674 research outputs found
Global Stabilization of Triangular Systems with Time-Delayed Dynamic Input Perturbations
A control design approach is developed for a general class of uncertain
strict-feedback-like nonlinear systems with dynamic uncertain input
nonlinearities with time delays. The system structure considered in this paper
includes a nominal uncertain strict-feedback-like subsystem, the input signal
to which is generated by an uncertain nonlinear input unmodeled dynamics that
is driven by the entire system state (including unmeasured state variables) and
is also allowed to depend on time delayed versions of the system state variable
and control input signals. The system also includes additive uncertain
nonlinear functions, coupled nonlinear appended dynamics, and uncertain dynamic
input nonlinearities with time-varying uncertain time delays. The proposed
control design approach provides a globally stabilizing delay-independent
robust adaptive output-feedback dynamic controller based on a dual dynamic
high-gain scaling based structure.Comment: 2017 IEEE International Carpathian Control Conference (ICCC
Robust nonlinear control of vectored thrust aircraft
An interdisciplinary program in robust control for nonlinear systems with applications to a variety of engineering problems is outlined. Major emphasis will be placed on flight control, with both experimental and analytical studies. This program builds on recent new results in control theory for stability, stabilization, robust stability, robust performance, synthesis, and model reduction in a unified framework using Linear Fractional Transformations (LFT's), Linear Matrix Inequalities (LMI's), and the structured singular value micron. Most of these new advances have been accomplished by the Caltech controls group independently or in collaboration with researchers in other institutions. These recent results offer a new and remarkably unified framework for all aspects of robust control, but what is particularly important for this program is that they also have important implications for system identification and control of nonlinear systems. This combines well with Caltech's expertise in nonlinear control theory, both in geometric methods and methods for systems with constraints and saturations
Improving Transient Performance of Adaptive Control Architectures using Frequency-Limited System Error Dynamics
We develop an adaptive control architecture to achieve stabilization and
command following of uncertain dynamical systems with improved transient
performance. Our framework consists of a new reference system and an adaptive
controller. The proposed reference system captures a desired closed-loop
dynamical system behavior modified by a mismatch term representing the
high-frequency content between the uncertain dynamical system and this
reference system, i.e., the system error. In particular, this mismatch term
allows to limit the frequency content of the system error dynamics, which is
used to drive the adaptive controller. It is shown that this key feature of our
framework yields fast adaptation with- out incurring high-frequency
oscillations in the transient performance. We further show the effects of
design parameters on the system performance, analyze closeness of the uncertain
dynamical system to the unmodified (ideal) reference system, discuss robustness
of the proposed approach with respect to time-varying uncertainties and
disturbances, and make connections to gradient minimization and classical
control theory.Comment: 27 pages, 7 figure
Yet Another Tutorial of Disturbance Observer: Robust Stabilization and Recovery of Nominal Performance
This paper presents a tutorial-style review on the recent results about the
disturbance observer (DOB) in view of robust stabilization and recovery of the
nominal performance. The analysis is based on the case when the bandwidth of
Q-filter is large, and it is explained in a pedagogical manner that, even in
the presence of plant uncertainties and disturbances, the behavior of real
uncertain plant can be made almost similar to that of disturbance-free nominal
system both in the transient and in the steady-state. The conventional DOB is
interpreted in a new perspective, and its restrictions and extensions are
discussed
Disturbance Observer
Disturbance observer is an inner-loop output-feedback controller whose role
is to reject external disturbances and to make the outer-loop baseline
controller robust against plant's uncertainties. Therefore, the closed-loop
system with the DOB approximates the nominal closed-loop by the baseline
controller and the nominal plant model with no disturbances. This article
presents how the disturbance observer works under what conditions, and how one
can design a disturbance observer to guarantee robust stability and to recover
the nominal performance not only in the steady-state but also for the transient
response under large uncertainty and disturbance
Experimental Validation of L1 Adaptive Control: Rohrs' Counterexample in Flight
The paper presents new results on the verification and in-flight validation of an L1 adaptive flight control system, and proposes a general methodology for verification and validation of adaptive flight control algorithms. The proposed framework is based on Rohrs counterexample, a benchmark problem presented in the early 80s to show the limitations of adaptive controllers developed at that time. In this paper, the framework is used to evaluate the performance and robustness characteristics of an L1 adaptive control augmentation loop implemented onboard a small unmanned aerial vehicle. Hardware-in-the-loop simulations and flight test results confirm the ability of the L1 adaptive controller to maintain stability and predictable performance of the closed loop adaptive system in the presence of general (artificially injected) unmodeled dynamics. The results demonstrate the advantages of L1 adaptive control as a verifiable robust adaptive control architecture with the potential of reducing flight control design costs and facilitating the transition of adaptive control into advanced flight control systems
Robust model-based controller synthesis for the SCOLE configuration
The design of a robust compensator is considered for the SCOLE configuration using a frequency-response shaping technique based on the LQG/LTR algorithm. Results indicate that a tenth-order compensator can be used to meet stability-performance-robustness conditions for a 26th-order SCOLE model without destabilizing spillover effects. Since the SCOLE configuration is representative of many proposed spaceflight experiments, the results and design techniques employed potentially should be applicable to a wide range of large space structure control problems
외란 관측기의 이론적 해석 : 안정성 및 성능
학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 8. 심형보.This dissertation provides the stability and performance analysis of the disturbance observer and proposes several design methods for guaranteeing the robust stability and for enhancing the disturbance rejection performance. Compared to many success stories in industry, theoretic analysis on the disturbance observer itself has attracted relatively little attention. In order to enlarge the horizon of its applications, we provide some rigorous analysis both in the frequency and time domain.
