This paper takes advantage of the high control flexibility and fast response time of the interfacing power electronic converter for doubly fed wind turbine grid-connected systems to address inter-area oscillations caused by inadequate system damping in power systems. A reactive-power-coordinated damping controller for a doubly fed induction generator (DFIG) is proposed, and it makes use of second-order sliding-mode technology. The suggested controller improves damping performance by controlling the reactive power. It provides benefits such as a quicker damping rate and resilience to modeling errors and parameter changes. The simulation results indicate the system’s improved performance in inter-area oscillation damping and the robustness of the suggested control technique over a broad range of functional areas.

Aiming at the problems of power flow fluctuation and voltage exceeding standard caused by high permeability distributed power supply access, this paper proposes a load state perception early warning method for distribution networks. Firstly, the random behavior characteristics and voltage early warning mechanisms of power supply and load in distribution networks are analyzed, the dynamic model of distribution networks based on complex network theory is established, and the risk index of voltage exceeding limits under the conditions of high permeability distributed power supply access is put forward. Secondly, the random power flow of distribution networks based on the Monte Carlo method is studied by sampling and analyzing the dynamic model of distribution networks. Then, the risk calculation and safety assessment of voltage exceeding limits are carried out on the currently extracted model, and the risk control strategy of distribution network operation is put forward. Finally, an impr... [more]

European Union (EU) countries pay meticulous attention to environmental issues and achieve carbon-free development. In this direction, reducing greenhouse gas emissions and extending renewable energy are the primary goals. At the same time, the energy price and declining energy efficiency increase countries’ environmental expenditures and hinder their capabilities for economic growth. Against this backdrop, this research aims to examine the influence of environmental regulations, renewable energy, and energy efficiency on green economic growth. The originality of the study is twofold: first, it evaluates the green economic growth of a country, which simultaneously reveals the options for economic growth and the capability to eliminate its negative effect on the environment by applying the Global Malmquist−Luenberger productivity index; second, it develops an econometric model based on panel data for EU countries for 2000−2020 to investigate the nonlinear impact of environmental regulat... [more]

In mobile devices such as aircraft and electric vehicles, due to limited space, there are strict requirements on the volume and weight of the compressor mounted on the vehicle. Therefore, high-speed scroll compressors have attracted more and more attention because of their small size and light weight. In this paper, the numerical calculations and analysis of the three-dimensional (3D) transient flows in a high-speed scroll refrigeration compressor were established and validated. Circumferential gas intake was used in the simulation. According to the actual compressor size, the mesh generation accurately considers clearances. The radial and the axial clearances were both set as 0.01 mm. A dynamic and high-quality hexahedral structured mesh was generated for the working chamber, and the problem of insufficient grid density in radial clearance was solved. When the rotational speed was set as 3000 rpm, 6000 rpm, and 9000 rpm alternatively, the difference in the volume efficiency of the sim... [more]

Liquid-cooled servers can be deployed to reduce the energy consumption and environmental footprint of hybrid-cooled data centers. A computational fluid dynamics (CFD) model can bring extremely useful insights and results for thermal simulations of air- and liquid-cooled servers in a single environment. In this study, a conjugate heat transfer (CHT) numerical model is developed and validated with experimental data to simulate heat transfer from the CPU to the air and cold plate considering the effect of thermal paste. The cooling performance of an in-house developed cold plate design is thoroughly investigated via the validated CHT model. A dataset containing one hundred samples of various flow, thermal and workload conditions was generated using the Latin hypercube sampling (LHS) method, which was further utilized in the series of CHT simulations. Finally, a novel empirical equation is proposed for the prediction of heat transfer from the CPU to the air. The accuracy of the proposed eq... [more]

Carbon dioxide (CO2) and hydrogen (H2) are essential energy vectors in the green energy transition. H2 is a fuel produced by electrolysis and is applied in heavy transportation where electrification is not feasible yet. The pollutant substance CO2 is starting to be captured and stored in different European locations. In Denmark, the energy vision aims to use this CO2 to be reacted with H2, producing green methanol. Typically, the production units are not co-located with consumers and thus, the required transportation infrastructure is essential for meeting supply and demand. This work presents a novel scheme to allocate the transportation costs of CO2 and H2 in pipeline networks, which can be applied to any network topology and with any allocation method. During the tariff formation process, coordinated adjustments are made by the novel scheme on the original tariffs produced by the allocation method employed, considering the location of each customer connected to pipeline network. Loc... [more]

