The requirement for clean energy has increased drastically over the years due to the emission of CO2 and the degrading of the environment by introducing Renewable Energy Systems (RES) into the existing power grid. While these systems are a positive change, they come at a cost, with some issues relating to the stability of the grid and feasibility. Hence, this research paper closely investigates the modeling and interlinking of photovoltaic (PV)-based solar power and Double-Fed Induction Generator (DFIG)-based wind turbines with the conventional power systems. RES has been known to contribute to a highly non-linear system and complexity. To return the power systems to their original state after a load disturbance, a novel control technique based on the fractional-order Type-2 Fuzzy logic system, well developed via particle swarm optimization (PSO), has been utilized for solving the frequency control problem of a renewable interlinked power system. The efficacy of the proposed technique... [more]

Wearable thermoelectric generators (WTEGs) can incessantly convert body heat into electricity to power electronics. However, the low efficiency of thermoelectric materials, tiny terminal temperature difference, rigidity, and neglecting optimization of lateral heat transfer preclude WTEGs from broad utilization. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of flexibility and high normalized power density in thermoelectric generators by establishing the links among materials, TE performance, and advanced design of WTEGs (structure, heatsinks, thermal regulation, thermal analysis, etc.) based on inorganic bulk TE materials. Each section starts with a concise summary of its fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of wearable thermoelectric devices and potential applications. Overall, this review will serve to help materials scie... [more]

Recently, we demonstrated for Curaçao that renewable electricity generation from wind combined with energy storage in the form of ammonia is competitive with imported fossil fuels, such as LNG, oil, and coal. In the current work, we have expanded the model by considering imported green ammonia as an alternative to local electricity generation and storage. Local production of ammonia as an energy storage medium was compared with imported ammonia to make up the electricity produced from onshore wind, for Curaçao and Fiji’s largest island Viti Levu. Curaçao and Viti Levu have been selected as two interesting extremes with favorable and non-favorable wind conditions, respectively. Assuming a market price of 500 USD/t NH3, it is found that importing ammonia is the most feasible solution for both islands, with a levelized cost of electricity (LCOE) of 0.11 USD/kWh for Curaçao and 0.37 USD/kWh for Viti Levu. This compares to 0.12 USD/kWh for Curaçao; however, for Viti Levu, this value increas... [more]

This paper is devoted to solving the problem of how to comprehensively control coal seam gas and hydrogen sulfide in the mining face, distributed from the coal seam in abandoned oil wells in coal mining resource areas. The abandoned oil wells of Ma tan 30 and Ma tan 31 in the No. I0104105 working face of the Shuang Ma Coal Mine were taken as examples. Through parameter testing, gas composition analysis, field investigation at the source distribution, and the influence range of gas and hydrogen sulfide in coal seam in the affected range of the abandoned oil wells were studied. The results show that the coal-bearing strata in Shuang Ma coal field belong to the coal−oil coexistence strata, and the emission of H2S gas in the local area of the working face is mainly affected by closed and abandoned oil wells. Within the influence range of the abandoned oil wells, along the direction of the working face, the concentration of CH4 and H2S gas in the borehole increases as you move closer to the... [more]

Typhoons are a serious threat to transmission towers and lines in coastal areas. The anti-wind performance of a transmission tower needs to be reinforced and optimized to avoid tower collapse. Here, an improved real-time wind-field mathematical model and a tower-line coupled simulation model were established to reproduce the wind field distribution, mechanical vibration, and interaction between the wind field and tower. The damage prediction of the transmission tower was analyzed. Furthermore, an actual scaled tower-line model was built, which was used to measure the acceleration and displacement responses in the anti-wind experiments. The research results show that the improved model is feasible and correct based on the verification of Typhoon Mujigae. The tower’s vibration response is mainly characterized by low frequencies, whereas the lines indicate a high frequency response. The transmission line has a remarkable impact on tower vibrations in high turbulence. A flow direction angl... [more]

