STUDY OF THE APERIODIC REGIME DURING THE TRANSIENT PROCESS IN AN OSCILLATING CIRCUIT IN ORDER TO CONVERT THE ENERGY OF AN ELECTRIC CURRENT INTO THE HEAT OF A JOULE

Purpose. Research initiated by revealing the paradox of disturbed energy balance based on the position of the virial theorem and studying examples of the Van de Graaf generator, a capacitor containing a ferroelectric, and a heat pump capable of providing an energy conversion factor greater than 100%, as well as an idealized theoretical known as the Maxwell demon, showed the possibility of increasing the efficiency of converting current energy into Joule heat. Methodology. The results are verified by comparing the relative efficiency of the conversion of current energy into heat in the oscillatory, critical and aperiodic modes of the transient process in a series oscillating circuit. Mathematical modeling in a wide range of parameter changes has shown the advantage of using the aperiodic transient mode of a series oscillating circuit to convert current energy into heat, compared to the power supply of an electric heating system, which is based on the established method. Experimental tests of the experimental sample fully confirm the qualitative results of mathematical modeling. Results. An achievable limit level of conversion efficiency in the active resistance of energy accumulated by inductance and capacitance according to the virial theorem is established. Originality. For the first time, the application of the aperiodic transient mode in a series oscillatory circuit is proposed in order to convert the energy of current to Joule heat. Practical value. As a practical result, a method of converting current energy into pulse energy has been developed, which implements the algorithm of simultaneous energy accumulation by inductance and capacitance, and its simultaneous conversion in a series oscillating circuit, for which a patent has been obtained. Possibilities of application of the developed method for the purpose of induction heating of metals by Foucault currents as replacement of a method of shock excitation of fluctuations are studied. To this end, the conductivity of metals, which causes the flow of Foucault currents, should be considered as the introduction of equivalent active resistance in the oscillating circuit. The introduction of the method will not require changes in the process equipment, except for the power supply scheme, and should eliminate the fundamental disadvantage of the method of shock excitation of powerful oscillations, which is low efficiency.

ON TACTICS OF DEVELOPING ARCHITECTURE OF THE GENERALIZED ALGORITHM OF ENERGY-ORIENTED POWER CONSUMPTION CONTROL AT IRON ORE UNDERGROUND MINING COMPANIES

Purpose. The article substantiates and confirms the thesis about the need for energy-oriented power consumption control levels in power complexes: the system of power supply at iron ore underground mining enterprises on the basis of experiment data analysis. Methodology. It is estimated that along with the current positive trend suitable for developing architecture of power consumption control levels when a limited number of energy-intensive enterprises consume about 80 % of the total power produced, their functioning modes in day hours vary. Analysis of varied realtime modes of power consumption in hours indicates absence of enterprises’ control over this process. Results. The suggested methods enable forecasting efficiency of power consumption control in hours in any variant of time-of-day tariff integration. In non-standard and changeable conditions of technological parameters in mining production, on the basis of the results of stochastic optimization analysis, it is proven that even when applying a small number of iterations N = 10, it is possible to improve the initial solution by over 60 % (the initial value of the objective function is I* = 27.7 and the final value on the last iteration is I* = 10.7). There are determined required vectors to specify a connection of the time-of-day tariff of ore mining (Р*) and the corresponding power consumption (Е*) which corresponds to the suboptimal value of the objective function (I*). The obtained results can be applied to developing recommendations for a more efficient planning of an enterprise’s performance. Practical value. The suggested algorithm implemented in power consumption control systems enables receiving a final result with any quality required for the level. If the quality of the obtained results needs improving, the number of iterations is to be increased by two or three orders of magnitude.

