Stability Of Adaptive System Research Articles

Comb-partitioned frequency-domain constraint adaptive algorithm for active noise control

Active noise control (ANC) is gaining credence as an effective approach in mitigating low-frequency urban noise. Current ANC algorithms that attenuate noise across the full audio frequency band, often exert control effort excessively at higher frequencies. Moreover, such unrestrained control unavoidably attenuates some critical sounds, such as alarms and warning signals. In practice, excessive control effort in ANC usually results in output-saturation distortion, which affects the adaptive system stability and degrades the residual audio quality. To provide greater flexibility of control in frequency bands of interest without incurring output saturation, this paper proposes two variants of the filtered reference comb-partitioned frequency-domain adaptive filter (FxCFDAF) algorithm, namely the leaky FxCFDAF and drop-out FxCFDAF algorithms, which exert output-effort constraint at the control filter in the frequency domain. In addition, the comb-partitioning approach in the proposed FxCFDAF algorithms is delayless and computationally-efficient, which are essential for practical implementation, unlike the conventional frequency-domain adaptive algorithm. Experimental simulations carried out on measured primary and secondary paths validate the proposed algorithms’ advantage over the conventional FxLMS algorithm in mitigating large-amplitude noise without output saturation.

Structural-Identification Aspects of Decision-Making in Systems with Bouc-Wen Hysteresis

Considering the structural analysis problem of systems properties with Bouc-Wen hysteresis (BWH), various approaches are proposed for the identification of BWH parameters. The applied methods and algorithms are based on the design of parametric models and consider a priori information and the results of data analysis. Structural changes in the BWH form a priori. Methods for the Bouc-Wen model (BWM) identification and its structure estimation are not considered under uncertainty. The study’s purpose is the analysis the structural problems of the Bouc-Wen hysteresis identification. The analysis base is the application of geometric frameworks (GF) under uncertainty. Methods for adaptive estimation parameters and structural of BWM were proposed. The adaptive system stability is proved based on vector Lyapunov functions. An approach is proposed to estimate the identifiability and structure of the system with BWH. The method for estimating the identifiability degree based on the analysis of GF is considered. BWM modifications are proposed to guarantee the system’s stability and simplify its description.

An Adaptive Semiactive Control Algorithm for Magnetorheological Suspension Systems

In this paper, we will present a nonlinear-model-based adaptive semiactive control algorithm developed for magnetorheological (MR) suspension systems exposed to broadband nonstationary random vibration sources that are assumed to be unknown or not measurable. If there exist unknown and∕or varying parameters of the dynamic system such as mass and stiffness, then the adaptive algorithm can include on-line system identification such as a recursive least-squares method. Based on a nonparametric MR damper model, the adaptive system stability is proved by converting the hysteresis inherent with MR dampers to a memoryless nonlinearity with sector conditions. The convergence of the adaptive system, however, is investigated through a linearization approach including further numerical illustration of specific cases. Finally the simulation results for a magnetorheological seat suspension system with the suggested adaptive control are presented. The results are compared with low-damping and high-damping cases, and such comparison further shows the effectiveness of the proposed nonlinear model-based adaptive control algorithm for damping tuning.

유압 굴삭기의 궤적 추종을 위한 강인 제어

This paper studies the coordinated trajectory control of an excavator as a kind of robotic manipulators driven by hydraulic actuators. Hydraulic robot system has many non-linearity in dynamics and kinematics, and strong coupling among joints(or hydraulic cylinders). This paper proposes a combined controller frame of the adaptive robust control(ARC) and the sliding mode control(SMC) for the trajectory tracking control of the excavator to preserve the advantages of the both methods while overcoming their drawbacks, namely, asymptotic stability of adaptive system for parametric uncertainties and guaranteed transient performance of sliding mode control for both parametric uncertainties and external disturbance. The suggested control technique is applied for the tracking of a straight-line motion of end-effector of manipulators, and through computer simulations, its trajectory tracking performances and the robustness to payload variation and uncertainties are illustrated.

