Disturbance Observer Design Research Articles

A Robust Emulation of Mechanical Loads Using a Disturbance-Observer

This paper deals with a new control strategy for the programmable dynamometer to emulate dynamic loads. The main idea is to employ the disturbance-observer-based design and take the nominal model involved in the disturbance-observer design as the desired dynamics to be emulated. Compared to previous approaches, the proposed approach does not require exact system parameters of the motor under test, and the range of emulation parameters is wider than previous results. A rigorous stability analysis, as well as a constructive design incorporating system uncertainty and the steady state error bound are presented. An experimental system is developed to verify the performance of the proposed method, and it is demonstrated that up to 20-times of inertia emulation with relatively small emulation error (speed error less than 6 % ) is achieved and that various loads such as friction can be emulated.

Extended PI Feedback Tracking Control for Synchronous Motors

A new dynamic feedback tracking control method of desired velocity and current profiles for permanent magnet synchronous motors, without the additional synthesis of disturbance observers and parametric identification methods, is introduced. Proportional-Integral (PI) feedback is properly extended for both efficient planned motion tracking control and simultaneous fast disturbance estimation. In this fashion, design of additional high-gain disturbance observers becomes unnecessary. This is, on-line dynamic load uncertainty estimation is simultaneously achieved by proposed tracking control implementation. Analytical and numerical results prove the efficient and robust tracking performance of controlled system variables on planned smooth motion profiles and a high-accuracy estimation of unknown high-order variable disturbances.

Trajectory tracking control of hypersonic vehicle considering modeling uncertainty

The tightly coupled, highly nonlinear, and notoriously uncertain nature of hypersonic vehicle dynamics brings a great challenge to the control system design. In this paper, an integrated controller based on Differential flatness theory and L1 adaptive theory is designed, and a nonlinear disturbance observer is added to solve the problem of model uncertainty. Differential flatness is applied to the outer loop to linearize the nonlinear model, and L1 adaptive control is applied to the inner loop to stabilize the attitude. The combination realizes the complementarity of their shortcomings. It can not only retain the advantages of L1 adaptive controller, but also avoid wide range of state changes and makes it easy to design parameters satisfying global convergence. The computational order of differential flatness is also reduced and the design of nonlinear disturbance observer becomes feasible. Simulation results for the hypersonic vehicle are presented to demonstrate the effectiveness and robustness of the proposed control scheme.

A Novel Disturbance Observer Design for a Larger Class of Nonlinear Strict-Feedback Systems via Improved DSC Technique

A novel scheme for disturbance observer is designed for an extended class of strict-feedback nonlinear systems with possibly unbounded, non-smooth, and state-independent compounded disturbance. To overcome these problems in disturbance observer design, the typical slide mode differentiators are improved by introducing hyperbolic tangent function to make the signals smooth, and then the improved slide mode differentiators are constructively used to estimate the errors of variables in the presence of disturbances. The unbounded, non-smooth or state-independent disturbances are therefore able to be eliminated by using the estimated variable errors. Thus, the bounded or differentiable conditions for disturbance observer design are removed. Furthermore, the convergence of the new disturbance observer is rigorously proved based on Lyapunov stability theorem, and the tracking error can be arbitrarily small. Finally, the simulation results are given to validate the feasibility and superiority of the proposed approach.

Iterative Learning Approaches for Discrete-Time State and Disturbance Observer Design of Uncertain Linear Parameter-Varying Systems

Iterative learning approaches are well developed for the design of feedback controllers of dynamic systems which perform identical control tasks during multiple successive executions. Such tasks are characterized by identical reference trajectories in each of the iterations to be run. Exploiting this information, it becomes possible to reduce tracking errors by adapting the control signal not only on the basis of information of the state variables from the current iteration but also by accounting for the history of the tracking errors from previous trials. Although such control strategies are part of an active field of research, the corresponding dual task, namely, the design of state and disturbance observers for systems with successively repeated state trajectories has not yet received the same amount of attention. Therefore, a discrete-time iterative learning observer design, aiming at the combined state and disturbance estimation, is presented in this paper. The resulting approach is validated in numerical simulations for the simplified model of the charging/discharging dynamics of Lithium-Ion battery systems.

