Disturbance Observer-based Control Research Articles

Robust Output Regulation of a Class of Nonlinear Systems Via Disturbance Observer in the Presence of Matched and Unmatched Uncertainties

The purpose of this paper is to propose a controller for nonlinear systems to achieve robust asymptotic tracking of a class of reference signals, in the presence of matched and unmatched disturbances and model uncertainties. The disturbances and reference signals are generated using two linear exosystems. In the proposed controller, instead of using the upper bound of disturbances in the design process, their instantaneous values are estimated disturbance observer. Therefore, disturbance observer-based control (DOBC) methods are less conservative with respect to conventional approaches. In addition to the DOBC design, a new stepwise procedure based on backstepping technique and sliding mode control is proposed. In the proposed approach, in each step, estimations of disturbances and the upper bound of model uncertainties are used to compose virtual control laws; these virtual control laws compose the final control law. Finally, numerical and practical examples are simulated to show the efficiency of the proposed technique and also to verify the theoretical results.

A Novel Disturbance Observer for Multiagent Tracking Control with Matched and Unmatched Uncertainties

In this paper, multiagent tracking control problem of second-order multiagent systems with unknown leader acceleration, input saturation, and matched and unmatched disturbances is investigated. An auxiliary system is constructed to approximate system position states, and a novel sliding mode disturbance observer is designed to estimate matched and unmatched uncertainties. A sliding mode disturbance observer-based control protocol is proposed by constructing a novel sliding mode manifold based on the sliding mode disturbance observer outputs. In addition, the input saturation and the unknown leader acceleration become a part of lumped uncertainties by using mathematic transformation. The lumped uncertainties estimated by the sliding mode disturbance observer are compensated by the sliding mode disturbance observer-based control protocol. Stability of the second-order multiagent systems is guaranteed via Lyapunov method. Finally, a simulation example is proposed to exhibit advantages and availability of the developed techniques.

Extended harmonic disturbance observer-based attitude control for flexible spacecraft with control moment gyroscopes

In the flexible spacecraft with control moment gyroscopes, there are multiple disturbances including not only internal disturbances from actuators and flexible appendages, but also external disturbances from space environment. These disturbances are characterized by a wide frequency range and may degrade attitude control performance to a great extent. In this paper, the lumped disturbance is modeled as a harmonic plus a polynomial model, and an extended harmonic disturbance observer (EHDO) is proposed to estimate the total disturbance. Since the rotor dynamic imbalance disturbance from control moment gyroscopes is described by an internal harmonic model, the lumped disturbance can be estimated precisely via EHDO even with a lower bandwidth. Afterwards, a backstepping-based composite controller is designed to compensate the disturbances by combining the output of EHDO and realize high-precision attitude control for flexible spacecraft with control moment gyroscopes. Simulation results are presented to demonstrate the effectiveness of the proposed method.

Disturbance Rejection for Nonlinear Uncertain Systems With Output Measurement Errors: Application to a Helicopter Model

As a virtual sensor, disturbance observer provides an alternative approach to reconstruct lumped disturbances (including external disturbances and system uncertainties) based upon system states/outputs measured by physical sensors. Not surprisingly, measurement errors bring adverse effects on the control performance and even the stability of the closed-loop system. Toward this end, this paper investigates the problem of disturbance observer-based control for a class of disturbed uncertain nonlinear systems in the presence of unknown output measurement errors. Instead of inheriting from the estimation-error-driven structure of Luenberger-type observer, the proposed disturbance observer only explicitly uses the control input. It has been proved that the proposed method endows the closed-loop system with strong robustness against output measurement errors and system uncertainties. With rigorous analysis under the semiglobal stability criterion, the guideline of gain choice based upon the proposed structure is provided. To better demonstrate feature and validity of the proposed method, numerical simulation and comparative experiments of a helicopter model are implemented.

Vision-based autonomous landing of a quadrotor using a gimbaled camera

This paper proposes a novel vision-based autonomous landing scheme for micro aerial vehicles with perturbations by using a gimbaled camera. There are no sensors available on the moving target in the task. The relative position between the drone and moving target is obtained by the camera mounted on a two-degree-of-freedom pan-tile platform. Firstly, the detection algorithm runs in real time and outputs the pixel tracking errors. Then, an adaptive vision-based controller for the pan-tilt platform guarantees that the line of sight of the camera always tracks the target. Next, the relative position tracking error is approximated according to the gimbal's rotation angles. Disturbance observer-based control is applied for flight control to attenuate the effect of disturbance and recover the hign tracking performance, where relative velocity and lumped disturbances are estimated by extend disturbance observers. The proposed flight controller guarantees that the tracking errors are ultimately bounded with tunable ultimate bounds. The convergence property is demonstrated through Lyapunov theory. The simulations and experiments illustrate the effectiveness and the superiority performance of the proposed control system.

