Página 1 dos resultados de 504 itens digitais encontrados em 0.027 segundos

Recursive parameter estimation algorithms

Coelho, J.P.; Cunha, José Boaventura; Oliveira, Paulo
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
35.84%
Main adaptive control design approaches assume that a suitable dynamic model of the controlled process can be computed. In this way, recursive parameter estimation algorithms play can important role in tracking the time variant parameters of the process dynamic model. Thois paper describes the major algorithms used to compute the ttransfer function parameters of time varying ssssystems. The advantages and limitations of these techniques are illustrated by computing the parameters of a time varying discrete system, with known structure, under the presence of persistent and non-persistent information.

Desenvolvimento de metodologia de projeto de sistema de posicionamento dinâmico aplicado a operações em alto-mar. ; Development of a new methodology for offshore dynamic positioning system design.

Tannuri, Eduardo Aoun
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 20/09/2002 PT
Relevância na Pesquisa
35.85%
O presente trabalho aborda três tópicos de pesquisa e desenvolvimento em Sistemas de Posicionamento Dinâmico (SPD). Desenvolveu-se uma nova metodologia para o projeto de controlador de posição e aproamento baseada na teoria de controle robusto não-linear por modos deslizantes. O controlador integra uma malha de compensação direta dos esforços ambientais (ondas, vento e correnteza) a uma malha de realimentação que realiza correções de erros residuais. A estrutura não-linear do controlador assegura o desempenho e estabilidade para qualquer aproamento da embarcação. A malha de compensação direta, por sua vez, garante maior faixa de aplicabilidade em termos de condições ambientais, não apresentando degradação de desempenho em condições extremas. A malha de realimentação possui apenas nove parâmetros, existindo equações e regras que tornam suas calibrações simples. Já a malha de compensação direta possui, internamente, modelos para a estimativa das forças ambientais que agem sobre o navio. Graças às características de robustez, o controlador não requer um ajuste refinado dos diversos parâmetros destes modelos e das condições ambientais, podendo-se utilizar estimativas pouco acuradas dos mesmos. O controlador desenvolvido foi testado em simuladores computacionais do VLCC Vidal de Negreiros amarrado pelo sistema turret e de uma barcaça de lançamento de dutos...

Ajuste de taxas de mutação e de cruzamento de algoritmos genéticos utilizando-se inferências nebulosas.; Adjusments in genetic algorithms mutation and crossover rates using fuzzy inferences.

Burdelis, Mauricio Alexandre Parente
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 31/03/2009 PT
Relevância na Pesquisa
45.68%
Neste trabalho foi realizada uma proposta de utilização de Sistemas de Inferência Nebulosos para controlar, em tempo de execução, parâmetros de Algoritmos Genéticos. Esta utilização busca melhorar o desempenho de Algoritmos Genéticos diminuindo, ao mesmo tempo: a média de iterações necessárias para que um Algoritmo Genético encontre o valor ótimo global procurado; bem como diminuindo o número de execuções do mesmo que não são capazes de encontrar o valor ótimo global procurado, nem mesmo para quantidades elevadas de iterações. Para isso, foram analisados os resultados de diversos experimentos com Algoritmos Genéticos, resolvendo instâncias dos problemas de Minimização de Funções e do Caixeiro Viajante, sob diferentes configurações de parâmetros. Com base nos resultados obtidos a partir destes experimentos, foi proposto um modelo com a troca de valores de parâmetros de Algoritmos Genéticos, em tempo de execução, pela utilização de Sistemas de Inferência Nebulosos, de forma a melhorar o desempenho do sistema, minimizando ambas as medidas citadas anteriormente.; This work addressed a proposal of the application of Fuzzy Systems to adjust parameters of Genetic Algorithms, during execution time. This application attempts to improve the performance of Genetic Algorithms by diminishing...

