With the rapid development of power electronics technology and its successful application, many demonstration projects of medium/low-voltage DC (M-LVDC) distribution systems have been constructed. The DC transformer (DCT) is the key equipment in the M-LVDC distribution system for interconnecting the MVDC and LVDC buses. In this paper, the characteristics of DCTs are summarized. The existing topologies of DCTs are analyzed, and the relevant control strategies are researched, including steady-state control, transient control, and cascaded control. The engineering application examples of DCTs are introduced by interpreting the medium and low-voltage DC distribution system demonstration project in Wujiang City, Suzhou. Finally, the challenges faced by the DCT are given, and the future development trend is predicted. This perspective provides a constructive basis for DCTs and an important reference for M-LVDC distribution systems.

Energy-intensive industries (EIIs) refer to industries that are highly dependent on energy (fuel), which are primarily responsible for industrial energy consumption [...]

Lithium-ion batteries (LIBs) from electrified vehicles (EVs) that have reached the automotive end of life (EoL) may provide a low-cost, highly available energy storage solution for grid-connected systems, such as peak shaving and ancillary services. There are several issues related to the integration of second life batteries (SLBs) in power systems, such as the variability of the pack design and cell chemistry, in-field assessments of the state of health (SoH), and estimations of the expected lifetimes of SLBs in different power system applications. Model-based approaches are commonly used in the automotive industry for estimating/predicting the capacity and power fade trajectories of LIBs during their life. However, a large variety of models are available with different fidelities, complexities, and computational costs. The accuracy of these estimations is critical for the derivation of business models for SLB applications. This paper presents a qualitative and quantitative assessment... [more]

A reliable power grid system based on renewable energy sources is a crucial step to restrict the climate crisis. Stationary battery energy storage systems (BESS) offer a great potential to repel power fluctuations in the grid at different timescales. However, for a reliable operation and cost estimation, the degradation in the batteries needs to be understood. We present an accelerated battery degradation study, on single as well as multi-service applications, of NCM532/Gr lithium-ion battery cells. Frequency regulation (FR) was the least harmful for the battery, with an expected lifetime of 12 years, while peak shaving (PS) resulted in an expected lifetime of 8 years. The combined cycle (FRPS) accelerated the capacity loss, and degradation of the positive electrode was induced from the start of cycling, causing power limitations after only 870 equivalent full cycles (EFC). Tracking the 1C-rate discharge capacity was proven to be a good indication of the accelerated cell polarization,... [more]

The paper examines the challenges related to solar photovoltaic (PV) development with a pivotal focus on the impacts of the dynamics of the relevant markets and technological advancements in the solar industry. In this regard, household investments into rooftop solar PV modules as one of the available incentives are investigated based on a conducted experiment in Lithuania for selecting rooftop solar PV systems for the prosumer by measuring the attractiveness of solar PV modules by a categorical-based evaluation technique (MACBETH). While a variety of multiple-criteria decision-making (MCDM) methods used by scholars have their specifics in terms of application and the divergence of results, the findings of the conducted experiment reveal MACBETH’s utility when based upon qualitative judgments about the differences in the attractiveness of offers, quantifying their relative value and accordingly ranking the latter. The findings also confirm MACBETH’s potential to be used not only to sol... [more]

Array spectroradiometers are increasingly being used to measure natural and artificial optical radiation because of their many advantages compared to traditional instruments. This study aims to thoroughly characterise a commercially available, cost-effective array device (AvaSpec ULS2048-LTEC) and compare its measurements of global solar irradiance in the 290−1100 nm wavelength range with those collected during three short-term field campaigns from more advanced, or specifically designed instruments. Moreover, the AvaSpec observations were compared with the output of a radiative transfer model. The results show that, despite its conceptually simple instrumental design, the AvaSpec can provide measurements of nearly comparable quality to those from reference instruments (e.g., UV index and global horizontal irradiance generally within ±5%) if all corrections are performed. These preliminary observations will be the basis of a long-term series at the Aosta−Saint-Christophe observatory, w... [more]

As a representative new energy source, solar energy has the advantages of easy access to resources and low pollution. However, due to the uncertainty of the external environment, photovoltaic (PV) modules that collect solar energy are often covered by foreign objects in the environment such as leaves and bird droppings, resulting in a decrease in photoelectric conversion efficiency, power losses, and even the “hot spot” phenomenon, resulting in damage to the modules. Existing methods mostly inspect foreign objects manually, which not only incurs high labor costs but also hinders real-time monitoring. To address these problems, this paper proposes an IDETR deep learning target detection model based on Deformable DETR combined with transfer learning and a convolutional block attention module, which can identify foreign object shading on the surfaces of PV modules in actual operating environments. This study contributes to the optimal operation and maintenance of PV systems. In addition,... [more]

