In recent years, solar photovoltaic power generation has emerged as an essential means of energy supply. The prediction of its active power is not only conducive to cost saving but can also promote the development of solar power generation industry. However, it is challenging to obtain an accurate and high-quality interval prediction of active power. Based on the data set of desert knowledge in the Australia solar center in Australia, firstly, we have compared twelve interval prediction methods based on machine learning. Secondly, six ensemble methods, namely Ensemble-Mean, Ensemble-Median (Ensemble-Med), Ensemble-Envelop (Ensemble-En), Ensemble-Probability averaging of endpoints and simple averaging of midpoints (Ensemble-PM), Ensemble-Exterior trimming (Ensemble-TE), and Ensemble-Interior trimming (Ensemble-TI) are used to combine forecast intervals. The result indicates that Ensemble-TE is the best method. Additionally, compared to other methods, Ensemble-TE ensures the prediction i... [more]

One of the greatest challenges in stand-alone photovoltaic irrigation systems (PVIS) without batteries is the tuning of PID controllers and the evaluation of their performance once the system is tuned. Tuning method must be applied in clear days (constant irradiance) while performance must be evaluated in the most unfavourable circumstances, which occur when the passage of a cloud causes a sudden drop in available power. In short, tuning and testing must be done under different weather conditions. To solve this problem, a tuning method that is complemented by a method to simulate voltage fluctuations due to cloud passage has been developed. This allows tuning and evaluation of the system’s performance in the same session. Furthermore, the new PI tuning method achieves a better adjustment of the parameters and solves the instability problems that arise when applying traditional closed-loop tuning methods. Both methods use the feedforward input that most variable frequency drivers have.... [more]

Modular input-series−output-parallel (ISOP) converters are very suitable for high-voltage and high-power applications. In order to ensure the normal operation of ISOP converters, it is necessary to realize the input-voltage and output-current equalization of each submodule. However, there are few studies on the input-voltage and output-current equalization performance of the ISOP system. In this paper, the input-voltage and output-current equalization characteristics of a Boost + LLC modular ISOP converter are studied based on the small-signal model. In this paper, the small-signal model of an ISOP system is first established, and then the input-voltage and output-current equalization performance of the ISOP system under the condition of inconsistent submodule parameters are analyzed. Finally, simulations and experiments are reported to verify the results. The experimental results show that the ISOP system composed of a Boost + LLC cascaded module has excellent voltage and current self... [more]

The reliability assessment of smart grid-integrated distributed power-generating coordination is an operational measure to ensure appropriate system operational set-ups in the appearance of numerous issues, such as equipment catastrophes and variations of generation capacity and the connected load. The incorporation of seasonable time-varying renewable energy sources such as doubly fed generator-based wind turbines into the existing power grid system makes the reliability assessment procedure challenging to a significant extent. Due to the enormous number of associated states involved in a power-generating system, it is unusual to compute all possible failure conditions to determine the system’s reliability indicators. Therefore, nearly all of the artificial intelligence methodology-based search algorithms, along with their intrinsic conjunction mechanisms, encourage establishing the most significant states of the system within a reasonable time frame. This review’s finding indicates t... [more]

The paper focuses on developing an energy-modeling tool called ENECO2Calc, which allows the determination of current ecologic and economic footprints based on calculating the final energy demand within several sectors for municipalities. Furthermore, different energy transition paths until 2050 can be investigated and compared to the business-as-usual reference scenario. ENECO2Calc is the first municipality-based energy-modeling tool that allows the development of meaningful scenarios until 2050 by considering climate policy goals and RES potentials, and it involves the mobility emission forecast tool “PROVEM”. ENECO2Calc is exclusively based on consistent statistical datasets. Additionally, the energy-modeling process was demonstrated as exemplary for the Austrian municipality St. Margareten im Rosental. For the selected municipality, three different scenarios were investigated. It could be concluded that a mix of decentral RES technologies and central cogeneration units in the heat s... [more]

The virtual synchronous generator (VSG) technique is used to simulate the external characteristics of a synchronous generator (SG) to provide certain damping and inertia to power systems. However, it may easily cause low-frequency oscillation of the power system. We studied the small-signal stability of a grid-connected virtual synchronous generator. Firstly, the small-signal models of single-VSG and multi-VSG grid-connected systems were established. Subsequently, the system eigenvalues were obtained by solving the state matrix, and the system oscillation modes were analyzed. The eigenvalue analysis method was used to analyze the impacts of parameter changes, such as virtual moment of inertia, virtual damping coefficient, line resistance, and line inductance, on system stability. Finally, our conclusions were verified by numerous simulation models.

