Selecting the Switching Frequency of the 6500 V IGBT High Voltage DC Converter

The high-voltage converter with the input voltage of 3000 V DC is considered for use as a power supply for auxiliary circuits of commuter electric trains and passenger cars that are used on Russian railways. The limitations on the use of semiconductor devices in converters with an input voltage of 3000 V are shown. The power electrical circuits of the input units of the considered high-voltage converters are shown when using of 1700 and 6500 V IGBT. The expressions for calculating the power losses and the algorithm for selecting the switching frequency of 6500 in IGBT are given. This article is of interest to developers of high-voltage DC converters with an input voltage of 3000 V and higher, which choose IGBT for the power circuit of input units with using the high frequency principle of the electrical energy transformation.

Digital Modeling of Electromagnetic Processes in Technological Induction Devices

Development of an electrical calculation method plays the leading role in simulating induction devices. In modeling electrical devices and complexes, it is often necessary to simultaneously solve both chain and field problems, i.e., to deal with both lumped and distributed parameters. The article considers the method of integral equations for induction systems with non-magnetic and ferromagnetic loading, which is based on the theory of long-range action. The method’s key statement is that the field at any point is determined as the sum of the fields produced by all sources, including primary and secondary ones. Another finite element method is based on the theory of short-range action, which describes the electromagnetic wave propagation from point to point, its refraction and reflection at the boundaries of media. The article substantiates the development of a combined method based on using the method of integral equations for calculating the input parameters of inductors (an external problem) and the finite element method for calculating the field distribution in the load (an internal problem). The combined method has well proven itself in modeling induction heating and melting of metals and oxides, heating a tape in a transverse magnetic field, induction plasmatrons, and casting aluminum into an electromagnetic crystallizer.

Controlling a Direct Matrix Frequency Converter of Secondary Power Supply Sources for Autonomous Objects

A version of using "sliding modes" in performing discontinuous control of dynamic objects for matrix frequency converters (MFC) as part of an on-board aircraft network is proposed. Unlike the way used in the existing MFC control algorithms, the sinusoidal voltages available in the primary network are processed according to the proposed modernized technology of "sliding modes". The level of discontinuous voltages is selected from the condition of minimum deviations from the target, which has a favorable effect on the spectrum of output voltages. On the selected time interval, the input primary network phase voltages and the specified output network phase voltages are sampled. A positive minimum difference between the primary network phase voltage closest to its desired value and the specified secondary network phase voltage is produced. This difference acts as a positive discontinuous control. A negative difference acts as a negative discontinuous control. Over the calculated interval, the average deviation from the specified phase voltage is zero. Owing to this feature, the smallest distortions in the MFC output voltage spectrum are obtained at arbitrary loads and evolutions of the primary network voltage frequency and amplitude. Versions of three-phase and six-phase primary sources are considered. The effectiveness of the proposed version of using "sliding modes" has been confirmed by simulation.

The Use of Concentrated Windings for High-Power Synchronous Wind Generators

Low-power machines were commonly considered as the main application field of concentrated windings. However, a lot of paper have recently been published, which address both the theory of these windings and specific cases of their application for large synchronous machines. The article presents an analysis of the parameters of concentrated windings having various configurations intended for use in high-power gear and gearless wind generators. In assessing the winding, not only the high winding factor value was taken into account, but also the star of slot EMFs, harmonic spectra of the MMFs and EMFs, the cogging torque component and torque pulsation under load, as well as emerging losses. It is shown that the well-known advantages of concentrated windings over distributed windings can be fully realized by choosing the appropriated numbers of slots and poles.

The Poynting Vector and the New Theory of a Transformer. Part 11. Three-Phase Three-Core Transformers without a Neutral Wire

A topological equivalent circuit for a three-phase three-core transformer reflecting the spatial structure of its magnetic system is developed. Owing to this approach, it became possible to represent the magnetic fluxes of the magnetic circuit’s all main sections and the apertures for each of three phases directly in the circuit in the absence of the windings’ neutral wires. The circuit is constructed by stitching together the anatomical circuit models of single-phase transformers obtained in the previous parts with taking into account the relationships between the fluxes at the junctions of the phase zones in iron. Its validity is confirmed by the rigor nature of the physical and mathematical relations for idealized transformers with infinite magnetic permeability of iron and simplified magnetic field patterns, which corresponds to the generally accepted approach with neglecting the magnetization currents. The difference lies in the fact that the developed model takes into account the heterogeneity of magnetization in different parts of the magnetic circuit with allocating more than 30 sections in the iron and apertures. The transition to the model of a real three-core transformer is carried out by adding four nonlinear transverse magnetization branches in each extreme phase zone and eight branches in the central phase zone to the idealized equivalent circuit. It is shown that in cases of winding connections without neutral wires, there is no flux of the Poynting vector in interphase zones in any unbalanced mode. In this case, the problems connected with the occurrence of fluxes exceeding the no-load fluxes under the conditions of symmetric and asymmetric short circuits, as well as the occurrence of buckling fluxes in these modes in the region outside the transformer iron, are solved.

