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Control Theory and Applications, IEE Proceedings -

Issue 1 • Date 17 Jan. 2004

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Displaying Results 1 - 19 of 19
  • Robust adaptive control of nonlinear systems with unmodelled dynamics

    Page(s): 83 - 88
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (241 KB)  

    A robust adaptive output feedback controller is proposed for a class of nonlinear systems represented by input-output models. In the design of the adaptive controller, a signal is used to characterise the unmodelled dynamics and a nonlinear damping term is introduced to counteract the effects of the unmodelled dynamics and bounded disturbances. With the proposed controller, all the variables in the closed-loop system are bounded in the presence of unmodelled dynamics and bounded disturbances. Moreover, the mean-square tracking error can be made arbitrarily small by choosing appropriate design parameters. View full abstract»

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  • Fault estimation in nonlinear uncertain systems using robust/sliding-mode observers

    Page(s): 29 - 37
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (295 KB)  

    Under a single 'fault-type hypothesis', either actuator/component faults or sensor faults, geometric conditions are given such that the original nonlinear system can be transformed into two different subsystems with uncertainty. The first is in the generalised observer canonical form, which is not affected by faults. The second, whose states can be measured, is affected by the faults. Constructing a nonlinear observer for the first subsystem allows estimation of the faults from the second subsystem. Robust (sliding mode) observers are proposed depending on different assumptions on the system uncertainties. The decision logic associated with the proposed bank of observers, and some extensions to simultaneous actuator and sensor faults case are also discussed. Two numerical examples are given to illustrate the design procedures and the efficiency of the proposed methods. View full abstract»

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  • Variable structure system control design method based on a differential geometric approach: application to a wind energy conversion subsystem

    Page(s): 6 - 12
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    A design method for variable structure system control is presented. It is based on a differential geometric approach and it is intended to deal with the class of nonlinear systems affine in the control with uncertainties and disturbances. The main goals of the proposed method are: (i) robustness; (ii) tuning simplicity; (iii) chattering reduction; and (iv) reaching mode control. Its application to the wind subsystem of an electricity generation hybrid system is discussed in detail. Extensive simulation experiments were conducted with a comprehensive model of the plant and they are presented to illustrate the controller performance. View full abstract»

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  • Robust stability of cellular neural networks with delay: linear matrix inequality approach

    Page(s): 125 - 129
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    A criterion for the global asymptotic stability and uniqueness of the equilibrium point of uncertain cellular neural networks with delay is presented. The uncertainties are assumed to be norm-bounded. The criterion is computationally efficient, since it is in the form of a linear matrix inequality. View full abstract»

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  • Stabilisation of first-order plus dead-time unstable processes using PID controllers

    Page(s): 89 - 94
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (270 KB)  

    The problem of stabilising first-order plus dead-time unstable processes using PID controllers is considered. The D-partition technique is applied to characterise the stability domain in the space of system and controller parameters. Moreover, analytical expressions are derived for describing the stability domain boundaries. These analytical expressions can be used to construct the complete set of stabilising PID controller parameters for open-loop unstable time-delay processes. They can also be used to investigate the effect of time delay on the stabilisability of the process. View full abstract»

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  • Optimal Routh approximants through integral squared error minimisation: computer-aided approach

    Page(s): 53 - 58
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (241 KB)  

    A computer-aided method for obtaining a reduced-order approximant of a given (stable) single-input single-output system based on the minimisation of integral squared error (ISE) pertaining to a unit-step input is presented. Both the numerator and denominator coefficients of the model are treated as free parameters in the process of optimisation. The method has a built-in stability-preserving feature. The problem of formulating the ISE is circumvented by introducing a set of equality constraints. View full abstract»

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  • Sliding-mode control for uncertain neutral delay systems

    Page(s): 38 - 44
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (255 KB)  

    The problem of sliding-mode control for a class of neutral delay systems with uncertainties in both the state matrices and the input matrix is considered. By selecting a sliding surface depending on the current state and delayed state, the paper gives a sufficient condition in terms of linear matrix inequalities (LMIs) such that the closed-loop system is guaranteed to be asymptotically stable. When LMIs are feasible, the design of the sliding surface and the sliding-mode control law can be easily obtained by convex optimisation. State trajectories are attracted onto the sliding surface in a finite time and remain there for all subsequent time. A simulation illustrates the application of the method. View full abstract»