SIMULATION MODEL AND RESEARCH OF QUASI-STEADY-STATE AND DYNAMIC OPERATION MODES OF THE AUTONOMOUS DC POWER ENERGY SYSTEM WITH PARALLEL OPERATED INVERTER EXCITED INDUCTION GENERATORS

Purpose. The development of theory and research of autonomous DC power systems based on contactless electrical machines is an important element in ensuring the improvement of the reliability and energy efficiency of autonomous power supply of remote from centralized networks facilities, ship equipment, critical to power outages consumers. Originality. The use of induction generators with squirrel-cage rotor and an electronic converter in stator circuits in the design of autonomous DC power systems is advisable due to presence of a DC power output in these generators and the possibility of stabilizing the output voltage at variable speed. One of the scientific issues needed to be solved at creating induction generators-based DC power systems with inverter-assisted self-excitation of the generators is the determination of means and as well as development and verification of algorithms for regulating the generators load. Solving this issue requires the creation of appropriate simulation models. Methodology. In this work, a simulation dynamic model of an autonomous DC power system with two parallel operated induction generators with inverterassisted self-excitation and the six-step switching control algorithm has been developed. Results. A study of quasisteady-state and dynamic operating modes of the system was carried out. The duration of the initial excitation of the generators was determined for different values of the capacitance of the filter. Practical value. The results obtained showed the compliance of the parameters of electrical energy in the system with the standards established by the relevant regulatory documents and stable operation of the system with load changing from idle to rated. Further work is planned to focus on improving control algorithms for autonomous DC power systems with parallel operating induction generators and inverter-assisted self-excitation, studying the energy performance of such systems and developing recommendations for their design.

MATHEMATICAL MODEL OF AN INDUCTION GENERATOR TAKING INTO ACCOUNT HIGH SATURATION OF THE MAGNETIC SYSTEM

Purpose. Development of a mathematical model of transition processes for a detailed study of the harmonic components of the voltage and current of the IG as part of autonomous generator sets at high saturation of the magnetic system. Result. The article presents an analysis of the steady-state mode of a self-excited induction generator based on a mathematical model in a three-phase coordinate system, which makes it possible to take into account the influence on the dynamic characteristics of an asynchronous generator of such physical phenomena as the nonlinearity of the magnetization curve, the phenomenon of hysteresis and eddy currents. The article simulates and evaluates the influence of the value of the connected load on the quality of the generator output voltage. The Fast Fourier transform algorithm is used to analyze the harmonic components of the voltage and current of an induction generator in a steady state. The change in the harmonic coefficient and its compliance with the boundary permissible values are analyzed. The results of experimental studies of an asynchronous generator in an autonomous mode of operation were obtained, and the adequacy of the proposed mathematical model was assessed. Practical value. The carried out theoretical studies of the capacitive self-excitation of IM machines have created a good basis for solving issues related to the practical use of autonomous sources based on an asynchronous generator.

ELECTROMAGNETIC FIELDS IN A CYLINDRICAL INDUCTOR SYSTEM WITH AN EXTERNAL COAXIAL BIFILARY SOLENOID

Purpose. Bifilar structures are widely used in modern electrical devices for various purposes. The specific interest is the using of inductor systems with external bifilar coils in the elements of modern metalworking equipment. In particular, it is very important to study the possibility of using such devices as elements of equipment for magnetic-pulse processing of metals. The aim of this research is a derivation of design expressions for theoretical analysis and numerical estimates of the characteristics of electromagnetic processes in a cylindrical inductor system. The case when the inductor is located inside a coaxial solenoid, the winding of which is made in the form of a bifilar with oppositely directed currents is considered. Methodology. Maxwell’s equations with appropriate boundary conditions and Laplace transforms are used to solve this problem. This made it possible to determine the expression for the z-th component of the magnetic field intensity excited in the considered inductor system. Results. It was found that the excited magnetic fluxes are subtracted outside the bifilar coil windings, which leads to a decrease in the resulting field compared to the magnetic field of each of the currents separately. Thus, it is possible to reduce the inductance of the coil as an element of the electrical circuit. It is shown that the formulas obtained for the fields and currents remain valid for the case of unidirectional currents when the sign of the corresponding algebraic term changes. Numerical estimates for the experimental model of the inductor system showed that the induced current as a percentage of the value of the exciting current does not exceed ~ 6.3 %. Originality. The novelty of this work lies in proposing the idea of constructive execution of the inductor system itself, as well as in considering its physical and mathematical model and obtaining calculated expressions for analyzing the ongoing electromagnetic processes with numerical estimates of the characteristics of the excited fields. Practical value. The obtained time dependences for voltages and currents induced in the bifilar winding are applicable depending on the design conditions for various specific designs of the inductor system

