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Dive into the research topics where Bostjan Polajzer is active.

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Featured researches published by Bostjan Polajzer.


ieee international magnetics conference | 2005

Evaluation of experimental methods for determining the magnetically nonlinear characteristics of electromagnetic devices

Gorazd Štumberger; Bostjan Polajzer; Bojan Štumberger; Matej Toman; Drago Dolinar

The properties of magnetic material are normally described by the permeability tensor, while the magnetically nonlinear properties of electromagnetic devices (EMDs) can be described by the current-dependent characteristics of flux linkages. This paper presents and evaluates different experimental methods appropriate for determining the magnetically nonlinear characteristics of EMDs. The tested device is supplied by a controlled voltage source. Sinusoidal voltages, sinusoidal voltages with offset, and stepwise changing voltages are applied. Current-dependent characteristics of flux linkages are determined from the measured voltages and currents, either by numerical integration or by Fourier analysis and calculation of impedances.


IEEE Transactions on Magnetics | 2004

Impact of magnetic nonlinearities and cross-coupling effects on properties of radial active magnetic bearings

Bostjan Polajzer; Gorazd Štumberger; Joze Ritonja; Oto Tezak; Drago Dolinar; Kay Hameyer

The impact of magnetic nonlinearities and cross-coupling effects on the properties of the discussed radial active magnetic bearings (AMBs) is evaluated in the entire operating range. The characteristics of flux linkages and radial force are all determined by finite element computation, while the current and position dependent partial derivatives of the flux linkages are calculated by analytical derivations of the continuous approximation functions. Calculated current and position-dependent partial derivatives, as well as the radial force characteristics are incorporated into the proposed dynamic AMB model. The results presented show that the magnetic nonlinearities and cross-coupling effects can change the electromotive forces and the radial force considerably. These disturbing effects have been determined and can be incorporated into the real-time realization of nonlinear control in order to achieve cross-coupling compensations.


ieee international magnetics conference | 2006

A Three-Phase Core-Type Transformer Iron Core Model With Included Magnetic Cross Saturation

Matjaz Dolinar; Drago Dolinar; Gorazd Štumberger; Bostjan Polajzer; Joze Ritonja

The behavior of a power transformer (PT) depends considerably on the properties of the magnetically nonlinear iron core. This paper deals with the modeling of a three-phase, three-limb power transformer laminated iron core. The proposed iron core model is given by the corresponding partial derivatives of measured flux linkage characteristics. The magnetically nonlinear characteristics of flux linkages are determined by the controlled simultaneous magnetic excitation of all three limbs. This enables determination of magnetic cross couplings between different limbs, due to the saturation. The obtained iron core model integrated in the circuit model of PT is compared to the classical saturated iron core model without cross couplings, by analyzing the transient behavior of an unsymmetrically excited transformer. The numerical results obtained by the proposed iron core model agree with the measured results much better than those obtained by the existing nonlinear iron core model known from literature


ieee industry applications society annual meeting | 2008

Generalization of Methods for Voltage Sag Source Detection Using Vector Space Approach

Bostjan Polajzer; Gorazd Štumberger; Sebastijan Seme; Drago Dolinar

This paper discusses methods for voltage sag source detection, which are based either on energy, current or impedance criteria. It is shown that methods known from the literature do not work well, particulary in cases of asymmetrical voltage sags. Therefore generalized methods for voltage sag source detection are proposed, using a vector space approach. All the discussed methods, both the already known and proposed ones, were tested by applying extensive simulations, as well as laboratory and field tests. The correctness of the proposed generalized methods was verified in this way. The obtained results show, that all the proposed methods are highly effective in all cases of voltage sags, whereas the overall effectiveness of those methods known from literature is mainly unacceptable.


IEEE Transactions on Magnetics | 2012

Evaluation of Iron Core Quality for Resistance Spot Welding Transformers Using Current Controlled Supply

Martin Petrun; Beno Klopcic; Bostjan Polajzer; Drago Dolinar

This paper reflects a newly developed method for evaluation of iron core quality for resistance spot welding (RSW) transformers. The classical methods for determination of the iron core quality are mostly based on a sinusoidal excitation. The proposed method is based on corresponding excitation by hysteresis controlled current in primary winding under no load operation, whereas consequently the primary current changes between its maximum and minimum value. Therefore, the operation point during the test is defined by the maximum magneto motive force (mmf) of the magnetic circuit. The tested iron core that reaches higher value of the magnetic flux density with the same maximum mmf, has lower average magnetic resistance and it is categorized as a better one, for the discussed RSW application. Furthermore, the value of the input reactive power is considered as an additional indicator for evaluation of the iron core quality. The proposed method is fully verified with numerical computations and laboratory measurements. The main advantage of the proposed method is that no extra equipment is required when testing the RSW systems.