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  • Diagnosis of nonlinear systems using an unknown-input observer: an algebraic and differential approach

    Page(s): 130 - 135
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (259 KB)  

    The authors address the diagnosis problem in nonlinear systems by using the concept of the differential transcendence degree of a differential field extension. The authors also consider the algebraic observability concept of the variable which models the failure presence for the solvability of the diagnosis problem. The construction of a reduced-order uncertainty observer (unknown-input observer) to estimate the fault variable is the key step in the proposed approach. A simulation example that deals with a bioreactor process is presented to illustrate the effectiveness of the suggested approach. View full abstract»

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  • Nonlinear PID control of a six-DOF parallel manipulator

    Page(s): 95 - 102
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (450 KB)  

    A nonlinear proportional integral derivative (N-PID) algorithm in linkspace is proposed to realise high precision tracking control of a general six-DOF parallel manipulator. In practice, the performance of the controlled system is limited by how to pick out the differential signals of the noncontinuous measured signals with stochastic noise. Therefore, the developed N-PID controller uses two nonlinear tracking differentiators to yield high quality differential signals in the presence of disturbances and measurement noise. A nonlinear combination of proportional, integral and derivative action on the control error is used to synthesise the control law for enhanced performance in areas such as increased damping and reduced tracking error. Experimental results indicate that the nonlinear control method is easy for the engineer to implement and achieves a superior performance. View full abstract»

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  • Fuzzy-logic-based control applied to a hybrid electric vehicle with four separate wheel drives

    Page(s): 73 - 81
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (858 KB)  

    The authors present a detailed modelling study and a control system for a hybrid electric vehicle with four separate wheel drives. This configuration allows an improvement in the operability and thereby the safety of vehicles either during cornering or under slippery road conditions. Using electric motors it is possible to implement a quick and precise torque control. In order to obtain a better and precise dynamic performance a combined strategy Slip-ESP (electronic stability program) is created. A 'fuzzy estimator of vehicle speed' which assures the reference vehicle speed used in the control system is also presented. View full abstract»

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  • Fault-tolerant spatial control of a large pressurised heavy water reactor by fast output sampling technique

    Page(s): 117 - 124
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (286 KB)  

    A method is presented to design a spatial control system of a large pressurised heavy water reactor (PHWR) with the constraint that the closed loop system be stable even if one sensor or actuator has failed. Linear state models are obtained corresponding to the normal operating condition and different failure modes of the reactor. Each model is found to possess the two time scale property. Using similarity transformation each two time scale model is converted into a block diagonal form by which two subsystems, namely a fast subsystem and a slow subsystem, are easily obtained. State feedback is designed separately for the slow and the fast subsystems for each model. Then a composite state feedback gain is obtained from the state feedback gains computed for the slow and fast subsystems separately for each model. The composite state feedback so designed assigns the poles at arbitrary locations for the respective models. These composite state feedback gains are realised simultaneously by fast output sampling gains. Thus the states of the system are not needed for feedback purposes. An LMI formulation is used to overcome the undesired effects of poor error dynamics and noise sensitivity which are encountered if state feedback is realised exactly. View full abstract»

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  • LMI approach to L2-gain analysis and control synthesis of uncertain switched systems

    Page(s): 21 - 28
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    L2-gain analysis is used to characterise conditions under which an uncertain switched system is uniformly quadratically stable (UQS) with an L2-gain smaller than a constant γ. The control synthesis is to design switched-state feedback and switched output feedback controllers, guaranteeing that the corresponding closed-loop system is UQS with an L2-gain smaller than a constant γ. All the results are expressed in terms of linear matrix inequalities, which can be easily tested with efficient algorithms. View full abstract»

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  • Robust Kalman filtering via Krein space estimation

    Page(s): 59 - 63
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (233 KB)  

    A robust Kalman filter is proposed for the discrete-time system with norm-bounded parametric uncertainties. The uncertainties are described by the energy bound constraint, i.e. the sum quadratic constraint (SQC). It is shown that the SQC can be converted into an indefinite quadratic cost function to be minimised in the Krein space, and it is found that the Krein space Kalman filter is a solution of the minimisation problem. After introducing a Krein space state-space model, which includes the uncertainty, one can easily write a robust version of the Krein space Kalman filter by modifying the measurement matrix and the variance of measurement noises in the original Krein space Kalman filter. Since the resulting robust Kalman filter has the same recursive structure as a conventional Kalman filter, a robust filtering scheme can be readily designed using the proposed method. A numerical example demonstrates that the proposed filter achieves robustness against parameter variation and improvement in performance when compared with a conventional Kalman filter and an existing robust Kalman filter, respectively. View full abstract»