Layered Na0.8Co0.8Ti0.2O2 oxide crystallizes in the β-RbScO2 structure type (P2 modification) with Co(III) and Ti(IV) cations sharing the same crystallographic site in the metal-oxygen layers. It was synthesized as a single-phase material and characterized as a cathode in Na- and Na-ion batteries. A reversible capacity of about 110 mA h g−1 was obtained during cycling between 4.2 and 1.8 V vs. Na+/Na with a 0.1 C current density. This potential window corresponds to minor structural changes during (de)sodiation, evaluated from operando XRD analysis. This finding is in contrast to Ti-free NaxCoO2 materials showing a multi-step reaction mechanism, thus identifying Ti as a structure stabilizer, similar to other layered O3- and P2-NaxCo1−yTiyO2 oxides. However, charging the battery with the Na0.8Co0.8Ti0.2O2 cathode above 4.2 V results in the reversible formation of a O2-phase, while discharging below 1.5 V leads to the appearance of a second P2-layered phase with a larger unit cell, which... [more]

In order to make centrifugal blowers environmentally friendly, machines with a lighter weight and a more compact size are required. Thus, the axial length of the machine needs to be minimized within the diameter limit. However, in the design methodology, losses and thermal study become very significant; thus, losses increase significantly to achieve the desired output power when the volume is excessively reduced. Moreover, due to the machine’s compact size, heat is concentrated rapidly without adequate cooling. It might lead to a temperature rise of the critical part of the machine above the safe limit, such as winding, thereby affecting its lifespan. This study considers the 225 kW high-speed permanent magnet synchronous machine (HSPMSM) with the forced air cooling axial ventilation system (FACAVS) used in centrifugal blower applications. Firstly, four different analytical models (A2−A5) in the electromagnetic analysis are derived by minimizing the initial machine’s (A1) axial length... [more]

Pollution and the increase in greenhouse gas (GHG) emissions have long been linked to the world’s increasing need for fossil fuels to generate energy. Every day, the energy consumption is increasing; therefore, it is important to improve technologies that use renewable energy sources. With the abundant availability of sustainable energy, solar power is becoming a necessity. However, solar energy has a low energy density and therefore requires a large installation area, which requires heat collection and heat storage technology. Much research is now being done on the conical solar systems to improve efficiency including calculating an optimal cone angle, finding the best flow ratio and the best absorber design, etc. Therefore, in this study, thermal performance of a conical solar collector (CSC) was assessed with a new design of concentric tube absorber (addition of a coil) and compared to the existing circular tube absorber. It was found that 6 L/min flow rate of heating medium (distil... [more]

The accurate identification of Very Fast Transient Overvoltage (VFTO) is the key of overvoltage control in modern smart grids. In order to accurately identify VFTO generated by the operation of a disconnector in Gas Insulated Substation (GIS), a VFTO identification method based on Wavelet Transform (WT) and Singular Value Decomposition (SVD) is proposed. The simulation model of VFTO is established in ATP-EMTP software first, and then wavelet decomposition is used in MATLAB software for VFTO simulation of the waveform from the ATP-EMTP software. Then, the feature matrix is composed of the coefficients of each frequency layer of the wavelet. The SVD is used to decompose the feature matrix, and finally the characteristic parameters of the VFTO are obtained. The simulation results in Matlab software indicate that the characteristic parameters of VFTO have an obvious difference compared with those of power frequency AC voltage, especially in the load-side, which verifies the effectiveness o... [more]

The bipolar DC microgrid topology is characterized by three voltage levels and is able to transfer power more efficiently than a conventional DC microgrid. This paper proposes an advanced control strategy aiming to ensure the voltage balancing between the upper and lower terminals of a bipolar DC microgrid regardless of the distribution of loads. The proposed controller is based on the backstepping method, which is well known for its the robustness and the global asymptotic stability that can be guaranteed for the system. A particle swarm optimization algorithm has also been adopted for an optimal design of the proposed controller parameters. Simulation results in a Matlab/Simulink environment has been presented to verify the effectiveness and reliability of the proposed voltage-balancing controller.

