Owing to scale-up and complex wake effects, the centralized control that processes the command from turbines may be unsuitable, as it incurs high communication overhead and computational complexity for a large offshore wind farm (OWF). This paper proposes a novel decentralized non-convex optimization strategy for maxing power conversion of a large OWF based on a modified beetle antennae search (BAS) algorithm. First, an adaptive threshold algorithm which to establish a pruned wake direction graph while preserving the most critical wake propagation relationship among wind turbines are presented. The adaptive graph constraints were used to create wake sub-digraphs that split the wind farm into nearly uncoupled clustering communication subsets. On this basis, a Monte Carlo-based beetle annealing search (MC-BAS) nonlinear optimization strategy was secondly designed to adjust the yaw angles and axial factors for the maximum power conversion of each turbine subgroup. Finally, the simulation... [more]

Carbon dioxide and/or dry methane reforming serves as an effective pathway to mitigate these greenhouse gases. This work evaluates different oxide supports including alumina, Y-zeolite and H-ZSM-5 zeolite for the catalysis of dry reforming methane with Nickel (Ni). The composite catalysts were prepared by impregnating the supports with Ni (5%) and followed by calcination. The zeolite supported catalysts exhibited more reducibility and basicity compared to the alumina supported catalysts, this was assessed with temperature programmed reduction using hydrogen and desorption using carbon dioxide. The catalytic activity, in terms of CH4 conversion, indicated that 5 wt% Ni supported on alumina exhibited higher CH4 conversion (80.5%) than when supported on Y-zeolite (71.8%) or H-ZSM-5 (78.5%). In contrast, the H-ZSM-5 catalyst led to higher CO2 conversion (87.3%) than Y-zeolite (68.4%) and alumina (83.9%) supported catalysts. The stability tests for 9 h time-on-stream showed that Ni supporte... [more]

Even thoughdigestate, which is continually generated in anaerobic digestion process, can only be used as fertilizer during the growing season, digestate treatment is still a critical, environmental problem. That is why the present work aims to develop a method to manage digestate in agricultural biogas plant in periods when its use as fertilizer is not possible. A lab-scale system for the biological treatment of the digestate liquid fraction using the activated sludge method with a separate denitrification chamber was constructed and tested. The nitrogen load that was added tothe digestate liquid fraction accounted for 78.53% of the total nitrogen load fed into the reactor. External carbon sources, such as acetic acid, as well as flume water and molasses, i.e., wastewater and by-products from a sugar factory, were used to support the denitrification process. The best results were obtained using an acetic acid and COD (Chemical Oxygen Demand)/NO3−N (Nitrate Nitrogen) ratio of 7.5. The r... [more]

One of the biggest experimental programs helping to improve nuclear installation safety is PHEBUS, an international cooperative research program that provides data for validating computer codes dedicated to the analysis of severe accidents and their calculation results. In the European Union, HORIZON 2020 EURATOM project MUSA (Management and Uncertainties of Severe Accidents) is in progress. Modelling of the PHEBUS FPT-1 test within the frame of this project is provided by project partners using different severe accident codes. Uncertainty quantification of the received results is provided using different methods and statistical tools. The Lithuanian Energy Institute (LEI) is taking part in the MUSA project and this uncertainty exercise. LEI is using the RELAP/SCDAPSIM severe accident code together with GRS methodology and SUSA statistical tool to evaluate the uncertainties of modelling results of PHEBUS FPT-1 test. In this article, uncertainty quantification of the PHEBUS FPT-1 test m... [more]

