2009 (Volume 19)
Axial dispersion models and their basic properties
|D. Bartova, B. Jakes, J. Kukal|
(Institute of Chemical Technology, Prague, Czech Republic)
The paper is oriented to summary of important basic relations, which characterize behavior of four axial dispersion models (AEO: axial enforced closed-open model, ACO: axial closed-open model, ACC: axial closed-closed model, AOO: axial open-open model) and three referential models (ideal mixed model, plug flow model, cascade of ideal mixers without back-mixing). Selected basic properties (parametric characteristics) of these models can be used for parameter identification of included hydrodynamic flow structure models.
Mathematical description of models including initial and boundary conditions, transfer function, model transient response to Dirac impulse as weighting (impulse) function, model transient response to step function as step response are included in this study. There are also included further characteristics of impulse function: raw moments up to 4th order, variance, variation coefficient, skewness , kurtosis, location and value of mode. Complete set of these characteristics for all studied models is collected (model-by-model) in seven tables.
The authors declare several properties of weighting function as key ones: value of 1st raw (dimensional) moment, parametric values and mode properties, related to dependence on Peclet number. The plots of parametric values and mode properties vs. Peclet number are mentioned in the paper for four studied axial dispersion models.
keywords: axial dispersion, flow models, basic properties, moments, mode
Zeros and the output-zeroing problem in linear systems with time delay in control vector
(Warsaw University of Technology, Poland)
The notion of zeros in linear time-invariant multi input multi output systems with delay in state or/and control input is not extensively discussed in the relevant literature. The concept of invariant zeros in a linear time-invariant MIMO system with delay in control vector is considered. In the state-space framework the invariant zeros are treated as the triples: complex number, nonzero state-zero direction, input-zero direction. Such treatment is strictly related to the output-zeroing problem and in that spirit the zeros can be easily interpreted. The problem of zeroing the system output is also addressed. For systems of uniform rank the first nonzero Markov parameter comprises a certain amount of information concerning invariant zeros, output-zeroing inputs and the zero dynamics. General formulas for output-zeroing inputs, the corresponding solutions and the zero dynamics are provided. The obtained results are illustrated by simple numerical examples.
keywords: linear systems with time delay in control vector, state-space methods, output-zeroing problem, invariant zeros
Novel digital PWM strategies of multilevel voltage source inverters
|D. Beriber, A. Talha|
(University of Sciences and Technology Houari Boumediene, Algeria)
|E. Berkouk, M. Boucherit|
(Ecole Nationale Polytechnique d'Alger, Algeria)
(Ecole Centrale de Lille, France)
In this paper, two novel algorithms of algebraic PWM strategies for seven-level Neutral Point Clamped (NPC) Voltage Source Inverter (VSI) are presented. These algorithms use a control model of the inverter. In the first part, the authors develop a model of this inverter, without assumption on its control, by using design method associated to Petri nets and switching functions. In the second part, knowledge and control models of this converter are reviewed by using respectively instantaneous and continuous equivalent switching functions. In the last part, two algebraic PWM control strategies of the inverter are proposed. The obtained results are full of promise to use these digital strategies to control seven - level NPC VSI used in high voltage and high power applications as electrical traction.
keywords: multilevel NPC inverter, generating function, connection function, PWM strategies, algebraic modulation
Differential evolution applied to parameter estimation of induction motor
|B. Subudhi, D. Jena|
(Department of Electrical Engineering, NIT, India)
Control of induction motor drive system requires an exact knowledge of its parameters. Efficient parameter estimation techniques are essential to obtain the parameters such as stator and rotor resistances, leakage and magnetizing inductances, because any mismatch between the actual and computed parameter values may lead to deterioration of control performance of the induction motor drive. In this paper, the differential evolution (DE) strategy - a global optimizer has been exploited for estimation of the above parameters of the induction motor. The main focus of the paper is on the application of the DE strategies to parameter estimation of an induction machine drive system based on the information of its input and output data, where input data comprises the stator voltages and the output data comprises the stator currents. Five different DE strategies were employed for implementing the induction motor parameter estimation schemes. Comparison of the results obtained through an extensive simulation studies on parameter estimations provide an idea how to choose an efficient estimator and to use them for efficiently control the drive.
keywords: differential evolution, induction motor, parameter estimation
Neural network parallel force/position control of robot manipulators under environment and robot dynamics uncertainties
|F. Ferguene, N, Achour, R. Toumi|
(LRPE, Faculty of Electronics and Computer Science, Algeria)
The performance of a parallel force/position controller for robot force tracking is affected by the uncertainties in both the robot dynamics and the environment stiffness. This paper aims to improve the controller's robustness by applying the neural network (NN) technique to compensate for the robot dynamics at the input trajectory level and adaptive feed-forward compensation to cope with variations in the contact environment. A NN control technique is applied to a conventional PID force/position parallel control scheme which is composed of a PD action on position loop and a proposed adaptive I (integral) action on the force loop, which allows a complete use of available sensor measurements by operating the control action in a full dimensional space without using selection matrices. Simulation results for a three degrees-of-freedom robot show that highly robust position/force tracking can be achieved in the presence of a full dynamic robot and large environment stiffness uncertainties.
keywords: force/position control, parallel control, PID control, neural network controllers, adaptive control, robot manipulators
Experimental investigations of human-operator as a pressure force regulator in man-hand tool system
| Z. Basista, M. Ksiazkiewicz, J. Tarnowski|
(Cracow University of Technology, Poland)
In the paper the results of experimental investigations of system operator-handle-base have been presented. The aim of investigations was to record dynamical reactions of human operator volunteers participating in the experiments to a visual, suddenly appearing step signal. The main task of each operator was to track the signal as precisely as possible with a push force exerted on the immobile handle. The measurements were done on an especially designed stand. Time histories of step reference and forces realized by the operator were statistically elaborated and graphically presented.
keywords: man-machine system, manual control, human-operator, hand-tool