In the frequency domain, we focus on two main issues: disturbance rejection performance and robust stability.
In spite of its powerful ability for disturbance rejection, the conventional disturbance observer rejects the disturbance approximately rather than asymptotically.
To enhance the disturbance rejection performance, based on the well-known internal model principle, we propose a design method to embed an internal model into the disturbance observer structure for achieving the asymptotic disturbance rejection and derive a condition for robust stability. Thus, the proposed disturbance observer can reject not only approximately the unmodeled disturbances but also asymptotically the disturbances of sinusoidal or polynomial-in-time type. In addition, a constructive design procedure to satisfy the proposed stability condition is presented. The other issue is to design of the disturbance observer based control system for guaranteeing robust stability under plant uncertainties. We study the robust stability for the case that the relative degree of the plant is not exactly known and so it happens to be different from that of nominal model. Based on the above results, we propose a universal design method for the disturbance observer when the relative degree of the plant is less than or equal to 4. Moreover, from the observation about the role of each block, we generalize the design of disturbance observer and propose a reduced order type-k disturbance observer to improve the disturbance rejection performance and to reduce the design complexity simultaneously.
As a counterpart of the frequency domain analysis, we analyze the disturbance observer in the state space for the purpose of extending the horizon of the disturbance observer applications and obtaining the deeper understanding of the role of each block. Based on the singular perturbation theory, it reveals not only well-known properties but also interesting facts such as the peaking in the transient response. Moreover, we investigate robust stability of the disturbance observer based control systems with and without unmodeled dynamics and derive an explicit relation between the nominal performance recovery and the time constant of Q-filter.
Since the classical linear disturbance observer does not ensure the recovery of transient response, a nonlinear disturbance observer, in which all the benefits of the classical one are still preserved, is presented for guaranteeing the recovery of transient as well as steady-state response.Abstract
List of Figures
Symbols and Acronyms
1. Introduction
1.1 Motivation
1.2 Contributions and Outline of the Dissertation
2. Robust Stability for Closed-loop System with Disturbance Observer
2.1 Structure of Disturbance Observer
2.2 Robust Stability Condition for Closed-loop System with Disturbance Observer
2.3 Illustrative Example
3. Embedding Internal Model in Disturbance Observer with Robust Stability
3.1 Design Method for Embedding Internal Model of Disturbance
3.2 Design of Q-filter for Guranteeing Robust Stability
3.2.1 Robust Stability Condition of Closed-loop System
3.2.2 Selecting a_i's for Robust Stability
3.3 Illustrative Example
3.4 Discussions on Robustness
3.4.1 Pros and Cons of Proposed Design Procedure
3.4.2 Bode Diagram Approach
4. Disturbance Observer with Unknown Relative Degree of the Plant
4.1 Robust Stability
4.2 A Guideline for Selecting Q and P_n
4.2.1 A Universal Robust Controller
4.3 Technical Proofs
4.4 Illustrative Examples
5. Reduced Order Type-k Disturbance Observer under Generalized Q-filter
5.1 Concept of Disturbance Observer with Generalized Q-filter Structure
5.2 Robust Stability
5.3 Reduced Order Type-k Disturbance Observer
5.4 Illustrative Examples
6. State Space Analysis of Disturbance Observer
6.1 State Space Realization of Disturbance Observer
6.2 Analysis of Disturbance Observer based on Singular Perturbation Theory
6.3 Discussion on Disturbance Observer Approach
6.3.1 Relation of Robust Stability Condition between State Space and Frequency Domain Approach
6.3.2 Effect of Zero Dynamics
6.3.3 Stability of Nominal Closed-loop System
6.3.4 Infinite Gain Property with p-dynamics
6.3.5 Peaking in Fast Transient
6.4 Nominal Performance Recovery with respect to Time Constant of Q-filter
7. Nominal Performance Recovery and Stability Analysis of Disturbance Observer under Unmodeled Dynamics
7.1 Problem Formulation
7.2 Stability and Performance Analysis based on Singular Perturbation Theory
7.2.1 Nominal Performance Recovery
7.2.2 Multi-time-scale Singular Perturbation Analysis
7.3 Nominal Performance Recovery by Disturbance Observer under Unmodeled Dynamics
8. Extensions of Disturbance Observer for Guaranteeing Robust Transient Performance
8.1 Extensions to MIMO Nonlinear Systems
8.1.1 SISO Nonlinear Disturbance Observer with Nonlinear Nominal Model
8.1.2 MIMO Nonlinear Disturbance Observer with Linear Nominal Model
9. Conclusions
Appendix
Bibliography
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