified, and the system is endowed with robustness against this error via the proposed controller. A connected cruise control problem is used as illustrative example through simulations including real disturbance data.

Disturbance Observer-Based Robust Control Design for Uncertain Periodic Piecewise Time-Varying Systems With Disturbances

With the aid of disturbance observer strategy, this article aims to investigate the disturbance rejection and stabilization problems for periodic piecewise time-varying systems that are subject to time-varying delays, parameter uncertainties, nonlinear perturbations and exogenous disturbances. To be more specific, the periodic piecewise time-varying systems are built by segmenting the fundamental period of periodic systems into a limited number of subintervals. Further, the disturbances engendered from an exogenous system are estimated by deploying the disturbance observer and subsequently, on the premise of disturbance that is esimated, a robust controller protocol is constructed for the considered system. Moreover, by bridging the time-varying periodic piecewise Lyapunov-Krasovskii functional with a matrix polynomial lemma, a set of adequate criteria is framed, which confirms the asymptotic stability of the system that is being addressed. Subsequently, on the premise of established criteria, the design of periodic piecewise gain matrices of devised controller and configured observer are presented. Eventually, the importance and potential of the presented theoretical concepts are evidenced through offering a numerical illustration with the simulation results.

Disturbance Observer-Based PID Control System Using DNA Strand Displacement and Its Application in Exponential Gate

Disturbance Observer-Based PID Control System Using DNA Strand Displacement and Its Application in Exponential Gate

Disturbance Observer-based Higher-order Sliding Mode Controller for Frequency Regulation of Hybrid Power Systems

Disturbance Observer-based Higher-order Sliding Mode Controller for Frequency Regulation of Hybrid Power Systems

Disturbance Observer-Based Model Predictive Voltage Control for Electric-Vehicle Charging Station in Distribution Networks

This paper proposes a disturbance observer (DOB)-based model predictive voltage control (MPVC) method to improve the power quality of electric vehicle charging stations (EVCSs) with battery energy storage systems (BESSs) in distribution networks. As the volume of EVCS increases, we face challenges related to transformer overloading and power quality issues. In particular, voltage fluctuations in local EVCS become the most critical problem due to the highly unpredictable EV charging loads and renewable energy production. In this study, the DOB estimates the EV charging loads and PV generation power to ensure that the MPVC can compensate for them effectively and minimize the voltage fluctuation of the EVCS. The proposed MPVC with DOB does not require communication system and is obtained by solving a linear matrix inequality (LMI)-based optimization problem. Furthermore, the parameter uncertainties, caused by the inherent tolerances and aging degradation of circuit components, are considered. The effectiveness of the proposed control scheme is demonstrated based on simulations and experiments using a 10 kVA EVCS simulator.

Disturbance Observer-Based Control to Guarantee a Sliding Mode Without Sliding Mode Control

Disturbance Observer-Based Control to Guarantee a Sliding Mode Without Sliding Mode Control