No. 3, 2005


Petr Kokes, Stanislav Bartos : Vector control of the induction machine stator magnetic flux, pp.207-231

The paper deals with one of the prospective methods of induction machine control called the stator flux vector control (SFVC). To enhance the accuracy of the control, the currently used P-controller is replaced by the PI-controller. At the same time this disposition eliminates the dependence of the control on the machine stator resistance and simplifies the implementation of the regulator. The properties of the control loop of the stator magnetic flux are discussed in detail, together with selecting suitable constants for both the P- and PI-controller. The sensitivity of the proposed method to changes in machine parameters is discussed. The theoretical conclusions are verified via computer simulations and experimental tests.

Vaclav Nenicka, Jiri Sonsky : On the methodology of vortex structures identification in free plasma flows, pp.233-250

The vortex structures in free plasma flows are identified using the information on the radiation intensity scanned in two mutually perpendicular directions by the CCD camera. The method is based on the assumption that a dominant heat flow vector around the jet core is proportional to the product (hv), where h is the enthalpy of volume unit and v the velocity of the medium. The method developed in the kinetic theory of gases is adjusted for determination of components of the heat flow vector including its rotation. The evolution of radiation intensity and dynamics of vortex structures in both the axial and radial direction about the jet's core are captured using the series of 8 shots within time interval of 100 ms. The analysis of vortex structures dynamics at flow rates 25 slm and 50 slm and electric current 150 A and 200 A is presented.

Jiri Nohava, Frantisek Kroupa : Nonlinear stress-strain behavior of plasma sprayed ceramic coatings, pp.251-262

Stress-strain curves of selected plasma-sprayed ceramic coatings were measured by the four-point bending method, with the coating deposited on the compressive or tensile side of the substrate. Uniaxial stress s and deformation e in the central plane of the coating were determined. For deformations |e| < 0.1% Young's moduli can be considered constant and were found to be from 18 to 52 GPa. For deformations 0.1% < |e| < 0.4% the measured curves show that Young's modulus increases with the compressive deformation and decreases with the tensile deformation. The contribution of intrasplat microcracks to the nonlinearity is discussed. In tensile loading, microcracks are opening and Young's modulus is decreasing whereas in compression closing of microcracks leads to increase in Young's modulus. Two-parametric equation containing linear and quadratic term was successfully used to describe the nonlinear stress-strain curves of plasma sprayed ceramic coatings.

Chao Qin, Josef Tlusty, Suonan Jiale, Wang Yibo : Wind-hydro hybrid power system stability analysis and simulation, pp.263-277

The establishment and simulation of a mathematical module for a wind generator as well as the method of wind power stability analysis and simulation in wind-hydro hybrid power systems by means of MATLAB are described. Two case studies of the wind-hydro hybrid power system in Xinjiang Province, China are presented.

Jaroslava Zilkova, Jaroslav Timko, Jan Berko : Speed sensorless control of an induction motor drive using extended Kalman filter, pp.279-289

An extended Kalman filter is applied to estimating state variables of field oriented IM drive control. We need to know precisely the magnitude and angle of the rotor flux space vector for good performance of the field oriented control. An extended Kalman filter algorithm can be used for estimation of the rotor flux and rotor angular speed without using any mechanical sensors. For the estimation it is necessary to monitor only the stator voltage and stator current of the induction motor. The math model of the extended Kalman filter is presented and quality of the estimation is tested in the flux oriented IM drive control.

Irena Kovacova, Jan Kanuch, Dobroslav Kovac : DC permanent magnet disc motor design with improved EMC, pp.291-306,

The computer analysis of electromagnetic compatibility (EMC) for DC permanent magnet disc motors is carried out with special reference to suppressing the electromagnetic field radiation.