Class Of Disturbances Research Articles

Asymptotic rejection of unmatched general periodic disturbances in a class of nonlinear systems

The study deals with asymptotic rejection of unmatched general periodic disturbances in nonlinear systems in the output feedback form. The class of disturbances covers asymmetric wave forms in the half period such as alternating sawtooth wave form, as well as disturbances with symmetric half-period wave forms such as sinusoidal disturbances and triangular disturbances etc. The amplitude and phase of the disturbances are unknown. An equivalent input disturbance is introduced based on the periodic steady-state solutions of the system state variables. Conditions are identified for the existence of such an equivalent input disturbance. The half-period alternating feature is ensured for the equivalent input disturbance based on the fact that the steady state solutions of stable linear systems are shown to be half-period alternating if the inputs are. As the half-period alternating property is persevered in the equivalent input disturbances, recently proposed asymptotic rejection, based on the half-period integration and delay operations, of general periodic disturbances with asymmetric half-period wave forms can be applied, with a careful consideration of the phase offsets in the equivalent input disturbances. The proposed control design with the disturbance estimation asymptotically rejects the unknown disturbance and ensures the overall stability of the system.

A limit cycle approach for the parametric identification of hysteretic systems

This paper deals with the parametric identification of the Bouc–Wen model for smooth hysteresis. The interest of the problem stems from the fact that the Bouc–Wen model has been used experimentally to represent various hysteretic systems during the last few years. However, identifying the parameters of this model is not a trivial task due to the nonlinearity of the model. In the current literature, most methods devoted to the parametric identification of the Bouc–Wen model rely mainly on numerical simulations, and do not offer, to a large extent, a rigorous proof of the convergence of the estimated parameters to the true ones. This paper presents a new identification method that guarantees the exact determination of the parameters in the absence of perturbations. It is also shown that this method is robust with respect to a class of disturbances of practical interest. The applicability of this method is illustrated by means of experiments.

On the disturbance response and external stability of a saturating static-feedback-controlled double integrator

In this note, we identify a broad class of small but non-vanishing disturbances for which the state of a saturating static-feedback-controlled double integrator remains bounded.

Control with guaranteed performance for dual-rate sampled-data systems under stochastic disturbances

The paper considers the digital control of a continuous-time process under stochastic disturbances. The problem consists in finding a controller that guarantees a certain performance of the closed loop, while the disturbances belong only to a given class of disturbances. The digital controller has two parts with different sampling rates, where one rate is a multiple of the other one. The solution is found by applying the parametric transfer function (PTF) concept and the method of guaranteed performance control.

2A1-D09 不整地における大型ロボットのバランス制御(ヒューマノイド)

A humanoid robot should be able to keep balance in the presence of various disturbances. We address here a class of disturbances that are due to uneven ground, when the usual ZMP methods are not applicable. The equation of motion has the form of that of an underactuated system, e.g. of a free-flying or a flexible base/link robot. We apply an inertial coupling based control method used in previous works for vibration suppression of flexible base robots. Simulations with a planar robot are presented for two types of disturbances: (i) rotating surface and (ii) jointed-toe foot model. In both cases, balance can be recovered in a stable and efficient way.

Compressor Surge Suppression by Second-Order Sliding Mode Control Technique

Abstract Surge is one of the two main dynamic instabilities that can occur in compressor systems (the other is the rotating stall) preventing their satisfactory operation and being potential cause of serious damages. In this paper we consider a Close Coupled Valve (CCV) as actuator, and we suggest the use of a second-order sliding-mode (2-SM) technique for the active control of the surge phenomenon. We refer to the Moore-Greitzer model with cubic compressor characteristics, and we show that the proposed technique can drive the system towards a stable operating point by rejecting a significant class of persistent pressure and flow disturbances acting on the system. Furthermore, the perfect knowledge of the compressor and load characteristics is not required to design the controller.