In a sudden load increasing process (SLIP), the hydroelectric generating system (HGS) experiences a severe vibration response due to the sudden change of the hydraulic-mechanical-electric parameters (HMEPs). The instability of HGS limits the ability of sudden load increase, and its flexibility and reliability are reduced. Thus, in this study, a new transient nonlinear coupling model of HGS is proposed, which couples the hydro-turbine governing system (HTGS) and the hydro-turbine generator shafting system (HGSS) with the hydraulic-mechanical-electric coupling force, rotating speed, flow rate, hydro-turbine torque, electromagnetic torque, and guide vane opening. By using numerical simulation, the influences of different HMEPs on the vibration characteristics of HGS in SLIP are analyzed. The result shows that, compared with stable operating conditions, the vibration amplitude of HGS increases sharply in SLIP. The increase of the sudden load increasing amount, blade exit flow angle, mass e... [more]

This paper presents the modeling of high speed distributed networks characterized by S-parameters frequency data using the rational Krylov fitting (RKFIT) algorithm. Numerical examples illustrate the effectiveness of the method to compute stable rational approximation that fit given S-parameters data. In addition, it is shown that RKFIT has some advantages when compared to the well-established Vector Fitting (VF) method, such as more accurate fitting, less dependence on the choice of the initial poles of the algorithm, and faster convergence. Numerical examples are implemented using RKFIT and the results are compared with VF and the Loewner Matrix (LM) algorithm.

The utilization of air conditioning in public and private buildings is continuously increasing globally and is one of the major factors fueling the growth of the global electricity demand. The higher utilization of renewable energy sources and the transition of the electricity-generating industry to renewable energy sources requires significant energy storage in order to avoid supply−demand mismatches. This storage-regeneration process entails dissipation, which leads to higher energy generation loads. Both the energy generation and the required storage may be reduced using thermal energy storage to provide domestic comfort in buildings. The development and utilization of thermal storage, achieved by chilled water, in a community of two thousand buildings located in the North Texas region are proven to have profound and beneficial effects on the necessary infrastructure to make this community independent of the grid and self-sufficient with renewable energy. The simulations show that b... [more]

This article presents a new analytical procedure for pre-selecting gas wells for water shut-off treatments based on available at hand results of an analysis of integrated geological, reservoir and exploitation data. Attention was paid to assess the possibility of the appearance of cross flows between layers in the near wellbore zone. Their appearance always eliminated the well as a candidate for the treatment. The basis for assessing the possibility of the emergence of cross flows was based on the assessment of the presence or absence of impermeable barriers (e.g., shales or anhydrite) in intervals, completed by perforation. For this assessment, well logging data were used, which were carried out in different years with the use of various types of probes. Based on modified quantitative and qualitative interpretation techniques, permeable and impermeable layers were separated in the analysed borehole sections. In some cases, in the absence of other data, well logs are the only source of... [more]

This study aimed at analysing the influence of the position of the centre of gravity variability and the movement velocity on the demand for a torque and work time coverage of a wheelchair with an electromechanical drive. The variable parameter in the study was the configuration of the wheelchair, namely changes in the position of the batteries which changed the weight distribution. An analytical model describing the demand for torque was used in the analysis. The set of equations was introduced into the numerical calculation software. Simulations were carried out which allowed it to analyse selected parameters of the wheelchair dynamics. An increase in the torque demand was observed due to the increase in the mass of the system from 427.7 N to 533.1 N, ranging from 6.1% to 31.6% at the simulated velocity v7 = 4.2 m/s. The increase in the demand for torque due to the increase in velocity of the wheelchair from v2 = 1.05 m/s to v7 = 4.2 m/s ranged from 25.9% to 31.6% compared to the ref... [more]

Due to the rapid changes in the energy situation on a global scale, the amount of RES installed using clean renewable energy sources such as Photovoltaic (PV) and Wind-power Generators (WGs) is rapidly increasing. As a result, there has been a great deal of research aimed at promoting the adoption of renewable energy. Research on Demand-side Management (DSM) has also been important in promoting the adoption of RES. However, the massive introduction of PV has changed the shape of the demand curve for electricity, which significantly impacts the operational planning of thermal generators. Therefore, this paper proposes an Advanced Direct Load Control (ADLC) model to temporarily shutdown the electric connection between the power grid and Smart Houses (SHs). The most important feature of the proposed model is that it temporarily shuts down the electric connection with the power grid. The shutdown is performed twice to increase the load demand during daytime hours and reduce the peak load d... [more]

