ACTA TECHNICA CSAV |

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.

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 AlC_{1} and DS AlC_{2} are presented. (C_{1} and C_{2}
mean the contents of carbon in wt. % which define the volume fractions of Al_{4}C_{3}
particles in DS AlC alloys as well as in SiC/AlC composite matrices). The
volume fraction of SiC particulates in composites, denoted SiC/AlC_{1}, SiC/AlC_{2}
and SiC/AlC_{3}, 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 s* _{TH}*. 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 Al

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.

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.

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.

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.