Disturbance Observer-based Control Approach Research Articles

Enhanced trajectory tracking for quadrotors: disturbance observer state feedback control.

This study investigates the dynamics and trajectory tracking of quadcopters by utilizing the Disturbance Observer-based Control (DOBC) algorithm. The quadcopter's dynamic model, which consists of six degrees of freedom, includes both disturbances and uncertainties in the model. The DOBC approach incorporates the disturbance model into the system by introducing it at the input variables. It then compensates for disturbances to achieve accurate tracking of different reference trajectories. The simulated trajectories span a range of motion, varying from simple straight paths to complex spiral paths. In order to verify and evaluate the efficacy of the suggested control technique, simulations are performed using MATLAB. The simulations conclusively show that the disturbance observer-based method effectively achieves the tracking of specified reference trajectories in three-dimensional space. The study highlights the effectiveness of the DOBC algorithm in reducing the effects of disturbances and uncertainties, thereby improving the quadcopter's capacity to accurately track various trajectories.

Semi-global robust stabilisation of disturbed nonlinear systems with state-dependent uncertainties: a DOBC approach

The robust stabilisation for a general class of disturbed nonlinear systems subject to state-dependent uncertainties is addressed in this paper. Different from most existing results, the lumped uncertainty, including external disturbances and model uncertainties, is relaxed to be bounded by some nonlinear functions rather than constants in this paper. Based upon the classical design procedure of disturbance observer-based control (DOBC), a new continuous saturation-based dynamic controller is proposed to estimate the lumped uncertainty. By the delicate design of several compact sets, the qualitative robust stability of the closed-loop system is guaranteed in the sense that all the signals of the closed-loop system can converge to an arbitrarily small compact set in a finite time. Furthermore, when the external disturbances are constants, the semi-global asymptotic stability can also be guaranteed by the proposed controller. Finally, the relationship between system uncertainties and observer gain is shown by a numerical simulation example.

Output feedback control for overhead cranes subject to double-pendulum swing effects and uncertain disturbances

In this paper, a disturbance-observer–based control approach is developed for overhead crane systems. Different from existing control strategies, the issues consisting of the output feedback, input saturation, double-pendulum dynamics, and uncertain disturbances are taken into consideration here. In particular, a disturbance observer is designed first, which can exactly estimate uncertain disturbances. Next, to enhance the performance of the controller, a virtual position signal is constructed and a corresponding Lyapunov function is introduced. Then, based on the provided Lyapunov function and the designed disturbance observer, a composite control approach is developed for overhead crane systems with double-pendulum dynamics and the convergence of the system states is proved via rigorous theoretical analysis. Finally, the effectiveness and robustness of the proposed control approach are verified by simulation tests.

Fault Tolerant Control for Tilted Hexarotors Under a Rotor Failure

This paper addresses the active fault tolerant control problem for a tilted hexarotor under both actuator faults and failures, modelled respectively as partial or total losses of effectiveness. A disturbance observer based control approach is adopted in order to estimate faults and failures, and cope with them at the control level. An inner-outer loop tracking control law is then designed which, thanks to the actuation properties of the hexarotor, does not require any reconfiguration neither in response to a fault nor failure. The control scheme is tested in simulation, with parameters of a real hexarotor and realistic sensor noise.

Nonlinear disturbance observer-based direct joint control for manipulation of a flexible payload with output constraints

This paper discusses a nonlinear direct joint control scheme for manipulation of a flexible payload by a single-arm system with disturbances, parametric uncertainty and output constraints. The flexible payload can be considered as an Euler–Bernoulli beam. The equations of the coupled rigid-flexible motion are established on the basis of the ordinary differential equations (ODEs) and partial differential equation (PDE), which can avoid system spillover instability. A novel nonlinear disturbance observer-based control approach is proposed to enhance its disturbance attenuation ability. To handle the system parametric uncertainty, we apply adaptive direct joint control to approximate the unknown parameter, which does not require endpoint boundary control. Then a Barrier Lyapunov Function (BLF) is adopted to eliminate the impact of output restriction. The asymptotic stability of the closed-loop system is rigorously proven by semi-group theory and LaSalle's Invariance Principle extended to an infinite-dimensional system. Finally, the performance of the direct joint control is validated via numerical simulations.

