The purpose of this work is to build the analytical improved (with resistances estimation) real time computation of the reference inputs for rotor flux and torque in the vector control system of an induction motor of a traction electric drive. The reference inputs must maximize electromagnetic torque in conditions of voltage source instability, particularly in magnetic field weakening mode. The conventional way to control the field weakening mode is to form flux coupling task inversely proportional to the speed or inversely proportional to the square of the speed in second and third zones respectively. Such reference input signals are not able to provide the maximum torque capability over the entire speed range, and the improved torque capability is achieved in different ways. For instance, voltage feedback is useful for the torque capability enhancement in conditions of internal and external perturbations. A wide change in speed with the weakening of the flux reveals the nonlinear properties of an induction electric motor. However, in vector control systems, proportional-integrating (PI) regulators are usually used. Therefore, firstly, linear PI controllers must be robust, and secondly, the reference input signals for flux and torque must guaranty linear, not saturated state of each PI controller. The proposed expressions for calculating reference inputs for induction motor rotor flux and electromagnetic torque as functions of actual rotor speed are the approximate expressions. The estimation of the possible error shows that the error is acceptable. Simulation is performed for the vector control system of an induction motor and taking into account the calculation of the control signal by the microcontroller and the dynamics of the frequency invertor. The simulation of the resulting system validates the effectiveness of the control system using the proposed expressions for the formation of real-time reference input signals for setting the flux and torque.

. Electric energy storage systems are widely used in electric transport, power engineering and in order to provide autonomous power supply and load regulation of power systems. One of the ways to increase the technical and economic efficiency of storage devices is their hybridization, i. e. the creation of storage devices consisting of blocks of different types of batteries. The special literature contains no systematic analysis of qualitative and quantitative effects of hybridization and corresponding methodological recommendations for choosing a scheme and evaluating the effectiveness of hybridization. In the present article, this issue is considered from a theoretical and methodological standpoint, recommendations are given for the design of storage devices serving solar or low-power wind farms. A brief overview of data on the cost of buffering electricity with lithium-ion, lead-acid batteries and supercapacitors is made. A method is proposed for determining the necessity and degree of hybridization of an energy storage device based on the simplest dependencies of the storage parameters on the degree of hybridization. The notions of the coefficient of synergetic effect of hybridization and the degree of internal buffering of electricity are introduced. A quantitative-and-qualitative model for evaluating the effectiveness of hybridization is presented. A methodological approach is proposed for calculating the degree of internal recovery and evaluating the coefficient of synergetic effect of hybridization. It is shown that, in general, the adding of supercapacitor unit to lithium-ion batteries a does not lead to a reduction in the cost of buffering electricity due to the high ratio of the cost of buffering with a supercapacitor to the cost of buffering with lithium-ion batteries. At the same time, the economic feasibility of using supercapacitors to compensate for high pulse loads can be determined on basis of the analysis of the frequency spectrum of the load graph of the storage unit. The developed models and approaches can be used in the design of electrochemical energy storage systems for specified operating conditions.

When current transformer is saturated, mainly due to the presence of an exponentially decaying DC component in the fault current, its secondary current has a distinctive distorted waveform which significantly differs from its primary (true) waveform. It leads to an underestimation of the secondary current value calculated by the relay protection compared to its true value. Thus, in its turn, results in trip time delay or even in a relay protection devices operation failure, since its settings and algorithms are calculated and designed on the assumption that the secondary current waveform is sinusoidal and proportional to the primary. And since, when using classical electromagnetic current transformer, it is impossible to exclude the possibility of its saturation, the detection of such abnormal condition is an urgent technical problem. The article proposes to use an artificial neural network for this purpose, which, together with the traditional method of saturation detection based on adjacent secondary current samples comparison, allows implementing a fast and reliable current transformer saturation detector. The article details the stages of the practical implementation of such an artificial neural network. The MATLAB-Simulink environment was used for assess the proposed saturation detector operation. The experiments that had been performed confirmed that proposed method provides fast and accurate saturation detection within the wide range of the power system and current transformer parameters change.

The purpose of the mechanical calculation of flexible conductors of switchgears and power lines is to determine the sag, tensions, and loads on support structures, minimum distances to adjacent live parts and some other parameters. Calculations should be made taking into account distributed and concentrated loads. Distributed loads directed vertically are determined by the weight of the wire, insulator strings, and possible ice deposits on them. Distributed loads in the horizontal plane should be calculated in climatic conditions with lateral wind pressure. Concentrated loads are created by such elements as taps to electrical devices, phase-to-phase insulating spacers, barrier balls, loops, etc. Concentrated loads mainly act in the vertical plane, and in the case of taps, they can have an almost arbitrary spatial direction. The most accurate methods of mechanical calculation of flexible conductors include methods based on the numerical solution of the equation of wires in the form of a flexible elastic thread. Such an algorithm is implemented in the author's computer program MR21. However, in many cases, simplified methods of mechanical calculation are preferable, as they are available to a wider range of users. The simplified method of mechanical calculation of flexible conductors proposed in the article is based on the equation of state of the wire and allows taking into account concentrated and distributed loads. Various climatic regimes and loads are taken into account using the horizontal and vertical load factors in the calculated and initial modes. Expressions are proposed for calculating the above coefficients for any number of taps in a span and with an accurate approach to taking into account their spatial arrangement. Formulas for calculating sag and horizontal deflections of conductors are given, too. The MR21 computer program, tested earlier, has been used in this work as a tool for checking the calculation results using the proposed simplified method.