Piecewise Continuous -Communication Disturbance Observer Design for Networked Visual Servo Control Systems with Sampled and Variable Delayed Output

The paper deals with the state estimation of networked visual servo control systems (NVSCS) using sampled and delayed output measurements. A continuous state observer is proposed which makes possible to estimate the NVSCS state in the case of fixed sampling period and variable and bounded time delay. The stability of the new state observer is studied in detail. The performances of the proposed observer are compared by numerical simulations with those of the Lyapunov–Krasovskii state observer.DOI: http://dx.doi.org/10.5755/j01.itc.47.4.19872

Development of nonlinear disturbance observer based control and nonlinear PID: A personal note

This paper gives an overview of early development of nonlinear disturbance observer design technique and the disturbance observer based control (DOBC) design. Some critical points raised in the development of the methods have been reviewed and discussed which are still relevant for many researchers or practitioners who are interested in this method. The review is followed by the development of a new type of nonlinear PID controller for a robotic manipulator and its experimental tests. It is shown that, under a number of assumptions, the DOBC consisting of a predictive control method and a nonlinear disturbance observer could reduce to a nonlinear PID with special features. Experimental results show that, compared with the predictive control method, the developed controller significantly improves performance robustness against uncertainty and friction. This paper may trigger further research and interests in the development of DOBC and related methods, and building up more understanding between this group of control methods with comparable ones (particularly control methods with integral action).

Enhanced sensitivity shaping by data-based tuning of disturbance observer with non-binomial filter

This work presents a new method of sensitivity shaping for motion control systems with disturbance observer (DOB). Although the traditional DOB design has been proved to be an effective means of rejecting disturbances in many applications, shaping of the closed-loop sensitivity is constrained since the Q-filter in DOB is usually restricted to a standard Butterworth or binomial form, where the cutoff frequency is the only tunable parameter. To overcome this limitation and achieve better performance for more demanding motion systems, a general form of the Q-filter is employed in this work. An data-based iteratively tuning procedure is subsequently developed according to a pre-defined cost function, so that the disturbance rejection in the low-frequency band is improved while the high-frequency noise attenuation and robust stability are not compromised. This method is data-based in the sense that the sensitivity shaping process is conducted based on the input–output data collected from the operating motion system, instead of relying on the identified system model. Simulation and experimental results are presented to show the advantage of this data-based sensitivity shaping approach.

A Stability Analysis for the Acceleration-Based Robust Position Control of Robot Manipulators via Disturbance Observer

This paper proposes a new nonlinear stability analysis for the acceleration-based robust position control of robot manipulators by using Disturbance Observer (DOb). It is shown that if the nominal inertia matrix is properly tuned in the design of DOb, then the position error asymptotically goes to zero in regulation control and is uniformly ultimately bounded in trajectory tracking control. As the bandwidth of DOb and the nominal inertia matrix are increased, the bound of error shrinks, i.e., the robust stability and performance of the position control system are improved. However, neither the bandwidth of DOb nor the nominal inertia matrix can be freely increased due to practical design constraints, e.g., the robust position controller becomes more noise sensitive when they are increased. The proposed stability analysis provides insights regarding the dynamic behavior of DOb-based robust motion control systems. It is theoretically and experimentally proved that non-diagonal elements of the nominal inertia matrix are useful to improve the stability and adjust the trade-off between the robustness and noise sensitivity. The validity of the proposal is verified by simulation and experimental results.

Adaptive course control based on trajectory linearization control for unmanned surface vehicle with unmodeled dynamics and input saturation

This paper presents a novel course control strategy for unmanned surface vehicles (USV) subject to unmodeled dynamics and time-varying external disturbance. A practical adaptive course controller is proposed by trajectory linearization control (TLC) technology, neural network minimum learning parameter method (MLP), disturbance observer (DOB) and auxiliary design system. MLP and DOB are introduced to compensate for unmodeled dynamics and time-varying external disturbance, respectively. In addition, auxiliary design system is hired to deal with input saturation issue. By Lyapunov stability theory, it is proved that all the error signals in the course control system are uniform ultimate bounded. The advantages of the developed control strategy are that first, from the author’s point of view, TLC technology is applied to the field of USV motion control for the first time, which opens a new research direction of this algorithm; second, MLP with a smaller computational burden is used to replace radial basis function (RBF) neural network, which is more convenient for engineering implementation; third, the proposed scheme has strong anti-interference ability, which can compensate for the inherent defect that the USV with a smaller volume is susceptible to external disturbance. Finally, numerical simulations prove the effectiveness and correctness of the proposed control strategy.

