Disturbance Observer-based Control Method Research Articles

High-Performance Adaptive Attitude Control of Spacecraft With Sliding Mode Disturbance Observer

A new disturbance observer-based control method is presented in this paper to address the attitude tracking problem of rigid-body spacecraft in the presence of external disturbances and parameter uncertainties. Particularly, a sliding mode disturbance observer (SMDO) is designed. The most important feature of this SMDO is the relaxation of the assumption that external disturbances must be constants or changing at a slow rate, which is a typical assumption required in these classes of problems concerning disturbance observer (DO) design but hard to guarantee from the standpoint of practical engineering. In addition, a special adaptive integral sliding mode controller is combined with the SMDO to ensure system state convergence. The proposed control scheme’s primary advantage is the enhanced robustness against system parameter uncertainties and external disturbances. Stringent closed-loop system stability analysis is performed using Lyapunov-based stability theory. Numerical simulations are carried out on nonlinear model of spacecraft to validate the proposed control scheme’s efficiency compared to the existing methods in the literature.

On vibration rejection of nonminimum-phase long-distance laser pointing system with compensatory disturbance observer

This paper focuses on the vibration rejection problem for the nonminimum-phase long-distance laser pointing system on the moving platform. Due to the unstable approximate inverse of nonminimum-phase property, the disturbance-observer based control (DOBC) methods inevitably sacrifice numerous vibration rejection capabilities to stabilize the system. In this paper, a compensatory disturbance-observer-based control (CDOBC) method is proposed to ensure a much stronger vibration rejection performance. In this method, the stable nominal plant replaces the unstable approximate inverse. Limited by stability constraints, the primary filter still sacrifices performances to provide basic vibration rejection capabilities. In the premise of a stable primary filter, the proposed compensatory filter naturally and effectively satisfies its stability constraint. Thus, the novel compensatory filter has sufficient flexibility to make up for the sacrificed vibration rejection capabilities of the primary filter without breaking the system’s stability. The CDOBC method has quite enough capability to reject the vibrations of the nonminimum-phase long-distance laser pointing system, which is impossible for the DOBC methods. Furthermore, the analytical system’s stability and tuning laws for the proposed method are presented. The simulations and experiments demonstrated the effectiveness of the proposed method despite various vibrations.

Switched safe tracking control design for unmanned autonomous helicopter with disturbances

In this paper, the switched safe tracking control scheme is investigated for the attitude and altitude system of a medium-scale unmanned autonomous helicopter with output constraints and unknown external disturbances. To keep the attitude angles and altitude within the desired constrained range, an output boundary protection approach is adopted to generate an output constrained trajectory which is piecewise differentiable. The disturbance observer-based control method is employed to handle the unknown external disturbances of the system. Because of the piecewise differentiability of the output constrained trajectory, the closed-loop error system with the safe tracking controller can be seen as a switched system with jump dynamics. The multiple Lyapunov function method is adopted to guarantee the tracking performance with designed average dwell time. Simulation results of an example are provided to illustrate the effectiveness of the proposed control scheme for the unmanned autonomous helicopter system.

Anti-disturbance control for attitude and altitude systems of the helicopter under random disturbances

In this paper, the issue of anti-disturbance control is investigated for the helicopter attitude and altitude systems with multiple random disturbances. The disturbances are divided into two parts: one is described by the switching systems with Markovian jump parameters; the other one is from the random modeling noise, and considered as random perturbations in the controller design. Combining the disturbance observer based control method, the backstepping control approach and the stochastic Markovian jump system control theory, a flight controller is constructed to guarantee that the attitude and altitude helicopter systems track the predefine attitude and altitude within reasonable bounds. Finally, simulations are given to show the effectiveness of the proposed method.

Disturbance observer based control for four wheel steering vehicles with model reference

This paper presents a disturbance observer based control strategy for four wheel steering systems in order to improve vehicle handling stability. By combination of feedforward control and feedback control, the front and rear wheel steering angles are controlled simultaneously to follow both the desired sideslip angle and the yaw rate of the reference vehicle model. A nonlinear three degree-of-freedom four wheel steering vehicle model containing lateral, yaw and roll motions is built up, which also takes the dynamic effects of crosswind into consideration. The disturbance observer based control method is provided to cope with ignored nonlinear dynamics and to handle exogenous disturbances. Finally, a simulation experiment is carried out, which shows that the proposed four wheel steering vehicle can guarantee handling stability and present strong robustness against external disturbances.

Direct power control for grid-connected doubly fed induction generator using disturbance observer based control

Abstract A disturbance observer based control method for a grid-connected doubly fed induction generator is presented in this study. The proposed control method consists of a state-feedback controller and a disturbance observer (DO). The DO is used to compensate for model uncertainties with the aim of removing the steady-state error. The control objective consists of regulating the stator currents instead of the rotor currents in order to achieve direct control of the stator active and reactive powers. Such a control scheme removes the need for an exact knowledge of the machine parameters to achieve accurate control of the stator active and reactive powers. The main advantage of this control method is ensuring a good transient performance as per the controller design specifications, while guaranteeing zero steady-state error. Moreover, the proposed control method was experimentally validated on a small scale DFIG setup.

Neural Network-Based DOBC for a Class of Nonlinear Systems With Unmatched Disturbances.

