The aim of this paper is presentation and comparison of calculation methods of the inductance matrix of a 3-column multi-winding autotransformer. Main and leakage autotransformer inductance was obtained using finite elements method. Static calculations were made at the current supply for 2D and 3D models, and mono-harmonic calculations were made at the voltage supply. In the mono-harmonic calculations the eddy current losses were taken into account, this made it possible to study relationship between the autotransformer parameters and the frequency. Calculations were made using Ansys and the authors' own programs in Matlab.
The 15-winding and 3-column autotransformer supplying an 18-pulse rectifier circuit was developed. Presented methods can be used also for the autotransformers of other topologies supplying different kinds of converters. Presented methods make it possible to exactly calculate main and leakage inductances of the multi-winding autotransformer. The presented analysis of the eigenvalues and eigenvectors of the inductance matrix makes it possible to identify the influence nature of individual modes on the inductance matrix, and to compare the calculation results obtained using the presented methods. Frequency dependence of autotransformer parameters was shown. Also modes of the impedance matrix of the multi-winding autotransformer was investigated, this made it possible to identify the influence nature of individual modes on the inductance matrix. Using presented methods one can exactly calculate main and leakage inductances of the autotransformer. Thanks to this, one can design in optimal way autotransformers for supplying, for example, rectifier circuits, THD coefficients. The results of the measurements and simulations were also shortly presented at the end of the article.
Accurate prediction of power loss distribution within an electrical device is highly desirable as it allows thermal behavior to be evaluated at the early design stage. Three-dimensional (3-D) and two-dimensional (2-D) finite element analysis (FEA) is applied to calculate dc and ac copper losses in the armature winding at high-frequency sinusoidal currents. The main goal of this paper is showing the end-winding effect on copper losses. Copper losses at high frequency are dominated by the skin and proximity effects. A time-varying current has a tendency to concentrate near the surfaces of conductors, and if the frequency is very high, the current is restricted to a very thin layer near the conductor surface. This phenomenon of nonuniform distribution of time-varying currents in conductors is known as the skin effect. The term proximity effect refers to the influence of alternating current in one conductor on the current distribution in another, nearby conductor. To evaluate the ac copper loss within the analyzed machine a simplified approach is adopted using one segment of stator core. To demonstrate an enhanced copper loss due to ac operation, the dc and ac resistances are calculated. The resistances ratio ac to dc is strongly dependent on frequency, temperature, shape of slot and size of slot opening.
The aim of this paper is to derive an analytical equations for the temperature dependent optimum winding size of inductors conducting high frequency ac sinusoidal currents. Derived analytical equations are useful designing tool for research and development engineers because windings made of foil, square-wire, and solid-round-wire windings are considered. Temperature dependent Dowell’s equation for the ac-to-dc winding resistance ratio is given and approximated. Thermally dependent analytical equations for the optimum foil thickness, as well as valley thickness and diameter of the square-wire and solid-round-wire windings are derived from approximated thermally dependent ac-to-dc winding resistance ratios. Minimum winding ac resistance of the foil winding and local minimum of the winding ac resistance of the solid-round-wire winding are verified with Maxwell 3D Finite Element Method simulations.
Simultaneous perception of audio and visual stimuli often causes concealment or misrepresentation of information actually contained in these stimuli. Such effects are called the "image proximity effect" or the "ventriloquism effect" in the literature. Until recently, most research carried out to understand their nature was based on subjective assessments. The authors of this paper propose a methodology based on both subjective and objectively retrieved data. In this methodology, objective data reflect the screen areas that attract most attention. The data were collected and processed by an eye-gaze tracking system. To support the proposed methodology, two series of experiments were conducted - one with a commercial eye-gaze tracking system Tobii T60, and another with the Cyber-Eye system developed at the Multimedia Systems Department of the Gdańsk University of Technology. In most cases, the visual-auditory stimuli were presented using a 3D video. It was found that the eye-gaze tracking system did objectivize the results of experiments. Moreover, the tests revealed a strong correlation between the localization of a visual stimulus on which a participant's gaze focused and the value of the "image proximity effect". It was also proved that gaze tracking may be useful in experiments which aim at evaluation of the proximity effect when presented visual stimuli are stereoscopic.