Disturbance Observer Design Research Articles

Memoryless disturbance-observer-based adaptive tracking of uncertain pure-feedback nonlinear time-delay systems with unmatched disturbances

This paper presents a delay-independent nonlinear disturbance observer (NDO) design methodology for adaptive tracking of uncertain pure-feedback nonlinear systems in the presence of unknown time delays and unmatched external disturbances. Compared with all existing NDO-based control results for uncertain lower-triangular nonlinear systems where unknown time delays have been not considered, the main contribution of this paper is to develop a delay-independent design strategy to construct an NDO-based adaptive tracking scheme in the presence of unknown time-delayed nonlinearities and non-affine nonlinearities unmatched in the control input. The proposed delay-independent scheme is constructed by employing the appropriate Lyapunov-Krasovskii functionals and the same function approximators for the NDO and the controller. It is shown that all the signals of the closed-loop system are semi-globally uniformly ultimately bounded and the tracking error converges to an adjustable neighborhood of the origin.

Design of Disturbance Observer Based Sliding Mode Control for Fuzzy Systems

In this paper, the disturbance observer (DO) based sliding mode control (SMC) for fuzzy system is proposed. Compared with conventional sliding mode control, this approach incorporates the disturbance estimates into the design of the sliding surface and sliding mode controllers. The new approach can deal with the problem of mismatched disturbance for fuzzy system effectively while those problems can’t be solved by traditional sliding mode control. The disturbance observer, sliding surface and DO-based sliding mode controllers are proposed in the paper, respectively. An adaptive DO-based sliding mode controller is also established in order to deal with the problem about unknown upper norm bound of disturbance. Finally, the effectiveness of the new approach is illustrated by the ball-beam system.

Finite-Time Disturbance Observer Design and Attitude Tracking Control of a Rigid Spacecraft

This paper considers the problem of finite-time disturbance observer (FTDO) design and the problem of FTDO based finite-time control for systems subject to nonvanishing disturbances. First of all, based on the homogeneous systems theory and saturation technique, a continuous FTDO design approach is proposed. Then, by using the proposed FTDO design approach, a FTDO is constructed to estimate the disturbances that exist in a rigid spacecraft system. Furthermore, based on a baseline finite-time control law and a feedforward compensation term produced by the FTDO, a composite controller is constructed for the rigid spacecraft system. It is shown that the proposed composite controller will render the rigid spacecraft track the desired attitude trajectory in a finite-time. Simulation results are included to demonstrate the effectiveness of the proposed control approach.

미지의 제어 방향성과 비어파인 비선형성을 고려한 신경망 기반 외란 관측기와 추종기 설계

A disturbance-observer-based adaptive neural tracker design problem is investigated for a class of perturbed uncertain non-affine nonlinear systems with unknown control direction. A nonlinear disturbance observer (NDO) design methodology using neural networks is presented to construct a tracking control scheme with the attenuation effect of an external disturbance. Compared with previous control results using NDO for nonlinear systems in non-affine form, the major contribution of this paper is to design a NDO-based adaptive tracker without the sign information of the control coefficient. The stability of the closed-loop system is analyzed in the sense of Lyapunov stability.

Semi‐Global Exquisite Disturbance Attenuation Control for Perturbed Uncertain Nonlinear Systems

AbstractMotivated by the design of disturbance observers with active elimination of the adverse effects caused by system uncertainties and disturbances, the problem of semi‐global exquisite disturbance attenuation control for a class of perturbed nonlinear systems is investigated in this paper. A feedback domination technique is utilized to integrate with the disturbance observer design and then a general composite active anti‐disturbance control law is proposed. With a recursive design procedure, the mismatched lumped disturbances are compensated in a novel step‐by‐step way while the non‐vanishing nonlinearities are treated via a feedback domination approach, rather than utilizing the straightforward feedback linearization method. The closed‐loop control performance and disturbance rejection ability now can be improved. A rigorous stability analysis assures the effectiveness of the proposed strategy. Numerical simulation results affirm the improved control and disturbance rejection performances with respect to several related existing results.