Experimental investigations are conducted to determine the mechanism and characteristics of a jet in an L-shape crossflow simulating the radial swirl injector of a lean premixed-prevaporized (LPP) combustor. To simplify the radial flow of the actual injector while ignoring the centrifugal effect, the L-shaped 2D-channel is used for the crossflow, and water is used as a fuel simulant. The jet breakup is captured using a high-speed camera, and the density gradient magnitude is post-processed to clarify the spray. The Sauter mean diameter (SMD) of the spray is measured via a laser diffraction method with a helium−neon laser optical system (HELOS). The characteristics of the jet in the L-shape crossflow are compared with the characteristics of the jet in a typical crossflow through the flat channel. The results for different outlet heights of the L-shape channel (H/d0) and different injector positions (L/d0) are presented. A dimensionless number (τ) consisting of a time ratio is introduced... [more]

Fault-tolerant control (FTC) of a star-connected Five-phase Permanent Magnet Synchronous Motor (5Φ-PMSM) under open-circuit faults has been extensively studied, among which the decoupled control is attractive and finds a broad application in many fields. Pentacle- and pentagon-connected (generally known as “Penta-connected”) 5Φ-PMSMs are popular due to their low voltage and high-power density, and especially, the demanded DC voltage level for the pentacle-connection mode accounting for merely 1/1.9021 of the star-connection mode, which is very appealing today. On the other hand, as one of the recent advances, the fault-tolerant decoupling control for penta-connections is still yet to be reviewed, and so this study investigates this issue and attempts to find the similarities and dissimilarities between star- and penta-connections under either single-line or single-phase open faults. Torque behavior analysis under, respectively, the fault-tolerant MPPT and id = 0 is conducted to confirm... [more]

Optical fiber seismic exploration technology has been widely used in marine oil and gas hydrate exploration due to its wide frequency band and high sensitivity. However, there are more types of noise in the collected data by optical fiber hydrophone than by a conventional piezoelectric seismic exploration system. Considering that the conventional denoising method is time-consuming, this paper proposes a convolutional neural network (CNN) and a ResUNet network based on deep learning to suppress the noises. ResUNet is improved on the basis of CNN; it is composed of a feature extraction part, a feature reconstruction part and a residual block. Both CNN and ResUNet networks achieved obvious denoising effects on optical fiber towed streamer seismic data and improved the signal-to-noise ratio of data effectively. The ResUNet network has better denoising effects than CNN, even better than conventional denoising methods. The ResUNet network can solve the problem of gradient disappearance cause... [more]

In CO2 sequestration projects, assessing caprock structural stability is crucial to assure the success and reliability of the CO2 injection. However, since caprock experimental data are sparse, we applied a Monte Carlo (MC) algorithm to generate stochastic data from the given mean and standard deviation values. The generated data sets were introduced to a neural network (NN), including four hidden layers for classification purposes. The model was then used to evaluate organic-rich Draupne caprock shale failure in the Alpha structure, northern North Sea. The train and test were carried out with 75% and 25% of the input data, respectively. Following that, validation is accomplished with unseen data, yielding promising classification scores. The results show that introducing larger input data sizes to the established NN provides better convergence conditions and higher classification scores. Although the NN can predicts the failure states with a classification score of 97%, the structural... [more]

This paper presents the development of a global and integrated sizing approach under different performance indexes applied to fuel cell/battery hybrid power systems. The strong coupling between the hardware sizing process and the system supervision (energy management strategy EMS) makes it hard for the design to consider all the possibilities, and today’s methodologies are mostly experience-based approaches that are impervious to technological disruption. With a smart design approach, new technologies are easier to consider, and this approach facilitates the use of new technologies for transport applications with a decision help tool. An automotive application with a hybrid fuel cell (PEMFC)/battery (Li-Ion) is considered to develop this approach. The proposed approach is based on imbricated optimization loops and considers multiple criteria such as the fuel consumption, reliability, and volume of the architecture, in keeping with industry expectations to allow a good trade-off between... [more]