Attitude Tracking With Adaptive Rejection of Rate Gyro Disturbances

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The classical attitude control problem for a rigid body is revisited under the assumption that measurements of the angular rates obtained by means of rate gyros are corrupted by harmonic disturbances, a setup of importance in several aerospace applications. This note extends previous methods developed to compensate bias in angular rate measurements by accounting for a more general class of disturbances, and by allowing uncertainty in the inertial parameters. By resorting to adaptive observers designed on the basis of the internal model principle, it is shown how converging estimates of the angular velocity can be used effectively in a passivity-based controller yielding global convergence within the chosen parametrization of the group of rotations. Since a persistence of excitation condition is not required for the convergence of the state estimates, only an upper bound on the number of distinct harmonic components of the disturbance is needed for the applicability of the method. </para>

Probabilistic reversing operation with fidelity and purity gain for macroscopic quantum superposition

It is shown that a large class of weak disturbances on macroscopic quantum superpositions can be canceled by a probabilistic reversing operation on the system. We illustrate this for spin systems undergoing an Ising-type interaction with the environment and demonstrate that both the fidelity to the original state and the purity of the amended state can simultaneously be increased by the reversing operation. A possible experimental scheme to implement our scheme is discussed.

Asymptotic rejection of a class of periodic disturbances in nonlinear output-feedback systems

Asymptotic rejection of periodic disturbances whose basic wave patterns can be described by odd functions is considered. This class of disturbances covers asymmetric waveforms in a half-period such as sawtooth waveforms, as well as disturbances with symmetric half-period waveforms such as sinusoidal and triangular disturbances. The systems considered can be transformed to a nonlinear output-feedback form. The amplitude and phase of the disturbances are unknown. The newly proposed half-period integration technique is used to estimate the unknown disturbances in the systems, together with observer design techniques to deal with nonlinearity. The proposed control design with disturbance estimation asymptotically rejects the unknown disturbance, and ensures the overall stability of the system.

Asymptotic rejection of asymmetric periodic disturbances in output-feedback nonlinear systems

This paper deals with asymptotic rejection of periodic disturbances which may have asymmetric basic wave patterns. This class of disturbances covers asymmetric wave forms in the half-period such as alternating sawtooth wave form, some disturbances which are generated from nonlinear oscillation such as Van de Pol oscillators, as well as disturbances with symmetric half-period wave forms such as sinusoidal disturbances and triangular disturbances etc. The systems considered in this paper can be transformed to the nonlinear output feedback form. The amplitude and phase of the disturbances are unknown. The novel concept of integral phase shift is introduced together with the newly introduced half-period integration operator to investigate the invariant properties of asymmetric periodic disturbances. They are used for the estimation of unknown disturbances in the systems, together with observer design techniques to deal with nonlinearity. The proposed control design with the disturbance estimation asymptotically rejects the unknown disturbance, and ensures the overall stability of the system.

A Novel Detection and Classification Algorithm for Power Quality Disturbances using Wavelets

This study presents a novel method to detect and classify power quality disturbances using wavelets. The proposed algorithm uses different wavelets each for a particular class of disturbance. The method uses wavelet filter banks in an effective way and does multiple filtering to detect the disturbances. A qualitative comparison of results shows the advantages and drawbacks of each wavelet when applied to the detection of the disturbances. This method is tested for a large class of test conditions simulated in MATLAB. Power quality monitoring together with the ability of the proposed algorithm to classify the disturbances will be a powerful tool for the power system engineers.

Adaptive control for a class of chaotic systems with nonlinear inputs and disturbances

In this paper, an adaptive controller design method based on hyperstability theory is proposed for a class of unified chaotic systems with so-called sector-bounded inputs and disturbances. Under the norm-bounded assumption of disturbances, for the controlled system, system states can be regulated to zero levels asymptotically in the presence of this class of disturbances. To show the validity and feasibility of the proposed adaptive controller, some simulations on controlling different chaotic systems with disturbances, are made and investigated.