Identifiability of Closed-loop Systems and Stability of Adaptive Systems

Identifiability of Closed-loop Systems and Stability of Adaptive Systems

Adaptive system stability robustness via burst recovery

Adaptive systems which are based on a posteriori parameter update algorithms are shown to possess a specific type of ‘self-stabilization’ property, termed burst recovery. This results in bounded-disturbance bounded-error stability, provided that unbounded parameter drift does not occur. Persistent excitation prevents unbounded parameter drift, but only when both upper and lower bounds on excitation exist. For many adaptive systems, an upper bound on excitation cannot be assured using standard perturbation analyses, which require the disturbance to be ‘suitably small’ compared to the lower bound on excitation. This paper proves that burst recovery in conjunction with only a lower bound on excitation provides bounded-disturbance bounded-error stability. The disturbance need not be small, and additional algorithm modifications (such as parameter projection) are not necessary.

Experimental study of robustness in adaptive control for large flexible structures

An experimental study is performed to investigate the robustness of model reference adaptive control for the large flexible structures control application. The main nonidealities of concern are unmodeled dynamics, input saturation, and time-delay effects (here, actuator and sensor dynamics are lumped into the last item for convenience). This study focuses on the robustness with respect to input saturation and time-delay effects, since robustness to unmodeled dynamics is inherent to the basic algorithm and has been demonstrated experimentally elsewhere. N experimental study is performed to investigate the robustness of model reference adaptive control for the large flexible structures control application. Although adaptive control methods are robust to parametric uncertainty by design, other types of nonidealities are known to lead to degradation and even instability of the closed-loop adaptive system. The main nonidealities of concern in the flexible structures control application are unmodeled dynamics, input saturation, and time-delay effects (here, actuator and sensor dynamics are lumped into the last item for convenience). Because of the use of the command generator tracker (CGT) approach, the adaptive algorithm considered here achieves tracking objectives that are in theory robust to unmodeled dynamics.1'2 This theoretical robustness to unmodeled dynamics has also been verified experimentally in Refs. 3 and 4 and will not be an issue in the present study. In contrast, there are presently no assurances as to the stability of the adaptive system to input saturation and time-delay effects. These latter issues will be the focus of the present study. It is shown experimentally in this paper that the basic adaptive algorithm is robust to input saturation, whereas timedelay effects can cause significant degradation and even instability. It is also shown experimentally that stability in the presence of time delay can be recovered by using a technique advocated by Bar-Kana5 of placing a small feedforward on the plant (or equivalently for the regulation problem, of placing a small feedback on the compensator). This stabilizes the closedloop system and recovers a certain degree of performance in the process. As a side benefit, the input torque requirements are also reduced. Certain theoretical results are included in this paper to support the experimental effort. In particular, it is shown that for structures with collocated actuators and sensors, there always exists a bounded feedforward gain that guarantees L2 stability of the closed-loop adaptive system in the presence of a pure time delay.

Switch-off/Switch-on Algorithms for Robust Adaptive Control

The fundamental objective of the research reported here is to further develop procedures for adaptive controllers designed on an assumed low order or simple structured parametric system model. By connecting point-wise stability with the stability criteria given by frequency domain conditions a general robust stabilization theorem is derived for those adaptive systems designed according to the certainty equivalence principle. Based on this theorem, a switch-off/switch-on algorithm is proposed to ensure robust stability of adaptive systems having unmodelled dynamics

Stability of Adaptive Systems: Passivity and Averaging Analysis (B. D. O. Anderson, R. R. Bitmead, C. R. Johnson, Jr., P. Y. Kokotovic, R. L. Kosut, I. M. V. Mareels, L. Praly and B. D. Riedle)

Stability of Adaptive Systems: Passivity and Averaging Analysis (B. D. O. Anderson, R. R. Bitmead, C. R. Johnson, Jr., P. Y. Kokotovic, R. L. Kosut, I. M. V. Mareels, L. Praly and B. D. Riedle)