Akira Kumamoto

Speed regulation of an induction motor using model reference adaptive control

A novel approach of constructing a robust variable-speed drive system using an induction motor supplied from a voltage-source-type PWM inverter is discussed. The inverter is controlled so as to generate the fabricated terminal voltages based on the voltage-decoupled transvector control theory where neither a current feedback loop nor a current limiter circuit is required. Although the hardware for this decoupling method becomes simplified, it still has some disadvantages, such as the discrepancy between the command currents and actual currents. Incorporated into the drive system described herein is the optimal-speed regulator adopting the exact model-matching method, which fulfills the function of a compensator for unfavorable errors. The operating characteristics of the proposed drive system are compared with conventional PI control to verify the effectiveness under various conditions by investigating the transient responses for the step change of the speed command, the load torque, and so forth.

Adaptive document clustering using incrementally expanded queries

This paper describes a method of increasing the effectiveness of browsing by clustering large numbers of information retrieval results, and discusses the implementation of adaptive document clustering. In the proposed method, query information is successively expanded and refined in the course of browsing, and it is utilized as a clustering viewpoint that expresses the interests of the user. The proposed method is experimentally evaluated in an application to WWW information retrieval and its effectiveness is demonstrated.

Constructing Continuous-Time Chaos-Generating Templates Using Polynomial Approximation.

Aiming at developing a methodology for constructing continuous-time chaotic dynamical systems as flexible pattern generators, this paper discusses a strategy for binding desired unstable periodic orbits into a chaotic attractor. The strategy is comprised of the following two stages: constructing an interim “chaos-generating template”, and deforming the template according to the specifically desired orbits. INTRODUCTION Chaos is a fascinating phenomenon arising from nonlinearities in dynamical systems, and investigations on its applications to intelligent and flexible systems have appeared in many fields. An important aspect of chaos is that chaotic attractors embed or “host” an infinite number of unstable periodic orbits (UPO’s) bifurcated from prechaotic states (Ott, 2002). Among them, some distinctive orbits can be used for characterization or control purposes. For example, a variety of chaos control methods (Ott et al., 1990; Pyragas, 1992; Zhang et al., 2009) can stabilize UPO’s embedded in chaotic attractors, enlarging the operation range and/or enhancing the functionality of the system. In more recent years, the synthesis of chaos from various approaches (Chen and Ueta, 2002; Zelinka et al., 2008; Munoz-Pacheco and Tlelo-Cuautle, 2009) has been an active direction of research along the line of exploiting chaos. Primary concerns of these efforts include statistical and topological characteristics (e.g., invariant measure, Lyapunov spectrum, novel scrolling behaviors) that would be important in designing chaos-based information processing and communication applications. While the present study share some common motivation with the above-mentioned studies, we have put more focus on the geometrical shape and dynamical properties of UPO’s themselves from the viewpoint of the adaptive generation of periodic behaviors. Here our intention lies in extending the functionality of (stable) periodic pattern generators based on function approximation of vector fields, e.g., polynomial approximation (Okada and Nakamura, 2002) and neural network learning (Kuroe and Miura, 2006). In this paper, we consider continuous-time chaotic attractors as a container of UPO’s (patterns) where they can be stabilized, entrained, or targeted by external inputs into the dynamical system. In what follows, we propose a design strategy for binding desired UPO’s into a chaotic attractor governed by a polynomial vector field. The strategy is comprised of the following two stages: constructing an interim “chaos-generating template”, and deforming the template according to the specifically desired orbits. POLYNOMIAL VECTOR FIELDS We consider polynomial dynamical systems of the form ẋ = f(x)(x ∈ R ) where the vector field f(x) is represented as f(x) = [f1(x) · · · fN (x)] T = Φ(a(p1p2···pN ))θ(x), (1) θ(x) = [x1 · · · x ` N x `−1 1 x2 · · · 1] T . (2) Here, ` denotes the maximum degree of the polynomials, and the matrix Φ is comprised of the coefficients a(p1p2···pN ) of the polynomials. For example, with 3rdorder polynomials, the first element of a two-dimensional vector field is represented as f1(x) = a1(30)x 3 1 + a1(21)x 2 1x2 + a1(12)x1x 2 2 + a1(03)x 3 2 + a1(20)x 2 1 + a1(11)x1x2 + a1(02)x 2 2 + a1(10)x1 + a1(01)x2 + a1(00).(3) In our design process of the dynamical system, the coefficients are obtained by least-square fitting. To this end, we set up target vectors f(ηi) (i = 1, 2, · · · , L) at design points ηi on and in the vicinity of the target orbits, and construct matrices F = [f(η1) f(η2) · · · f(ηL)], (4) Θ = [θ(η1) θ(η2) · · · θ(ηL)]. (5) With these matrices, the least-square solution for Φ is given by Φ(a(p1 p2 ··· pN )) = FΘ # (6) where Θ is the Moore-Penrose pseudo inverse of Θ. Proceedings 24th European Conference on Modelling and Simulation ©ECMS Andrzej Bargiela, Sayed Azam Ali David Crowley, Eugene J.H. Kerckhoffs (Editors) ISBN: 978-0-9564944-0-5 / ISBN: 978-0-9564944-1-2 (CD)

E-learning support for students to generate questions originated from descriptions in course materials

In any e-learning system, students are required to study some course materials normally prepared in the form of textbooks. However it is not an easy task for many students to understand these textbooks. When some doubts and/or questions arise as to descriptions within textbooks, they usually tend to solve this difficulty by themselves or with their friends. This paper gives a prototype of a feedback support system in an e-learning where students are encouraged to feedback questions to lecturers by sending selected portions of descriptions in the textbook showing where and why they are in a trouble in understanding the textbook materials.

An electronic circuit simulator for educational purposes adopting graphic human interface

The author proposes an electronic circuit simulator for educational use with special attention given to the user-friendly and easy-to-handle human interface. The system is implemented on a Macintosh personal computer using HyperCard as a developing platform. This system aims to provide an artificial environment that makes it seem as if the user were actually handling such devices as instrumenting equipment and resistors in the circuit. This environment is prepared mainly using graphical objects with an attached script program to be activated in accordance with user action. The author gives a brief summary of the software configuration and the users response to the designed simulator.<<ETX>>