Observer-based terminal sliding mode control of non-affine nonlinear systems: Finite-time approach

This paper studies the problem of observer based fast nonsingular terminal sliding mode control schemes for nonlinear non-affine systems with actuator faults, unknown states, and external disturbances. A hyperbolic tangent function based extended state observer is considered to estimate unknown states, which enhances robustness by estimating external disturbance. Then, Taylor series expansion is employed for the non-affine nonlinear system with actuator faults, which transforms it to an affine form system to simplify disturbance observer and controller design. A finite time disturbance observer is designed to address unknown compound disturbances, which includes external disturbances and system uncertainties. A fast nonsingular terminal sliding mode with exponential function sliding mode is proposed to address output tracking. Simulation results show the proposed scheme is effective.

Offset‐free model predictive control of diesel engine by combined design of disturbance model and observer

The diesel engine is a typical multi-input multi-output system with strong couplings, actuator constraints, and fast dynamics. The objective is to operate the engine to meet driver's speed demand and reduce exhaust emissions of nitrogen oxides (NOx) during transient process. Interactions between the actuators and nonlinear behavior of the system make the problem difficult to handle using classical control design methods. Instead, we propose an offsetfree model predictive control system. It is based on the combined design of integrating disturbance model and state observer. The dynamic observer is designed by solving an H-infinity control problem aimed at minimizing the effect of unmeasured disturbances and model mismatch on the output prediction error. The proposed approach has a low computation requirement and is suitable for implementation in the engine control unit on board. The application of this system in continuous working process by using dSPACE MicroAutoBox verified its feasibility and effectiveness for achieving precise reference tracking of engine speed and reducing emissions.

Backstepping Control with Disturbance Observer for Permanent Magnet Synchronous Motor

For the speed tracking control problem of Permanent Magnet Synchronous Motor (PMSM), a disturbance observer-based (DOB) backstepping speed tracking control method is presented in this paper. First, to reconstruct the load disturbance, a slowly time-varying disturbance observer for PMSM is constructed. Next, by stability theory, the norm of the observation error and disturbance observer design method are obtained. On the basis of these, through the designing of the virtual control input that include the reconstruction disturbances, and using backstepping control strategy, the DOB controller of the closed-loop system is proposed. The obtained controller can achieve high precision speed tracking and disturbance rejection. Finally, some results of evaluative experiments verified the effectiveness of the proposed method for high-performance control and disturbance rejection for the PMSM drive.

재귀최소자승법 기반 상태 및 외란 관측기 설계에 관한 실험 연구 : CMG 이차시스템

재귀최소자승법 기반 상태 및 외란 관측기 설계에 관한 실험 연구 : CMG 이차시스템

Observer-based backstepping boundary control for a flexible riser system

Abstract In order to achieve the disturbance rejection and vibration abatement of a flexible marine riser system, this article discusses the design of disturbance observers and controller. The riser system subjected to external disturbances is a distributed parameter system in essence and represented by infinite-dimensional equation coupled with finite-dimensional equations. In addition to designing a basic boundary disturbance observer to deal with the time-varying boundary disturbance in this paper, an innovative infinite dimensional disturbance observer is also designed to compensate for the spatially distributed disturbance. Applying these two observers as feedforward compensators, an observer-based boundary controller is formulated by means of combining backstepping technique with boundary control method. Moreover, the well-posedness of the closed-loop riser system is discussed, and simulations are presented to display the effectiveness of formulated control approach.

