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Hamid Khaloozadeh,Mohammad Ali Nekoui,Farid Shahni 제어·로봇·시스템학회 2010 International Journal of Control, Automation, and Vol.8 No.3
The goal of this paper is global disturbance rejection in nonlinear systems. An output feedback control-ler with disturbance rejection is developed for a class of nonlinear multi input-multi output (MIMO) systems. The availability of state variables and the bound of disturbances are not required to be known in advance and reference tracking will is guaranteed. By the aid of designing an adaptive ob-server, a robust adaptive nonlinear state feedback controller using the estimated states is proposed. For tracking problem, an adaptive pre-compensator is used. The control methodology is robust against both constant and time varying bounded disturbances, maintaining effective performance. The adaptive laws are derived based on the Lyapunov synthesis method, therefore closed-loop asymptotic stability is also guaranteed. Moreover, for chattering reduction we use a low-pass filter. Consequently, small gain theorem is adopted to prove the stability of the closed-loop system. Simulation results are employed to illustrate the effectiveness of the proposed controller.
Real-time regulated sliding mode controller design of multiple manipulator space free-flying robot
Hamid Khaloozadeh,M. Reza Homaeinejad 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.6
The problem of controlling Space Free-flying Robots (SFFRs), which have many degrees of freedom caused by their mechanical manipulators,is challenging because of the strong nonlinearities and their heavy computational burden for the implementation of modelbased control algorithms. In this paper, a chattering avoidance sliding mode controller is developed for SFFR as highly nonlinear-coupled systems. To fulfill stability requirements, robustness properties, and chattering elimination, a regulating routine is proposed to determine the proper positive values for the coefficient of sliding condition. To solve the run-time problem, an explicit direct relationship between the SFFR’s output of actuators (force/torque) and the measurement of distances from the corresponding sliding surfaces is also assumed. To reach perfect performance, the parameters are estimated recursively using the Kalman filter as a parameter estimator. The explicit dynamics of a 14-DOF SFFR is derived using SPACEMAPLE, and the recursive prediction error method (RPEM) is used to parameterize the SFFR model. To alleviate the chattering trend, a multi-input sliding mode control law is proposed and applied to the given SFFR based on the online estimated dynamics to control its orientation and position to catch a moving target. To evaluate the new proposed algorithm in a more complicated condition, only on–off actuators are assumed for controlling the base of SFFR because it is the case in real systems. The obtained results show that the proposed regulated sliding mode controller can significantly reduce the chattering trend. Consequently, energy consumption will be substantially decreased, and running the control algorithm will be within a reasonable time duration.
Fully Characterization of Strictly Positive Real Transfer Function Matrices
Mojtaba Hakimi Moghaddam,Hamid Khaloozadeh 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10
Several necessary and sufficient conditions for characterization of strict positive realness property of transfer function matrices have been derived in the literature. However, some of them are inconsistent with definition of strict positive realness and the others have been restricted to proper transfer function matrices. Besides, there is a necessary condition in the previous correct statements which is difficult to check. In this paper, using Markov parameters of linear time invariant multivariable systems, we will remove the aforementioned deficiencies. On the other hand, we will prove new equivalent conditions to characterize strict positive realness such that not only it can be easily checked but also it can be used when the transfer function matrix is improper.
Revision on the Frequency Domain Conditions for Strict Positive Realness
Mojtaba Hakimi Moghaddam,Hamid Khaloozadeh 대한전기학회 2007 International Journal of Control, Automation, and Vol.5 No.1
In this paper, the necessary and sufficient conditions for strict positive realness of the rational transfer functions directly from basic definitions in the frequency domain are studied. A new frequency domain approach is used to check if a rational transfer function is a strictly positive real or not. This approach is based on the Taylor expansion and the Maximum Modulus Principle which are the fundamental tools in the complex functions analysis. Four related common statements in the strict positive realness literature which is appeared in the control theory are discussed. The drawback of these common statements is analyzed through some counter examples. Moreover a new necessary condition for strict positive realness is obtained from high frequency behavior of the Nyquist diagram of the transfer function. Finally a more simplified and completed conditions for strict positive realness of single-input single-output linear time-invariant systems are presented based on the complex functions analysis approach.
Generalized Necessary and Sufficient Conditions for Strictly Positive Real Matrices
Mojtaba Hakimi-M,Hamid Khaloozadeh 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
In this paper a review on the necessary and sufficient conditions for strict positive realness property of rational matrices is presented. Then a necessary condition that imposed by high frequencies is demonstrated for SPR matrices by using Laurent and Taylor series. Furthermore, a generalized version of necessary and sufficient conditions for SPR matrices including improper one is developed. Finally, the results are illustrated by several examples.
Essential Frequency Domain Properties of Positive Real Matrices
Mojtaba Hakimi-M,Hamid Khaloozadeh 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
Despite importance of positive realness in the control theory, properties of PR matrices are not discussed in the correlated literature in detail. In this paper some basic frequency domain properties of PR matrices are demonstrated by using concepts of network synthesis theory and complex variable analysis. These properties consist of positive realness of diagonal elements, relative degree constrains on the diagonal and off-diagonal elements, transmission zeros constrain and finally high frequency constrains.