Three-phase squirrel-cage induction generator excited by capacitor battery

The generation of electrical energy in small power plants which use renewable energy sources is often implemented with the use of induction generators. This paper presents a proposal of an energy generation system which is constructed with the use of a three-phase self-excited squirrel-cage induction generator. The idea of this proposal consists of a control method of the generator rotor magnetic flux linkage via fully controlled power electronic switches. The energy produced by the induction generator is transferred to a DC link via an uncontrolled rectifier and a DC-DC chopper. The proposed solution allows us to generate energy with the use of a relatively simple and reliable electrical machine. Additional important advantages of this concept are a small number of controlled elements, and an easy control method

Switching losses in three-phase voltage source inverters

The efficiency of three-phase voltage source inverters depends mainly on power losses that occur in semi-conductor elements. Total losses in these elements are a sum of conduction losses and switching losses. The switching losses are dependent on the supply voltage, load current, operating frequency and on the dynamic parameters of the switching elements; these losses can be limited with the use of soft switching methods. This paper discusses the switching loss dependence on the above mentioned factors. An analysis was carried out on power losses in voltage source inverters which generate the output voltage in the form of a rectangular wave and losses in these inverters operating with pulse width modulation. A comparison of switching losses was performed for two voltage source inverters with different nominal power ratings

Influence of magnetic anisotropy on flux density changes in dynamo steel sheets

Abstract: Magnetic measurements, carried out by means of the Epstein frame, have shown that most typical dynamo steel sheets have certain anisotropic properties. In numerical analysis, anisotropic properties are taken into account with the use of the special function of the grain distribution in the given dynamo sheet. For engineering purposes, it is desirable to assess the influence of these properties on the changes of the magnetic flux density in typical dynamo steel sheets, especially during the rotational magnetization. For this purpose, measurements of the flux density changes and field strength changes in the circular-shaped samples of two selected typical dynamo sheets were performed. These measurements were carried out for several values of the current flowing in windings which generated the axial or rotational magnetic field in the test dynamo sheet. The influence of the magnetic anisotropy on the magnetization process was briefly discussed for both types of the magnetization processes

A novel proposal of cooperation between a cage induction generator and the three-phase grid

In the paper, a new concept of the cooperation between a cage induction generator and the three-phase grid is presented. The induction generator is excited by a capacitor battery connected to the stator winding terminals. In order to ensure a stable operation, the battery capacity should be continuously adjusted. Three appropriate selected capacitors are connected to the stator winding terminals by means of two bi-directional controlled switches. The generator output voltage is stabilized by a suitable control of these switches. The stator winding terminals are also connected to the diode bridge rectifier. Energy in the DC bus is converted to the parameters of the three-phase grid (400 V, 50 Hz) by means of a three-phase voltage source inverter. Examples of numerical calculation results of the proposed energy generation system are presented in the end part of the paper

A New Soft-Switching Solution in Three-Level Neutral-Point-Clamped Voltage Source Inverters

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

Influence of magnetic anisotropy on flux density changes in dynamo steel sheets

Magnetic measurements, carried out by means of the Epstein frame, have shown that most typical dynamo steel sheets have certain anisotropic properties. In numerical analysis, anisotropic properties are taken into account with the use of the special function of the grain distribution in the given dynamo sheet. For engineering purposes, it is desirable to assess the influence of these properties on the changes of the magnetic flux density in typical dynamo steel sheets, especially during the rotational magnetization. For this purpose, measurements of the flux density changes and field strength changes in the circular-shaped samples of two selected typical dynamo sheets were performed. These measurements were carried out for several values of the current flowing in windings which generated the axial or rotational magnetic field in the test dynamo sheet. The influence of the magnetic anisotropy on the magnetization process was briefly discussed for both types of the magnetization processes

Calculations of magnetic field in dynamo sheets taking into account their texture

Magnetic measurements have shown that the most dynamo steel sheets have certain anisotropic properties, which are due to the presence of textures in these sheets. These anisotropic properties have been taken into account usually in a simplified way assuming that iron particles of the dynamo sheets have only one axis of the easy magnetization. In the proposed approach, these particles are treated as grains which have three axes of the easy magnetization, and therefore the magnetization processes can be considered along each of these axes. These processes depend on the actual value and on the direction of the field strength and also on textures occurring in the given dynamo sheet. A method which allows calculations of the field distribution as a function of the assumed changes of external currents is described in this paper

Equation of the magnetic field distribution of dynamo sheets taking into account crystallographic structure

The main purpose of the paper is to present a method which allows taking into account the anisotropic properties of dynamo steel sheets. An additional aim is to briefly present anisotropic properties of these sheets which are caused by occurrences of some textures. In order to take into account textures occurring in dynamo sheets, a certain sheet sample is divided into elementary segments. Two matrix equations, describing changes of the magnetic field, are transformed to one non-linear algebraic equation in which the field strength components are unknown. In this transformation the flux densities assigned to individual elementary segments are replaced by functions of flux densities of easy magnetization axes of all textures occurring in the given dynamo sheet. The procedure presented in the paper allows determining one non-linear matrix equation of the magnetic field distribution; in this equation all textures occurring in a dynamo sheet are included. Information about textures occurring in typical dynamo sheets may be used in various approaches regarding the inclusion of anisotropic properties of these sheets, but above all, the presented method can be helpful in calculations of the magnetic field distribution in anisotropic dynamo sheets