Papers

Recent Journal publications

Editorial (to the special issue on autonomous adaptive control of vehicle systems)

International Journal of Adaptive Control and Signal Processing, Volume 21, Number 1, February 2007

Components of a vision assisted constrained autonomous satellite formation flying control system

International Journal of Adaptive Control and Signal Processing, Volume 21, Number 1, February 2007

This paper examines a complete solution to autonomous formation flying of satellites where problems of position, velocity and attitude estimation, data fusion across the cluster, constrained actuators, fuel efficient manoeuvres and robustness are all considered. The joint problem of inaccurate state estimation combined with low thrust is addressed through the use of Kalman filter and an LP-solvable constrained predictive controller. Attitude control is ensured by a globally stable quaternion-based adaptive feedback controller. Calibration of control signals for translational force actuation is introduced. Options of solutions are analysed and the system and its parts are illustrated in realistic simulations. Preview of the paper is available at the journal's website. PDF

Discussion on "A robust approximation scheme for the LQG control of an undamped flexible beam with a tip mass"

European Journal of Control, Volume 12, Number 6, December 2006.

This is a brief review and comments on the development of robust approximation techniques for infinite dimensional optimal controllers of PDE modelled systems during the pas 2 decades. PDF

Universal adaptive control of satellite formation flying

International Journal of Control, Volume 78, Number 1/January 2005

In this paper, a new universal adaptive control scheme for satellite formation flying is developed. The underlying idea of our design is to combine the domination design and the monotone adaptive gain. This scheme is guaranteed to have the properties of position tracking and full adaptivity against ...PDF

Application of Ellipsoidal Estimation to Satellite Control Design

Mathematical and Computer Modelling, to appear in 2005

The equations of motion of a small satellite moving along a prescribed trajectory underdisturbances are analysed. Problems of this kind have been extensively investigated. The corresponding equations for relative motion errors, caused by the uncertainties in initial conditions and control implementation imperfections, are linearized. The linear equations are reformulated and the evolution equations for optimal ellipsoidal estimates of these errors are derived. It is shown that ellipsoidal bounding of reachable sets is an efficient approach to modeluncertain linear dynamical systems. ...PDF

Robust control of microvibrations with experimental verification

Proceedings of the I MECH E Part C Journal of Mechanical Engineering Science, Number C5, May 2005, pp. 453-460(8)

The paper addresses the problem of actively attenuating a particular class of vibrations, known as microvibrations, which arise, for example, in panels used on satellites. A control scheme that incorporates feedback action is developed which operates at a set of dominant frequencies in a disturbance spectrum, where the control path model is estimated online. Relative to earlier published techniques, a new feature of the presented controller is the use of the inverse Hessian to improve adaptation speed. The control scheme also incorporates a frequency estimation technique to determine the relevant disturbance frequencies with higher precision than the standard fast Fourier transform (FFT). The control scheme is implemented on an experimental test-bed and the total achieved attenuation, as measured from the experiments, is 26 dB.... PDF

Iterative design for active control of fluid flow

International Journal of Control,Volume 76, Number 14/20 September 2003

This paper considers iterative controller design for planar Poiseuille flow by model unfalsification and controller redesign. The main contribution is to show that model-unfalsification-based iterative design can be useful in flow control problems. The a priori knowledge of ...PDF

Model-free frequency domain iterative active sound and vibration control

Control Engineering Practice, Vol. 11 (2003), pp. 1049–1059

paper, a model-free iterative feedback tuning method is presented to tune a frequency domain controller for a set of narrow-band disturbances. A single control problem with multiple tones of the disturbance is split into a set of parallel control problems. Due to the repr esentation in the frequency domain, there are only control amplitude and phase to be tuned for each tone. Tuning is performed through a sequence of experiments which enables the calculation of a model-free gradient of a quadratic cost function. The number of experiments at each iterative step is R S þ 1; where R is the number of controls signals and S is the number of output signals. Results on a laboratory active sound control system are shown. The example demonstrates the practical effectiveness of the method...PDF

Frequency selective feedback for active noise control

Control Systems Magazine, IEEE, Aug. 2002, Volume: 22 , Issue: 4, pp.: 32 - 41

This article presents a frequency-selective, filter-based adaptive feedback solution in the frequency domain for periodic noise attenuation... PDF

Analysis of Formation Flying Control of a Pair of Nanosatellites

AIAA Journal of Guidance, Control and Dynamics, Sept-Oct 2002, Vol. 25, No. 5, pp. 971-974.