Estudos sobre os efeitos do treinamento no mini trampolim sobre o controle postural de idosos; Effects of mini trampoline training on the postural control of elderly subjects

Aragão, Fernando Amâncio
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
35.9%
As quedas são responsáveis pela maior causa de lesões em idosos. Além disso, tratase do incidente mais freqüente que acomete essa população, aumentando de forma exponencial a fragilidade e muitas vezes levando os idosos à morte. Após perturbações inesperadas, a capacidade de readequar o controle postural está notadamente diminuída em idosos, o que leva ao aumento da propensão a quedas nessa população. A reduzida capacidade de reagir a perturbações inesperadas é atribuída a deficiências cumulativas relacionadas ao envelhecimento, tais como a redução da força muscular, diminuição da velocidade de contração muscular e modificações no tempo de reação e capacidade de processamento de informações. Estudos disponibilizam informações sobre uma grande quantidade de procedimentos que foram propostos a fim de minimizar os efeitos do envelhecimento e aumentar a capacidade de controle postural em idosos. Apesar da grande variedade de intervenções disponíveis, poucos estudos reconhecem de fato a razão pela qual a intervenção proposta é, em certos casos, bem ou mal sucedida. Recentemente os mecanismos responsáveis por manter a estabilidade dinâmica do corpo foram determinados em modelos de expressões matemáticas que identificavam as variáveis físicas que atuam no corpo durante a manutenção do equilíbrio postural. A partir de então...

Técnicas não lineares de controle e filtragem aplicadas ao problema de rastreamento de trajetórias de robôs móveis com deslizamento longitudinal das rodas; Nonlinear techniques of control and filtering applied to the trajectory tracking problem of mobile robots with longitudinal wheel slip

Juliano Gonçalves Iossaqui
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Formato: application/pdf
Publicado em 28/02/2013 PT
Relevância na Pesquisa
35.87%
Esta tese trata do problema de controle de trajetórias de robôs móveis não holonômicos com deslizamento longitudinal das rodas. As estratégias de controle propostas são projetadas usando dois modelos, um cinemático e um dinâmico, que consideram os deslizamentos longitudinais das rodas como parâmetros desconhecidos. A primeira estratégia de controle consiste em um controlador adaptativo projetado com base em um modelo cinemático que utiliza como entrada de controle, as velocidades angulares das rodas. Essas velocidades angulares são fornecidas por uma lei de controle cinemática que utiliza estimativa dos parâmetros de deslizamento desconhecidos, obtidas por meio de uma lei de adaptação. A segunda estratégia de controle consiste em um controlador adaptativo projetado com base em um modelo dinâmico simplificado que utilizam como entrada de controle, forças de propulsão aplicadas no centro das rodas. A lei de controle, que fornece essas forças, é projetada aplicando-se a técnica backstepping ao modelo dinâmico reduzido, que foi obtido com a utilização do método da dinâmica inversa. Os parâmetros de deslizamento longitudinal desconhecidos, necessários para a utilização do método da dinâmica inversa, são estimados por uma lei de adaptação. O filtro de Kalman unscented também é utilizado para estimar os parâmetros de deslizamento desconhecidos. Essas estimativas são utilizadas...

Dynamic approach to behavior-based robotics : design, specification, analysis, simulation and implementation

Bicho, E.
Fonte: Shaker Publicador: Shaker
Tipo: Livro
Publicado em //2000 ENG
Relevância na Pesquisa
35.91%
Tese de doutoramento em Electrónica Industrial, ramo de Automação e Controlo. Guimarães : Universidade do Minho, 1999.; The aim of this thesis is to investigate how behavior-based robots can be modeled by non-linear dynamical systems. Taking the example of navigation as a case study, dynamic control architectures are developed and implemented on low-level vehicles. These architectures combine a number of behaviors and lead to flexible and smooth overt behavior which is stably coupled in closed loop with sensory information. Moreover, these architectures also comprise dynamical representations of information which enable the vehicles to exhibit cognitive behaviors such as decision making, memory, forgetting and robustness against noisy sensory information. The design of the individual behaviors, of the representations of particular types of information, as well as of their coupling is based on the qualitative theory of dynamical systems and dynamic field theory. These provide a general theoretical language in which autonomous robot architectures can be built.; Dynamical systems theory was used as a theoretical language and tool to design, specify, analyze, simulate and implement behavior-based control architectures. The architectures were fully formulated in terms of dynamics and implemented on computationally modest vehicle platforms based on very low-level sensory information. The main ideas and achievements are the following: 1. Attractor dynamics can be used to control motion based on low-level sensors (a) Robot action can be generated in the manner of control systems...