METHOD FOR DETERMINING THE MECHANICAL DEVICE FOR PAIRING OF ROTATION FREQUENCIES VEHICLE WHEELS AND ASYNCHRONOUS GENERATOR SHAFT UNDER GUARANTEED EXCITATION

Purpose. Development of a method for calculating and selecting a mechanical device for coupling the speeds of the vehicle wheel and the shaft of an asynchronous generator under the condition of its guaranteed excitation. Methodology. The method of selection of transmission rollers of the mechanical device of conjugation of rotational frequencies is offered and the algorithm of its calculation is resulted. A method for determining the minimum allowable speed of the asynchronous generator shaft is proposed and the results of graphical and analytical solution for an asynchronous machine type AOL 21-4 are given. Result. The analytical dependence of the minimum allowable speed of the induction shaft as a function of the parameters of the drive motor of internal combustion, capacitive excitation and load, which must be provided by selecting the gear ratio of the mechanical coupling device. Originality. The general criterion for selecting the size of the transmission rollers is presented in the form of a quality functional, which takes into account the range of variation of the crankshaft speed of the primary engine, the range of variation of the diameter of the transmission roller and the range of fuel consumption at the corresponding crankshaft speed. Practical value. The proposed methods and the obtained research results allow to calculate and design devices for mechanical coupling of rotational frequencies of the shafts of the primary propulsion and asynchronous generator, which will expand the scope of the latter as part of local autonomous power supplies.

COMPARISON OF METHODS FOR COMPENSATION FOR DAMAGE TO H-CELLS IN HIGH-VOLTAGE CASCADE FREQUENCY CONVERTERS

Purpose. The aim of this work is to find a method of controlling high-voltage frequency converters that would provide the smallest voltage drop on the motor, the least loads and oscillation of electromagnetic torque in an accident modes, and evaluate the effectiveness of pulse width modulation (PWM) methods with the injection of third harmonic and space-vector PWM in emergency modes. Methodology. We have applied the mathematical simulation of the electric drive “High voltage frequency converter with cascaded H-bridges – High power asynchronous machine” in Matlab/SimPowerSystem software for comparison of four PWM types – Sinusoidal PWM (SPWM), Balanced sinusoidal PWM (BSPWM), Balanced PWM with injected third harmonic (THPWM) and Space Vector PWM (SVPWM). Results. The method of balancing the line voltage minimizes shock loads during the transition from normal to emergency mode due to such a shift of the zero point and rotation of the phase vectors, in which the amplitude of the line voltage decreases to the minimum possible value, the spatial position of linear vectors remains unchanged. The conditions of optimal injection of the 3rd harmonic are found, which increases the efficiency of power supply use by 7… 30 % in comparison with symmetric sinusoidal PWM. But in some accidents (6-4-4, 4-3-2, 3-2-2) the 3rd harmonic is not effective. The method of balancing the space vectors provides the same conditions and increases the utilization of power supplies by 15.6 %, regardless of the number of damaged modules, which increases the amplitude of the 1st harmonic in case of accidents by 10 ... 26 % compared with sinusoidal PWM. Comparison of methods of space vector PWM (SVPWM), balancing of phase-to-phase voltage with the injection of the 3rd harmonic (THPWM) with sinusoidal PWM shows that SVPWM is the best method at damage of one or two modules and during normal work of the converter (except for the 3-3-2 configuration), ie in the most common cases. Originality. For the first time, a comparison of all methods of pulse-width modulation in emergency modes and the optimal method for each type of accident for 3-6-stage frequency converters is indicated. Practical value of the work is to provide the necessary mathematical apparatus for calculating signals using BSPWM, THPWM and SVPWM in emergency modes. References 17, table 1, figures 6.