This paper analyzes and provides implementable solutions for stabilisation and maneuver control of two nanosatellites subject to control and state constraints. Reduced complexity computation of reachable states from given initial states is presented.

Error Control in Polytope Computations

Journal of Oprimization Theory and Applications Vol. 113, No. 2, pp. 325–355, May 2002

This paper presents solutions for numerical computation on convex hulls; computational algorithms that ensure logical consistency and accuracy are proposed. A complete numerical error analysis is presented.It is shown that a global error bound for vertex-facet adjacency does not exist under logically consistent procedures. To cope with practical requirements, vertex preconditioned polytope computations are introduced using point and hyperplane adjustments. A global bound on vertex-facet adjacency error is affected by the global bound on vertices; formulas are given for a conservative choice of global error bounds. ...PDF

Frequency selective dual control for periodic disturbance cancellation

Int. J. Robust Nonlinear Control 2000; Vol. 10: pp. 709-727

A general framework is introduced for iterative/adaptive controller design schemes by model unfalsification. An important feature of the schemes is their convergence near to the best possible controller given a set of model and controller structures. The problem of stability assured controller tuning is examined through unfalsified Riemannian bands of the Nyquist plot. Instability tolerant H- and l-norm-based controller tuning schemes are introduced. Computational problems are discussed and a simulation is used to illustrate the new scheme....PDF

Convergence of control performance by unfalsifcation of models - levels of conidence

Int. J. Adapt. Control Signal Process.2001; Vol. 15: pp. 471-502

A general framework is introduced for iterative/adaptive controller design schemes by model unfalsification. An important feature of the schemes is their convergence near to the best possible controller given a set of model and controller structures. The problem of stability assured controller tuning is examined through unfalsified Riemannian bands of the Nyquist plot. Instability tolerant H and l-norm-based controller tuning schemes are introduced. Computational problems are discussed and a simulation is used to illustrate the new scheme. ...PDF

Adaptive harmonic control

International Journal of Control, Volume 115, Number 12, 2001

This paper presents adaptive feedback control at individual harmonics for cancellation of periodic disturbances. It is shown that the original idea, that has been around for a long time, can be developed much further to produce robust and highly adaptable controllers. Frequency selective feedback harmonic ...PDF

Self-tuning control by model unfalsification (Part I)

International Journal of Control, Volume 73, Number 17/November 20, 2000

The transient problem in self-tuning control is analysed in a non-stochastic framework based on model unfalsification and solutions are proposed. It is assumed that the disturbance bounds or norm bounds on the unmodelled dynamics are not known a priori. Depending on the transient requirements the problem ...PDF

Self-tuning control by model unfalsification (Part II)

International Journal of Control, Volume 73, Number 17/November 20, 2000

The transient problem in self-tuning control is further analysed in a non-stochastic framework based on model unfalsification and solutions are proposed. It is not assumed that the noise bounds or norm bounds on the unmodelled dynamics were known a priori. Depending on the transient requirements on ...PDF

Worst-case dual control: basic results

International Journal of Control, Volume 73, Number 18/December 15, 2000

This paper considers the worst-case-dual control problem and discusses its basic properties. The Bellman equation is derived and some simple cases are analysed. Unmodelled dynamics bounded in l1norm is accounted for. The case of infinite horizon cost function is considered for a special ...PDF

