No. 5, 1998


Viktor Valouch: Space vector modulation-based fuzzy control of active filter, 423–434

A simple SVM-based fuzzy control is presented in the paper. The outputs of the fuzzy controller represent the switching schemes of the voltage-type inverter and lengths of the time intervals composing the switching period. The errors in instantaneous active and reactive powers, which should be generated to compensate high harmonics of a nonlinear load, are the input variables of the fuzzy control of an inverter-based active filter. In order to keep phase currents sinusoidal also in case of unsymmetrical voltage system, a modification of reference average powers is suggested. The control algorithm has been verified by a simulation.

S.J. Zhu, L.M. Peng, Q. Zhou, Z.Y. Ma, K. Kucharova, J. Cadek: Creep behaviour of aluminium strengthened by fine aluminium carbide particles and reinforced by silicon carbide particulates DS Al-SiC/Al4C3composites, 435–455

Creep behaviour of aluminium strengthened by fine aluminium carbide particles and reinforced by silicon carbide particulates is investigated. For comparison, the results for two dispersion strengthened (DS) alloys denoted DS AlC1 and DS AlC2 are presented. (C1 and C2 mean the contents of carbon in wt. % which define the volume fractions of Al4C3 particles in DS AlC alloys as well as in SiC/AlC composite matrices). The volume fraction of SiC particulates in composites, denoted SiC/AlC1, SiC/AlC2 and SiC/AlC3, was fixed to 10 vol. %. The creep in both DS A1C alloys as well as in SiC/AlC composites is associated with relatively high true threshold stress sTH. The linear regression analysis showed that the true stress exponent of minimum creep strain rate of 8 should be preferred to that of 5. The creep strain rate was found to be controlled by lattice diffusion in the matrix metal-aluminium. The creep strength of the SiC/AlC composites increasing with the volume fraction of Al4C3 particles is entirely due to the effect of this fraction on the threshold stress. This is not the case of DS AlC alloys. The difference of the creep strength in SiC/AlC composites and the respective DS AlC alloys could be accounted for by the load transfer effect. The athermal detachment of dislocations from fine Al4C3 (and Al2O3) particles dispersed in the composite matrix is considered as the creep strain rate controlling process.

Daniel Mayer, Tomas Muzik: The synthesis of symmetrizing circuit for generalized three-phase network, 457–468

It is becoming evident that the behaviour of a symmetrizing circuit used for connecting one-phase load to three-phase network is strongly dependent on the values of parameters of circuit elements. The hitherto formulas for the parameters of symmetrizing elements are valid on very simplified assumptions and thus can lead to design of a poor quality. The algorithm suggested in the present work allows for specification of a perfect symmetrizing circuit under quite general conditions.

Viktor Valouch, Jiri Skramlik, Ivo Dolezel: Common and differential mode currents in an inverter-fed induction motor drive, 469–491

The paper deals with analysis of the common and differential mode currents in a system transistor PWM inverter-long cable-induction motor. Several representations of the motor and the cable suitable for determining both steady state and transient responses in a wide range of frequencies (tens kHz-tens MHz) have been proposed in common with finding the transfer functions of individual parts of these models in the particular modes. The results are compared with data obtained from a lot of experiments and simulations.

Ales Tondl: Nonlineary coupled systems: parametric and self-excitations, 493–505

System consisting of at least two subsystems which are mutually coupled by pure nonlinear couplings are considered. It is supposed that only one of these subsystems is self-excited or parametrically excited. It is shown that the boundaries between stable and unstable trivial solutions of the differential equations of motion of the whole system are not influenced by the non-excited subsystem, i.e. they are the same as for the excited subsystem alone. Some characteristic features of vibration are illustrated by the example where the excited subsystem is self-excited by flow. The vibration amplitudes of the excited subsystem, in the case when the whole system is oscillating, are usually smaller in comparison with the case of zero coupling. But this is not a generally valid rule.

David Vokoun, Vratislav Kafka: Training of two-way shape memory effect in NiTi wire: one experimental procedure, 507–513

An experimental procedure for training two-way shape memory effect is suggested and demonstrated. It is similar to the procedure used by Liu and McCormick (1990), but makes use also of the effect of preceding one-way process.