Experimental investigation of shaping disturbance observer design for motion control of precision mechatronic stages with resonances

In this paper, shaping disturbance observer (SDOB) is investigated for precision mechatronic stages with middle-frequency zero/pole type resonance to achieve good motion control performance in practical manufacturing situations. Compared with traditional standard disturbance observer (DOB), in SDOB a pole-zero cancellation based shaping filter is cascaded to the mechatronic stage plant to meet the challenge of motion control performance deterioration caused by actual resonance. Noting that pole-zero cancellation is inevitably imperfect and the controller may even consequently become unstable in practice, frequency domain stability analysis is conducted to find out how each parameter of the shaping filter affects the control stability. Moreover, the robust design criterion of the shaping filter, and the design procedure of SDOB, are both proposed to guide the actual design and facilitate practical implementation. The SDOB with the proposed design criterion is applied to a linear motor driven stage and a voice motor driven stage, respectively. Experimental results consistently validate the effectiveness nature of the proposed SDOB scheme in practical mechatronics motion applications. The proposed SDOB design actually could be an effective unit in the controller design for motion stages of mechanical manufacture equipments.

Design and implementation of a modified communication disturbance observer for teleoperation systems

In this paper, a novel structure for a communication disturbance observer in teleoperation systems is proposed to achieve robust stability. A time delay compensation method based on the concept of network disturbance and a communication disturbance observer (CDOB) has been proposed in past research. Unlike model-based approaches, it works without a time delay model. Therefore, it can be implemented in teleoperation systems with unknown and time-varying delay. However, it has been observed that the system model errors and external disturbances seriously affect the steady-state characteristics. Hence, in this paper, to achieve robustness against disturbance and model uncertainty, the structure of the conventional CDOB is modified and a new structure for the CDOB in teleoperation systems is proposed, which uses the slave's delayed torque instead of its delayed position for time delay compensation. The desired transient response characteristic is achieved by designing the controller parameters. The time delay in the communication channel has been simulated by PCs in past studies, but in this paper, by implementing the communication channel through the TCP/IP protocol in the experimental setup, the effectiveness of the proposed structure is studied in the presence of real time delay and compared with the Smith predictor, the conventional CDOB, and other structures of CDOBs.

Finite-time output regulation for linear 2×2 hyperbolic systems using backstepping

This contribution presents the backstepping design of output feedback regulators for boundary controlled linear 2×2 hyperbolic systems, that achieve regulation in finite time. It is assumed that the disturbances can act in-domain, at both boundaries and at the output to be controlled. The latter need not be available for measurement and consists of in-domain pointwise, distributed or boundary outputs. Firstly, a solution of the finite-time state feedback regulator problem is given on the basis of the regulator equations. They are formulated in backstepping coordinates so that a solution is attainable in closed-form. This leads to a very straightforward regulator design for 2×2 hyperbolic systems with a general class of outputs. Then, a finite-dimensional reference observer that converges in finite-time is introduced, which consists of two observers and a delay. This result is extended to the backstepping design of finite-time disturbance observers for 2×2 hyperbolic systems with a collocated measurement. In particular, two backstepping disturbance observers are determined so that after introducing a delay the disturbance model and plant states can be estimated in finite-time. Hence, by combining the state feedback regulator with these observers a finite-time output feedback regulator is obtained. For the state feedback regulator and the disturbance observer existence conditions are derived in terms of the plant transfer behaviour. A simple example with an in-domain pointwise and distributed output illustrates the theoretical results.

Disturbance observer and finite-time tracker design of disturbed third-order nonholonomic systems using terminal sliding mode

This paper proposes a novel recursive terminal sliding mode structure for tracking control of third-order chained–form nonholonomic systems in the presence of the unknown external disturbances. Finite-time convergence of the disturbance approximation error is guaranteed using the designed disturbance observer. Under the proposed terminal sliding model tracking control technique, the finite-time convergence of the states of the closed-loop system is guaranteed via Lyapunov analysis. A new reaching control law is proposed to guarantee the existence of the sliding mode around the recursive TSM surface in a finite-time. Simulation results are illustrated on a benchmark example of third-order chained-form nonholonomic systems: a wheeled mobile robot. The results demonstrate that the proposed control technique achieves promising tracking performance for nonholonomic systems.

Integrated Finite-Time Disturbance Observer and Controller Design for Reusable Launch Vehicle in Reentry Phase

AbstractAn integrated finite-time disturbance observer (FDO) and attitude controller is designed for a reusable launch vehicle (RLV) in this paper. In accordance with the multiple-timescale features, RLV attitude dynamics are divided into an outer-loop subsystem and an inner-loop subsystem. Based on the recently developed sliding mode control (SMC), a novel multivariable supertwisting sliding mode controller driven by a FDO is designed to achieve a fast and accurate reentry attitude tracking. This integrated design can generate a continuous control law which has excellent robustness to uncertainty and disturbances with known bounds while achieving an arbitrarily fast convergence. The finite-time stability of the overall system is proved by using the Lyapunov function technique and the multiple-timescale separation principle. In addition, an optimal control allocation for allocating torque commands into aerodynamic surface deflection commands with constraints is also proposed. Finally, the effectiveness an...

