Energy efficiency in the mineral resources and raw materials complex

Energy efficiency and energy saving at all times and especially at the present stage of development of industry and economy have played an extremely important role. Regardless of which countries and according to what criteria they build energy development plans, energy efficiency and energy saving are always a priority. This fully applies to the mineral resources complex, in which energy consumption as a whole makes up a large share of total consumption. The resources mined in the mineral resources complex are themselves a source of energy. The energy sector is evolving in many ways. Many scientific works, the results of which are reflected in publications, confirm the relevance of research in the energy efficiency field. But the approach to individual decisions in the mineral resource industry is specific and it is worth of separate consideration. Recently, much attention has been paid to “green energy” and renewable energy sources. However, energy efficiency in the field of traditional generation and consumption remains an urgent problem and its solution is in constant development. One of the main directions for improving energy efficiency is the development of autonomous systems for the electrical and thermal power engineering. All these problems are reflected in a special volume of the Journal of the Mining Institute, the articles are divided into four sections: energy efficiency of the electric drive in the mineral resources complex (MRC); energy efficiency of industrial plants and enterprises in MRC; power quality and renewable sources in MRC; autonomous power supply systems in MRC. The presented articles contain valuable material from the scientific and practical points of view and can form the basis for further research in the energy efficiency field

Multi-terminal dc grid overall control with modular multilevel converters

This paper presents a control philosophy for multiterminal DC grids, which are embedded in the main AC grid. DC transmission lines maintain higher power flow at longer distances compared with AC lines. The voltage losses are also much lower. DC power transmission is good option for Russian north. Arctic seashore regions of Russia don't have well developed electrical infrastructure therefore power line lengths are significant there. Considering above it is possible to use DC grids for supply mining enterprises in Arctic regions (offshore drilling platforms for example). Three different control layers are presented in an hierarchical way: local, primary and secondary. This whole control strategy is verified in a scaled three-nodes DC grid. In one of these nodes, a modular multilevel converter (MMC) is implemented (five sub-modules per arm). A novel model-based optimization method to control AC and circulating currents is discussed. In the remaining nodes, three-level voltage source converters (VSC) are installed. For their local controllers, a new variant for classical PI controllers are used, which allow to adapt the values of the PI parameters with respect to the measured variables. Concerning the primary control, droop control technique has been chosen. Regarding secondary level, a new power flow technique is suggested. Unbalance conditions are also verified in order to show the robustness of the whole control strategy

Espacio y territorios: razón, pasión e imaginarios

En este caleidoscopio de acercamientos hacia lo espacial y territorial, las visiones se mueven desde aquellas románticas y existencialistas, pasando por aquellas objetivistas y positivistas, hasta las estructuralistas y postestructuralistas. Por el espacio y el territorio se interesan con enfoques diversos numerosas disciplinas, desde la psicología, la etología o la literatura, y las ciencias naturales como la biología o la ecología, hasta las ciencias sociales y políticas, como la geografía, la antropología, la economía y la sociología. Este interés multidisciplinario demuestra la importancia y la complejidad del tema espacial y territorial, y reclama la necesidad de su estudio y comprensión interdisciplinarios, como se intenta con esta publicación

A new power flow method for mixed AC-DC power systems

International audienceThis article presents a new tool to solve the power flow problem for electric mixed AC-DC grids. It is based on the fixed-point theorem of contractive function. This algorithm provides some advantages over classics methods, as for example the guarantee of converge, if some mild constraints are fulfilled, or fewer calculations in each iteration with respect other methods. Different devices, as for example AC/DC converters, DC/DC converters and AC transformer are contained in the formulation. The method is tested by means of a 14 nodes mixed AC-DC grid

Optimal power flow in multi-terminal HVDC grids with offshore wind farms and storage devices

International audienceThis work presents a power flow strategy for multi-terminal HVDC grids. Energy is mainly generated via renewable energy sources and there are nodes in the network with the possibility to store energy. This energy is generated taking into account real weather conditions in order to make the best scheduling of the system in a realistic approach. An optimization scheme is proposed in which all these elements are included as well as real operation constraints. Distribution losses are minimized for the whole network. This gives as a result a control strategy being able to deal with the whole system and its inherent constraints giving the framework for a multi-objective optimization control