Determination of the attenuation coefficients from the measured frequency characteristics of the windings of power transformers. Part 1. Theoretical consideration

To model high-frequency processes and determine the stresses on the internal insulation of transformer windings, reliable high-frequency models of power transformers are required. The accuracy of modeling high-frequency resonance processes in the windings depends on how correctly the model reproduces the natural frequencies and damping of free oscillations in the windings. To construct and verify high-frequency models of power transformers, it is necessary to have experimentally obtained data on the values of damping factors. There is a known method for determining the winding damping factors based on measurements of the voltage transfer functions at the internal points of the windings and their subsequent processing using the vector fitting technique, but its application is not always possible in practice. The article presents the results of theoretical studies performed for a simplified transformer winding equivalent circuit. It is shown that the damping factors can be estimated from the width of the resonance peaks of the frequency responses of the voltage modulus and reactive component at the midpoint of the equivalent circuit, and from the input admittance resistive component and current in the neutral of the considered resonance circuit.

Factors Causing Unreliable Accounting of Electricity Consumption on the Electrified Transport “Two Wires-Rail” Longitudinal Power Supply Lines

As is known, the “two wires–rail” power supply system (TWR line) does not meet the modern electromagnetic compatibility requirements, which is a factor causing increased damageability of alarming, centralized control and interlocking devices, as well as other non-traction electric power consumers. In addition, there often occur unexplained differences (unbalance) in the accounting of electricity received by end users and consumed by the TWR line at a traction substation. The accomplished studies have shown that in almost all sections of the network, the actual electricity consumption is significantly lower than that recorded by the TWR line metering devices. The discrepancy in the readings could be explained by unauthorized taps of electricity. However, such a statement will be superficial. The article considers the real factors causing the unbalance in accounting the electricity consumed on the TWR line, which are explained by the magnetic influence of the contact system. An equivalent circuit of the contact system magnetic influence on the TWR line is presented for any configuration of the section with different placements of self-contained transformer substations at different levels of their power capacity. The magnetic influence of the contact system on the TWR line is illustrated by a phasor diagram.

Contactless DC Motors with Discrete Control of Current in the Armature Winding Sections Using the Rotor Position Feedback Signal

The article considers contactless DC motors with discrete control of the current in the three- and two-section armature winding using the rotor position feedback signal by means of a converter containing six and four power transistors, respectively. The motors are additionally equipped with a pulse width modulator (PWM) and a rectifier of the rotor position sensor signals. In the PWM, the periodic line-to-line voltage is compared with the rectified sensor signals to produce periodic rectangular pulses with the duration depending on the rotor position, which close the power transistors. Since the motor torque without PWM and the rectified sensor signals vary in a sine wave manner with turning the rotor (i.e., in the same way), a lower motor torque pulsation is obtained. The sensor and PWM designs and operation are described, and the requirements for their output voltages are formulated. Expressions for the contactless DC motor electromagnetic torque and its limit values are obtained. It is established that the electromagnetic torque pulsation levels in the contactless DC motors with three- and two-section armature windings do not exceed 1 and 1.5%, respectively, which is significantly lower than the pulsation level in the well-known contactless motors (4%).

Crosstalk in Electrical Connectors

Crosstalk electromagnetic interference occurs in on-board electrical wire bundles of aircraft electrical systems under the effect of external electromagnetic fields. Efficient reduction of crosstalk and elimination of their propagation paths in wire bundles can be achieved by shielding the conductors in the bundles and the bundles as a whole without breaks and discontinuities between the shields and housings of electrical connectors. The shielding of conductors in bundles does not eliminate the crosstalk completely, which can propagate through the contacts of electrical connectors. For estimating the influence of electrical connectors on the levels of crosstalk in electrical system circuits, their experimental studies should be carried out. In the course of these experimental studies, the interference voltage induced at the receptor contacts when voltage is applied to the source contacts in the specified frequency band is measured. The results from experimental studies of crosstalk for various types of electrical connectors in a specified frequency band make it possible to evaluate the resonance nature and levels of crosstalk interference levels depending on the relative position of the contacts and frequency.

The Model of a Homopolar Electric Motor with High-Temperature Superconductors

The electromechanical model for analyzing a homopolar electric motor with a magnetic system made using second-generation high-temperature superconductors (HTSC 2G) is described. Homopolar electric motors made with a disk-shaped rotor have the simplest design of their magnetic system and heavy-current contact. Owing to the use of HTSC 2G conductors for producing constant magnetic field in the rotor area, it becomes possible to achieve a higher current density in the windings, thereby increasing the motor power capacity. Due to the HTSC ability to operate at the liquid nitrogen temperature (77 K), it becomes possible to have a simpler cryostat design in comparison with magnetic systems based on low-temperature superconductors. For large-capacity homopolar motors, the use of liquid metal contacts for supplying current to the rotating rotor seems to be the most promising design solution. The advantage of motors of this type is that their torque depends linearly on the rotor current. The homopolar motor operation governed by a proportional-integral-differentiating (PID) controller was simulated using the SciLab Xcos software. The application of the analysis model for selecting the optimal PID-controller coefficients is demonstrated. The electric motor dynamic operation modes are analyzed. The numerical simulation results are compared with the previously obtained experimental data.