international power electronics and motion control conference | 2006

Decentralized Control for Active Magnetic Bearings

Jozef Ritonja; Bostjan Polajzer; Drago Dolinar

In the paper a decentralized control for active magnetic bearings is discussed. For the numerical evaluation of different control algorithms a mathematical model of the controlled plant is determined. For this reason basic characteristics and fundamental operation principle of magnetic levitation as well mathematical model of the rigid shaft are presented. Modern control systems for magnetic levitations are discussed. The majority of industrial applications of active magnetic bearings were still based on conventional PID control system. The control system design is presented as rule based procedure. The sensitivity of control system on supplementary dynamics, parameter variations and measurement noise is analyzed. The active magnetic bearing laboratory system is shown. The obtained simulation and experimental results are compared


IEEE Transactions on Power Systems | 2016

Estimation of Area's Frequency Response Characteristic During Large Frequency Changes Using Local Correlation

Bostjan Polajzer; Drago Dolinar; Jozef Ritonja

This paper discusses methods for estimation of areas frequency response characteristic (AFRC) during large frequency changes. The operating point changes significantly during such transient events; consequently the estimation method should adapt to the time-varying nature of the AFRC. Moreover, available measurements have a poor time resolution and are considerably contaminated by errors. Therefore, new estimation methods are proposed that are based on local correlation between the frequency deviation and interchange power variation measured on all areas tie-lines. The presented estimation methods were compared with a classical approach that is based on the ratio of mean changes as well as with conventional least squares parameter estimators. Extensive numerical simulations and field measurements were applied for performance evaluation, where the obtained results show robust and satisfactorily accurate responses of the proposed estimation methods.


ieee industry applications society annual meeting | 2008

The Impact of Voltage Generation on Harmonic Spectra of Current and Flux Density in the Welding Transformer for a Middle Frequency Resistance Spot Welding System

Gorazd Štumberger; Klemen Dezelak; Bostjan Polajzer; Drago Dolinar; Beno Klopcic

This paper deals with a middle frequency direct current (MFDC) resistance spot welding system (RSWS). It consists of a semiconductor input converter, a single-phase welding transformer with one primary coil and two secondary coils, and a full-wave output rectifier connected to the transformers secondary coils. The unwanted current spikes in the input converter, caused by interaction among the asymmetrical design of the transformer, its magnetically nonlinear behavior, and unequal characteristics of the diodes in the output rectifier, can cause over-current protection switch-off of the discussed system. These current spikes can be effectively avoided by the closed- loop control of the load current and flux density in the welding transformers iron core. The welding transformer supply voltage can be generated either by the pulse width modulation or by the hysteresis controllers. This paper analyzes the impact of voltage generation method applied in the MFDC RSWS on harmonic spectra of current and iron core flux density responsible for acoustic noise.


conference on computer as a tool | 2003

Determination of force and flux linkage characteristics of radial active magnetic bearings

Bostjan Polajzer; Gorazd Stumberger; Drago Dolinar; Kay Hameyer

The current and position dependence force and flux linkage characteristics of the studied radial active bearings are determined by the finite element computations in the entire operating range. Based on results of the performed computations the considerable impact of magnetic nonlinearities and cross coupling effects on properties of radial active magnetic bearings is established. The obtained characteristics are incorporated into the dynamic mathematical model, which is based on the current and position dependent radial forces and partial derivatives of flux linkages.


IEEE Transactions on Power Systems | 2017

Evaluation of Load Frequency Control Performance Based on Standard Deviational Ellipses

Bostjan Polajzer; Robert Brezovnik; Jozef Ritonja

This paper discusses new criterion for the evaluation of load frequency control (LFC) performance. The proposed LFC performance evaluation is based on a standard deviational ellipse that characterizes a bivariate relationship between the frequency deviation and the areas interchange power variation. The standard deviational ellipse is evaluated using Tylers maximum-likelihood estimator, which is distribution-free within the family of elliptical distributions. In addition, a target standard deviational ellipse is proposed, using predefined values for a target frequency bound and the areas frequency bias. The presented approach is based on the accordance of the estimated ellipse with the target ellipse, resulting in several grades for the LFC performance. A comparison of the proposed criterion is made with other LFC performance criteria known from the literature. Extensive measurements were applied, and the obtained results show the correctness of the proposed approach.

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Kay Hameyer

RWTH Aachen University

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