Two geopolymer foams were prepared from a thermally activated coal gangue containing kaolinite. As the foaming agent, aluminium powder and 36% hydrogen peroxide were used to obtain two levels of porosity. The materials’ high temperature performances were investigated: tensile and compressive strength evolution with temperature. This study shows that the mechanical performances of developed geopolymer foams are similar to foam concrete of the same apparent density. The geopolymer foams from coal gangue present stable mechanical performances up to 600 °C. When the glass transition temperature is achieved, sintering occurs and mechanical performance increases. SEM observations confirm the glass transition and densification of the matrix at temperatures above 800 °C. Moreover, the XRD measurements revealed a high amount of mullite that forms at 1000 °C that explained the observed strength increase. The synthesis of good-quality geopolymer foams from coal gangue and its application as a the... [more]

Using renewable energy sources instead of fossil fuels is one of the best solutions to overcome greenhouse gas (GHG) emissions. However, in designing clean power generation microgrids, the economic aspects of using renewable energy technologies should be considered. Furthermore, due to the unpredictable nature of renewable energy sources, the reliability of renewable energy microgrids should also be evaluated. Optimized hybrid microgrids based on wind and solar energy can provide cost-effective power generation systems with high reliability. These microgrids can meet the power demands of the consuming units, especially in remote areas. Various techniques have been used to optimize the size of power generation systems based on renewable energy to improve efficiency, maintain reliability, improve the power grid’s resilience, and reduce system costs. Each of these techniques has shown its advantages and disadvantages in optimizing the size of hybrid renewable energy systems. To increase t... [more]

Salinity gradient energy (SGE) allows the difference in salt concentration in two volumes of water to be harnessed and transformed into clean energy. The most advanced SGE technology is reverse electrodialysis (RED) cells. Recent studies have focused on ways to optimize the flow distribution in the compartments containing the water, for which it is necessary to consider the characteristics of the solutions, the cell dimensions, the operating conditions, as well as their influence on the hydrodynamics and mass transport in the system. In this study, two spacers with different gasket geometry were designed, fabricated, and compared experimentally through voltage and current measurements. The power output was computed, obtaining a maximum power density of 0.14 W/m2. Results show that the geometry of the cell components directly influences the physicochemical principles governing the RED process and is closely related to the cell output parameters. In turn, it is possible to increase the p... [more]

The dynamic ice load of conical offshore wind turbines (OWTs) in cold regions is unclear. The ice force period is the key parameter used to establish an ice force model for conical structures. To obtain ice load data, a field monitoring system was installed on an OWT in a cold region in China. Based on the monitoring data, a new formula for calculating the ice force period of conical structures was established. By comparing the period calculated with this formula and the measured ice force period, it was found that the calculated data generally agreed with the measured data. Then, a random dynamic ice force model for conical OWTs can be established. Based on this ice force model, the ice-induced vibration of an OWT was analyzed with the ANSYS finite element software. The results are in good agreement with the measured data obtained from the OWT in the time and frequency domains. Therefore, the random dynamic ice force model established in this paper can be used to evaluate the ice resi... [more]

The auto-ignition caused by oblique shocks was investigated experimentally in a supersonic flow regime, with the incoming flow at a Mach number of 2.5. The transient characteristics of the auto-ignition caused by shock evolvements were recorded with a schlieren photography system, and the initial flame kernel generation and subsequent propagation were recorded using a high-speed camera. The fuel mixing characteristics were captured using NPLS (nanoparticle-based planar laser scattering method). This work aimed to reveal the flame spread mechanism in a supersonic flow regime. The effects of airflow total temperature, fuel injection pressure, and cavity length in the process of auto-ignition and on the auto-ignitable boundary were investigated and analyzed. From this work, it was found that the initial occurrence of auto-ignition is first induced by oblique shocks and then propagated upstream to the recirculation region, to establish a sustained flame. The auto-ignition performance can b... [more]