A Double Disturbance Observer Design for Compensation of Unknown Time Delay in a Wireless Motion Control System

Unknown time delay poses a significant challenge to the design of networked motion control systems. Moreover, modeling uncertainties, mechanical disturbance, and sensor noise coexist with time delay in such systems, which makes the controller synthesis even more challenging. It has been proven effective to model the time delay as fictitious disturbance so that a disturbance observer (DOB) can be employed to cancel the negative effect of time delay. In this brief, a new double DOB (DDOB) design is proposed by adding one more DOB into the control system to handle actual external disturbance and enable satisfactory tracking performance. Design considerations of the baseline controller and the two DOBs are illustrated, and robust stability analysis is provided to handle modeling uncertainties. A real-time wireless communication protocol, RT-WiFi, is integrated with a DC motor to examine the performance of the proposed DDOB by simulations and experiments.

Comprehensive design of uniform robust exact disturbance observer and fixed‐time controller for reusable launch vehicles

The comprehensive design of uniform robust exact disturbance observer (UREDO) and fixed-time controller for reusable launch vehicles is investigated. A UREDO which can estimate the disturbance after a fixed-time independent of the initial error is presented. Based on the disturbance estimation, a non-singular terminal sliding mode controller is designed to ensure that the guidance command can be tracked within a fixed-time in the presence of model uncertainties and external disturbances. A proof of the fixed-time convergence of the closed-loop system under the control scheme is derived with complete stability analysis using the Lyapunov technique. The features of the proposed control scheme contain that the disturbance estimation, as well as the attitude tracking, can be achieved within a fixed-time, which is independent of initial conditions and the derivative information of states is not essential, which is valuable in engineering application. Numerical simulations are performed to demonstrate the fixed-time convergence performance of the proposed control scheme.

DO-DAT: A MATLAB toolbox for design & analysis of disturbance observer

Abstract Although the disturbance observer (DOB)-based controller has been extensively applied and various theoretical results on the DOB have been presented, the exclusive, user-friendly, and unified tool for the computer-aided design of DOB has not been developed yet. In this paper, the MATLAB toolbox DO-DAT (Disturbance Observer - Design & Analysis Toolbox) is introduced. Particularly, we explain the way of using the toolbox and present the applications of main functions in terms of the stabilization of the system and the time-domain performance analysis.

Design of Novel Fixed-time Disturbance Observer and Improved Sliding Mode Controller for PMSM

This paper presents a novel fixed-time disturbance observer (FTDOB) and an improved sliding mode controller (IPSMC) with saturation function of adaptive variable fractional power times for the permanent magnet synchronous motor (PMSM) to solve the problems that PMSM are susceptible to parameter uncertainties and disturbances of external loads. The proposed FTDOB utilizes the uniform convergent part to drive the error trajectories into a compact set and then switches to the finite time convergent part to achieve exact convergence. It can achieve exact disturbance estimation within finite time independent of initial estimation error. In addition, the improved sliding mode control law for speed controller is developed through combining the rotate speed and q-axis stator current’s second-order model. A saturation function of adaptive variable fractional power times is designed to realize the coordinated control between chattering and tracking accuracy. Numerical simulations are provided to demonstrate that IPSMC+FTDOB is robust to the parameter perturbation, model errors and external disturbances, and it can effectively weaken the chattering and ensure the steady speed precision of PMSM.

Disturbance observer design and vibration control for a flexible aircraft wing

This study focuses on the disturbance observer design and vibration control problems for a flexible aircraft wing system. The flexible aircraft wing is modeled as a coupled twist-bending infinite dimensional distributed parameter system. The dynamic equations and boundary conditions are described by partial differential equations and ordinary differential equations, respectively. In this paper, an infinite dimensional disturbance observer is proposed to estimate both the boundary disturbances and the distributed spatiotemporally varying disturbances. Considering the coupling between the bending deformation and the twist deformation, a boundary controller is proposed to suppress the vibration and inhibit the adverse effects of external disturbances. By using the proposed disturbance observer and controller, the uniform boundednesss of the closed-loop system is validated through theoretical analysis. Finally, simulation results are carried out to illustrate the effectiveness of the proposed infinite dimensional disturbance observer and boundary controller.