Considering loads when optimizing wind-farm layouts or designing farm-control strategies is important, but the computational cost of using high-fidelity wake models in the loop can be prohibitively high. Using simpler models that consider only the spatial variation of turbulence statistics is a tempting alternative, but the accuracy of these models with respect to the aeroelastic response is not well understood. This paper therefore highlights the effect of replacing wake meandering with spatially varying statistics (“profile functions”) in the inflow to a downstream turbine. Profile functions at different downstream and lateral locations are extracted from a large-eddy simulation with an upstream turbine and compared with two lower-fidelity models: one that prescribes both the mean and standard deviation of the turbulence and one that prescribes only the mean. The aeroelastic response of an NREL 5 MW wind turbine is simulated with the three different wake-model fidelities, and various... [more]

This paper presents an improved Teaching-Learning-Based Optimization (TLBO) for optimal tuning of power system stabilizers (PSSs) and static VAR compensator (SVC)-based controllers. The original TLBO is characterized by easy implementation and is mainly free of control parameters. Unfortunately, TLBO may suffer from population diversity losses in some cases, leading to local optimum and premature convergence. In this study, three approaches are considered for improving the original TLBO (i) randomness improvement, (ii) three new mutation strategies (iii) hyperchaotic perturbation strategy. In the first approach, all random numbers in the original TLBO are substituted by the hyperchaotic map sequence to boost exploration capability. In the second approach, three mutations are carried out to explore a new promising search space. The obtained solution is further improved in the third strategy by implementing a new perturbation equation. The proposed HTLBO was evaluated with 26 test functi... [more]

In a competitive electricity market, both electricity retailers and generators predict future prices and volumes and execute electricity delivery contracts through power exchange. In such circumstances, they may suffer from uncertainties caused by fluctuations in spot prices and future demand due to their high volatility. In this study, we develop a unified approach using derivatives and forwards on the spot electricity price and weather data to mitigate the cashflow fluctuation for power utilities. We aim to clarify the applicability of our proposed methods and provide a new and useful perspective on hedging schemes involving various electricity utilities, such as power retailers, solar photovoltaic (PV) generators, and thermal generators. Moreover, we analyze the risk of risk takers (such as the insurance companies in this study) in the derivatives market. In addition, we perform empirical simulations to measure out-of-sample hedging effects on their cashflow management using actual... [more]

The real driving emission (RDE) testing for certification of vehicles is performed in conditions that are well defined in legislation. For emissions inventories and for research, the influences of some extended driving conditions on emissions are an interesting issue. In the present work, some examples of RDE results from two common passenger cars with gasoline and diesel propulsion are given. The varying driving conditions were “winter/summer”, “mild/aggressive”, and “higher altitude/slop”. The driving conditions: “winter”, “aggressive”, and “higher slope/altitude” generally require more energy, cause higher fuel consumption, and therefore, higher CO2-emissions. The condition of “winter driving”, especially in the urban type of operation, may cause some longer phases with not enough warmed-up exhaust aftertreatment and consequently some increased gaseous emissions. The DPF eliminates the nanoparticles (PN) independently on the driving conditions. Nevertheless, the DPF regeneration has... [more]

To expand the airfoil database and realize the reverse digital airfoil design, this paper proposes a new sectional expression function of wind turbine airfoil based on the Joukowski transformation and derives the function equation for the novel airfoil. Compared with the existing airfoil function, the new airfoil function can adjust the parameter values to control the relative thickness, relative thickness position, relative camber, and relative camber position of the airfoil. Taking the common airfoil (NACA63-212) as an example, the existing airfoil is fitted according to the expected direction. The maximum fitting deviation is 1.22135×10-3, better than the four existing methods for airfoil shape fitting, which demonstrates well the practicability and accuracy of this method. It also shows that changing the parameter values can generate a new airfoil to enrich the airfoil database. Therefore, the proposed method broadens the ideas for airfoil design and method research.