Robust scheduling control of aeroelasticity.

Prime, Zebb David
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
Relevância na Pesquisa
35.93%
Aeroelasticity is a broad term describing the often complex interactions between structural mechanics and aerodynamics. Aeroelastic phenomena such as divergence and flutter are potentially destructive, and thus must be avoided. Passive methods to avoid undesirable aeroelastic phenomena often involve the addition of mass and/or limiting the achievable performance of the aircraft. However, active control methods allow both for the suppression of undesirable aeroelastic phenomena, and for utilisation of desirable aeroelastic phenomena using actuators, thus increasing performance without the associated weight penalty of passive systems. The work presented in this thesis involves the design, implementation and experimental validation of novel active controllers to suppress undesirable aeroelastic phenomena over a range of airspeeds. The controllers are constructed using a Linear Parameter Varying (LPV) framework, where the plant and controllers can be represented as linear systems which are functions of a parameter, in this case airspeed. The LPV controllers are constructed using Linear Matrix Inequalities (LMIs), which are convex optimisation problems that can be used to represent many linear control objectives. Using LMIs, these LPV controllers can be constructed such that they self-schedule with airspeed and provide upper performance bounds during the design process. The aeroelastic phenomena being suppressed by these controllers are Limit-Cycle Oscillations (LCOs)...

Fault-tolerant control design for near-space vehicles based on a dynamic terminal sliding mode technique

Zhao, J.; Jiang, B.; Shi, P.; Gao, Z.; Xu, D.
Fonte: Professional Engineering Publishing Ltd Publicador: Professional Engineering Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
35.9%
In this paper, a fault-tolerant control scheme based on a second-order dynamic terminal sliding mode is proposed for a near-space vehicle attitude dynamical system in the presence of actuator faults, model parameter uncertainties and external disturbances. The principle of the proposed dynamic terminal sliding mode scheme is firstly introduced. Then, a near-space vehicle attitude faulty model with parameter uncertainty is established. Furthermore, two dynamic terminal sliding mode controllers are designed for the inner and outer loops. It is shown that the proposed algorithm can reduce chattering phenomenon and guarantee system stability and asymptotic state tracking. Finally, simulation results are provided to demonstrate the performance of the proposed fault-tolerant control scheme.; Jing Zhao, Bin Jiang, Peng Shi, Zhifeng Gao and Dezhi Xu

Neural network-based adaptive dynamic surface control for permanent magnet synchronous motors

Yu, J.; Shi, P.; Dong, W.; Chen, B.; Lin, C.
Fonte: IEEE Publicador: IEEE
Tipo: Artigo de Revista Científica
Publicado em //2015 EN
Relevância na Pesquisa
55.72%
This brief considers the problem of neural networks (NNs)-based adaptive dynamic surface control (DSC) for permanent magnet synchronous motors (PMSMs) with parameter uncertainties and load torque disturbance. First, NNs are used to approximate the unknown and nonlinear functions of PMSM drive system and a novel adaptive DSC is constructed to avoid the explosion of complexity in the backstepping design. Next, under the proposed adaptive neural DSC, the number of adaptive parameters required is reduced to only one, and the designed neural controllers structure is much simpler than some existing results in literature, which can guarantee that the tracking error converges to a small neighborhood of the origin. Then, simulations are given to illustrate the effectiveness and potential of the new design technique.; Jinpeng Yu, Peng Shi, Wenjie Dong, Bing Chen, and Chong Lin

