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Control Theory and Applications, IEE Proceedings -

Issue 2 • Date 13 March 2006

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Displaying Results 1 - 11 of 11
  • Adaptive neural motion control of n-link robot manipulators subject to unknown disturbances and stochastic perturbations

    Page(s): 127 - 138
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    The position tracking control problem for rigid n-link robot manipulators operating under unknown external disturbances and stochastic perturbations is addressed. The robot model is considered to be completely uncertain and therefore the proposed controller uses suitable neural network designs and adaptive bounding algorithms for the approximation of all the unknown non-linear uncertainties and the deterministic and stochastic disturbances while effectively penalises the position tracking error. Stability analysis based on Lyapunov functions proves that all the error variables are bounded in probability; simultaneously, the mean square tracking error enters in finite time in an arbitrarily selected small region around the origin wherein it remains thereafter. The controller performance is evaluated by two representative examples: a two-link and a three-link robot manipulator. An excellent tracking response is verified while the effective approximation achieved by the adaptive neural design is clearly demonstrated. View full abstract»

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  • Passivity-based integral control of a boost converter for large-signal stability

    Page(s): 139 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (242 KB)  

    This paper presents a new integral control law for a boost converter that ensures the stability of large-signal operation. The integral controller is derived in two steps by means of passivity-based control theory. First, a static law, which ensures global stability, is obtained. Secondly, a combination of the storage function of this static law and a new positive semidefinite storage function results in a new integral control law. The proposed regulator satisfies the usual transient specifications and behaves robustly for parameter uncertainty. Global stability is guaranteed even if the duty cycle saturation is taken into account. Simulation and experimental results verify the theoretical predictions. View full abstract»

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  • Equivalence between transfer-matrix and observed-state feedback control

    Page(s): 147 - 155
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (166 KB)  

    An observed-state feedback is built for a given multiple input-multiple output (MIMO) control loop, where the controller is specified in transfer-matrix form. This contribution solves for the first time, for MIMO systems, the classical problem of finding a feedback gain and an observer gain such that the observed-state feedback control loop has the same sensitivity as that provided by a one-degree-of-freedom classical control loop. View full abstract»

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  • Finite horizon robust model predictive control with terminal cost constraints

    Page(s): 156 - 166
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (211 KB)  

    A finite horizon model predictive control (MPC) algorithm that is robust to modelling uncertainties is developed along with the construction of a moving average system matrix to capture modelling uncertainties and facilitate the future output prediction. The authors' main focus is on the step tracking problem. Using linear matrix inequality techniques, the design is converted into a semi-definite optimisation problem. Closed-loop stability, known to be one of the most challenging topics in finite horizon MPC, is treated by adding extra terminal cost constraints in the semi-definite optimisation. A simulation example demonstrates that the approach can be useful for practical applications. View full abstract»

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  • Use of the Lambert W function for time-domain analysis of feedback fractional delay systems

    Page(s): 167 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    The Lambert W function is defined as the multivalued inverse of the function w→wew=z. It has been applied to stability analysis of a class of fractional delay systems whose transcendental characteristic equation (TCE) can be remodelled in the form (as+b)ecs+d=0. The approach of using the Lambert W function to time-domain analysis of a class of feedback fractional-order time-delay systems is extended. It should be noted that, owing to the multivaluedness of a transfer function of fractional order, the approach has two pitfalls that must be circumvented with care. Because remodelling the TCE of a feedback fractional delay system to allow for the Lambert W function representation of roots introduces superfluous poles to the original TCE, a clarification of the relationship between the roots of the remodelled TCEs and the poles of the system is provided. As a result, the time response function of the system can be approximated by a finite series of eigenmodes written in terms of Lambert W functions. As the singularities of a fractional-order system include both the poles and the branch cut(s) of the transfer function, the neglect of the response portion contributed by the branch cut(s) incurs a significant transient response error. In order to compensate for such a transient response error, three schemes of optimal approximation with specified poles are developed. Simulation results show that the proposed approaches to time-domain analysis of feedback fractional delay systems can indeed enlarge the application scope of the emerging Lambert W function. View full abstract»