Method for Evaluation of the Utility’s and Consumers’ Contribution to the Current and Voltage Distortions at the PCC

In this article, a method that allows sharing responsibilities for the generation of harmonic currents between the utility and consumers powered by one point of common coupling (PCC) is addressed. For these purposes, mathematical modeling of the power supply system (PSS) with two consumers is carried out in order to introduce new indices using the simplest PSS structure as an example. Two indices are introduced that quantify the consumers’ contribution to the distortion of current and voltage at the PCC and that evaluate harmonic emission from the utility side. Experimental tests are carried out where both linear and nonlinear loads are considered, capacitive loads are taken into account, and harmonic distortions from the utility side are modeled to show the applicability of the indices in a wide range of load types. The experiments confirmed the theoretical results and illustrated that the quantitative assessment of the contributions is unambiguous. It suggests that the proposed criterion could be a reasonable basis for further tax policy on harmonic pollution for each consumer at the PCC and for the utility

Method for Evaluation of the Utility’s and Consumers’ Contribution to the Current and Voltage Distortions at the PCC

In this article, a method that allows sharing responsibilities for the generation of harmonic currents between the utility and consumers powered by one point of common coupling (PCC) is addressed. For these purposes, mathematical modeling of the power supply system (PSS) with two consumers is carried out in order to introduce new indices using the simplest PSS structure as an example. Two indices are introduced that quantify the consumers’ contribution to the distortion of current and voltage at the PCC and that evaluate harmonic emission from the utility side. Experimental tests are carried out where both linear and nonlinear loads are considered, capacitive loads are taken into account, and harmonic distortions from the utility side are modeled to show the applicability of the indices in a wide range of load types. The experiments confirmed the theoretical results and illustrated that the quantitative assessment of the contributions is unambiguous. It suggests that the proposed criterion could be a reasonable basis for further tax policy on harmonic pollution for each consumer at the PCC and for the utility

Upgrading the Power Capacity of a Three-Conductor MVAC Line by Converting to DC

Several countries around the world are undergoing a radical transformation of their electricity networks, with the widespread integration of distributed generation based on renewable energy sources at the center of the change. Under these scenarios, DC links are becoming an attractive option for the infrastructure of modern networks, especially at medium voltage levels. This work is devoted to the integration of DC systems in existing AC networks by converting AC power lines to DC. The work presents a novel method for converting a three-conductor medium voltage AC transmission line to DC. The efficiency of the proposed conversion is assessed in terms of increased power capacity. It is shown that the proposed approach allows for increasing the power capacity of the line by at least 10%. The feasibility and effectiveness of the proposed method are then confirmed by laboratory experiments

Control-Induced Time-Scale Separation for Multiterminal High-Voltage Direct Current Systems Using Droop Control

International audienceThis paper introduces a control induced time-scale separation scheme for a multiterminal high-voltage direct current system used for large scale integration of renewable energy sources. The main idea is to provide a detailed theoretical analysis to the long stand practice that consists of the empirical design of two control loops for the terminals. Experience has shown that such loops, i.e., current and voltage control loops, when heuristically tuned, often display very different dynamics. In this paper, singular perturbation theory is applied to give explanation and fundamental analysis on why and how the two control loops work and how to achieve the timescale separation between various state variables. Mathematical analysis is also carried out to illustrate a clear tradeoff between system performance (actuator constraint) and the size of the region of attraction of the controller. Numerical simulations for a system with four terminals are presented to evaluate the system performance and illustrate the theoretical analysis

Bilinear and nonlinear control algorithms for a DC/DC converter for Multi-Terminal HVDC networks

International audienceThis paper presents the modeling and control of a multilevel DC/DC bidirectional converter suitable for medium voltage and medium power applications, with a special interest in renewable applications. The multilevel converter is based on Dual Active Bridge (DAB) and its average dynamic model. Two different control strategies are addressed in this paper in order to achieve the overall control of the DC/DC converter: a bilinear systems' control based on quadratic feedback control, and a nonlinear control based in Lyapunov theory. System's controllability and stability are studied, in particular by the analysis of zero dynamics. The performance of both controllers are illustrated by computer simulations, and the concluding remarks analyze theirs characteristics and draw some comparisons