Plastics are versatile materials used in a variety of sectors that have seen a rapid increase in their global production. Millions of tonnes of plastic wastes are generated each year, which puts pressure on plastic waste management methods to prevent their accumulation within the environment. Recycling is an attractive disposal method and aids the initiative of a circular plastic economy, but recycling still has challenges to overcome. This review starts with an overview of the current European recycling strategies for solid plastic waste and the challenges faced. Emphasis lies on the recycling of polyolefins (POs) and polyethylene terephthalate (PET) which are found in plastic packaging, as packaging contributes a signification proportion to solid plastic wastes. Both sections, the recycling of POs and PET, discuss the sources of wastes, chemical and mechanical recycling, effects of recycling on the material properties, strategies to improve the performance of recycled POs and PET, an... [more]

The near-wall flame structure and pollutant emissions of the laminar premixed biogas-hydrogen impinging flame were simulated with a detailed chemical mechanism. The spatial distributions of the temperature, critical species, and pollutant emissions near the wall of the laminar premixed biogas−hydrogen impinging flame were obtained and investigated quantitatively. The results show that the cold wall can influence the premixed combustion process in the flame front, which is close to the wall but does not touch the wall, and results in the obviously declined concentrations of OH, H, and O radicals in the premixed combustion zone. After flame quenching, a high CO concentration can be observed near the wall at equivalence ratios (φ) of both 0.8 and 1.2. Compared with that at φ = 1.0, more unburned fuel is allowed to pass through the quenching zone and generate CO after flame quenching near the wall thanks to the suppressed fuel consumption rate near the wall and the excess fuel in the unbur... [more]

This article has been developed to assess the economic feasibility of a rooftop photovoltaic installation of industrial self-consumption. Numerical models that enable an interested person to obtain the main expected parameters will be generated, with those models being the article’s main contribution to the field. To do this, a calculation methodology will be developed through which the reader, knowing the location of the facility and dimensions of the roof, will be able to calculate the maximum installable power, the main parameters related to production, the cost of the installation, and the LCOE of the plant. The use of actual costs will be facilitated in case they are known. Still, it will remain possible to apply the major equipment costs (modules, inverter, and structure) considered throughout the article. This developed calculation methodology will also allow a quick comparison of the forecasts of production, CAPEX, and LCOE of plants designed with different inclinations and dif... [more]

4H-SiC Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) with embedded Schottky barrier diodes are widely known to improve switching energy loss by reducing reverse recovery characteristics. However, it weakens the static characteristics such as specific on-resistance and breakdown voltage. To solve this problem, in this paper, an Asymmetric 4H-SiC Split Gate MOSFET with embedded Schottky barrier diode (ASG-MOSFET) is proposed and analyzed by conducting a numerical TCAD simulation. Due to the asymmetric structure of ASG-MOSFET, it has a relatively narrow junction field-effect transistor width. Therefore, despite using the split gate structure, it effectively protects the gate oxide by dispersing the high drain voltage. The Schottky barrier diode (SBD) is also embedded next to the gate and above the Junction Field Effect transistor (JFET) region. Accordingly, since the SBD and the MOSFET share a current path, the embedded SBD does not increase in RON,SP of MOSFET. Therefore,... [more]

The European Union (EU), which has led international discussions on global warming, officially announced its plan for the Carbon Border Adjustment Mechanism (CBAM) in July 2021. Many existing studies have indicated the CBAM will curtail greenhouse gases, and will subsequently be positive in terms of reducing global warming. However, serious legal issues and trade disputes are expected in terms of the compatibility of the CBAM with the trade rules of the General Agreement on Tariffs and Trade (GATT). Contrary to the EU’s explanation, the international community has a strong view of CBAM as a new trade barrier under the guise of preventing global warming. Above all, this is because it is an arbitrary measure by the EU and not the one that has been internationally agreed upon. Therefore, this paper tries to identify the pitfalls and estimate the global cost of CBAM, arguing that the mechanism is not in line with international trade rules, and that many countries will not sit back and suff... [more]

