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Том 88, № 4 (2017)

Article

An electric traction drive for electric vehicles

Belousov E., Grigor’ev M., Gryzlov A.

Аннотация

Problems of expanding the range of speed regulation in electric transport vehicles by replacing gear-shift transmission with a two-channel electric drive comprising two electric motors, each coupled with its own reducing gear units possessing different gear ratios. The output shafts of these reducing gear units are coupled to one differential speed-reduction device. To solve this problem, a mathematical model of the electric-motor drive has been developed and the static characteristics of the individual motors and characteristics of the motors with their output shafts driving one differential speed-reduction device have been determined. Steady conditions of the operation of a two-channel electric drive are considered. To describe real changes in the speed variables, the electromechanical transducer is approximated in the mathematical model with nonperiodic first-order links. The functions of the controlling effects, which are formed on the basis of the criterion of fullest utilization of electric machines with respect to their electromagnetic torque in stable conditions and in transient processes, were determined. Recommendations are given on application of the proposed solution to traction mechanisms, which should meet increased requirements to acceleration of electric-motor vehicles.

Russian Electrical Engineering. 2017;88(4):185-188
pages 185-188 views

An evaluation of frequency methods for creating a system to control semiconductor converters

Grigor’ev M.

Аннотация

I explore the possibility of increasing the response speed of the semiconductor converters that operate in the pulse mode by increasing the carrier frequency or rejecting pulse-width modulation (PWM) in favor of frequency PWM. The relation between the PWM carrier frequency and the limit response speed of the current loop achievable in closed control systems using classical frequency methods for creation of linear systems has been established. A model of mathematical simulation of a semiconductor device is proposed. The model is approximated by ideal elements without considering the voltage drop on the semiconductor keys and the dead-time interval. Using the simulation model, the frequency characteristics of of the frequency converters are compared with one converter operating in the linear mode and the other in the pulse mode. The limiting value of the frequency starting from which the frequency characteristics of the linear and pulse systems diverge has been determined for different kinds of the transfer functions of the “unchangeable” part. It has been established that this frequency approaches the Nyquist frequency most closely at resonance-peak amplitude Am > 1.

Russian Electrical Engineering. 2017;88(4):189-192
pages 189-192 views

Improving the reliability of semiconductor converters for supplying electric drives of exhausters

Gryzlov A., Grigor’ev M., Imanova A.

Аннотация

This article analyzes the existing methods of increasing reliability through multiple overstatement of the installed power of electric equipment according to the criterion of minimum total yearly costs. The proposed method of optimization of power circuits of semiconductor converters includes stages of choosing the configuration of power circuits on the basis of the limit of semiconductor switches and choosing the optimal number of phases and redundant units. The distinguishing characteristic of the method is the criterion used, namely, the probability of failure-free operation. This new method reduces the cost of installed power of a semiconductor converter compared to the known synthetic method on the level of total annual costs. It is shown that this method has some degree of flexibility; e.g., the development of the element base can be considered on the basis of the corresponding coefficients that depend on the operating temperature of power semiconductor valves. The proposed method can be successfully used in the design of semiconductor converters for supplying powerful electric drives, where, in the general case, the number of phases of a power circuit is not three. In this case, multiphase windings of an electric machine are connected according to a scheme with potential phase separation, which can be considered as an equivalent multiple redundancy system.

Russian Electrical Engineering. 2017;88(4):193-196
pages 193-196 views

Analysis of start-retardation modes in high-power synchronous electric drives

Khayatov E., Grigor’ev M.

Аннотация

The article analyzes the start-retardation modes of synchronous electric drives of high-power exhausters, which are accompanied by high starting currents, not only under a direct start, but also under control of electric energy flows from a semiconductor converter. A mathematical model of electric drive is proposed and substantiated for the analysis of transition processes of ac electric drives. This model has an electromechanical converter that constitutes the links with distributed parameters. A distinctive feature of the model is refinement of the magnetization characteristic of the magnetic-circuit steel, which was carried out during full-scale measurements of the variables of the synchronous electric drive with direct start of the exhauster. To check the adequacy of the mathematical model, the results of a full-scale test were compared with the simulation results by statistical methods using Student’s criterion. The computational results using the proposed model were compared with the calculations by the classical models with lumped parameters. It has been noted that, in the overload zone (for M > 1.5 MN) the calculated values differ considerably, with this being especially evident at low speeds. The obtained results can be recommended for selection of the parameters of semiconductor converters.

Russian Electrical Engineering. 2017;88(4):197-200
pages 197-200 views

Calculations of the losses and thermal operation conditions for controlled alternating-current drives

Gorozhankin A., Gryzlov A., Khayatov E.