Based on the analysis of thermohydraulic processes and the structural and functional structure of the proposed system of heat and cold supply of buildings, a multifactorial dependence of the actual conversion coefficient was established to assess the efficiency of transformation of the heat taken from the soil massif and ventilation air. It allows modeling the individual influence of the initial parameters and operational modes of the system in the search for rational conditions for the highly efficient use of energy flows for heat and cooling supply of buildings during the corresponding periods of the year. The results of a qualitative assessment of the multifactorial interrelation of the actual conversion coefficient substantiated the possibility of energy efficient operation of the analyzed system, which is provided under the design conditions of the heating period when the ratio of circulating flow rate through the evaporator and condenser of heat pump is higher than 1.8, which is rational for sports, recreation, shopping and entertainment complexes. The improved structural and functional arrangement of the system based on a binary low-temperature source increases the efficiency of vapor compression transformation of energy flows, indirectly confirming the advisability of maximizing the use of the energy potential of ventilation air during the year with a corresponding accumulation of excess heat in the soil mass, and, consequently, the possibility of reducing the depth of expensive wells or the number of probe heat exchangers.

A separate generating complex is considered in this paper. The main feature of the complex under consideration is its functioning during the control period when the fuel resource is severely limited. The main function of the complex is the production of electrical and heat energy for the needs of the consumer. A control model for production has been developed for two scenarios, viz. of the unconditional provision of the consumer’s needs with electric energy and of the mandatory implementation of the schedule for the release of heat energy. The features of the implementation of the model for a separate thermal power plant (mini-thermal power plant) with a guaranteed supply of electric energy to the consumer are considered, cogeneration modes are substantiated in conditions of a limited fuel supply, regardless of the consumer category. An optimization option is shown when choosing an additional source of heat to meet the needs of the consumer. In the case of choosing a renewable energy source (RES), the management of the ‘cogeneration – RES’ complex according to the proposed strategy allows minimizing the required RES capacity. The basis of production management is the mathematical model of the generating complex, presented in our paper. In terms of describing the behavior of a complex physical system as a whole, an ener-gy approach (Hamilton's method) was used, which turned out to be very convenient for solving the problem, since the variational principles do not depend on the choice of a coordinate system. The description of the turbine plant as an object included in the generating complex and largely determining the relationship between fuel consumption and the amount of electrical and ther-mal energy produced is made with the unconditional fulfillment of the following requirement: fuel consumption is a function of the state of the system. The proposed cogeneration strategy in the conditions of a severe limitation of the amount of fuel does not depend on the type of fossil fuel used and is not tied to the control period calendar dates.

Among the considered options for schemes of prefabricated water conduits of borehole water intakes, the main ones are linear and ring schemes. The article presents a comparative analysis of the linear and ring schemes for the placement of prefabricated water conduits when choosing an option for designing a group well water intake with a circular arrangement of wells. It is founded that a small water intake with individual radial connections to the prefabricated unit can have advantages in reducing energy consumption for water transportation as compared to a water intake with an annular prefabricated conduit, which in any case should be justified by a feasibility comparison of options, which is based on hydraulic calculation water supply systems. Equations have been obtained for calculating the pumping rates of water intake wells with linear prefabricated conduits. It is shown that in an annular prefabricated conduit, in contrast to a linear one, in which the direction of movement of water flows is unambiguously known, there is always a point of separation of two flows directed along the ring to the prefabricated unit clockwise and counterclockwise, which makes it difficult to calculate such water intakes. Moreover, the position of this point depends on the number of water intake wells involved in the work and the parameters of the pipes connecting the sections of the water conduit. The absence of algorithms for calculating the ring prefabricated conduit with non-fixed flow rates at the well connection points complicates the hydraulic calculation, and, hence, finding the optimal water intake option. The article presents an algorithm for the hydraulic calculation of a water intake with a single-ring prefabricated conduit, which is based on the equation for the equality of pressure losses when water moves from the point of separation of two flows to the prefabricated unit along various paths and the continuity equation. The resulting algorithm can be easily extended to any number of wells. A numerical example of the hydraulic calculation of a group water intake, consisting of eight wells connected to an annular prefabricated, is considered.