One of the challenges which the electrical power industry has been facing nowadays is the adaptation of the power system to the energy transition which has been taking place before our very eyes. With the increasing share of Renewable Energy Sources (RES) in energy production, the development of electromobility and the increasing environmental awareness of the society, the power system must constantly evolve to meet its expectations regarding a reliable electricity supply. This paper presents the issue of deploying energy storage facilities in the meshed power distribution network in order to reduce transmission losses. The presented multi-objective approach provides an opportunity to solve this issue using multi-objective optimisation methods such as Non-dominated Sorting Genetic Algorithm II (NSGA-II), Multiobjective Particle Swarm Optimization (MPSO) and Biased Random Keys Genetic Algorithm (BRKGA). In order to increase the efficiency optimisation process, the Pareto Adaptive ϵ-domi... [more]

This paper proposes a full-order terminal sliding-mode (FOTSM) control scheme for brushless doubly fed induction generator (BDFIG)-based islanded microgrids. To deal with mismatched uncertainties in the BDFIG system, virtual control technique-based full-order sliding-mode control is applied to stabilize the amplitude and frequency of terminal voltage. In the current loops, two full-order terminal sliding-mode controllers are designed to make sure that the current tracking errors can reach their equilibrium points in finite time. It is demonstrated by the comprehensive simulations that the proposed method can significantly improve the tracking accuracy, the rapidness, and the robustness to the uncertainties of the BDFIG control system and can enhance the output voltage quality. Furthermore, an experimental study of the proposed control method for BDFIG-based islanded microgrids would be another important future work.

The key to overcome PEMFC cold start failure is to raise the stack temperature above 0 °C before the electrochemical reaction. As the electrochemical reaction progresses, reaction heat is released inside the stack, which will heat the PEMFC stack. This heating method is called passive heating, referred to as PH in this article. Another method, called active heating, or simplified to AH in this article, involves artificially adding a device to the stack to input extra heat to the stack to increase the stack temperature more quickly and reduce the icing rate of the stack water. In this study, an optimal cooperative control strategy of AH and PH is explored by integrating AH and PH. The most effective cold start can be achieved when the temperature of the stack is raised to −20 °C by using AH with the reaction heat of the stack itself. This study provides guidance for optimizing the cold start performance of a PEMFC.

The operating costs of breaking coal particles into fine powder, to achieve optimum combustion for the boilers in a power plant, are made up of power input to carry on an energy intensive comminution mechanism and to overcome friction losses within pulverising machines. The operating costs also include the cost of the replacement of the processing system’s components due to wear. This study presents the development and application of an attrition test machine that enables an investigation of the factors that influence pulverizing efficiency. The attrition tester simulates grinding conditions in real vertical spindle mills. In this kind of mill, as with the tester, the size reduction process results from a shearing action during the redistribution of the coal particles. The redistribution and attrition within the coal bed are forced by movement of the rollers (or by a disc rotation, in the case of the tester). The testing method was oriented toward mechanical properties, i.e., internal... [more]

Ammonia is gaining popularity around the world due to its advantages as an energy vector over other zero-carbon fuels and has the potential to be a key component for deep decarbonisation of energy systems. However, little is known about public attitudes and concerns about the technology, one of the factors that will determine its successful implementation. This research examined public perception of green ammonia technologies through online surveys conducted in Mexico (n = 563) and the UK (n = 357). The results suggest that most of the participants in the two countries support the development of these technologies, with men being more likely to show support than women. Participants in Mexico and the UK had both negative and neutral associations of ammonia as a chemical, but overall perceptions of green ammonia were surprisingly positive. A multiple regression analysis indicates that support for this technology is highly dependent on the way participants perceive the benefits and the ri... [more]