The acceleration time of induction machines (IMs) is essential for proper protection-relay settings of the machine to prevent voltage sags in local power areas. In this paper, mathematical modeling of IMs’ speed-time characteristics during no-load direct startup has been presented. Unlike the approaches presented in the literature, the proposed approach includes the bearing losses, in which two expressions of the speed-time characteristics of IMs during no-load direct startup are derived. The first expression was derived based on the Kloss equation used for representing the torque, and the second expression was derived based on the torque expression determined from the Thevenin equivalent circuit of the machine. The derived expressions’ accuracy was validated using laboratory measurement and computer simulation approaches. The results obtained show a good agreement between the measured and simulated speed-time characteristics of two IMs. Finally, the proposed formulations can provide a simple analytical base to enable accurate IM modeling.

The aim of this paper is to present a comprehensive approach to analyse and interpret power loss in ferromagnetic materials with particular attention devoted to excess power loss. Experimental results obtained with an Epstein frame and toroidal core made of electrical steel are presented in the paper, including quasistatic and dynamic hysteresis loops. According to the time waveforms of the measured magnetic field and magnetic flux density, an instantaneous power loss is calculated for the quasistatic and dynamic case. Moreover, the instantaneous power loss due to eddy current is calculated, as well as the instantaneous excess power loss and excess magnetic field. This excess magnetic field is compared to the excess magnetic field calculated by Bertotti?s model. Analysis and discussion of the results obtained is given in the paper.

This paper shows an analysis of torque ripple reduction in modified DTC algorithm by using multiple voltage vectors with the appropriate multilevel hysteresis controller. A short theoretical background of classical and proposed DTC algorithm was given at the beginning. Experimental results of the proposed DTC algorithm, implemented on digital signal processor F2812, were analysed in comparison with classical DTC. It is shown that the torque ripple can be reduced by selecting voltage vectors with an appropriate intensity. Motor current oversampling was used to analyse the estimated torque behaviour during one DSP sampling period. Furthermore, the analysis of torque ripple reduction with oversampled torque values was conducted in relation to the number of available voltage vectors. The analysis shows that the proposed DTC algorithm allows significant torque ripple reduction while retaining the simplicity, small computational burden and good dynamic characteristics of the classical DTC

The aim of this paper is to present a methodology for the calculation of the R-L parameters of a model of a nonlinear hysteretic inductor. The methodology is based on the analysis of the instantaneous magnetising power calculated from the hysteresis loop of the inductor and is completely developed in the time domain. The instantaneous magnetising power is firstly separated into the oscillatory and absorbed components. Thereafter, the parameter R is calculated using the absorbed component and the parameter L using the oscillatory component. The methodology is validated through the comparison of the results for parameters R and L obtained with the proposed method and the existing method based on the Poynting theorem. The validation is demonstrated on the specific simulated cases with idealised parameters of a nonlinear circuit. Additionally, the paper presents results for the parameters R and L calculated from the hysteresis loops measured at frequencies from 1 to 300 Hz. Furthermore, the fitting functions representing the variation of these parameters with the rate of change of magnetic flux density, and the corresponding results, are presented in the paper. A discussion of all the results presented and applicability of the methodology proposed, as well as the concluding remarks, are given thereafter.

A description of magnetic hysteresis is important for the prediction of losses in soft magnetic materials. In this paper, a viscosity-type equation is used to describe dynamic hysteresis loops in an amorphous ring core for symmetric excitation, as prescribed by international standards. The value of the exponent appearing in the viscosity-based equation can be assumed to be constant if the maximum induction is away from the saturation value. The viscosity-type equation is used to describe the shape variation of magnetization curves due to eddy currents in different time and space scales. Modeling is carried out for various excitation frequencies and induction amplitudes. The discrepancies between the experimental and modeled curves (and also losses) are acceptable in the wide range of the frequency and maximum induction. The paper indicates that the viscosity-type effects, mostly due to eddy currents generated in the conductive material, play an important role in energy dissipation at increased excitation frequencies. The modeling results might be interesting to the designers of magnetic circuits.