Worldwide, the demand for power load forecasting is increasing. A multi-step power-load forecasting model is established based on Informer, which takes the historical load data as the input to realize the prediction of the power load in the future. The constructed model abandons the common recurrent neural network to deal with time-series problems, and uses the seq2seq structure with sparse self-attention mechanism as the main body, supplemented by specific input and output modules to deal with the long-range relationship in the time series, and makes effective use of the parallel advantages of the self-attention mechanism, so as to improve the prediction accuracy and prediction efficiency. The model is trained, verified and tested by using the power-load dataset of the Taoyuan substation in Nanchang. Compared with RNN, LSTM and LSTM with the attention mechanism and other common models based on a cyclic neural network, the results show that the prediction accuracy and efficiency of the... [more]

Developing renewable energy has become a major strategy for China to accelerate the energy transition and combat climate change. Accordingly, a guarantee mechanism for renewable energy consumption with renewable portfolio standards (RPS) has been set in China. However, currently, the top-down allocation of regional renewable energy consumption targets often has issues of unfairness and inefficiency. It is necessary to investigate the issue of how to stimulate the renewable energy consumption potential on the demand side and reasonably formulate the consumption responsibility weights of various market entities. This paper aimed to develop a new methodology for the weight allocation of renewable energy consumption responsibilities. In doing so, an integrated model of an evolutionary game and stochastic optimization was constructed between market entities and governments. Then, the equilibrium strategies of market entities and governments were obtained through the evolutionary game. Furth... [more]

The scarce availability of non-renewable sources and the staggering amount of pollution have inevitably provoked many countries to opt for renewable sources. Thence, invariably, more renewable energy-based applications are hoarded by market stakeholders. Compared to all spheres of renewable energy applications, a considerable part of the energy is pulled into transportation. Wireless power transfer techniques play a significant role in charging infrastructure, considering the current development and advancement in the automotive industry. It will promise to overcome the widely known drawbacks of wired charging in electric vehicles. The effectiveness of wireless charging depends on coil design, compensation techniques, and the airgap between the coils. However, coil misalignment, improper compensation topologies, and magnetic materials reduce the efficacy. We can improve efficacy by overcoming the problems mentioned above and optimizing charging distance, time, and battery size. This pa... [more]

Renewable energy sources are nowadays a viable choice to satisfy the rising energy consumption and promote the advancement of sustainable development. These systems are integrated into microgrids using a variety of technological solutions to ensure customer communication and distributed generation facilities in an optimal way. Energy management in microgrids refers to the information and control system that provides the necessary functionality to guarantee that the generating and distribution systems produce energy at the lowest expenses. This study analyzes the various optimization objectives, constraints, problem-solving techniques, and simulation tools used for connected and freestanding microgrids. It reviews the literature on energy control in microgrids powered by sustainable energy. Energy storage technology is also viewed as an intriguing alternative to managing the intermittent nature of renewable energy because of its advanced techniques, increased energy efficiency, and capa... [more]

This article presents the results of a techno-economic analysis of repowering a coal-fired power plant’s steam turbine system to instead accept heat produced by a pressurized water reactor-type small modular nuclear system (PWR SMR). This type of repowering presents a challenge due to the significantly lower steam pressure and temperature produced by the nuclear system. A 460 MW supercritical power unit with steam parameters of 28 MPa/560 °C/580 °C, operated in the Łagisza Power Plant in Poland, was selected for the analysis. After repowering, the turbine system would be fed with saturated steam from the steam generators of the SMRs at a pressure of 7 MPa and a temperature of 285 °C. In total, four options for repowering were analyzed. In all cases, the existing high-pressure section of the turbine was disconnected, and the existing low-pressure stages of the turbine, as well as all auxiliary and outward components (feedwater heaters, pumps, generator, condenser, condenser cooling, etc... [more]

Nowadays, there are many technological-intensive applications that claim to be “smart”. From smartphones to the smart grid, people relate the word smart with technical novelty, automation, enabled communication, and service integration. There is indeed a gap between those smart technologies and their intended “intelligence”; this has arisen an indirect debate between works focusing on automation and mechatronics design and others pursuing a conceptual approach based on fulfilling determinate objectives. One last approach relates the said smartness to deep learning methodologies. In this work, it is attempted to explore both perspectives by providing an overview of recent works around energy usage toward smart cities and the smart grid, pointing out the main conceptual pillars upon which both approaches stand. Certainly, there are enabling technologies supporting the smart concept overall; thus, this work addresses them to characterize “smart” not from technological or conceptual one-si... [more]

A gas-lifted system in a mature oil well can experience casing-heading instability, which reduces the mean oil production and it is not healthy for the downstream equipment. This instability was removed by implementing a terminal equality-constrained nonlinear model predictive control (NMPC) having input targets with control zones in the system. The input-dependent stability behaviour of the gas-lifted system was visualised through the bifurcation diagram and the step responses of the linearised model at various operating points. The controller was then presented. Then, the close-loop feasibility, as well as the convergence, were discussed. The controller stabilised the undisturbed gas-lifted system, improving production by 5.63% compared to the open-loop operation when the system was in casing-heading instability. For the two input case, the steady-state production, aided by the high-input target, reached 12.25 kg/s, which was far more than 9.57 kg/s for the one input case. This contr... [more]