Adaptive robust nonlinear control of spacecraft formation flying: a novel disturbance observer-based control approach

Adaptive robust nonlinear control of spacecraft formation flying: a novel disturbance observer-based control approach

Disturbance observer-based control schemes for quadrotors – a tutorial

This paper presents a short tutorial introduction to disturbance observer-based control approaches for the quadrotors. With this tutorial, researchers, engineers and students would be able to implement disturbance observer-based model-in-loop simulations and experiments more easily to design robust autopilot system for the quadrotors. To achieve this, first of all, the modeling and controlling of a quadrotor are explained and all linear disturbance observer-based control approaches in the literature are adapted in its overall nonlinear architecture. Disturbance observer-based control design steps are given in detail by design challenges. To show their disturbance rejection capabilities and practical applicability, two flight simulation scenarios are carried out. For all simulation cases, we only take into account the external disturbances in rotational motions. While we give the attitude trajectory commands to quadrotor attitude control architecture in the first scenario, we issue both way-point and trajectory commands to an outer loop controlling the translational motions in the second one. Presented disturbance observer-based control approaches have successfully completed the given reference commands in the presence of the external disturbances even under the measurement noise. Moreover, simulation experiments have shown that UDEBC approach transmits the external disturbance and measurement noise effects to the actuators directly. As a result, for UDEBC approach, it should be kept in mind that flight accidents may occur due to excessive ESC heating. Baseline attitude controller without disturbance observer-based control approach have failed to follow the given reference commands. The simulation studies have also proved the practical applicability of these methods, which are successful even under measurement noise.

Resilient [formula omitted] control for uncertain turbofan linear switched systems with hybrid switching mechanism and disturbance observer

In this paper, a composite resilient anti-disturbance H∞ control scheme is presented for the turbofan linear switched systems with uncertainties and external disturbances via the disturbance observer-based control (DOBC) approach. Since the single-point linearization model cannot be used to accurately describe the engine characteristics of the whole envelope, the multi-model switching method is adopted to preferably describe the working characteristics of the turbofan. A hybrid switching scheme based on state-dependent switching and minimum dwell time constraint is developed to ensure the stability of closed-loop systems and satisfy the dwell-time requirement of turbofan systems. Then, a robust resilient controller is built by combining the DOBC approach and resilient control technique. Based on the multiple Lyapunov functions method, some easy-to-test results are given to guarantee that the closed-loop switched systems are asymptotically stable with H∞ property. Finally, the effectiveness of the proposed method is verified through some simulations and comparisons.

A frequency domain comparison of disturbance observer based control schemes

In this article, an analysis and synthesis of widely used linear disturbance observer based robust control approaches are presented. The main objective of this article is to provide an exhaustive comparison of disturbance observer based robust control approaches and to handle the structural details of each approach for gaining insight about the complexity of each approach. Toward this goal, nine performances and robustness equations portraying useful insights for understanding and analyzing control systems are derived by examining their common and equivalent block diagrams. Four of them are selected as gang of four equations, namely complementary sensitivity function, sensitivity function, disturbance sensitivity function and noise sensitivity function. Robustness and disturbance rejection performance analysis of all linear disturbance observer based control schemes and classical feedback control scheme are done using gang of four equations. With these representations, two tables discussing all prime issues and facilitating the selection of the best approach are obtained. Our research stipulates critical facts and figures of each scheme by considering the derived gang of four equations, which can be used for choosing the most appropriate disturbance observer based control approach for a given robust control problem. It is concluded that the uncertainty disturbance estimator approach is superior when time delay type uncertainty is involved in the model. Unfolding this is critical as time delay is an inevitable fact in most industrial control systems. The findings also emphasize that time domain disturbance observer based control approach is proficient if there is no process time delay.