In this paper, the encapsulation of lithium atoms in spherical fullerenes of varying sizes is investigated. The 6−12 Lennard−Jones potential function and the continuum approximation, in which it is assumed that the atoms can be replaced with a uniform distribution across the surface of the molecules, are exploited to model the interaction energies between lithium atoms and spherical fullerenes. Thus, the total interaction energies can be approximated by applying surface integrations. The results show that for a lithium atom interacting inside a spherical fullerene, the interaction energies are minimized at a position that approaches the fullerene wall as the size of the fullerene increases. However, the results show that an external force would need to be applied to a lithium atom in order to overcome the repulsive energy barrier so that it can be encapsulated in CN fullerenes with a radius of less than 2 Å. The present study indicates that the optimal radius that gives the minimum ene... [more]

The ceramic industry is one of the pillars of the Brazilian economy, characterized by making low-cost products and an obsolete manufacturing process from a technological point of view. Among the various stages of production of ceramic materials, drying is one of the most energy-consuming and, in general, causes structural damage to the product, compromising its mechanical performance and final quality. Despite the relevance, studies on the drying of ceramic materials are mostly conducted at the experimental level and limited to some specific operational conditions. In this scenario, this research aims to theoretically study the heat and mass transfers in industrial ceramic blocks during drying. Based on the lumped analysis method, and considering the dimensional variations of the material, new phenomenological mathematical models and their respective analytical solutions are proposed to describe the kinetics of mass loss and heating of the material. The predicted results referring to t... [more]

Low-permeability near-critical volatile reservoirs are characterized by light oil, complex fluid phase, and strong reservoir inhomogeneity, etc. Purely injecting CO2 will create a series of problems, such as serious gas channeling, low sweep efficiency, and low oil recovery. Therefore, in this paper, through a combination of experiments and simulations and in the process of studying the problem from simple to complex, we carried out phase equilibrium experiments for CO2-near-critical volatile oil and CO2-near-critical volatile oil-formation water, as well as experiments for minimum miscible pressure of slim-tube with pure CO2 and CO2−water co-injection to the comparative study of the miscible characteristics and displacement oil efficiency between pure CO2 injection and CO2−water co-injection. It provides an important reference for improving oil recovery by CO2−water co-injection in low-permeability near-critical volatile reservoir. The results of CO2-near-critical volatile oil/CO2-nea... [more]

In this study, a mathematical model of hydrogen production from glycerol gasification in supercritical water was established based on the CFD-DEM method. The fluidization process of a supercritical water fluidized bed and the effects of bed height and feed structure on particle distribution and residence time of feedstock were analyzed. Additionally, the temperature field in the fluidized bed, the reaction rate distribution of each reaction and the influence of wall temperature on gas yields were also studied. The simulation results show that the bubble channel is easy to form along the wall at one side of the feed inlet. When the initial bed height is high, and the double symmetric feed inlet structure is used, the residence time of the feedstock is prolonged. The pyrolysis of glycerol mainly occurs in the middle and lower part of the fluidized bed reactor, and the reaction rate of the water gas shift reaction and methanation reaction are highest near the outlet, and a high wall tempe... [more]

Horizontal axis wind turbines are used for energy generation at domestic as well as industrial levels. In the wind turbines, a reduction in drag force and an increase in lift force are desired to increase the energy efficiency. In this research work, computational fluid dynamics (CFD) analysis has been performed on a turbine blade’s frontal section with an NACA S814 profile. The drag force has been reduced by introducing an array of dimpled structures at the blade surface. The dimpled structures generate a turbulent boundary layer flow on its surface that reduces the drag force and modifies the lift force because it has greater momentum than the laminar flow. The simulation results are verified by the experimental results performed in a wind tunnel and are in close harmony with the simulated results. For accurate results, CFD is performed on the blade’s frontal section at the angle of attack (AOA) with a domain of 0° to 80° and at multiple Reynolds numbers. The local attributes, lift f... [more]

This paper introduces a novel free space optics (FSO) communication system for future-generation high-speed networks. The proposed system integrates orbital angular momentum (OAM) modes with an optical code division multiple access (OCDMA) technique. Two OAM beams are used (LG0,0 and LG0,10), each of which is used for transmitting three independent channels. Each channel is assigned by fixed right shift (FRS) codes and carries 10 Gbps of information data. The performance of the proposed model is evaluated under different foggy and dust storm conditions. Furthermore, the performance of two cities with different geographical locations, Alexandria city in Egypt and Srinagar city in India, is investigated to demonstrate its ability to be implemented in future generations. Bit error rate (BER), eye diagrams, received optical power (ROP), and channel capacity are used for studying the performance of the proposed system. The observed simulation results show successful transmission of 60 Gbps... [more]

