• Energy Research
• Closed Access close
• engineering and technology close
• CO close

Abstract A bilinear proportional-integral (PI) controller based on passivity-based formulations for integrating superconducting magnetic energy storage (SMES) devices to power ac microgrids is proposed in this paper. A cascade connection between a dc–dc chopper and a voltage source converter is made to integrate the SMES system. The proposed controller guarantees asymptotically stability in the Lyapunov's sense under closed-loop operation. This controller exploits the well-known advantages of the proportional-integral (PI) actions via passivation theory. Active and reactive power compensation in the ac system through the SMES integration is proposed as the control objective. To achieve this goal, a radial ac distribution feeder with high penetration of distributed energy resources and time-varying loads is employed. The effectiveness and the robustness of the proposed bilinear PI controller verified by comparing its dynamical performance to conventional approaches such as conventional PI and feedback controllers. All simulation results are conducted via MATLAB/SIMULINK software by using SimPowerSystem library.

Abstract Conventional spouted beds have been extensively used in many real-life applications but are not suited for all types of materials, especially fine particles, which require internal devices to improve their motion in the spouted bed. However, unlike conventional spouted beds, there are almost no mechanistic or empirical models available for the design of spouted beds with internals. Given the availability of an extensive but not experimentally designed database, the main purpose of this study is to present an analysis of neural networks and empirical models in terms of their suitability to fit and predict average cycle times in conical spouted beds with and without draft tubes. The parameters investigated are particle size, density, contactor angle, gas inlet diameter, static bed height, and draft tube features. Although the amount of information is always a key factor when fitting models, the size of the database used in this study strongly affects the fitting performance of empirical models, whereas artificial neural networks are more influenced by how the data are scaled. Results of model verification show that both techniques are suitable for predicting average cycle times for data outside the range covered by the database.

Symmetrical components theory, presented by Fortescue in 1918, and its analysis of the time domain presented by Lyon in 1954, have been widely used for fault analysis and power system protection algorithms. In recent times, applications in time domain have been deeply studied given their potential for getting a quicker failure detection, there are two main techniques which apply signal processing methods in the time domain: Travel-wave and incremental quantities. The theoretical background of symmetrical components to fault analysis is well recognized. Currently, the fault protection algorithms using symmetrical components are based on frequency domain. This paper presents a theoretical analysis of the use of symmetrical components in time domain, particularly in asymmetrical faults. A Signal processing algorithm to obtain the instantaneous symmetrical quantities from phases quantities are presented. A study case is simulated to validate the time domain technique and fault analysis permits show the potential of the results to develop protection algorithms.

AbstractFly ash is currently a problem in different companies, mainly in thermoelectric plants, which must follow a production and consumption model that involves reusing, renewing, and recycling, thus contributing to the circular economy. This work aims to evaluate the reactivity and compressive strength of different types of ashes in concrete monoliths. For this purpose, sugarcane bagasse (SCBA), bituminous coal (BC), and untreated hazardous waste (RUD) were evaluated as replacements for cement. Monoliths and mortars have been manufactured in different mixtures, taken to a curing room, and their compressive strength and reactivity have been determined at different times (up to 28 days for the monoliths and up to 90 for the mortars), mainly in order to check the formation of calcium silicate hydrate (CSH) gels. In the monolith tests, the best performances have been with SCBA and BC, which have been used for the manufacture of the mortars. On day 56, the behavior of the replacement of 30% fly ash (15% BC:15% SCBA) presents a type H mortar behavior, with better results than the control. By day 90, all replacements had the same resistance as M mortars and even higher resistances than the control. This demonstrates the feasibility of its use in the production of Portland cement for the manufacture of low‐performance inputs. This implies the possible reduction of impacts, both in waste disposal sites and in emissions caused by the construction industry, thus contributing to the circular economy.

