The Goss texture is a characteristic feature of grain-oriented transformer steel sheets. Generator sheets, which are produced as non-oriented steel sheets, should have isotropic features. However, measurement results of generator sheets, confirmed by crystallographic studies, indicate that these sheets are characterized by certain, quite significant anisotropy. The first purpose of this paper is to present the influence of textures of generator and transformer steel sheets on their magnetization characteristics. The second aim is to propose a method which takes into account the sheet textures in the calculations of magnetization curves. In calculations of magnetization processes in electrical steel sheets, models in which the plane of a sheet sample is divided into an assumed number of specified directions are used. To each direction a certain hysteresis loop, the so-called direction hysteresis, is assigned. The parameters of these direction hystereses depend, among other things, on the texture type in these steel sheets. This paper discusses the method which calculates the parameters of these direction hystereses taking into account the given sheet texture. The proposed method gives a possibility of determining the magnetization characteristics for any direction of the field intensity changes.

This paper presents a new soft-switching system for three-phase two-level voltage source inverters. In this system, capacitors are not connected in parallel to the main transistors, and inductors are not connected in series with the auxiliary transistors. Avoiding these types of connections protects inverter transistors against damage in cases of disturbances in the inverter control system. The control algorithm of the main transistors of the inverter is the same as that of the transistors of an inverter operating with the hard-switching technique because the auxiliary transistors are switched depending on the operation state of the main transistors. The structure and operation principles of the new soft-switching solution are comprehensively described herein. Additionally, the control algorithm and the principles for selecting the elements of the new soft-switching circuits are discussed. The validity of the system operation was verified by performing laboratory tests with a three-phase voltage source inverter (3 kW, 250 V, 12 A, 3 kHz) supplying an inductive-resistive load or an induction motor, whereas numerical calculations were performed for inverters with a higher rated power. The switching losses of the inverter operating with the proposed soft-switching solution were compared with those of an inverter operating with the hard-switching technique.

This paper describes a simple method of approximating hysteresis changes in electrical steel sheets. This method is based on assumptions that flux density or field strength changes are a sum or a difference of functions that describe one curve of the limiting hysteresis loop and a certain ‘transient’ component. Appropriate formulas that present the flux density as functions of the field strength and those that present inverse dependencies are proposed. An application of this approximation requires knowledge of the measured limiting hysteresis loop and a few minor loops. Algorithms for determining changes in the flux density or field strength are proposed and discussed. The correctness of the proposed approximation of hysteresis changes was verified through a comparison of measured hysteresis loops with the loops calculated for several different excitations of the magnetic field occurring in dynamo and transformer steel sheets. Additionally, an example of the application of the proposed approximation of hysteresis changes is discussed in the paper. The proposed approximation of hysteresis changes is recommended for numerical calculations of the magnetic field distribution in dynamo and transformer steel sheets.

This paper presents a new soft-switching solution recommended for three-level neutral-point-clamped inverters. The operation principles of the proposed solution, working stages, selection of elements, and the control algorithm are comprehensively discussed herein. The control method of the inverter main switches is the same as that of the switches of an inverter operating according to the hard-switching technique. The correctness of the proposed solution was confirmed by the results of different tests using a laboratory neutral-point-clamped inverter with rated parameters of 3 kW, 2 × 150 V, 12 A, and 3 kHz. Numerical analyses were performed for the inverter of rated power 1.2 MW. The switching losses of the inverter operating with the proposed solution were compared with those of an inverter with hard-switching method. The proposed soft-switching solution increased the inverter efficiency and its competitiveness in relation to other proposals because there were no connections between switches and capacitors or inductors, which pose a risk of damaging the inverter when disturbances in the control system appear.

This article presents a modified soft-switching system for three-phase voltage source inverters. Similar to the basic soft-switching system, capacitors are not connected in parallel to the main transistors, and inductors are not connected in series with the auxiliary transistors. These connections protect the inverter from damage when disturbances occur in the control system. Unlike the basic version, the modified soft-switching system does not allow resonant processes to affect the voltage waveform on the load, and the modified system features a simpler control algorithm for the main and auxiliary transistors. The structure and operating principles of the modified soft-switching solution are comprehensively described herein. Additionally, the principles for selecting the elements of the modified soft-switching system are discussed. The system's operation is validated through laboratory tests using a three-phase voltage source inverter (10 kW, 400 V) to supply a squirrel-cage induction motor, whereas numerical calculations are performed for inverters with higher rated power. The switching losses of the inverter operating under the modified soft-switching solution are compared with those of an inverter operating under the hard-switching technique. Results show that the proposed modified soft-switching system increases inverter efficiency .

This study describes a method that allows the modelling of magnetisation processes in transformer steel sheets for any direction of the magnetic field strength. In the proposed approach, limiting hysteresis loops for the rolling and transverse directions were used. These loops are modified depending on the magnetisation angle between the direction of the field strength vector and rolling direction. For this purpose, unique correction coefficients, which are functions of the magnetisation angle, were applied for both hysteresis loops. An algorithm for determining the limiting hysteresis loops for any magnetisation angle is presented herein. The calculation results for several cases of magnetisation were compared with the measured hysteresis loops.