Fixed-time disturbance observer-based chattering-free sliding mode attitude tracking control of aircraft with sensor noises

The challenging attitude tracking control problem of aircraft with external disturbance and sensor noises is investigated. A disturbance observer-based control approach is presented. In this approach, a fixed-time disturbance observer is preliminarily developed. The external disturbance is estimated with the estimation error governed to zero after a fixed-time regardless of any initial state. Moreover, with measurement noises explicitly considered, a discrete tracking differentiator extracting the real signals from the polluted measurement is introduced into that fixed-time observer to improve its application potential. Invoking the estimation information, a sliding mode attitude controller is then synthesized. The main feature of the proposed approach is that the closed-loop attitude tracking system is guaranteed to be exponentially stable. External disturbance rejection is achieved, while its upper bound is not required to implement that approach. In contrast to the conventional sliding mode control schemes, the proposed controller is chattering-free. Numerical simulation and experimental tests are finally carried out to verify the effectiveness of the proposed approach.

Disturbance observer–based event-triggered tracking control of networked robot manipulator

We investigate the event-triggered tracking control of networked manipulator in the presence of external disturbance and a variety of system uncertainties. The event-triggered controller is designed by the nonlinear disturbance observer–based control approach, which can dynamically compensate for both errors caused by disturbances and the undesirable effects caused by event-triggering rules. A rigorous Lyapunov stability analysis method is proposed to show that the boundedness of all the signals in the closed-loop system can be guaranteed while in the absence of the input-to-state stability assumption related to measurement errors, tracking error can be constrained to an arbitrarily small set without escaping. Finally, by some simulation results, the feasibility and effectiveness of the proposed control approach is demonstrated.

A fuzzy disturbance observer based control approach for a novel 1-DOF micropositioning mechanism

This paper presents the design, analysis, and control of a novel compact, large range 1-DOF micro manipulation mechanism. Leaf flexures were incorporated into a modular multilayer design configuration to achieve large range motion with a high natural frequency. The modular design of the proposed mechanism makes it usable as a building block to construct higher DOF-mechanisms. Computational analysis was conducted to verify the static and dynamic responses of the proposed mechanism and to ensure low flexures stress, high natural frequency, and large workspace. The mathematical model was developed to establish the derivation of a robust observer-based Sliding Mode (SM) controller. To improve the precision of tracking performance, the SM controller was augmented with adaptive Fuzzy Disturbance Observer (SM-FDO). Another robust control technique (H∞) was implemented in this work to characterize and compare the performance of SM-FDO. The mechanism was fabricated using 3D printing technology and a Voice Coil Motor (VCM) was used to deliver the actuation for its capability to provide large displacements. Experiments were performed to verify the computational modeling of the proposed mechanism and to evaluate the performance of the developed controllers. Several experimental results showed that the adaptive nature of SM-FDO allowed this controller to have superior robustness and tracking performance over the other implemented robust controller.

Containment control of multi-agent systems via a disturbance observer-based approach

This paper deals with the containment control problem for multi-agent systems with exogenous disturbances. A disturbance observer-based control approach is employed to estimate the disturbances generated by an exogenous system. Consequently, distributed disturbance observer-based containment control protocols are proposed by using the state feedback control and the output feedback control, respectively. Furthermore, with the help of algebraic graph theory and Lyapunov stability theory, sufficient conditions are established to ensure that multi-agent systems with exogenous disturbances can achieve containment control via the disturbance observer-based approach. Finally, the effectiveness of our theoretical results is verified by providing numerical simulation examples.

Decoupled PI current controller for grid‐tied inverters with improved transient performances

This study proposes a novel decoupled proportional–integral (PI) current controller for grid-tied inverters. The proposed controller can be viewed as the modification of the existing decoupled PI current controller to include the reference jump in order to achieve nominal performance recovery in response to step changes in the current reference. The modified decoupled PI current controller is derived based on combining feedback-linearisation technique with a disturbance observer-based control approach that belongs to the high-gain observer technique. The key feature of the composite controller is its ability to retain the transient performance specified under the feedback-linearising control, particularly when the control does not saturate. Furthermore, by considering the control saturation in the observer design, an anti-windup scheme arises naturally into the controller, leading to an improved transient performance in the presence of saturation. The effectiveness of the proposed controller was verified by simulation and experimental results.

Robust Control of Uncertain Nonlinear Systems: A Nonlinear DOBC Approach

This paper advocates disturbance observer-based control (DOBC) for uncertain nonlinear systems. Within this framework, a nonlinear controller is designed based on the nominal model in the absence of disturbance and uncertainty where the main design specifications are to stabilize the system and achieve good tracking performance. Then, a nonlinear disturbance observer is designed to not only estimate external disturbance but also system uncertainty/unmodeled dynamics. With described uncertainty, rigorous stability analysis of the closed-loop system under the composite controller is established in this paper. Finally, the robust control problems of a missile roll stabilization and a mass spring system are addressed to illustrative the distinct features of the nonlinear DOBC approach.