Hydrogen production from biogas over alumina-supported Ce1−xNixO2−x catalysts was studied in a temperature range of 600−850 °C with an initial gas composition of CH4/CO2/H2O of 1/0.8/0.4. To achieve a high and stable hydrogen yield, highly dispersed Ni catalysts were prepared through the exsolution approach. A solid solution of Ce1−xNixO2−x was firstly formed on the surface of Al2O3 and then activated in H2/Ar at 800 °C. The genesis and properties of the Ce1−xNixO2−x/Al2O3 catalysts were established using X-ray fluorescence analysis, thermal analysis, N2 adsorption, ex situ and in situ X-ray diffraction, Raman spectroscopy, electron microscopy, EDX analysis, and temperature-programmed hydrogen reduction. The performance of Ce1−xNixO2−x/Al2O3 catalysts in biogas conversion was tuned by regulation of the dispersion and reducibility of the active component through variation of content (5−20 wt.%) and composition (x = 0.2, 0.5, 0.8) of Ce1−xNixO2−x as well as the mode of its loading (co-im... [more]

Off-grid hybrid renewable energy systems represent the most modern and flexible solutions that can cover a wide range of energy efficiency needs for household consumers. In the current context, these systems must be taken into account by most household consumers, given the fact that the price of energy has increased. This paper proposes an experimental analysis of the behavior of such a system, in real operating conditions, considering two renewable energy sources, wind and photovoltaic sources, using an experimental stand. It can be considered a testing platform for hybrid energy production systems, in that the power installed in the two sources can be scaled up. The platform has the advantage of allowing the implementation of different load and wind curves through a programmable logic controller; in this way, it is possible to evaluate the degree of coverage of the energy consumption produced from renewable sources, in the north-east of Romania, in the Suceava County region. The expe... [more]

Renewable energy sources have been characterized by a persistent and rapid proliferation, which has resulted in a notable reduction in grid inertia over an extended period. There is a widely held belief that the primary source of inertia within the grid stems from generation-side conventional units. However, in power consumption, a significant number of induction motors are present, which can inherently offer rotational inertia by virtue of their kinetic energy. To investigate the influence of induction motors on grid inertia, in this paper, we propose two types of models, i.e., a detailed grid model and a dynamic equivalent model that considers multiple induction motors. Specifically, the detailed grid model with multiple induction motors is first established. However, the detailed model requires the specific parameters of induction motors, which are hard to acquire in large systems. Moreover, the accuracy of the model is unsatisfactory. To fill these gaps, the dynamic equivalent mode... [more]

Future wireless communication systems require higher performance requirements. Based on this, we study the combinatorial optimization problem of power allocation and dynamic user pairing in a downlink multicarrier non-orthogonal multiple-access (NOMA) system scenario, aiming at maximizing the user sum rate of the overall system. Due to the complex coupling of variables, it is difficult and time-consuming to obtain an optimal solution, making engineering impractical. To circumvent the difficulties and obtain a sub-optimal solution, we decompose this optimization problem into two sub-problems. First, a closed-form expression for the optimal power allocation scheme is obtained for a given subchannel allocation. Then, we provide the optimal user-pairing scheme using the actor−critic (AC) algorithm. As a promising approach to solving the exhaustive problem, deep-reinforcement learning (DRL) possesses higher learning ability and better self-adaptive capability than traditional optimization m... [more]

The deposition of sulfur particles in gathering and transportation pipeline system can cause serious safety problems and economic losses. When the high sulfur content natural gas (HSCNG) flows through the throttle valve of the gathering and transportation system, it will cause the supersaturation of elemental sulfur in the gas phase, and then the sulfur crystal nuclei and sulfur particles will appear in the pipeline system. Studying the initial growth behavior of sulfur crystal nuclei and sulfur particles can lay a necessary prerequisite for the accurate prediction of sulfur particle deposition in high sulfur content natural gas gathering and transportation (HSCNGGT) pipelines. Based on the homogeneous nucleation theory in crystallization kinetics, a mathematical model of elemental sulfur nucleation was established. Taking the throttling condition in the process of HSCNGGT as an example, the effects of temperature, pressure and H2S concentration in HSCNG on the critical nucleation radi... [more]

A new method including suspension and wheel vibration energy regeneration is proposed in this study to coordinate the contradiction between vibration energy regeneration and dynamic performance of in-wheel motor electric vehicles (IWM-EVs). The influence mechanism of unsprung mass on the dynamic characteristics of IWM-EVs is investigated from the perspective of energy flow, and potential of energy regeneration of IWM-EVs is explored on this basis. A parameter sensitivity analysis of the proposed new method is conducted, and the optimal parameters are determined for a comparative simulation analysis among focus-driven electric vehicles, IWM-EVs, and IWM-EVs with linear electromagnetic dynamic vibration absorber (LEM-DVA). Results show that the proposed new method effectively improves the dynamic performance and achieves coordination between energy regeneration and dynamic performance despite its reduction of the vibration energy regeneration potential of IWM-EVs. A new structure, which... [more]