Thermal storage is very relevant for technologies that make thermal use of solar energy, as well as energy savings in buildings. Phase change materials (PCMs) are positioned as an attractive alternative to storing thermal energy. This review provides an extensive and comprehensive overview of recent investigations on integrating PCMs in the following low-temperature applications: building envelopes, passive systems in buildings, solar collectors, solar photovoltaic systems, and solar desalination systems. Moreover, techniques for improving heat transfer in PCM systems are described. All applications studies indicate that all applications improve their performance when applying a PCM. One of the most beneficiated technologies is the combined PV-Thermal systems (PVT), where some authors reported an increase in overall efficiency greater than 40%.

In order to realize an online power supply, this article develops an explicit design of induction power extraction technology combined with wireless power transmission (WPT) technology. Unlike the power supply mode of traditional batteries of online monitoring devices of high-voltage transmission lines, this technology solves the short battery life cycle problems. First, the principle of induction power extraction is analyzed. Based on the equivalent circuit of the mutual inductance model, expressions of induction power extraction without and with core saturation are derived, respectively. According to the current transformer (CT) magnetic coupling diagram, the open-circuit voltage of the secondary side of the CT is deduced. Therefore, the CT material and size could be selected. The CT coupling model is used to equivalent the current transformer to the ideal voltage source. Then, the four basic topological spaces of the magnetic coupling resonant WPT system are analyzed and calculated,... [more]

Accurate medium- and long-term power load forecasting is of great significance for the scientific planning and safe operation of power systems. Monthly power load has multiscale time series correlation and seasonality. The existing models face the problems of insufficient feature extraction and a large volume of prediction models constructed according to seasons. Therefore, a hybrid feature pyramid CNN-LSTM model with seasonal inflection month correction for medium- and long-term power load forecasting is proposed. The model is constructed based on linear and nonlinear combination forecasting. With the aim to address the insufficient extraction of multiscale temporal correlation in load, a time series feature pyramid structure based on causal dilated convolution is proposed, and the accuracy of the model is improved by feature extraction and fusion of different scales. For the problem that the model volume of seasonal prediction is too large, a seasonal inflection monthly load correcti... [more]

Compressed natural gas (CNG) main stations are critical components of the urban energy infrastructure for CNG distribution. Due to its high electrification and significant power consumption, researching the economic operation of the CNG main station in demand response (DR)-based electricity pricing environments is crucial. In this paper, the dehydration process is considered in the CNG main station energy consumption model to enhance its participation in DR. A bilevel economic dispatch model for the CNG main station is proposed, considering critical peak pricing. The upper-level and lower-level models represent the energy cost minimization problems of the pre-system and rear-system, respectively, with safety operation constraints. The bilevel programming model is solved using a genetic algorithm combined with a bilevel programming method, which has better efficiency and convergence. The proposed optimization scheme has better control performance and stability, reduces the daily electri... [more]

A vibrating blade was arranged in a channel to enhance heat transfer. The effects of the frequency and amplitude of the blade on the heat transfer characteristics were numerically researched. The phase space reconstruction and maximum Lyapunov index were used to analyze the transition path and degree of chaos. The results show that the vibrating blade can generate chaos; thus, the heat transfer is enhanced. The convective heat transfer performance is positively correlated with the degree of chaos. In addition, when the frequency is 10 Hz, and the inlet velocity is 0.5 m s−1, the heat transfer can be improved by 16%. When the maximum amplitude of the blade is 8 mm and the inlet velocity is 0.8 m s−1, the heat transfer can be improved by 15%.

Facing the goal of carbon neutrality, energy supply chains should be more low-carbon and flexible. A solar chemical heat pump (SCHP) is a potential system for achieving this goal. Our previous studies developed a silicone-oil-based phase-change material (PCM) mixture as a PCM fluid for enhancing heat recovery above 373 K in the solar collector (SC) of the SCHP. The PCM fluid was previously tested to confirm its dispersity and flow properties. The present study proposed a 3D computational fluid dynamics model to simulate the closed circulation loop between the SC and reactor using the PCM fluid. The recovered heat in the SC was studied using several flow rates, as well as the PCM weight fraction of the PCM fluid. Furthermore, the net transportable energy is considered to evaluate the ratio of recovered heat and relative circulation power. As a result, it was verified that the recovered heat of the SC in the experiment and simulation is consistent. The total recovered heat is improved us... [more]