Design and Qualitative Robustness Analysis of an DOBC Approach for DC-DC Buck Converters With Unmatched Circuit Parameter Perturbations

A disturbance observer-based control (DOBC) approach is proposed in this paper for control design and qualitative robustness analysis of PWM-based DC-DC buck power converters. A disturbance compensation gain is constructed for the composite control algorithm to cancel the unmatched uncertainties in the output voltage channel. Rigorous criterion is provided to show the quantitative robustness between controller parameters and circuit uncertainties. The DOBC approach delivers not only a promising disturbance rejection performance but also a superior property of tracking performance recovery. The feasibility and efficiency of the proposed approach is validated by experimental results based on LabVIEW real-time control test setup.

Global output regulation for strict-feedback nonlinear systems with mismatched nonvanishing disturbances

Summary This paper concerns the problem of global output regulation for a class of strict-feedback nonlinear systems subject to mismatched nonvanishing disturbances. A composite control scheme is developed using a nonlinear disturbance observer-based control approach. A novel idea is that the disturbance estimation is introduced into the design of virtual control laws in each step. Global stability analysis for the closed-loop system is presented by the direct Lyapunov function method. It is shown that the system output asymptotically converges to zero in the presence of mismatched nonvanishing disturbances without the requirement of solving any partial differential equations involved with the traditional output regulation theory. An application design example of a single-machine infinite-bus system with static var compensator is presented with simulation results to demonstrate the effectiveness of the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.

High Gain Disturbance Observer-Based Control for Nonlinear Affine Systems

This paper proposes a high gain disturbance observer based control approach for nonlinear systems. Compared with previous works, it can admit a much larger class of disturbances produced by nonlinear exo-systems. Our approach will follow the framework of the two-stage design procedure, which separates the disturbance observer design from the controller design. Under certain conditions, the observer error for the disturbances generated by nonlinear exo-systems globally and asymptotically converges on zero and the stability of the closed-loop system is guaranteed. An illustrative example of a two-link robot manipulator with limit cycles disturbance is presented to show the effectiveness of the proposed method.

Robust autopilot design of uncertain bank-to-turn missiles using state-space disturbance observers

Robust autopilot design for bank-to-turn (BTT) missiles under disturbances and uncertainties is investigated in this article using the disturbance observer concept. It is well known that the BTT missile dynamics undergo substantial change during its flight. In this disturbance observer-based control (DOBC) setting, the influences caused by parameter variations are merged into disturbance terms and regarded as parts of the lumped disturbances. Disturbance observers are employed to estimate the lumped disturbances, and then a disturbance observer-based robust control (DOBRC) method is proposed in this article to compensate the influences of parameter variations and the disturbances from the output channels. Similar to the baseline linear quadratic regulator design, the DOBRC is analysed and designed using linear techniques. Very promising performance has been achieved for the BTT missile as shown in simulation. It is demonstrated that DOBC approach provides a simple, intuitive, and practical solution for many challenging control problems where systems are subject to significant external disturbances, and uncertainties such as BTT missiles.

Robust control of nonlinear MAGLEV suspension system with mismatched uncertainties via DOBC approach

Robust control of a class of uncertain systems that have disturbances and uncertainties not satisfying “matching” condition is investigated in this paper via a disturbance observer based control (DOBC) approach. In the context of this paper, “matched” disturbances/uncertainties stand for the disturbances/uncertainties entering the system through the same channels as control inputs. By properly designing a disturbance compensation gain, a novel composite controller is proposed to counteract the “mismatched” lumped disturbances from the output channels. The proposed method significantly extends the applicability of the DOBC methods. Rigorous stability analysis of the closed-loop system with the proposed method is established under mild assumptions. The proposed method is applied to a nonlinear MAGnetic LEViation (MAGLEV) suspension system. Simulation shows that compared to the widely used integral control method, the proposed method provides significantly improved disturbance rejection and robustness against load variation.