Foundation pit excavation is common in urban construction, while safety evaluation is always significant in every specified project. The soil material properties, groundwater level, excavation method, supporting structure, monitoring points’ arrangement, and so on distinguish from one site from another. Thus, many studies have looked into the safety and reliability of designated projects. This paper was based on the co-construction underground tunnel project of a deep foundation pit excavation in Suzhou, China. This paper aimed to perform a safety evaluation on this foundation pit by means of numerical simulation for parameter influence analysis, as well as scientific comparison with in-site monitoring data. To minimize the energy consumption and contribute to the carbon neutrality, a brief energy consumption analysis was also conducted. The results indicated that the maximum deformation of the foundation pit bottom is 4.5 cm and the deformation of the foundation pit is within the allo... [more]

In the present study, the turbulent flow field and the heat transfer in a single started helically ribbed pipe with a discontinuous rib are investigated. A large-eddy simulation (LES) technique is applied in a pipe section with cyclic boundary conditions. The aim of this study is to explain and further analyze the findings from the heat transfer measurements at such complex structures with the help of detailed flow simulations. The simulation results are validated with measurements at a Reynolds number of Re = 21,100 and a Prandtl number of Pr = 7 with water as fluid. The comparison clearly shows that the current method delivers accurate results concerning average flow field, turbulence quantities and local heat transfer. The results demonstrate that the applied method is capable of correctly simulating flows with heat transfer in complex three-dimensional structures. The overall heat transfer performance of the helically ribbed pipe with a discontinuous rib is compared to a smooth pip... [more]

Many thermal resources are not reasonably used in the chemical industry’s production process. To recover the waste heat from organic waste residue-calcium carbonate (CaCO3), which is added to inhibit hydrogen production, an organic Rankine cycle (ORC) system is applied in this research. An ORC system can reuse the low-temperature waste heat that is not fully utilized. In this study, the mathematical model of the biomass ORC power generation system is constructed. Five organic working fluids, R11, R113, R123, R141b, and R245fa, were selected from the physical characteristics and safety of working fluids. The system application case is the low-temperature heat absorption in a chemical industry’s production process. The system is simulated by Aspen Plus V11 software, so as to study and analyze the influence of different working fluids and working conditions on the system performance and to obtain the preferred working fluids under different working conditions. At the same time, the econom... [more]

The effective displacement of the shale oil from organic nanopores plays a significant role in development of the shale oil reservoirs. In order to deeply understand the microscopic displacement mechanism of alkane of shale oil by CO2 in organic nanopores, microscopic pore model of organic matter and molecular model of CO2 and n-dodecane were established to investigate the influences of key parameters on the displacement process by using the Monte Carlo and molecular dynamics simulation method. The instantaneous adsorption of molecules demonstrates that the displacement of n-dodecane and the adsorption of CO2 are proportional to the increase of the injection pressure of CO2 as well as the pore size. In addition, the results also show that the adsorption capacity of CO2 first increases and then decreases with the increase of the temperature, which indicates that the optimum temperature exists for the adsorption of CO2. This work can provide critical insights into understanding the micro... [more]

Photovoltaics (PV) can make a significant contribution to achieving carbon neutrality in buildings. Geographic information systems (GIS) make it easy to model cities and simulate PV with high accuracy. However, the computational burden from 3D urban models remains high. In this study, the complex geometry of a city was represented in 2D images, and we propose a method for performing multiple PV simulations in a short amount of time by using these 2D images. The ratio of electricity generation to primary energy consumption (EG/E) was calculated for 415 office buildings in Sapporo, Japan, and conditions for achieving carbon neutrality in these buildings were explored. For buildings with a small gross floor area, EG/E can be higher than one, and carbon neutrality can be achieved by improving the performance of the exterior walls and windows and by increasing the area of the PV installed. However, to improve EG/E in buildings with a large gross floor area, it is necessary to consider impro... [more]

Many kinds of defects are present in the different layers of GaN-on-Si epitaxy. Their study is very important, especially because they play a significant role on the device characteristics. This paper investigates the cause of the temperature dependence of the output and Miller capacitance at three temperatures: 25 °C, 75 °C and 150 °C of GaN-on-Si power transistors. In particular, this study focuses on the temperature dependence of the depletion voltage seen in these characteristics due to the progressive depletion of the two-dimensional electron gas (2DEG) under the device field plates. First, variations of the epitaxial growth are studied, showing that the intrinsic carbon concentration does not play a significant role. Secondly, the deep acceptor trap origin of the temperature dependence is analyzed with a TCAD simulation study. Thirdly, by adjusting TCAD parameters and binding them with experimental concentrations to fit experimental data, trap properties were obtained. The compar... [more]

As an energy-saving technology, the ejector is widely used in the heating, aerospace, and chemical industry. The ejector performance is closely related to its structure, so the structure of the ejector needs to be optimized. In the present study, single-factor optimization is first carried out, and the main structural parameters affecting the ejector performance are screened out. Then, the response surface method is used to analyze the combined effect of the multiple structural parameters of the ejector, find out the optimal structure, and analyze the flow field inside the ejector. This study shows that, through numerical simulation, the ejector performance obtained by the response surface method is better than that obtained by the single-factor optimization method or theoretically designed ejector, and the ejector performance is 35.4% higher than that of the theoretically designed ejector. Moreover, the optimal structure of the ejector obtained by the response surface method has high... [more]