Аннотация

A survey of methods of calculating losses has been proposed for a class of controlled ac drivers that work under extreme conditions with arbitrary control laws of currents and configurations of magnetic systems for electrical machines. It is shown that the existing methods have low calculation accuracy for the considered class of electric drivers (error up to 30%). The results of calculations by the finite-element method and the experimental data of simulations of thermal conditions and losses using 3D models, in which an electromechanical converter is regarded as a system with distributed parameters, have been considered; moreover, the parallel calculating algorithms have been used. For example, the calculations of losses in the 3D models of a field-regulated reluctance machine have shown that the discrepancy with the experimental data is not higher than 2%. Note that the main share of losses in steel is eddy currents. The results of calculations by numerical methods using 3D models allow one to determine the losses in controlled ac drivers for nonsinusoidal control laws of phase current of the stators with complex configurations of the magnet system of the electromechanical converter. For the considered class of electric drivers, the largest share of losses (from 60 to 80%) is eddycurrent losses.

Russian Electrical Engineering. 2017;88(4):201-204
pages 201-204 views

An electrical feed drive-control system for a cold reducing mill

Belykh I., Grigor’ev M., Belousov E.

Аннотация

Methods of control synthesis with the selection of parameters of the electrical-power equipment of a cold reducing mill using the example of the Chelyabinsk Pipe-Rolling Plant have been proposed. The proposed methods of a multiconnected system based on the minimum-error criterion for positioning of a movable element, and it is different in that the selection of the control structure is determined by the frequency ratio of the contour cutoff “unchangeable part” of the electric drive and electromagnetic-torque control loop. The task of control synthesis was divided into three stages. The first stage is the search for the optimal curve of movable-element variable speed based on the criterion of minimum electric losses. The second stage is parametric optimization of the electric-power-system parameters. Finally, the third stage is selection of the structure and parameters of the control-system corrective links. Control measures in systems with subordinate regulation and modal control with a change of the frequency ratio of the contour cutoff “unchangeable part” of the system and torque control were compared during research. The developed control-synthesis methods for the positioning electric drive may be recommended for any technological facilities of steel production in which an electric drive provides motion for a movable element with a high level of accuracy.

Russian Electrical Engineering. 2017;88(4):205-208
pages 205-208 views

Ways to decrease losses in electric drives and improvement of electrical safety during their service

Kuznetsov K., Gorozhankin A., Funk T., Khusainov S., Kruglov G., Korzhov A.

Аннотация

A list of recommendations to increase the energy efficiency of an electric drive by decreasing the total losses has been given. Three ways in which an energy-saving drive can be developed have been differentiated. The first approach is improvement of conventional solutions. This can be achieved by means of using new high-quality active materials in electric machines and by optimization of their power circuits. The second approach is a systematic approach to designing and taking into account the combined work of all the components of an electric drive. In this case, improvement entails development of new types of electric drives, such as switched reluctance drives, electric drives with a field-regulated reluctance machine, and others. New solutions actively use the advantages of control and power electronics. The third approach provides improvement of both the existing solutions and taking into account the combined work of a semiconductor converter and motor. Using the example of an electric drive with a field-regulated reluctance machine, calculations of total losses have been carried out and ways to decrease losses by means of choosing efficient control laws for stator currents and power transfer circuits have been demonstrated. Recommendations that allow improvement of the electrical safety of technical personnel who service electrical systems have also been suggested.

Russian Electrical Engineering. 2017;88(4):209-211
pages 209-211 views

Control of a multilevel frequency converter of a power-efficient electric drive

Vinogradov A., Korotkov A.

Аннотация

The paper is devoted to an investigation of the control algorithms of a high-voltage electric drive, the converting part of which is represented by the well-known multilevel Series Connected H-Bridge Voltage Source Converter (SCHB VSC) topology. The control algorithm in the framework of the method forming a Space Vector Pulse-Width Modulation (SPWM) is based on the known principle of choosing the three nearest vectors on the voltage diagram of the converter and calculation of the durations of their switching per modulation cycle. A technique that is the same for all converters of creation of a switching algorithm of power valves based on this principle was proposed. The technique uses the principle of a “centered” SPWM with minimization of switching component of the losses in IGBT inverters of the converter cells. The technique of uniform distribution of the switching load by the cells in the phases of the converter and the method of estimation of the power efficient of a high-voltage electric drive and comparison of SPWM based on the results of the computer modeling were proposed. Results of the integrated simulating and modeling test of a 17-level SCHB VSC composed of a high-voltage variable-frequency electric drive, showing a decrease in the total power losses in the power modules of the converter with a modulator of the developed structure of the space-vector PWM by 43–46% compared to the traditional algorithm of sinusoidal PWM, were obtained.

Russian Electrical Engineering. 2017;88(4):212-218
pages 212-218 views

A three-phase high-frequency AC/DC converter with power-factor correction

Burlaka V., Gulakov S., Podnebennaya S.