Improved efficiency of adaptive robust control by model unfalsification

Automatica 35 (1999), pp . 981-986

The adaptive robust control scheme introduced by Veres and Sokolov (see below or: Automatica, 34, 723-730) provides optimal asymptotic performance under unmodelled dynamics, unknown disturbance bounds and unknown model orders that make the scheme desirable in practical applications. The amount of numerical computations associated with that scheme is large because of the possible large complexity of the appearing polyhedra. The geometrical details of the polyhedra need large memory space and their updating a lot of computation. This note gives a modi"cation of the scheme so that polyhedron complexity is limited....PDF

Adaptive robust control under unknown model orders

Automatica 34 (1998), pp . 723-730

A robuts indirect adaptive controller is introduced in this paper...PDF

Laguerre filter reduced-order l1 identification

International Journal of Control, Volume 68, Number 4/November 10, 1997

Calculable l upper bounds for the truncation error of Laguerre filters are 1 presented. A new solution to the finite-dimensional l approximation problem is 1 also detailed. The numerical performance of this algorithm is shown to be better than existing solutions. An l identification method, which makes ...PDF

Recent IEEE/IEE Conference Publications

Principles, architectures and trends in autonomous control

Autonomous Agents in Control, 2005. The IEE Seminar on (Ref. No. 2005/10986), 10 May 2005 Pages: 1- 9

Feedback systems introduced some degree of autonomy of machines throughout the history of engineering. Feedback has been introduced to the operations of engines, servos, production processes, aircraft, car and ship control systems. These systems are....PDF .

A class of BDI agent architectures for autonomous control

43rd IEEE Conference on Decision and Control, 2004. CDC2004, Volume: 5 14-17 Dec. 2004, Pages: 4746- 4751

A class of beliefs-desires-intentions (BDI) agent architecture is presented for control systems with a high degree of autonomy. The architecture contains agents for modelling, controller optimization, implementation and to monitor performance. The global convergence of performance of the agent system is proven under three mild assumptions. Relevant features of the agent structure are competing modellers and controllers. The benefit is an enhanced ability to learn new plant dynamics of varying complexity and controller adaptation. The new family of control agent architectures is called cautiously optimistic, a name to reflect the most important property of the new architecture: modelling results are applied with caution for control but current models are accepted until measurements do not contradict them with a margin. A cautiously optimistic control agent (COCA) is proven to have converging performance to a nearly optimal performance for stationary dynamics of a real plant under fairly general assumptions.....PDF

Satellite vibration control using frequency selective feedback

42nd IEEE Conference on Decision and Control, 2003. Volume: 2 9-12 Dec. 2003, Pages: 1693- 1698

This paper addresses the problem of actively attenuating the vibration of plates on satellites. A pure feedback controller is demonstrated which operates at a set of dominant frequencies in a disturbance spectrum, where the control path model is estimated...PDF

Application of exploratory modelling to active headrest control

42nd IEEE Conference on Decision and Control, 2003. Volume: 4 9-12 Dec. 2003

Pages: 3936- 3941

A new technique of iterative modelling and controller tuning is presented and its applicability demonstrated on a model of an active headrest which attenuates the ambient noise for the comfort of a passenger. The underlying scheme relies on internal model control (IMC) which is shown to have self-excitation for identification for control. Application of IMC creates synergy of identification and control and models tuned for control can bring enhanced and more reliable performance. The allowed gain error (AGE) is used which is compared with model uncertainty to form a criterion of modelling for control. This modelling criterion quantifies the maximum violation of robust stability and performance robustness along the frequency axes, as such it is a criterion of modelling for control. The new scheme is called exploratory modelling for controller optimization (EMCO) and its objective is to obtain simple robust controllers. The EMCO scheme can be used both on-and off-line. ....PDF

Microwave super conductivity filter tuning by multi-stage-unfalsification-based robust adaptive scheme

7th International Conference on Control, Automation, Robotics and Vision, 2002. ICARCV 2002. Volume: 2 2-5 Dec. 2002, Pages: 681- 686