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  • Robust mixed H2/H control for a class of nonlinear stochastic systems

    Page(s): 175 - 184
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    The problem of mixed H2/H control is considered for a class of uncertain discrete-time nonlinear stochastic systems. The nonlinearities are described by statistical means of the stochastic variables and the uncertainties are represented by deterministic norm-bounded parameter perturbations. The mixed H2/H control problem is formulated in terms of the notion of exponentially mean-square quadratic stability and the characterisations of both the H2 control performance and the H robustness performance. A new technique is developed to deal with the matrix trace terms arising from the stochastic nonlinearities and the well-known S-procedure is adopted to handle the deterministic uncertainities. A unified framework is established to solve the addressed mixed H2/H control problem using a linear matrix inequality approach. Within such a framework, two additional optimisation problems are discussed, one is to optimise the H robustness performance, and the other is to optimise the H2 control performance. An illustrative example is provided to demonstrate the effectiveness of the proposed method. View full abstract»

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  • Identification of continuous-time systems

    Page(s): 185 - 220
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1052 KB)  

    System identification is a well-established field. It is concerned with the determination of particular models for systems that are intended for a certain purpose such as control. Although dynamical systems encountered in the physical world are native to the continuous-time domain, system identification has been based largely on discrete-time models for a long time in the past, ignoring certain merits of the native continuous-time models. Continuous-time-model-based system identification techniques were initiated in the middle of the last century, but were overshadowed by the overwhelming developments in discrete-time methods for some time. This was due mainly to the 'go completely digital' trend that was spurred by parallel developments in digital computers. The field of identification has now matured and several of the methods are now incorporated in the continuous time system identification (CONTSID) toolbox for use with Matlab. The paper presents a perspective of these techniques in a unified framework. View full abstract»

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  • Parameterisation of extended systems

    Page(s): 221 - 227
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    The Youla-Jabr-Bongiorno-Kucera (YJBK) parameterisation approach to stabilising controllers is extended to handle systems with additional sensors and/or actuators. It is shown that the closed-loop transfer function is still an affine function of the YJBK parameters in the nominal case. Furthermore, some closed-loop stability results are also given for uncertain systems. These results are important in connection with fault-tolerant control. View full abstract»

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  • GA-optimised PID and pole placement real and simulated performance when controlling the dynamics of a supply ship

    Page(s): 228 - 236
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (231 KB)  

    Two decoupled PID controllers and a state feedback pole placement control configuration have been designed for the navigation and propulsion systems of CyberShip II, a scale model of an oil platform supply ship. These control structures have parameters that need to be tuned to improve their performance. The values of these parameters have been optimised using genetic algorithms. The performance of these controllers has been analysed through computer-generated simulations based on a non-linear hydrodynamic model of CyberShip II. The robustness has been evaluated through simulation in the presence of environmental disturbances. Subsequently, the optimised controllers have been tested in the real plant and the results are shown. View full abstract»

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  • Discretisation of continuous-time T-S fuzzy system: global approach

    Page(s): 237 - 246
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (197 KB)  

    A new discretisation technique (so-called global discretisation approach) for the continuous-time Takagi-Sugeno (T-S) fuzzy system is suggested. The proposed global discretisation method takes account of the non-linear behaviour among the fuzzy rules. The authors' main idea is to utilise the dual-rate sampling scheme. The proposed approach is to discretise the overall dynamics of the fuzzy system in the slow-rate sampling period and then to perform the approximation for the polytopic structure in the fast-rate sampling period. In addition, to reduce the number of the IF-THEN rules, the convex minimisation problem is formulated in terms of the linear matrix inequalities. A chaotic Lorenz system is used to show the feasibility of the proposed discretisation method. View full abstract»

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  • Improving frequency-response estimates by reduction of end effects

    Page(s): 247 - 250
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (106 KB)  

    The use of Fourier analysis as a step in building a model of a linear dynamic system involves end effects which introduce bias and variance in estimates. The source of these errors is considered, and their detailed form is estimated. This leads to a significant improvement in the accuracy of the final model. Simulation results are included. View full abstract»

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