Models of series–parallel (SP) photovoltaic (PV) generators under nonhomogeneous conditions commonly represent each submodule with the single-diode model. However, most of those models require high calculation burdens because they need to evaluate the LambertW function for each submodule in the generator to calculate the submodule current as a function of its voltage. This paper proposes a model for SP generators, operating under nonhomogeneous conditions, which uses the implicit current–voltage relation of each submodule to propose a system of nonlinear equations that describes the electrical behavior of an SP generator. The generator can be divided into strings, which are analyzed independently since they are parallel connected. Each string is composed of $N$ submodules and one blocking diode connected in series; hence, the model has $N+2$ unknown: $N+1$ voltages of the submodules and the blocking diode, and the string current. The system of $N+2$ nonlinear equations is formed by the $N$ implicit current–voltage relationships of the submodules, the blocking diode model, and the Kirchhoff's voltage law applied to the string. The system of nonlinear equations can be solved with the same numerical methods used by traditional models. The main advantage of the proposed model is the avoidance of evaluating the LambertW function, which reduces the computational burden and the calculation time. Moreover, simulation and experimental results show the feasibility of using implicit submodules’ current–voltage relationships for models of PV generators, since it significantly reduces the calculation time with the same errors provided by traditional models.

In this paper we describe the successful part-privatization of Empresa de Energia de Bogota (EEB), the city-owned electricity company in Bogota, Colombia. We describe the reason, the preparation and the actual sale process as well as the outcome following the part-privatization. EEB went from being a company on the edge of bankruptcy to one of the most financially secure electricity companies in South America. We also place the case in relation to the standard views on direct foreign investment and their social benefit. Finally, we aim to generalize the experience to see what other organizations in a similar position can learn.

This paper presents an algorithm for solving the Transmission Expansion Planning (TEP) problem when large scale wind generation is considered. Variability of wind speed and demand uncertainty are also taken into account. The formulation includes the DC model of the network, and the obtained expansion plans minimize the investment, the load shedding, and also the wind generation curtailment. The Chu-Beasley Genetic Algorithm (CBGA) is used for finding feasible optimal expansion plans. Uncertainties are included by scenario reduction to obtain robust expansion plans capable of meeting the uncertainty set. The approach allows finding robust expansion plans to cope with the uncertainties in load forecasting and also to take advantage of wind generation. The proposed algorithm is validated on the 6-bus Garver system, IEEE 24-bus RTS test system and the real life South-Brazilian 46-bus system. Comparison with other methods is carried out to demonstrate the performance of the proposed approach.

AbstractThis is a review of work on the potential of biorefineries. First, it considers the concept of a refinery, the differences between biomass and oil, and the advantages of a biorefinery over a refinery. It goes on to describe the bio‐based economy and biorefinery concepts, and to discuss its origin as a promising alternative to dependence on non‐renewable feedstocks. It provides an exhaustive description of the classification of biorefineries, considering aspects such as systems, technological implementation status, size, feedstocks, platforms, products, and conversion processes. It outlines the main methodologies for designing biorefineries – conceptual design, optimization, and the ‘early stage’ method. Methodologies for the economic, environmental, and social assessment of a biorefinery are presented. Finally, challenges linked to the implementation of biorefinery projects at industrial level are discussed. The authors conclude that the methodologies of conceptual design and optimization must complement each other to achieve a robust design from a conceptual and mathematical point of view. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

The incorporation of Energy Storage Systems (ESS) in an electrical power system is studied for the application of Energy Time Shift (ETS) or energy arbitrage, taking advantage of the turbinable energy discharged in hydroelectric plants. For this, three storage systems were selected: Lithium-Ion Batteries (LIB), Vanadium Redox Flow Battery (VRFB), and Hydrogen Storage Systems (H2SS). The spilled turbinable energy available at the Paute Integral hydropower complex in the Republic of Ecuador is taken as the case study. Based on real data from the operation of these plants, a distinctive element of the study, the performance of the selected energy storage systems was analyzed applying the Analytic Hierarchy of Process for decision-making, where technical, economic, and environmental criteria were considered. Electrical energy stored during the early morning seeks to displace the thermal generation during peak hours, close to the demand centers. The results show that all the storage systems analyzed satisfy the required demand, although VRFB is recommended for the ETS. From an economic point of view, LIB represents the best alternative. From a technical point of view, H2SS is slightly superior, while prioritizing environmental aspects, VRFB technology prevails. However, the selection of the best ESS alternative must be continually evaluated, due to permanent technological changes. It is concluded that ESS represent a viable alternative to improve the operational performance of hydroelectric plants, meet the variability of demand, improve the quality of the electrical energy delivered, and displace the pollution-generation plants. Ingeniería y Tecnología Digital