In this brief, the problem of composite anti-disturbance tracking control for a class of strict-feedback systems with unmatched unknown nonlinear functions and external disturbances is investigated. A disturbance-observer-based control (DOBC) in combination with a neural network scheme and back-stepping method is developed to achieve a composite anti-disturbance controller design that provides guaranteed performance. In the proposed method, a conventional disturbance observer and a radial basis function neural network (RBFNN) are combined into a new disturbance observer to estimate the unmatched disturbances. As compared with conventional DOBC methods, the primary merit of the proposed method is that the unknown nonlinear functions are approximated using the RBFNN technique, and not regarded as part of the disturbances or estimated by a conventional disturbance observer. Hence, the proposed method can obtain higher control accuracy than the conventional DOBC methods. This advantage is validated by simulation studies.

Disturbance Observer-Based Control: Methods and Applications [Bookshelf

This 340-page book is primarily based on the authors’ extensive ten-year research effort on disturbance-observer-based control (DOBC) theory and applications. The book covers the theoretical analysis of both basic and advanced concepts in DOBC, as well as engineering applications in process control, mechatronics, and flight control systems. The target audience is both researchers working on advanced control methods and related engineering fields and practicing engineers interested in disturbance estimation and compensation. This book attempts to fill the absence of an academic reference book on DOBC methods and applications, and, in this context, the authors provide a systematic perspective on the underlying philosophy of DOBC, its distinct features relative to other methodologies and design tools, and its major theoretical developments and application-related contributions. An ever-increasing demand for higher-precision control performance has been observed in the modern control systems community, such as in mechatronics and robotics, electrical machines and drives, power electronics, energy conversion, and the aerospace and automotive sectors. DOBC has been known as one of the most promising and effective methods in the control community for quite a long time. While there are many research papers, few academic books exist on the subject, and the authors attempt to fill this void. The book is well written and clearly illustrates the contributions of DOBC alongside established techniques in disturbance rejection. All theoretical results are given with rigorous mathematical proofs. In the applications sections, the simulation results are elegantly presented with plenty of comparative studies. Although most of the mathematical concepts and abbreviations are defined throughout the book, a glossary or list of symbols and abbreviations would be a welcome addition. The book would be a useful resource for an advanced graduate course in control, for researchers in the areas of systems and control, as well as an educational reference for practicing engineers.

Disturbance Observer Based Control of Small Unmanned Aerial Rotorcraft

As a complex system, the control performance of small unmanned aerial rotorcraft is easily affected by the dynamic model errors, measurement errors, and environment disturbances. This paper proposes a disturbance observer based control method to improve performance. The disturbance observer based control is constructed by the feedback control and a series of integral filters. The system stability can be guaranteed by the feedback control method. Furthermore, the disturbances can be estimated and eliminated quickly by the integral filters. Therefore, the control performance can be improved effectively. The control performance of the disturbance observer based control has been validated by a series of flight tests. Compared with feedback control, the disturbance observer based control yields a better tracking performance in the presence of disturbances.

Enhanced Disturbance-Observer-Based Control for a Class of Time-Delay System with Uncertain Sinusoidal Disturbances

This paper is concerned with disturbance-observer-based control (DOBC) for a class of time-delay systems with uncertain sinusoidal disturbances. The disturbances are decomposed as precise and uncertain parts using nonlinear disturbance observer (DO) after appropriate coordinate transformation. And then the two parts can be compensated by corresponding controller, respectively, such that the classic DOBC method is extended to uncertain disturbance rejection. One novel feature of the proposed method is that even if the precise disturbance parameters are inaccessible, the merits of DOBC can be inherited. By integrating the disturbance observers with feedback control laws with time delay, the disturbances can be rejected and the desired dynamic performances can be guaranteed. Finally, simulations for a flight control system are given to demonstrate the effectiveness of the results.

Nonlinear disturbance observer-based control for multi-input multi-output nonlinear systems subject to mismatching condition

For a multi-input multi-output (MIMO) nonlinear system, the existing disturbance observer-based control (DOBC) only provides solutions to those whose disturbance relative degree (DRD) is higher than or equal to its input relative degree. By designing a novel disturbance compensation gain matrix, a generalised nonlinear DOBC method is proposed in this article to solve the disturbance attenuation problem of the MIMO nonlinear system with arbitrary DRD. It is shown that the disturbances are able to be removed from the output channels by the proposed method with appropriately chosen control parameters. The property of nominal performance recovery, which is the major merit of the DOBCs, is retained with the proposed method. The feasibility and effectiveness of the proposed method are demonstrated by simulation studies of both the numerical and application examples.

Non-linear disturbance observer-based robust control for systems with mismatched disturbances/uncertainties

Robust control of non-linear systems with disturbances and uncertainties is addressed in this study using disturbance observer-based control (DOBC) technique. In this framework, the ‘disturbance’ is a generalised concept, which may include external disturbances, unmodelled dynamics and system parameter perturbations. The existing DOBC methods were only applicable for the case where disturbances and uncertainties satisfy so-called matching condition, that is, they enter the system in the same channel as the control inputs. By appropriately designing a disturbance compensation gain vector in the composite control law, a non-linear disturbance observer-based robust control method is proposed in this study to attenuate the mismatched disturbances and the influence of parameter variations from system output channels. The proposed method is applied to a missile system with non-linear dynamics in the presence of various uncertainties and external disturbances. Simulation shows that, compared with the widely used non-linear dynamic inversion control (NDIC) and NDIC plus integral action methods, the proposed method provides much better disturbance attenuation ability and stronger robustness against various parameter variations.

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.