Parameter estimation in nonlinear continuous-time dynamic models with modelling errors and process disturbances

Varziri, M. Saeed
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 1585120 bytes; application/pdf
EN; EN
Relevância na Pesquisa
35.87%
Model-based control and process optimization technologies are becoming more commonly used by chemical engineers. These algorithms rely on fundamental or empirical models that are frequently described by systems of differential equations with unknown parameters. It is, therefore, very important for modellers of chemical engineering processes to have access to reliable and efficient tools for parameter estimation in dynamic models. The purpose of this thesis is to develop an efficient and easy-to-use parameter estimation algorithm that can address difficulties that frequently arise when estimating parameters in nonlinear continuous-time dynamic models of industrial processes. The proposed algorithm has desirable numerical stability properties that stem from using piece-wise polynomial discretization schemes to transform the model differential equations into a set of algebraic equations. Consequently, parameters can be estimated by solving a nonlinear programming problem without requiring repeated numerical integration of the differential equations. Possible modelling discrepancies and process disturbances are accounted for in the proposed algorithm, and estimates of the process disturbance intensities can be obtained along with estimates of model parameters and states. Theoretical approximate confidence interval expressions for the parameters are developed. Through a practical two-phase nylon reactor example...

DynDE : a differential evolution for dynamic optimization problems

Mendes, Rui; Mohais, Arvind
Fonte: Ieee Publicador: Ieee
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2005 ENG
Relevância na Pesquisa
45.71%
This paper presents an approach of using Differential Evolution (DE) to solve dynamic optimization problems. Careful setting of parameters is necessary for DE algorithms to successfully solve optimization problems. This paper describes DynDE, a multi-population DE algorithm developed specifically to solve dynamic optimization problems that doesn't need any parameter control strategy for the F or CR parameters. Experimental evidence has been gathered to show that this new algorithm is capable of efficiently solving the moving peaks benchmark.

Absolute extrema of invariant optimal control problems

Silva, C.J.; Torres, D.F.M.
Fonte: Dynamic Publishers Publicador: Dynamic Publishers
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.83%
Optimal control problems are usually addressed with the help of the famous Pontryagin Maximum Principle (PMP) which gives a generalization of the classical Euler-Lagrange and Weierstrass necessary optimality conditions of the calculus of variations. Success in applying the PMP permits to obtain candidates for a local minimum. In 1967 a direct method, which permits to obtain global minimizers directly, without using necessary conditions, was introduced by Leitmann. Leitmann's approach is connected, as showed by Carlson in 2002, with "Carathéodory's royal road of the calculus of variations". Here we propose a related but different direct approach to problems of the calculus of variations and optimal control, which permit to obtain global minima directly, without recourse to needle variations and necessary conditions. Our method is inspired by the classical Noether's Theorem and its recent extensions to optimal control. We make use of the variational symmetries of the problem, considering parameter-invariance transformations and substituting the original problem by a parameter-family of optimal control problems. Parameters are then fixed in order to make the problem trivial, in some sense. Finally, by applying the inverse of the chosen invariance-transformation...

Tuning equation ford dynamic matrix control in siso loops

Edinzo J. Iglesias; Universidad de los Andes; Marco E. Sanjuán; Universidad del Norte; Carlos A. Smith; University of South Florida
Fonte: Universidad del Norte Publicador: Universidad del Norte
Tipo: article; publishedVersion Formato: application/pdf
SPA
Relevância na Pesquisa
45.82%
El Control por Matriz Dinámica (DMC) es una de las estrategias de control avanzado que más aplicaciones industriales tiene en la actualidad. Sin embargo, la literatura presenta pocas opciones para el cálculo del parámetro de sintonización que gobierna la agresividad del controlador. Esta investigación propone una nueva ecuación de sintonización para calcular este parámetro de sintonización. Se presentan los análisis estadísticos realizados para formular la ecuación de sintonización. Para probar la eficacia de la ecuación propuesta, se presenta pruebas de rendimiento del controlador usando diferentes métodos de sintonización. Estas pruebas incluyen tanto sistemas lineales como no lineales./Dynamic Matrix Control (DMC) is one of the most used advanced control strategies used in industrial environments. However, the available literature does not present many alternatives to calculate the controller tuning parameter (also called suppression factor). This research proposes a new tuning equation to calculate this parameter. The statistical analysis and regression used to develop the equation, as well as the tests used to validate it are shown. Linear and nonlinear systems were used to compare different tuning methods.