On Relationship Between Time-Domain and Frequency-Domain Disturbance Observers and Its Applications

This paper provides a generic analysis of the relationship between time- and frequency-domain disturbance observer (DOB) design methodology. It is discovered that the traditional frequency-domain DOBs using a low-pass filter with unity gain can only handle disturbances satisfying matching condition, while the traditional time-domain DOBs always generate an observer with a high-order. A functional disturbance observer (FDOB) is proposed to improve the existing results together with its design guideline, frequency analysis, and existence condition. Compared with the existing frequency-domain DOBs, the proposed FDOB can handle more classes of disturbances, while compared with the existing time-domain DOBs, the proposed FDOB can generate an observer with a lower-order. Numerical examples are presented to illustrate the main findings of this paper including a rotary mechanical system of nonminimum phase.

한 바퀴 밸런싱 로봇의 조향 안정화를 위한 외란관측기 설계 및 실험 연구

한 바퀴 밸런싱 로봇의 조향 안정화를 위한 외란관측기 설계 및 실험 연구

Boundary and Distributed Control for a Nonlinear Three‐Dimensional Euler‐Bernoulli Beam Based On Infinite Dimensional Disturbance Observer

AbstractControl problems in spatially distributed systems are challenging because the disturbance is of infinite dimensions. To this end, this paper discusses an infinite dimensional disturbance observer design, which is illustrated based on a partial differential equation (PDE) model of a nonlinear three‐dimensional Euler‐Bernoulli beam. The basic idea of the observer design is to modify the estimations based on the difference between the estimated output and actual output. Moreover, an auxiliary parameter system is established to help with the analysis. Then a Lyapunov function candidate consisting of the energy of the system, the observer error and an auxiliary term is given. After a series of analyses of the function, distributed controllers and boundary controllers based on the proposed observer are given to restrain vibration. Finally, by numerical simulations, the convergence of the observer is demonstrated, and the efficacy of control performance is also shown.

DOB Fuzzy Controller Design for Non-Gaussian Stochastic Distribution Systems Using Two-Step Fuzzy Identification

This paper presents a novel non-Gaussian stochastic control framework for the problem of disturbance estimation and rejection by combining fuzzy identification technology with disturbance observer design. First, fuzzy logic models are used to approximate the output probability density functions (PDFs) of non-Gaussian processes such that the task of PDF shape control can be reduced to a fuzzy weight dynamics modeling and control problem. Next, Takagi–Sugeno fuzzy models with multiple disturbances are employed to describe the nonlinear relations between fuzzy weight dynamics and the control input, in which a novel disturbance-observer-based PI-type fuzzy feedback controller is designed to ensure the system stability and convergence of the tracking error to zero. Meanwhile, the disturbance estimation and attenuation performance as well as the state constrained requirement can also be guaranteed. Moreover, the novel composite observer is constructed by augmenting the disturbance estimation into the full-state estimation. The satisfactory tracking performance and full-state observation effect can be achieved by the designed optimization algorithm. Finally, simulations for paper-making process are given to show the efficiency of the proposed approach.

Dual-rate-loop control based on disturbance observer of angular acceleration for a three-axis aerial inertially stabilized platform

This paper presents a dual-rate-loop control method based on disturbance observer (DOB) of angular acceleration for a three-axis ISP for aerial remote sensing applications, by which the control accuracy and stabilization of ISP are improved obviously. In stabilization loop of ISP, a dual-rate-loop strategy is designed through constituting inner rate loop and the outer rate loop, by which the capability of disturbance rejection is advanced. Further, a DOB-based on angular acceleration is proposed to attenuate the influences of the main disturbances on stabilization accuracy. Particularly, an information fusion method is suggested to obtain accurate angular acceleration in DOB design, which is the key for the disturbance compensation. The proposed methods are theoretically analyzed and experimentally validated to illustrate the effectiveness.

Reduced-order disturbance observer design for discrete-time linear stochastic systems

Conventional disturbance observers for discrete-time linear stochastic systems assume that the system states are fully estimable and the disturbance estimate is dependent on the estimated system states, hereafter termed full-order disturbance observers (FODOs). This paper investigates the design of reduced-order disturbance observers (RODOs) when the system state variables are not fully estimable. An existence condition of RODOs is established, which is shown to be more easily satisfied than that of conventional FODOs and consequently it has substantially extended the scope of applications of disturbance observer theory. Then a set of recursive formulae for the RODO is developed for online applications. Finally, it is further shown that the conventional FODOs are a special case of the proposed RODO in the sense that the former reduces to the RODO when the states become fully estimable in the presence of disturbances. Examples are given to demonstrate the effectiveness and advantages of the proposed approach.