In electric vehicles, currents with high-frequency ripples flow in the power cabling system due to the switching operation of power converters. Inside the cables, a strong coupling between the thermal and electromagnetic phenomena exists, since the temperature and Alternating Current (AC) density distributions in the strands affect each other. Due to the different time scales of magnetic and heat flow problems, the computational cost of Finite Element Method (FEM) numeric solvers can be excessive. This paper derives a simple analytical model to calculate the total losses of a multi-stranded cable carrying a Direct Current (DC) affected by a high-frequency ripple. The expression of the equivalent AC cable resistance at a generic frequency and temperature is derived from the general treatment of multi-stranded multi-layer windings. When employed to predict the temperature evolution in the cable, the analytical model prevents the use of complex FEM models in which multiple heat flow and m... [more]

Lithium-ion batteries (LIBs) are widely used in electrochemical energy storage and in other fields. However, LIBs are prone to thermal runaway (TR) under abusive conditions, which may lead to fires and even explosion accidents. Given the severity of TR hazards for LIBs, early warning and fire extinguishing technologies for battery TR are comprehensively reviewed in this paper. First, the TR reaction mechanism and hazards of LIBs are discussed. Second, the TR early warning and monitoring methods of LIBs are summarized in five aspects consisting of acoustic, heat, force, electricity, and gas. In addition, to reduce the fire and explosion hazards caused by the TR of LIBs, the highly efficient extinguishing agents for LIBs are summarized. Finally, the early warning technology and fire extinguishing agent are proposed, which provides a reference for the hazard prevention and control of energy storage systems.

This paper presents a model for determining fuzzy evaluations of partial indicators of the availability of continuous systems at coal open pits using a neuro-fuzzy inference system. The system itself is a combination of fuzzy logic and artificial neural networks. The system availability is divided into partial indicators. By combining the fuzzy logic and artificial neural networks, a model is obtained that has the ability to learn and uses expert judgment for that learning. This paper deals with the ECC system (bucket wheel excavator-conveyor-crushing plant) of the open pit Drmno-Kostolac, which operates within the Electric Power Company of Serbia. The advantage of a model of this type is that it does not rely on the historical experiences of experts and usual predicted values for the fuzzy evaluation of partial indicators, which are based on the assumption that similar systems affect availability in a similar way. The fuzzy evaluation of partial indicators is based on historical data... [more]

Copper−indium−gallium−diselenide Cu(In,Ga)Se2 (CIGS) is a semiconductor compound belonging to group I-III-VI, with a chalcopyrite crystal structure. CIGS is promising for the development of high-performance photovoltaic applications in terms of stability and conversion efficiency. It is one of the main candidates to rival the efficiency and stability of conventional crystalline silicon cells, due to its high light absorption coefficient, lower material cost, and high stability. The limitation of its use is that CIGS integrates indium (In) and gallium (Ga), which are rare and expensive materials. The amount of these materials in the CIGS cell can be reduced by optimizing the thickness of the absorber. We show that the introduction of a layer of highly doped silicon in the structure of the solar cell between the absorber layer and the back surface field layer effectively allows for decreasing the thickness of the absorber. Within the same objective, we focus on the danger of cadmium in t... [more]

Lean premixed combustion mode has become attractive for utilization in industrial gas turbines due to its ability to meet strict emissions regulations without compromising engine efficiency. In this combustion mode, the mixing process is the key player that affect the flame structure and stability, as well as the generated emissions. Many studies have investigated the aspects that influence premixed flames, including the effects of turbulence, combustor geometry, and level of partial premixing, while mostly using conventional natural gas fuel represented by methane. Recently, ammonia, a sustainable energy source, has been considered in gas turbines due to its carbon-free fuel producing no CO2. Utilizing 100% ammonia or a blend of methane and ammonia alters the combustion performance of a premixed flame due to the variation associated with the physical and chemical properties of ammonia. Thus, investigating the coupling between blend ratios and mixing length of methane-ammonia on flame... [more]

This paper develops a model of the multi-wing finite-conductivity fractures considering stress sensitivity for low-permeability bi-zone composite gas reservoirs. A new semi-analytical solution in the Laplace domain is presented. The main solution includes the theory of source function, Laplace integral transformation, perturbation technique, and Stehfest numerical inversion. Wellbore pressure is obtained by coupling solutions of reservoirs and fractures. The results showed that the pressure and derivative curves generated by this model include a bi-linear flow stage. The model was validated by comparing its results with Wang’s results and the commercial well-test simulator; the results showed excellent agreement. This model illustrated the seepage characteristic of acid fracturing stimulated wells during refracturing treatment and how they are influenced by reservoir and hydraulic fractures parameters (asymmetrical factor and fractures distribution, etc.). The model is suitable to solv... [more]