Optimality of First-Order ILC Among Higher Order ILC

Higher order iterative learning control (HO-ILC) algorithms use past system control information from more than one past iterative cycle. This class of ILC algorithms have been proposed aiming at improving the learning efficiency and performance. This paper addresses the optimality of HO-ILC in the sense of minimizing the trace of the control error covariance matrix in the presence of a class of uncorrelated random disturbances. It is shown that the optimal weighting matrices corresponding to the control information associated with more than one cycle preceding the current cycle are zero. That is, an optimal HO-ILC does not add to the optimality of standard first-order ILC in the sense of minimizing the trace of the control error covariance matrix. The system under consideration is a linear discrete-time varying systems with different relative degree between the input and each output

Weakly nonlinear shock propagation in slowly varying one-dimensional flows

A theoretical model for the linear and nonlinear evolution of acoustic perturbations in nonuniform one-dimensional isentropic flows is developed. On the assumption that the length scale of the mean flow greatly exceeds that of the imposed disturbances, it is shown that the propagation of linear waves can be described in a closed form that is consistent with the conservation of acoustic power. This permits the application of a “nonlinearization” procedure (Landau [J. Phys. USSR 9, 496 (1945)],Whitham [Proc. R. Soc. London, Ser. A 201, 89 (1950)]), wherein the linear functional forms are assumed to hold for weakly nonlinear simple-wave disturbances, and the effects of amplitude on the wave speed are included to leading order. When nonlinear steepening results in the formation of shocks, they are fitted into the solution using the Rankine-Hugoniot relations. The method is applicable to arbitrary waveforms and, in the present study, the evolution of hump-like and periodic disturbances through nonuniform flows is examined. Focusing on the latter class of disturbances, the parametric range of applicability of the asymptotic theory is assessed by comparing the model predictions with numerical solutions of the Euler equations for different excitation frequencies and amplitudes. The usefulness of the present approach is illustrated by its application to periodic shocks propagating through accelerating and diffusive mean flows.

Asymptotic Rejection of General Periodic Disturbances in Output-Feedback Nonlinear Systems

This note deals with asymptotic rejection of general periodic disturbances in nonlinear systems. A novel approach based on integrations over the half of disturbance period is proposed to estimate disturbances which may not be harmonic or even smooth. The proposed algorithm uses the period and the knowledge of the basic disturbance patterns, while the amplitude and phase of the disturbances are unknown, and they are estimated. Based on the estimated disturbance, the disturbance rejection algorithm is then proposed for linear systems and nonlinear systems in the output feedback format, which asymptotically rejects the periodical disturbances. The proposed algorithm extends asymptotic rejection of unknown disturbances from sinusoidal disturbances to a more general class of periodical disturbances which includes zero-mean square waves, symmetric triangular waves etc.

Feedback control and adaptive control of the energy resource chaotic system

Abstract In this paper, the problem of control for the energy resource chaotic system is considered. Two different method of control, feedback control (include linear feedback control, non-autonomous feedback control) and adaptive control methods are used to suppress chaos to unstable equilibrium or unstable periodic orbits. The Routh–Hurwitz criteria and Lyapunov direct method are used to study the conditions of the asymptotic stability of the steady states of the controlled system. The designed adaptive controller is robust with respect to certain class of disturbances in the energy resource chaotic system. Numerical simulations are presented to show these results.

サンプル値Ｈ∞繰返し制御系の設計法

A design procedure is proposed for digital repetitive controllers satisfying (i) asymptotic rejection of a class of periodic disturbances and (ii) a sampled-data H∞ norm specification. The synthesis problem is formulated by extending the step disturbance rejection problem. A necessary condition for the periodic disturbance so that the synthesis problem has a solution is derived. The synthesis problem is finally reduced to a sampled-data H∞ control problem with a design parameter which can be used for adjusting the performance of the periodic disturbance rejection. The effectiveness of the proposed method is confirmed by a numerical example.