MODEL STUDIES WITH IDENTIFICATION OF ENERGY EFFICIENT MODES OF FUNCTIONING OF MAIN FAN UNITS

Purpose. The paper analyzes the system and methods of starting synchronous electric motors of fans of the main ventilation of iron ore mines. It is concluded that it is necessary to modernize the method of starting a synchronous electric motor, despite the fact that the installed direct start-up system has a number of disadvantages, and negatively affects the energy indicators of the electromechanical complex of the main ventilation fan of mines. The priority direction in solving the complex of the above problems is the use of modern achievements in the field of semiconductor conversion technology, in terms of the development of effective circuits and methods for starting and controlling a synchronous electric drive. Originality. The method of separate regulation of size and frequency of output voltage of the multilevel converter of a clock at quasi-frequency start of the synchronous electric drive is offered, limits admissible values of starting currents to admissible values. Methodology. Simulation of transient processes of starting a synchronous electric motor with step-by-step changes in voltage and frequency of supply, which made it possible to determine the energy efficiency of this method. Result. A new method of starting with a step-by-step change in the voltage and frequency of a synchronous motor is proposed. The modeling of the proposed starting method for a synchronous electric motor with a fan torque on the motor shaft was carried out, while it allowed to get rid of the main drawback, namely, a large starting current and made it possible to increase the energy efficiency of the electromechanical complex of the main ventilation fans due to the fact that the consumed active energy during start-up will decrease approximately 50% compared to a direct starting system. Practical value. The proposed method and the obtained results of the study made it possible to prove that the effectiveness of the proposed method is very high and this will save most of the electrical energy when starting the fans of the main ventilation of iron ore mines. Figures 15, references 15

SYNTHESIS OF A FUZZY TWO-LINKED REGULATOR FOR FREQUENCY ELECTRIC DRIVES OF A GRAIN MACHINE WITH A FOCUS OF THE GRAIN FLOW

Purpose. A control system for grain overloading during post-harvest processing with grain throwers has been proposed, the use of which will reduce damage and grain loss. An automated electromechanical system is presented that can be installed on agricultural machinery without additional modernization of the working bodies. Methodology. As a result of the analysis of control systems, a system with elements of fuzzy logic was selected, which will clearly define the necessary control actions and take into account additional parameters that can affect the overload process. A functional diagram of a microprocessor control system for an electric drive using a fuzzy system is proposed. The result of the system operation will be the definition of the control task for the frequency converters of the drive motors of the grain thrower mechanisms. Originality. Based on the simulation of grain flight trajectories, the dependences of the flight range on the conveyor speed and additional blowing were formed, which were used to determine the settings of the fuzzy controller. Results. Fuzzy system settings are performed: a set of input and output variables is defined; the number and location of terms are selected; a set of production rules for the system is formulated. As a result of experimental modeling, graphs of the formation of mastering influences by a fuzzy controller under the condition of the appearance and disappearance of the headwind for different given distances of movement were obtained. Practical value. Practical application of the offered system will allow to reduce material losses from injury of the overloaded grain and to increase efficiency of work of the grain thrower. Figures 8, references 21.

THERMAL MODEL OF THE "INDUCTION GENERATOR–INDUCTION MOTOR" SYSTEM WITH NON–SYMMETRY IN THE STATOR WINDINGS

Purpose. Development of the IG model for estimation of influence of variations of parameters of the generator on quality of process of self–excitation at definition of the basic and boundary operating modes and system of initial excitation at invariable parameters of the generator. Result. The article presents studies of the system "asynchronous generator-asynchronous motor" with parametric asymmetry to determine the quality of generated electricity in load modes of operation on a mathematical model. The assessment of the thermal state in steady-state conditions was carried out using an equivalent thermal equivalent circuit. Thermal transients were investigated when starting an asynchronous electric motor from an autonomous power source based on an asynchronous generator. On a thermal mathematical model, a study of the influence of the asymmetry of the output voltage and its deviation from the nominal value on the heating of the connected asynchronous motor was carried out. A regression model has been developed for studying the operating conditions of electricity consumers when powered by an asynchronous generator with an asymmetry of the stator windings. Practical value. The use of the obtained equations will make it possible to determine the most rational combination of factors affecting the heating of the stator windings of asynchronous machines, at which they will not overheat in excess of the maximum permissible temperature values of the corresponding insulation classes. Figures 9, tables 2, references 23.