Disturbance Observer Based Optimal Controller Design for Active Suspension Systems

This paper is concerned with the design of disturbance observer based optimal controller for an active control problem of a vehicle suspension system with saturated actuators against magnitude bounded disturbances. A quarter car model presented to analyze performance of proposed controller against bump road profile. Proposed control scheme composed of a disturbance observer and a control law with a state feedback and disturbance feedforward. Gain matrices belong to disturbance observer and the control law are simultaneously computed to minimize L2 gain of the closed loop system from disturbances to performance outputs by Linear Matrix Inequalities (LMIs) constraints. Finally, numerical simulations are carried out to demonstrate performance of proposed controller.

Disturbance Observer Design for Utilizing of Time-delayed Vision Measurements in High Dynamical Systems

The utilization of vision information for control in intelligent technical applications with high dynamics has been a central issue. The main obstacles are the low sampling rate of the cameras (about 60Hz of a commercial camera) compared to the required sampling rate of the high dynamic applications (over 1kHz) and the time-delayed measurements due to the image processing. A model-based Event-Triggered Observer (ETO) [12] has been proposed for linear systems to observe and predict the undelayed continuous state variables of the system from the sampled and delayed measurements where the sampling rate and the delay- time can be constant or variable. However, the disturbances like the sensor noise and the perturbations of the environment were not handled within [12]. As is well known, the disturbances decline the performance of the model-based observer. To keep the performance of the state-estimation and prediction, an effective solution is to adopt into account the unknown dynamic effects due to the disturbances by integrating them into the state-estimation. A survey [13] has shown different methods of dealing with the disturbance estimation to improve the accuracy of the estimation of the system internal states. Unlike other mentioned methods in [13], the so-called Unknown Input Observer (UIO), shows significant advantages with the ability to estimate the unknown input disturbances and the system internal states simultaneously by augmenting the state space of a classical state observer like Luenberger-Observer with a disturbance model [14,15]. In this paper, an Extended Event-Triggered Observer (EETO) is proposed, which based on the proposed ETO in [12] and is extended with an UIO. The new proposed EETO can estimate undelayed continuous state variables from the time-delayed measurements under the disturbances. An example system with a second-order delay behavior is simulated, whose output is sampled and delayed. The simulation results show the performance of the proposed Extended Event-Triggered Observer.

操舵場面に応じ運転負荷軽減を目指したステアリング機構特性に補償するEPS制御設計方法

This paper proposes the steering characteristic compensation functions to adapt the driving situations by electric power steering (EPS). The desired compensatory handling characteristics are defined depending on the compensatory handling situations. Therefore, compensatory handling situations are divided into on center region, off center region and outside of off center region and discussed the influence of steering characteristic. In on center area, stick slip phenomenon is caused by combination of steering friction and high hand and arm system compliance with relaxed muscle condition. For this problem, torsion bar damping control is proposed and its effectiveness is demonstrated by simulation. In off center region, both steering feedback and low steering effort which are normally considered as trade-off are required. To solve this problem, structural damping which characteristic is Coulomb's friction increasing according to self-aligning torque is effective. Thus, structural damping compensation function is proposed by applying disturbance observer design technique and its feasibility is demonstrated by experiments. In outside of off center region, it is showed that the power assist characteristic function design contributes the driver recognition of tire grip condition by letting the driver estimate future torque based on linear tire characteristic.

Consensus Disturbance Rejection With Disturbance Observers

This paper deals with consensus disturbance rejection of network-connected dynamic systems using disturbance observers. The control objective of consensus disturbance rejection is to achieve a common state trajectory for the network-connected subsystems that are under deterministic disturbances. The difference from the existing disturbance rejection methods is that only the relative state information is used for disturbance rejection, and as a consequence of using the relative state information, only the part of the disturbances that affect the common trajectories will be rejected. The conditions for designing disturbance observers for consensus control are identified for networked-connected multiagent systems. Certain features of the individual subsystems are analyzed for possible implementation of disturbance-observer-based rejection, and the disturbance observers are designed based on the relative state information obtained from the neighboring subsystems under different network connections. When the network connectivity is available for the disturbance observer design, consensus disturbance rejection is achieved for a directed network with a spanning tree. A fully distributed consensus disturbance rejection design is presented for an undirected network with the use of adaptive parameters for the estimation of the unknown network connectivity. Disturbance observers are also proposed for disturbance rejection in the leader–follower consensus control.