A new iterative robust adaptive identification and control scheme by unfalsification is applied to a complex microwave super conductivity filter tuning problem (SCFTP), and for the first time, it gave an im-plementable solution. ... PDF

Convergent iterative model unfalsification for control

41st IEEE Conference on Decision and Control, 2002, Volume: 4 10-13 Dec. 2002

Pages: 4221- 4226

Iterative controller design by model unfalsification and robust controller design is reexamined and developed. Two frequency dependent uncertainty functions are used to ease the process of modelling for control. One is the maximum allowed gain errors (AGE) of a nominal plant which depends on the controller, nominal model and the stability robustness requirement. The other functions used are frequency dependent unfalsified lower bounds of plant dynamical uncertainty around nominal models. The controller is called feasible if the allowed plant perturbation function bounds an estimated plant uncertainty for each frequency. If there is no feasible controller then more experiments are carried out with the same controller which excite the plant at the "offending frequencies". Otherwise the feasible controller with the largest stability margin and "most promising" performance is used in the next experiment with the testing input spectrum focusing on the frequencies where the stability margin is small and the performance is sensitive. .... PDF

Stability analysis of secondary path estimation during FSF-based feedback control

Proceedings of the 2002 International Conference on Control Applications, 2002. Volume: 1 2002

Page(s): 483- 488.

A pure feedback controller alternative is proposed to the feedforward filtered reference least mean method for active noise control under periodic disturbances. There is no need for pre-modelling of any dynamics. The scheme is a frequency selective filter based controller with secondary plant estimation during control. For each major disturbance signal, a complex controller gain of the frequency component is computed and a complex gain for the plant dynamics is updated. The main contribution in this paper is the proof of stability. The controller was implemented on a laboratory sound experiment. The controlled sound wave was measured with a microphone. Next to the disturbance speaker, the controlled speaker was placed to generate the destructive secondary sound wave. An output attenuation of about 37dB was achieved, clearly showing the usefulness of the approach. ...PDF

Tuning for robustness and performance using iterative feedback tuning

41st IEEE Conference on Decision and Control, 2002, Volume 4, 10-13 Dec. 2002 Pages:4682 - 4687

Iterative feedback tuning (IFT) is a direct tuning method using closed loop experimental data. The method is based on numerical optimization. In each iteration of the optimisation an unbiased gradient estimate is used. In this contribution the results of are refined and developed further. Improvements are introduced on the optimization procedures of the IFT scheme to allow for joint optimization of non-conflicting criteria of stability robustness and performance. Also the case of weighted additive uncertainty is considered as an alternative to the co-prime factor perturbations as used by Glover and McFarlane (1989). Optimization of the estimate of the H/sub /spl infin// robustness criterion is now based on global optimization to increase reliability. ...PDF

Some old IEEE papers

Strong consistency of ML estimators using partial fraction and elementary subsystem representation of multivariable systems

IEEE Transactions on Automatic Control,, Oct 1987, Volume: 32 , Issue: 10, pp. 867 - 876

The strong consistency of ML estimators for partial fraction matrix (PFM) and elementary subsystem (ESS) representations of vector ARMA processes is discussed for the case when the structure is overestimated. The main results of the paper are the off-line strong consistencytheorems of ML estimators for PFM representation, when the number of poles is overestimated and for the ESS representations when the number of ESS's associated with the poles is overestimated. PDF

Structure selection for bounded-parameter models: consistency conditions and selection criterion

IEEE Transactions on Automatic Control, April 1991, Volume: 36 , Issue: 4, pp. 474 - 481

Strong-consistency conditions for structure selection in bounded-parameter models are studied. A certain robust selection criterion, based on the volume of the exact parameter-bounding polytope, is proposed for linear regression models. The effectiveness of the polytope volume criterion is demonstrated on a model nonlinear in its variables but linear in its parameters. Its strong consistency is proved for a large class of noise distributions. The usual assumptions on the noise, namely independence, constant variance, or martingale difference properties,need not be made, but asymptotic independence is assumed. PDF