Аннотация

A circuit design of an ac/dc three-phase converter with an isolated output is proposed. The converter consists of identical phase modules with forward pulse transformers, the primary windings of which are fed with phase voltage through power switches. The secondary windings of the transformers are connected to rectifiers, the outputs of which are connected in series. The energy of magnetizing inductance is also transferred to the load through an auxiliary low-power converter. The presented circuit design provides control of the converter currents that makes it possible to perform an active power-factor correction. The design is characterized by a small number of semiconductor switches in the power circuit due to the use of a direct-conversion principle. In addition, the proposed circuit design makes it possible to use power switches with a reduced permissible voltage. High-frequency energy conversion makes it possible to reduce the mass and dimensions of the device. The converter can be used as a power supply for an electric arc for welding and plasma processes. It is possible to generate output characteristics of any type, from direct-voltage to direct-current regulation. If necessary, it is possible to provide increased open-circuit voltage to simplify electric-arc ignition.

Russian Electrical Engineering. 2017;88(4):219-222
pages 219-222 views

Modeling the saturation processes of a power-transformer core under simultaneous direct and alternating current passing through the winding

Vakhnina V., Kuznetsov V., Shapovalov V., Samolina O.

Аннотация

A mathematical model of a three-phase two-winding step-up power transformer with the winding circuit Δ/Yo with simultaneous ac and dc currents passed through the grounded winding has been developed. The proposed model is represented by a system of differential equations, which are nonlinear because of the nonlinearity of the inductive resistances of the magnetization curve. The calculation results for a TDTs-400000/242/20 shell–core transformer are given. The model takes into account the effect of dc on the saturation of the power-transformer core, which is especially important under asymmetrical modes that can occur during thunderstorms, seismic activities, or space-weather disturbances.

Russian Electrical Engineering. 2017;88(4):223-228
pages 223-228 views

Transient processes in welding inverters and their influence on the stability of welding current

Bardin V., Zemskov A.

Аннотация

Inverter converters used for dc-arc electric welding have been manufactured by many foreign and domestic companies and showed good results for decades. Until recently, ac welding was carried out only at an industrial frequency of 50 Hz. Earlier, we suggested carrying out arc welding at an increased frequency within the range of 25–75 kHz, proving it to be efficient taking into account welding physical processes. Results of investigations of “slow” electrical processes in a high-frequency inverter for ac welding at different stages of the welding cycle are given in this article. In particular, the transition processes in the inverter are studied in detail taking into account a whole variety of factors. We conducted a complex of investigations concerning the study of the character and duration of the transient processes in an alternative sign welding inverter with increased frequency, as well as the level of influence of the transition coefficient and time constant of the inverter-control system on these processes. The influence of design and parasitic data of the scheme on the nature of the “fast” and “slow” transient processes and changes in the parameters of the electric arc (loading) and parameters of the actuating signals were assessed. All this allowed determining the effect on the stability of the welding current and, therefore, on the welding quality.

Russian Electrical Engineering. 2017;88(4):229-232
pages 229-232 views

A comparative performance analysis of induction and synchronous reluctant motors in an adjustable-speed electric drive

Kazakbaev V., Prakht V., Dmitrievskii V.

Аннотация

This article is concerned with comparative analysis of the energy performance of induction motors (IM) and synchronous reluctance motors (SynRM) in an adjustable electric drive. A feasibility study of an economically viable adjustable electric drive with a SynRM of improved design that is free from electric losses in rotor winding and corresponds to the highest energy-efficiency classes (IE3 and IE4 according to GOST (State Standard) R 54413-2011) is carried out. Results of the comparative analysis of operating and power characteristics of the IM and SynRM with the same stator design are presented in respect to pumps using various principles of control. It is shown that the advantage in the SynRM efficiency is achieved to the fullest extent when the electric angle between the current vector and the axis of the maximum rotor magnetic conductivity is constant. The calculations are performed on the basis of the ac-motor equivalent circuit. A calculation of equivalent circuit parameters for motors of a certain power is performed on the basis of nominal data on the IM being considered. At the same time, the SynRM parameters are calculated from the ratio of inductance parameters for a particular rotor design according to the literature. It is concluded that the SynRM efficiency can be significantly higher than that of the IM of the same power in the entire range of electric-drive speed regulation.

Russian Electrical Engineering. 2017;88(4):233-238
pages 233-238 views

Transient analysis of super conducting fault current limiter integrated with multi-terminal direct current system

Ajay Kumar M., Archana K.

Аннотация

Since the extension of voltage source converter (VSC) based high voltage direct current (HVDC) transmission system to multi-terminal direct current (MTDC) system is easy, the application of MTDC system is more attractive than before. But the VSC based HVDC system is more vulnerable to DC line faults due to the high discharge current from the DC link capacitance. In this aspect, a super conducting fault current limiter (SCFCL) is a better choice to reduce the consequences of DC line faults. The main objective of this paper is to improve the dynamic performance of an offshore wind farm connected multi-terminal VSC-HVDC transmission system by incorporating SCFCL at different locations. Here, the SCFCL integrated MTDC system is modelled in MATLAB/Simulink and the results are presented for various AC/DC fault conditions.

Russian Electrical Engineering. 2017;88(4):239-246
pages 239-246 views