The railway system is one of the safest, most efficient, and environmentally friendly means of land transport for people and goods. However, as the demand for mobility has increased, the current railway system has shown some weaknesses, requiring an increase in catenary power in order to be able to supply power to longer trains and faster locomotives, as well as to increase rail traffic. This paper proposes a control algorithm to be implemented in a sectioning post-Rail Power Conditioner (sp-RPC). The sp-RPC is connected to the neutral section between two traction power substations (TPS). With the control algorithm, it is possible to minimize the existing unbalance of the active powers of each TPS. In a regenerative braking condition, this surplus energy can be used to assist the traction of another locomotive on the existing overhead line. In this way, it is possible to increase the capacity of the overhead line. The analysis was performed with computer models using a modular multilev... [more]

This document deals with the design of a Permanent Magnet Synchronous Motor (PMSM) to peripherally drive a counter-rotating pump inducer. The motor/pump is associated using a rim-driven principle where the motor’s active parts are located at the periphery of the inducer blades. It proposes using a Halbach array of permanent magnets for the active rotor of the motor. This solution allows the generation of a Sinusoidal Electromotive Force (EMF). Therefore, a more stable electromagnetic torque is reached. An optimum geometry suitable for the inducer specifications while respecting operational constraints is determined. The obtained geometry is then simulated using the Finite Element Method. The results are satisfactory in terms of average torque and EMF waveform. Use of the Halbach array allows a significant improvement of the flux density in the air gap compared to a designed surface-mounted machine. The experimental validation will be performed once the prototype is realized in the Labo... [more]

The performance of a laboratory-scale 40 L anaerobic membrane bioreactor (AnMBR) treating municipal wastewater with and without iron supplementation was evaluated at ambient temperatures at a hydraulic retention time (HRT) of 6 h and sludge retention time (SRT) of 50 days. The system exhibited satisfactory performance during the summer and winter periods with average COD removal efficiencies of 73 ± 4% and 60 ± 4%, respectively. Moreover, two different FeCl3 dosages were studied for optimizing operation in terms of organic load removal, phosphorus removal, biogas production, membrane fouling, and emerging contaminant removal. The addition of 25 mg FeCl3 L−1 improved the performance of the AnMBR. More specifically, average effluent COD concentrations without FeCl3 addition were 177 ± 21 mg/L, while after the addition of 25 mg FeCl3 L−1 and 30 mg FeCl3 L−1, COD decreased to 147 ± 8 mg/L and 149 ± 11 mg/L, respectively. Moreover, effluent TP decreased by 75% with the dosage of 25 mg FeCl3... [more]

The first aim of this paper is to study the influence of four parameters of the transesterification reaction—reaction temperature (40−80 °C), time (1−3 h), the molar ratio of 1-octanol to sunflower oil (4:1−10:1) and mass fraction of the catalyst (1−3 wt%)—on the conversion of oil to biodiesel (octyl esters of fatty acids), with potassium hydroxide as a catalyst. The highest conversion, of 99.2%, was obtained at 60 °C, a molar ratio of 1-octanol to sunflower oil of 10:1, and with 2 wt% of the catalyst after an hour. The optimal conditions determined with response surface methodology (RSM) when aiming for the lowest possible parameter values and a conversion of 95% or higher were a temperature of 40 °C, time of 1 h, 1-octanol to oil molar ratio at 8.11:1 and mass fraction of catalyst of 2.01%. Furthermore, post-synthesis and purification (>99%), the application properties of pure fatty acid octyl esters (FAOCE) and their blends with mineral diesel and 1-octanol were evaluated. Standardi... [more]

The leading edges of aero-engine fan and compressor blades suffer from severe erosion due to the inhalation of suspended particulates in the low-altitude atmosphere during long-term transport. A small deformation of the leading edge can significantly change the aerodynamic performance under a strong non-linear effect, leading to increased operation and maintenance costs for engines. This review first focuses on leading-edge erosion morphology during service, and models of these damages. Secondly, the performance degradation caused by eroded leading edges on different classes of engine components, including airfoils, blades, compression systems, and the whole engine, are reviewed. Finally, optimization methods for eroded blade leading edges and their effects on performance recovery are summarized. This paper contributes to an in-depth understanding of the erosion mechanism of blade leading edges in terms of status and its effect, and is a good reference for establishing erosion leading... [more]

In this work, gallium arsenide (GaAs), which has an adjustable band gap and low cost, was adopted as an absorption layer in which KNbO3, having good dielectric, photoelectric, and piezoelectric properties, served as a scattering element for the improvement in absorption efficiency of solar cells. Benefited by the high absorption efficiency of KNbO3, the utilization of the ultraviolet and infrared bands for solar cells can be strengthened. In addition, the ferroelectric and photovoltaic characteristics of KNbO3 enable the realization of decreased thickness of solar cells. Based on the simulation of the shape, width, and period of the scattering element, the effect of the thickness of the scattering element on the absorption efficiency, quantum efficiency, and total efficiency of absorption efficiency was comprehensively simulated. The results show that the absorption layer delivers the optimal performance when using a hexagonal KNbO3 scattering element. The absorption efficiency of the... [more]