Composite adaptive disturbance observer‐based control for switched stochastic systems with multiple disturbances subject to mode‐dependent average dwell time switching

The problem of composite adaptive disturbance observer-based control and weighted H ∞ performance analysis for a class switched stochastic systems with multiple disturbances subject to mode-dependent average dwell time switching are studied. A disturbance observer and an adaptive updated law are constructed to further design a state feedback controller. Some sufficient criteria are established to check the stability of the switched stochastic systems with multiple disturbances in terms of the multiple Lyapunov function technique. Furthermore, a composite adaptive disturbance observer based-controller is also given. Finally, two examples are proposed to prove the validity of the obtained results.

Load Disturbance Observer-Based Complementary Sliding Mode Control for PMSM of the Mine Traction Electric Locomotive

For the permanent magnet synchronous motor (PMSM) control system of the mine traction electric locomotive (MTEL), the fluctuation of the load will lead to the resonance of the velocity of the MTEL and result in mechanical damage. To solve this problem, a disturbance observer-based complementary sliding mode controller (DOB-CSMC) design method is proposed in this paper. A mathematical model of PMSM is first established. Then, a disturbance observer is designed to reconstruct the load disturbances. In order to realize the static and dynamic tracking performance of the PMSM system, a saturation function-based complementary sliding mode controller is designed and the reconstructed disturbance is introduced into the controller to counteract the influence of external disturbance. Finally, the simulation and experimental results show that the DOB-CSMC method has a smaller overshoot and a shorter settling time compared with the traditional SMC method.

Robust path-following control of a container ship based on Serret–Frenet frame transformation

A novel disturbance observer-based backstepping controller (DOBBC) is developed and applied to the path-following system of a container ship. Our control objective is to enable the ships to follow a desired path despite the presence of environmental disturbances caused by current, wind, and wave actions. It is particularly challenging to achieve such an objective due to the underactuation and nonlinearity of container ships. To simplify controller design, a tracking error model is developed based on Serret–Frenet frame transformation. The proposed path-following control system is constructed on the model. In DOBBC, the disturbance observer estimates both constant and time-variant environmental disturbances. The backstepping controller compensates the nonlinearity and underactuation of the container ship. A feedback-dominance technique is utilized to design the controller parameters. The stability and robustness of the control system are successfully justified through Lyapunov approach. Simulation results demonstrate that the DOBBC effectively drives the ship to follow a desired trajectory in spite of the existence of time-varying environmental disturbances.

T‐S modelling‐based anti‐disturbance finite‐time control with input saturation

Here, the problem of finite-time disturbance rejection is investigated for a class of MIMO non-linear systems with both unknown external disturbances and actuator saturation in the disturbance-observer-based control (DOBC) framework. In order to expand the application range of external disturbances, Takagi-Sugeno (T-S) fuzzy model is used to describe the complex non-linear disturbance. By constructing an appropriate Lyapunov function, an observer-based controller is designed to guarantee that the closed-loop system is finite-time stable. Finally, a simulation example for A4D flight control systems with non-linear disturbances is given to demonstrate the effectiveness of the proposed approach.

Adaptive Sliding Mode Disturbance Observer-Based Composite Control With Prescribed Performance of Space Manipulators for Target Capturing

The requirements for the control performances of space manipulators, especially for the stability and accuracy of the attitude control systems of the base spacecrafts, are ever increasing during the space target capturing tasks. However, the system uncertainties caused by parameter variations will degrade the system performances severely. This paper investigates the precise and fast trajectory tracking control problem for the free-flying space manipulator, after capturing a space target with uncertain mass. To compensate the system uncertainty with complex and uncertain dynamics, a novel adaptive sliding mode disturbance observer (ASMDO) is proposed. Then, a composite controller with prescribed transient and steady-state performances is developed. It is proved that the estimation error of ASMDO can be stabilized in finite-time, though the bound of the derivative of system uncertainty is unknown. Meanwhile, the trajectory tracking error can also be stabilized in finite-time and has preassigned maximum overshoot and steady-state error. Finally, numerical simulations and experimental studies are presented to demonstrate the effectiveness of proposed methods.

Adaptive neural tracking control for a class of non‐lower triangular non‐linear systems with dead zone and unmodelled dynamics

This study presents the disturbance observer-based adaptive neural tracking control approach for non-linear systems in non-strict-feedback form. The design difficulties including unmodelled dynamics and non-strict-feedback form are handled by resorting to a dynamic signal and the variable separation approach, respectively. A disturbance observer is constructed to cope with the effect of time varying disturbance. Neural networks are directly utilised to cope with the completely unknown non-linear functions and stochastic disturbances existing in systems. It is shown that the designed adaptive controller can guarantee that all the signals remain bounded and the desired signal can be tracked with a small domain of the origin. A numerical example is presented to illustrate the effectiveness of the proposed approach and an example of a real plant for one-link manipulator is provided to show the feasibility of the newly designed controller scheme.