The Structure of Posttraumatic Stress Disorder

Latent structure analysis of DSM-IV posttraumatic stress disorder (PTSD) can help clarify how persons who experience traumatic events might be sorted into clusters with respect to their symptom profiles. Classification of persons exposed to traumatic events into clinically homogeneous groups would facilitate further etiologic and treatment research, as well as research on the relationship of trauma and PTSD with other disorders. To examine empirically the structure underlying PTSD criterion symptoms and identify discrete classes with similar symptom profiles. Data on PTSD symptoms from trauma-exposed subsets of 2 community samples were subjected to latent class analysis. The resultant classes were studied in associations with trauma type and indicators of impairment. The first sample is from the Detroit Area Survey of Trauma (1899 trauma-exposed respondents with complete data) and the second is from a mid-Atlantic study of young adults conducted by The Johns Hopkins University Prevention Research Center, Baltimore, Md (1377 trauma-exposed respondents with complete data). Respondents in the 2 community samples who experienced 1 or more qualifying PTSD-level traumatic events. Number, size, and symptom profiles of latent classes. In both samples, analysis yielded 3 classes: no disturbance, intermediate disturbance, and pervasive disturbance. The classes also varied qualitatively, with emotional numbing distinguishing the class of pervasive disturbance, a class that approximates the subset with DSM-IV PTSD. Members of the pervasive disturbance class were far more likely to report use of medical care and disruptions in life or activities. The 3-class structure separates trauma-exposed persons with pervasive disturbance (a class that approximates DSM-IV PTSD) from no disturbance and intermediate disturbance, a distinction that also helps identify population subgroups with low risk for any posttrauma disturbance. The results suggest that the structure of PTSD is ordinal and configurational and that emotional numbing differentiates the class with pervasive disturbance. These results should motivate prospective research of persons who have experienced trauma to trace the emergence of posttrauma symptoms and the timing of emotional numbing relative to other symptoms.

Decentralized Adaptive Robust State Feedback for Uncertain Large-Scale Interconnected Systems with Time Delays

The problem of the decentralized robust control is considered for a class of large-scale time-varying systems withdelayed state perturbations and external disturbances in the interconnections. Here, the upper bounds of the delayed stateperturbations and external disturbances in the interconnections are assumed to be unknown. Adaptation laws areproposed to estimate such unknown bounds; by making use of the updated values of the unknown bounds, decentralized linear and nonlinear memoryless robust state feedback controllers are constructed. Based on Lyapunov stability theoryand Lyapunov–Krasovskii functionals, as well as employing the proposed decentralized nonlinear robust state feedback controllers, it is shown that the solutions of the resulting adaptive closed-loop large-scale time-delay system can be guaranteed to be uniformly bounded and that the states converge uniformly and asymptotically to zero. It is also shown that the proposed decentralized linear robust state feedback controllers can guarantee the uniform ultimate boundedness of the resulting adaptive closed-loop large-scale time-delay system. Finally, a numerical example is given to demonstrate the validity of the results.

A pivot nonlinearity compensation by use of variable structure estimator for hard disk drives

This paper discusses robust seeking control of hard disk drives by the use of a variable structure multi-rate estimator (VSME). Compensation of pivot nonlinearity is one concern in the design of the seeking control, systems. Pivot nonlinearity is subject to uncertainties, and is difficult to deal with by a linear controller. The VSME estimates a class of uncertain disturbances and nonlinearities and yields compensation current through the linear feedback gain, which reduces the residual vibration and error during settling. Several experiments were carried out on several drives including a 3.5 in. 7,200 rpm drive. These experiments confirmed that the off-track probability after settling, which is defined by the number of seek failures over all trials, is much reduced to less than 1% when the drive is operated under a special temperature condition that increases pivot nonlinearity while the corresponding performance of a conventional linear controller is 12%. The seek failure is defined as the case when the position cannot be maintained within ±2.5% of a track pitch for a certain duration after track seeking mode.