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Date submitted2019-03-31
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Date accepted2019-08-25
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Date published2020-02-25
Cascade frequency converters control features
The structures of systems with high-voltage cascade frequency converters containing multi-winding transformers and low-voltage low-power converters connected in series at each output phase of the load are considered. Low-voltage blocks contain three-phase diode or active rectifiers, DC capacitor filters, single-phase stand-alone voltage inverters and block disconnecting devices in partial modes (in case of failure when part of the blocks are disconnected). The possibilities of operation of cascade converters are determined, equations for correcting tasks to units in partial modes are given, tables of correction of tasks with estimates of achievable load characteristics are proposed. The results of experiments on the model of a powerful installation with a cascade frequency converter are presented, confirming the possibility of ensuring the symmetry of the load currents when disconnecting part of the blocks and the asymmetry of the circuit.
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Date submitted2018-10-27
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Date accepted2019-01-04
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Date published2019-04-23
Application of an active rectifier used to mitigate currents distortion in 6-10 kV distribution grids
The paper addresses issues of using the active rectifier in partially loaded variable frequency drive as active filter in the conditions of non-sinusoidal current and voltage disturbances caused by the presence of high-power non-linear load in the grid. The topology of transformless three-level converter for 6-10 kV suitable for proposed solution has been presented and its mathematical model has been de-rived. Based on the model, the direct power control algorithm with ability to compensate non-linear currents has been designed. The investigation of active rectifier efficiency was performed depending on the relation between linear and non-linear load currents of the grid node, as well as on active power load of the active rectifier. Efficiency analysis was based on the developed computer model of the grid node with connected non-linear load simultaneously with the variable frequency drive with active rectifier.
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Date submitted2015-12-24
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Date accepted2016-02-04
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Date published2016-12-23
Geodynamic methods for assessing methane distribution in bituminous coal deposits and measures to intensify methane fluxes during mine gas drainage
- Authors:
- E. V. Goncharov
- S. V. Tsirel
This paper explores states of methane within the coal bearing stratum and shows heavy dependency of the intrastratal gas migration on the forms of porous space and petrographic properties of coal. The adsorbed methane is found to be predominant in the coal of Kuznetsk Basin. Different forms of coal diffusion and filtration are described revealing their dependency on geological and thermodynamic conditions. The paper provides justification for the primary focus on geodynamic processes when designing gas drainage systems and applicability of morphometric methods and remote sensing data for their identification. The significance of researches into the processes activating exothermic reactions resulting in methane transition to free state is explained. The paper presents the results of using seismic-acoustic stimulation techniques as one of the practical approaches to addressing this issue. Results of successful industrial testing have been compared with the results of numerical modelling of stress-strain state, which can also be managed through seismic-acoustic stimulation.
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Date submitted2015-08-19
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Date accepted2015-10-17
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Date published2016-04-22
Development of institute of financial control in construction
- Authors:
- V. P. Grakhov
- O. L. Chazova
The article is devoted to the complex research of development of Institute of financial control in construction. Based on the analysis of approaches of researchers to definition of concept «financial control», sets out its objectives and importance. Identifies and describes the characteristic features of state and non-state financial control. To examine the existing mechanisms of financial control system in construction in General, to prevent violations and to create the basis for the adoption of specific management decisions, it is proposed to study three main areas. Special attention is paid to the analysis of the current legislation in the field of formation of financial control in the construction and practice of its application. Presents substantial changes in the legal regulation of the contract system in the sphere of procurement for state and municipal needs, including the adjustment of the scheme of carrying out of competitive procedures by the customer. In this regard, an important role plays the method of calculation of the final rating of participants of procurement procedures, allowing to determine the winner in accordance with predetermined criteria and their weighting factors. This area is also complemented by the consideration of issues related to the establishment of the procedure for the implementation of banking support contracts, allowing to provide the customer more effective control over the observance of contractual obligations with suppliers (contractors, performers). The conducted researches allow to draw a conclusion about the need to rethink and address issues related to efficiency of use of budget investments in objects of capital construction. In this regard, the main priorities of improving financial control in the construction industry to achieve the desired rates of economic development.