Transformer oil is conventionally used as an insulating liquid for the purpose of insulation and cooling in power transformers. The rise in the power demand has put stress on the existing insulation system used for power transmission. Nanotechnology provides an advanced approach to upgrade the conventional insulation system by producing nano-oil with enhanced dielectric characteristics. The aim of the study is to present the influence of area volume effect on the dielectric performance of mineral oil and its nanofluids. In this paper, nanofluids are prepared by dispersing two different concentrations of SiO2 nanoparticles in base transformer oil using a two-step method. The effect of area and volume is investigated on nanofluids in the laboratory using coaxial electrode configurations under different test conditions. The AC breakdown voltage and maximum electric stress is determined for the pure oil and nanofluids. The results show that the addition of SiO2 nanoparticles significantly... [more]

Quantifying the climatic effect on residential electricity consumption (REC) can provide valuable insights for improving climate−energy damage functions. Our study quantifies the effect of climate on the REC in Tibet using machine learning algorithm models and model-agnostic interpretation tools of feature importance scores and partial dependence plots. Results show that the climate contributes about 16.46% to total Tibet REC while socioeconomic factors contribute about 83.55%. Precipitation (particularly snowfall) boosts electricity consumption during the cold season. The effect of the climate is stronger in urban Tibet (~25.06%) than rural Tibet (~14.79%), particularly in September when electricity-aided heating is considered optional, as higher incomes amplified the REC response to the climate. With urbanization and income growth, the climate is expected to contribute more to Tibet REC. Hence, precipitation should be incorporated in climate−REC functions for the social cost of carbo... [more]

In general, severe load imbalances in small AC micro-grid systems can degrade their operational performance and their maintenance. This is because the unbalanced load in the micro-grid affects the energy flow and the voltage regulation functions of each phase. In order to solve the voltage imbalance problem, several algorithms for the 3-phase 4-leg CVCF inverter have been proposed, but the control algorithms are not enough to operate the 4-leg CVCF inverter in a stable manner. Therefore, this paper proposes a single-phase voltage and power control algorithm for the 3-phase 4-leg CVCF inverter based on a dq control in order to improve the voltage imbalance problem caused by a severely unbalanced load, where the single phase voltage control algorithm is composed of an αβ-dq and a dq-αβ transformer, a voltage and a current controller, and an off-set controller and a PWM, and the single-phase power control algorithm is also composed of an αβ-dq and a dq-αβ transformer, an active/reactive p... [more]

The development of each country depends on electricity. In this regard, conventional energy sources, e.g., diesel, petrol, etc., are decaying. Consequently, the investigations of renewable energy sources (RES) are increasing as alternate energy sources for the fulfillment of energy requirements. The output characteristics of RES are becoming non-linear. Therefore, the maximum power point tracking (MPPT) techniques are critical for extracting the maximum power point (MPP) from RES, e.g., photovoltaic (PV) and wind turbines (WT). RES such as the Fuel Cell (FC) has been hailed as one of the major capable RES for automobile applications since they continually create electricity for the dc-link (even if one or both RES are not supplied by solar and wind, the FC will continue to supply to the load). Adaptive Neuro-Fuzzy Inference System (AN-FIS) MPPT for PV, WT, FC, and Hybrid RES is employed in this research article to solve this problem. The high step-ups (boost converters) are connected w... [more]

The vibration signals for offshore wind-turbine high-speed bearings are often contaminated with noises due to complex environmental and structural loads, which increase the difficulty of fault detection and diagnosis. In view of this problem, we propose a fault-diagnosis strategy with good noise immunity in this paper by integrating the two-dimensional convolutional neural network (2DCNN) with random forest (RF), which is supposed to utilize both CNN’s automatic feature-extraction capability and the robust discrimination performance of RF classifiers. More specifically, the raw 1D time-domain bearing-vibration signals are transformed into 2D grayscale images at first, which are then fed to the 2DCNN-RF model for fault diagnosis. At the same time, three procedures, including exponential linear unit (ELU), batch normalization (BN), and dropout, are introduced in the model to improve feature-extraction performance and the noise immune capability. In addition, when the 2DCNN feature extrac... [more]