Adaptive techniques applied to offshore dynamic positioning systems

Tannuri,Eduardo A.; Kubota,Leonardo K.; Pesce,Celso P.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2006 EN
Relevância na Pesquisa
35.87%
Dynamic positioning systems (DPS) comprise the deployment of active propulsion to maintain the position and heading of a vessel. Several sensors are used to measure the actual position of the floating body, while a control algorithm is responsible for the calculation of forces to be delivered by each propeller, in order to counteract all environmental forces, such as wind, waves and current loads. The controller cannot directly compensate motions in the sea waves frequency range, since they would require an enormous amount of power to be attenuated, possibly causing damage to the propeller system. That is the reason why a filtering algorithm is to be put in place to separate high-frequency components from the low-frequency ones, which are, then, fed into the control loop. Usual commercial systems apply Kalman filtering technique to perform such task, due to the smaller phase-lag introduced in the control loop compared to conventional low-pass filters. The Kalman filter draws on a model of the system to be controlled, which, in turn, depends on an unknown parameter, related to the wave frequency. Adaptive filtering is called upon with a view to perform an on-line estimation of such parameter. Most control algorithms, however, rely on fixed gains...

A Contraction Theory Approach for Analysis of Performance Recovery in Dynamic Surface Control

Rayguru, M M; kar, I N
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 31/10/2015
Relevância na Pesquisa
55.84%
Dynamic surface control (DSC) method uses high gain filters to avoid the "explosion of complexity" issue inherent in backstepping based controller designs. As a result, the closed loop system and filter dynamics possess time scale separation between them. This paper attempts to design a novel disturbance observer based dynamic surface controller using contraction framework. In doing so the steady state error bounds are obtained in terms of design parameters which are exploited to tune the closed loop system performance. The results not only show that DSC technique recover the performance of a backstepping controller for a small range of filter parameter but also derive the maximum bound for it. Furthermore the stability bounds are also derived in the presence of disturbances and convergence of trajectories to a small penultimate bound is proved. The convergence results are shown to hold for less conservative choice of filter parameter and observer gain. The effectiveness of the proposed controller is verified through simulation example.

Concurrent learning for parameter estimation using dynamic state-derivative estimators

Kamalapurkar, Rushikesh; Reish, Ben; Chowdhary, Girish; Dixon, Warren E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 31/07/2015
Relevância na Pesquisa
35.86%
A concurrent learning (CL)-based parameter estimator is developed to identify the unknown parameters in a linearly parameterized uncertain control-affine nonlinear system. Unlike state-of-the-art CL techniques that assume knowledge of the state-derivative or rely on numerical smoothing, CL is implemented using a dynamic state-derivative estimator. A novel purging algorithm is introduced to discard possibly erroneous data recorded during the transient phase for concurrent learning. Since purging results in a discontinuous parameter adaptation law, the closed-loop error system is modeled as a switched system. Asymptotic convergence of the error states to the origin is established under a persistent excitation condition, and the error states are shown to be ultimately bounded under a finite excitation condition. Simulation results are provided to demonstrate the effectiveness of the developed parameter estimator.