Disturbance observer-based optimal longitudinal trajectory control of near space vehicle

Disturbance observer-based optimal longitudinal trajectory control of near space vehicle

Adaptive sliding mode enhanced disturbance observer-based control of surgical device

This paper presents an enhanced adaptive robust disturbance observer-based motion tracking control methodology. This control approach is established and investigated for a semi-automated hand-held ear surgical device for the treatment of Otitis Media with Effusion. The proposed control methodology is utilised for tracking a desired motion trajectory in the presence of unknown or uncertain system parameters, nonlinearities including hysteresis, and disturbances in the motion system. The stability of the control approach is analysed. The convergence of position and velocity tracking errors is proven theoretically. A precise tracking performance following desired motion trajectory is demonstrated in the experimental study.

Disturbance Observer-Based Attitude Control for Spacecraft With Input MRS

This paper considers the problem of attitude tracking control for uncertain rigid spacecraft subject to control input magnitude and rate saturation (MRS). First, a smooth input MRS model is proposed. Then, a robust attitude tracking control scheme is designed based on the backstepping and finite-time disturbance observer techniques. Finally, the effectiveness of the control scheme derived here is illustrated by numerical simulations.

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.

Disturbance observer-based elegant anti-disturbance saturation control for a class of stochastic systems

ABSTRACT In this paper, the elegant anti-disturbance saturation control problem is discussed for a class of stochastic systems with multiple heterogeneous disturbances, which include three kinds of disturbance. One is the disturbance with partially known information. The other one is satisfying -norm bounded. And the third one is white noise. A stochastic disturbance observer (SDO) is constructed to estimate the disturbance with partially known information. Based on the SDO and the characteristics of other two kinds of disturbance, a disturbance observer-based elegant anti-disturbance saturation control (DOBEADSC) scheme is proposed by combining disturbance observer based saturation control (DOBSC) and control. With the proposed DOBEADSC scheme, the desired system robustness performance and higher anti-disturbance control accuracy can be achieved. Finally, two simulation examples, including a wind turbine system, are given to demonstrate the feasibility and effectiveness of the proposed scheme.

Disturbance Observer-based Adaptive Fault-tolerant Dynamic Surface Control of Nonlinear System with Asymmetric Input Saturation

In this paper, a composite fault-tolerant control problem is studied for a class of uncertain nonlinear system with asymmetric input constraint, actuator fault and external unmatched disturbance. The radial basis function neural network (RBFNN) is employed to approximate the unknown uncertainty and asymmetric input saturation. The approximation error, external unmatched disturbance and actuator faults are integrated as the compounded disturbance. A nonlinear disturbance observer is designed to tackle the effect of the compounded disturbance which can be separated from the controller design. To handle the effect of asymmetric input saturation, a smooth continuous differentiable saturation model is explored. Adaptive NN fault-tolerant control scheme is developed to guarantee that all the signals in the closed-loop systems are semiglobally uniformly ultimately bounded (SGUUB) and the tracking errors converge to a small neighborhood of origin by choosing the appropriate design parameters. The effectiveness of the proposed control scheme is demonstrated in the simulation study.

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.

Multivariable Disturbance Observer Based Control with the Experiment on an Active Magnetic Bearing Spindle

This paper presents a new method of disturbance observer based control (DOBC) for multi-input-multi-output (MIMO) highly-coupled unstable systems based on the game theory and the H-infinity synthesis. First motivated by the Youla parameterization of full order state observer feedback control, a full order state observer (FOSO) based DOBC is proposed for single-input-single-output (SISO) systems. Then inspired by the FOSO based DOBC design, a disturbance decoupling method is proposed for MIMO systems using game theoretic observer design. By using error dynamics from the proposed observers, single-input-multi-output (SIMO) virtual plants are constructed. Inverses of those virtual plants for a certain bandwidth are found by solving the model matching problem using H-infinity solver. The proposed DOBC is applied to an open loop unstable MIMO Active Magnetic Bearing Spindle (AMBS). Simulation and experimental results show that the disturbances are effectively estimated and compensated.

Robust Control based on ADRC and DOBC for Small-Scale Helicopter

Abstract This paper introduces and compares two robust control techniques estimating disturbances for small-scale unmanned helicopters: adaptive disturbance rejection control (ADRC) and disturbance observer based control (DOBC). The six-degree-of-freedom dynamics model of the unmanned helicopter includes modeling errors and uncertainties that degrade control performance. Furthermore, the external disturbance and complex internal coupling seriously affect the control stability of the small unmanned aerial vehicle (UAV), but this is difficult to be considered in advance for controller design. For this reason, ADRC and DOBC are designed using a minimum nominal model to compensate for internal uncertainties and external disturbances. Simulation results based on slalom maneuvers show that the proposed controller successfully compensates for disturbance and provides excellent performance compared to the case of using only the PID controller. Other than to unmanned helicopters, it is applicable to most dynamic systems that can be approximated as a double integrator system.