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  • Robust stability of discrete time-delay uncertain singular systems

    Page(s): 45 - 52
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    The robust stability property of linear discrete time-delay singular systems with structured parametric uncertainties is considered. Under the assumptions that the nominal time-delay singular systems are regular, causal and stable, necessary and sufficient conditions based on μ-analysis and guardian map theory are obtained to guarantee the properties by transforming the problem into checking the nonsingularity of a class of uncertain matrices. A tight bound is obtained in terms of μ for keeping the discrete time-delay singular systems regular, causal and stable. The results can be easily extended to deal with robust D-stability problem. Two examples are given to show the feasibility of the approach. View full abstract»

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  • Design aspects of a continuous-time tracking filter

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (233 KB)  

    Continuous-time tracking filters based on the two-state exponentially correlated velocity (ECV) model are discussed, in which a correlation parameter is used to give the velocity an exponential correlation. It is shown that the correlation parameter in the model causes additional deterministic steady-state filter errors. For a given bandwidth, the performance declines with the correlation parameter even in the Kalman algorithm covariance sense. The covariance obtained from measurement noise only is also given and compared with the Kalman algorithm covariance. The paper illustrates, in a simple case, that a reasonable model extension from the Kalman filtering point of view could give a worse filter performance. The results are obtained by using filter transfer functions. View full abstract»

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  • Direct adaptive output-feedback fuzzy controller for a nonaffine nonlinear system

    Page(s): 65 - 72
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (295 KB)  

    A direct adaptive output-feedback controller for highly nonlinear systems is proposed by considering uncertain or ill-defined nonaffine nonlinear systems and employing a static fuzzy logic system (FLS) with flexible structure, i.e. online variation of the number of fuzzy rules. A linear error observer whose dynamic order is the same as that of the controlled system is employed and the FLS approximates and adaptively cancels an unknown plant nonlinearity using the observed state variables. A control law and adaptive laws for unknown fuzzy parameters and bounding constant are established so that the whole closed-loop system is stable in the sense of Lyapunov. The state observation error and tracking error are guaranteed to be uniformly ultimately bounded. No a priori knowledge of an upper bound on a lumped uncertainty is required. View full abstract»

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  • Regional stabilisation for infinite bilinear systems

    Page(s): 109 - 116
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (469 KB)  

    An output stabilisation technique for infinite dimensional bilinear systems is presented. It consists in studying the asymptotic behaviour of such a system only on a subregion of its geometrical domain, so we give sufficient conditions to obtain a stabilising control. Also, we concentrate on the determination of the control which ensures regional stabilisation by minimising a given performance cost. The obtained results are illustrated by numerical examples. View full abstract»

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  • Design and implementation of command and friction feedforward control for CNC motion controllers

    Page(s): 13 - 20
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    Motion controllers play a pivotal role in the development of high-performance CNC machines. Precision motion control is achieved with a control structure employing S-curve motion planning on the velocity command before interpolation, command feedforward and friction feedforward compensation. To evaluate the performance of the proposed control scheme, a servomechanism is controlled to track a circular curve in the form of nonuniform rational B-splines, where the desired motion information such as velocity and acceleration are also provided. Experimental results indicate that the proposed motion-control structure exhibits a better performance, when compared with conventional motion-control schemes. View full abstract»

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  • Tunable H robust guidance law for homing missiles

    Page(s): 103 - 107
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (242 KB)  

    The proposed robust guidance control law can attain satisfactory robust performance for pursuing an unpredictable maneuvering target. Sufficient condition analysis is also carried out for the proposed guidance control law with tunable parameters. The proposed method not only need not touch the hard-solved Hamilton-Jacobi partial differential inequality but also guarantees that the line-of-sight distance between homing missile and maneuvering target can quickly converge to zero. A previously-implemented simulation discussed elsewhere is performed using the guidance control law to illustrate the efficiency of the proposed design. View full abstract»

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