By taking into account the turbine type, terrain, wind climate and layout, the effects of wind turbine wakes and other losses, engineering models enable the rapid estimation of energy yields for prospective and existing wind farms. We extend the capability of engineering models, such as the existing deep-array wake model, to account for additional losses that may arise due to the presence of clusters of wind farms, such as the global blockage effect and large-scale wake effects, which become more significant with increasing thermal stratification. The extended strategies include an enhanced wind-farm-roughness approach which assumes an infinite wind farm, and recent developments account for the upstream flow blockage. To test the plausibility of such models in capturing the additional blockage and wake losses in real wind farm clusters, the extended strategies are compared with large-eddy simulations of the flow through a cluster of three wind farms located in the German sector of the... [more]

Due to the economic inefficiency of material recycling of general industrial waste and urban waste, the use of solid recovered fuels (SRFs) not only mitigates the environmental loadings from waste incineration plants and sanitary landfills but also creates green electricity and/or heat and thus reduces the use of fossil fuels. In this regard, the Taiwan government formulated the “Solid Recovered Fuel Manufacturing Guidelines and Quality Standards” in 2020 to ensure the manufacturing quality of SRFs. This paper focused on the status of waste management and energy supply, the current regulations for adopting SRFs, and the challenges in the development of SRFs from the viewpoints (or life cycle) of the environmental, economic, and engineering (or technological) characters in Taiwan. Based on the database of the official handbook/yearbook, the energy supply from indigenous biomass and waste was 1678.7 × 103 kiloliters of oil equivalent (KLOE) in 2021, which only accounted for about 1.2% of... [more]

This article proposes a novel framework to develop computationally efficient energy consumption models of electric and internal combustion engine vehicles. The number of calculations in a conventional energy consumption model prevents the model’s usage in applications where time is limited. As many fleet operators around the world are in the process of transitioning towards electric vehicles, a computationally efficient energy consumption model will be valuable to analyse the vehicles they trial. A vehicle’s energy consumption depends on the vehicle characteristics, drive cycles and vehicle mass. The proposed modelling framework considers these aspects, is computationally efficient, and can be run using open source software packages. The framework is validated through two use cases: an electric bus and a diesel truck. The model error’s standard deviation is less 5% and its mean is less than 2%. The proposed model’s mean computation time is less than 20 ms, which is two orders of magnit... [more]

In this article, a novelty control structure of grid-connected doubly-fed induction generator (DFIG) based on a function link (FL)-based Wilcoxon radial basis function network (FLWRBFN) controller is proposed. The back-propagation (BP) method is used online to train the node connecting weights of the FLWRBFN. To improve the online learning capability of FLWBFN, differential evolution with particle swarm optimization (DEPSO) is used to tune the learning rates of FLWRBFN. For high randomness of wave energy generation, the transmission power between generators and electrical grids is easy to unstable and AC bus voltage and DC voltage will also lose constant under the conditions of variable generator speed and variable load. Therefore, the proposed intelligent controller can maintain the above power balance and voltage constant and reduce fluctuation. Finally, PSCAD/EMTDC software is used to simulate and study various cases to confirm the robustness and usefulness of the proposed intellige... [more]

The purpose of this study is to determine the impact of households’ energy autonomy on a country’s energy independence level, to identify prospects and risks. To assess the economic efficiency of households’ energy autonomy, the study used a modeling method based on maximizing the net present value, determining the average notional cost of energy efficiency and the level of energy independence in 20 countries. Based on the analysis of the volumes of electricity consumption by households in the studied countries for the period 2000−2018, it was revealed that in developed and developing countries there is an increase in this indicator. Diagnostics of the investment attractiveness of the installation and operation of energy systems for households makes it possible to determine the boundaries of a possible increase in the level of their energy autonomy. The scientific novelty of the research is represented by the proposed methodological approach, which makes it possible to assess the level... [more]

Development of underground coal mines is reflected in increasing lengths of transport routes between shafts and workplaces. This is not an issue in terms of transportation of materials or groups of people, because suspended railways are efficient, safe, and fast mean of transport. However, transportation of individual people or small loads is an issue because of the lack of a means of individual transport and the high cost of transport using suspended railways. The development of individual means of transport, based on historical solutions, utilizes existing equipment of mine workings. This paper presents the stages of development of an underground bike, from the original idea to tests and analysis. The development process consists of simulations of different parameters of the bike using Working Model software and real-life tests conducted in an underground mine. The paper also presents analysis of the legal background of this new means of individual transport.