Least Squares Estimation-Based Synchronous Generator Parameter Estimation Using PMU Data

Mogharbel, Bander; Fan, Lingling; Miao, Zhixin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/03/2015
Relevância na Pesquisa
45.9%
In this paper, least square estimation (LSE)-based dynamic generator model parameter identification is investigated. Electromechanical dynamics related parameters such as inertia constant and primary frequency control droop for a synchronous generator are estimated using Phasor Measurement Unit (PMU) data obtained at the generator terminal bus. The key idea of applying LSE for dynamic parameter estimation is to have a discrete \underline{a}uto\underline{r}egression with e\underline{x}ogenous input (ARX) model. With an ARX model, a linear estimation problem can be formulated and the parameters of the ARX model can be found. This paper gives the detailed derivation of converting a generator model with primary frequency control into an ARX model. The generator parameters will be recovered from the estimated ARX model parameters afterwards. Two types of conversion methods are presented: zero-order hold (ZOH) method and Tustin method. Numerical results are presented to illustrate the proposed LSE application in dynamic system parameter identification using PMU data.; Comment: 5 pages, 6 figures, accepted by IEEE PESGM 2015

Customer Equilibrium and Optimal Strategies in an M/M/1 Queue with Dynamic Service Control

Dimitrakopoulos, Y.; Burnetas, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/12/2011
Relevância na Pesquisa
55.72%
We consider the problem of customer equilibrium strategies in an M/M/1 queue under dynamic service control. The service rate switches between a low and a high value depending on system congestion. Arriving customers do not observe the system state at the moment of arrival. We show that due to service rate variation, the customer equilibrium strategy is not generally unique, and derive an upper bound on the number of possible equilibria. For the problem of social welfare optimization, we numerically analyze the relationship between the optimal arrival rate, which maximizes the overall welfare of the customers, and the equilibrium ones as a function of various parameter values. We finally derive analytic solutions for the special case where the service rate switch occurs when the queue ceases to be empty.; Comment: 22 pages, 8 figures

Compressing measurements in quantum dynamic parameter estimation

Magesan, Easwar; Cooper, Alexandre; Cappellaro, Paola
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/08/2013
Relevância na Pesquisa
45.77%
We present methods that can provide an exponential savings in the resources required to perform dynamic parameter estimation using quantum systems. The key idea is to merge classical compressive sensing techniques with quantum control methods to efficiently estimate time-dependent parameters in the system Hamiltonian. We show that incoherent measurement bases and, more generally, suitable random measurement matrices can be created by performing simple control sequences on the quantum system. Since random measurement matrices satisfying the restricted isometry property can be used to reconstruct any sparse signal in an efficient manner, and many physical processes are approximately sparse in some basis, these methods can potentially be useful in a variety of applications such as quantum sensing and magnetometry. We illustrate the theoretical results throughout the presentation with various practically relevant numerical examples.; Comment: 15 pages, 4 figures

Predictive Control with Parameter Adaptation to Achieve ?-Protection in the RECONFIGURE Benchmark in the Presence of Icing

Hartley, E. N.
Fonte: International Federation of Automatic Control Publicador: International Federation of Automatic Control
Tipo: Article; accepted version
EN
Relevância na Pesquisa
45.76%
This is the accepted manuscript. It is currently embargoed pending publication.; Undetected ice accretions on aerodynamic surfaces can deeply change the dynamic behaviour of aircraft, leading to poor performance of the automatic control systems. This is characterised by oscillatory behaviour, and overshoot of setpoints and flight envelope protection values. To mitigate this undesirable behaviour, this paper applies predictive control in combination with online estimation of the first and second order partial derivatives of the lift and pitching moment coefficients with respect to the angle of attack using an Extended Kalman Filter, to achieve a constrained indirect adaptive flight control law. The design is evaluated on the RECONFIGURE benchmark, which is a nonlinear, high fidelity, industrially validated simulator of a large Airbus aircraft. In icing scenarios at high incidence, the resulting trajectories are shown to be better damped and more compliant with constraints when compared to a predictive control law employing only linear disturbance estimation.