Lightning is a perilous and unavoidable event of nature that presents major deleterious consequences on humans, tall structures, electrical power systems, forests, etc. Though several research studies have been carried out to analyse the sufficiency of a Lightning Protection System (LPS), very few research findings have been reported to assess the extent of risk due to lightning-human interaction in the vicinity of tall structures. This research aims at carrying out detailed modelling and simulation studies of LPS for heritage structure. Several current waveshapes as stipulated in IEC 62305 are modelled appropriately and presented to the electrical equivalent circuit representation of a heritage monument in South India (Brihadisvara Temple) to ascertain the impact of lightning parameters on heritage monuments. In addition, to assess the effectiveness of the earthing system, detailed earthing models during lightning is developed to assess the role played by aspects such as soil resistiv... [more]

Reliability and safety must be carefully considered in today’s power systems, which are rapidly evolving toward ever higher penetration of renewable, inverter-based generation units. Power systems are constantly stressed by active power disturbances, which can be exacerbated by wind and solar systems that are subject to rapid fluctuations in primary energy. In this framework, a comparative technical analysis of solutions to improve transient stability, both rotor angle stability and frequency stability, is carried out. These solutions can be adopted by the transmission system operator (e.g., an additional parallel transmission line), by the generation companies (e.g., a fast excitation system), or by both, such as SVC (static VAR compensator) and STATCOM (static synchronous compensator). Sensitivity analyses were carried out to assess the impact of the location of the wind turbines in the buses of the grid on their rated power and level of production. On the basis of these analyses, th... [more]

Accurate solar radiation forecasting is essential to operate power systems safely under high shares of photovoltaic generation. This paper compares the performance of several machine learning algorithms for solar radiation forecasting using endogenous and exogenous inputs and proposes an ensemble feature selection method to choose not only the most related input parameters but also their past observations values. The machine learning algorithms used are: Support Vector Regression (SVR), Extreme Gradient Boosting (XGBT), Categorical Boosting (CatBoost) and Voting-Average (VOA), which integrates SVR, XGBT and CatBoost. The proposed ensemble feature selection is based on Pearson coefficient, random forest, mutual information and relief. Prediction accuracy is evaluated based on several metrics using a real database from Salvador, Brazil. Different prediction time-horizons are considered: 1 h, 2 h and 3 h ahead. Numerical results demonstrate that the proposed ensemble feature selection app... [more]

Some electrical devices contain a solid nonlaminated magnetic core as a component. In the case of variable magnetic flux, eddy currents arise in such a core, which should be taken into account for computer simulation if higher precision is needed. The fractional order transfer function (FOTF) based on the simple traditional model of excitation circuit of a DC machine is proposed for eddy current simulation. This model is illustrated by mathematical (based on differential equations and the Laplace operator) and structural approaches to the excitation circuit of a common DC generator with a solid core. The skin effect for more precise simulation of eddy currents is also considered by means of fractional order transfer functions in the computer models. Magnetic saturation and hysteresis were not taken into account in this case. The proposed model is simple and ensures adequate accuracy, confirmed experimentally using the FOTF Toolbox for MATLAB and Simulink. This model is distinct and pro... [more]

This elaboration presents the concept of the design, parameters, experimental investigation, and thermal numerical model solved using the finite element method of a high-power-density DC−DC converter. The analyzed unit can be utilized as a stand-alone converter or as a module for a scalable high-voltage gain system. The converter has a decreased bill of materials since it does not use typical chokes and heatsinks. It is based on switched capacitor circuits supported by a resonant choke which protects against inrush currents. A printed circuit board is utilized not only for the resonant inductance design but also for cooling transistor and diode devices. The paper demonstrates the design concept and the achieved parameters. Experimental results show heat distribution on the printed circuit board and components in a steady state and dynamical states as well. The converter parameters and their efficiency are measured as well. The convergence of experimental results and heating simulations... [more]

Thermal response time is an important parameter for the control of fast reactors. Modern thermal hydraulic codes allow for the modeling of transient responses and can also be used to understand the dominant factors that affect them. However, simulations can be computationally expensive, particularly for performing parametric analyses of how thermophysical properties affect transient behavior. Here, we present a method for using linear stability analysis to estimate thermal response time and determine the key parameters that affect transient behavior without performing a forward simulation. The approach can also be used to corroborate simulation results and is tested against simulation results produced with a 2D finite difference model. The results show that this approach produces time-dependent temperature profiles that are within 2 × 10−5−0.1% of the numerical results for a single node perturbation. Changes in temperature have the greatest effect on thermal response time, followed by... [more]