This paper presents the design and implementation of a digital control strategy for a Buck converter, used as a solar charger of valve-regulated lead acid (VRLA) batteries. The control system consists of two fuzzy logic controllers (FLCs), which adjust the appropriate increment of the converter duty cycle based on battery state of charge according to a three-stage charging scheme. One FLC works as a maximum power point tracker (FLC-MPPT), while the other regulates the battery voltage (FLC-VR). This approach of using two different set of membership functions overcomes the limitations of the battery chargers with a single control function, where the voltage supplied to the battery is either not constant due to the operation of the MPPT algorithm (possibly damaging the battery) or is constant due to the operation of the voltage control (hence, MPP cannot be achieved). In this way, the proposed control approach has the advantage of extracting the maximum energy of the PV panel, preventing... [more]

This paper presents the design and position control scheme of an overhang-type rail mover system driven by a dual Brushless AC (BLAC) motor with a simple Hall position sensor inside each motor. The overhang-type roller is chosen to reduce the slip between the roller and rail surface due to gravity. The BLAC motors are used to provide smooth translation along the rail and effective turning. Imbalances on any part of the motor and the simplicity of the Hall position sensor can create additional disturbance load, unsteady movement, and position errors. To reduce the sudden moving position error between the two motors, a balancing compensator with a Proportional-Differential (PD) position controller, which is based on the instantaneous speed and position trajectories, is presented. Furthermore, speed and position reference models are designed to compensate for the low Hall sensor resolution in the low-speed range. Therefore, steady-state position errors can then be regulated simply by usin... [more]

Hexagonal boron nitride and silicone rubber (h-BN/SR) composites were prepared by the mechanical stirring method, and their crystal morphology, chemical structure, thermal properties, and compression stress−strain performance were investigated. The experimental results suggest that silicone rubber combined with h-BN exhibits better thermal conductivity and mechanical properties. When the proportion of h-BN is 30 wt%, the thermal conductivity of the h-BN/SR composite material is 0.58 W/m∙K, which is 3.4 times that of pure silicone rubber. At the same time, the compressive strength of h-BN/SR is 4.27 MPa, which is 6.7 times that of pure silicone rubber. Furthermore, the finite element model was employed to numerically analyze the thermal behavior of a battery with a h-BN/SR composite as the thermal interface material. The analytical results show that the highest temperature of the battery decreased when using h-BN/SR as the thermal interface material in the battery thermal management sys... [more]

Most already advanced developed heating control systems remain either in a prototype state (because of their relatively complex implementation requirements) or require very specific technologies not implementable in most existing buildings. On the other hand, the above-mentioned analysis has also pointed out that most smart building energy management systems deploy quite very basic heating control strategies limited to quite simplistic predesigned use-case scenarios. In the present paper, we propose a heating control strategy taking advantage of the overall identification of the living space by taking advantage of the consideration of the living space users’ presence as additional thermal sources. To handle this, an adaptive controller for the operation of heating transmitters on the basis of soft computing techniques by taking into account the diverse range of occupants in the heating chain is introduced. The strategy of the controller is constructed on a basis of the modeling heating... [more]

Recently, a growing interest has been observed in HVAC control systems based on Artificial Intelligence, to improve comfort conditions while avoiding unnecessary energy consumption. In this work, a model-free algorithm belonging to the Deep Reinforcement Learning (DRL) class, Soft Actor-Critic, was implemented to control the supply water temperature to radiant terminal units of a heating system serving an office building. The controller was trained online, and a preliminary sensitivity analysis on hyperparameters was performed to assess their influence on the agent performance. The DRL agent with the best performance was compared to a rule-based controller assumed as a baseline during a three-month heating season. The DRL controller outperformed the baseline after two weeks of deployment, with an overall performance improvement related to control of indoor temperature conditions. Moreover, the adaptability of the DRL agent was tested for various control scenarios, simulating changes of... [more]

In this work, the aerodynamic performance and optimization of a vertical-axis wind turbine with a high tip-speed ratio are theoretically studied on the basis of the two-dimensional airfoil theory. By dividing the rotating plane of the airfoil into the upwind and downwind areas, the relationship among the angle of attack, azimuth, pitch angle, and tip-speed ratio is derived using the quasi-steady aerodynamic model, and aerodynamic loads on the airfoil are then obtained. By applying the polynomial approximation to functions of lift and drag coefficients with the angle of attack for symmetric and asymmetric airfoils, respectively, explicit expressions of aerodynamic loads as functions of the angle of attack are obtained. The performance of a fixed-pitch blade is studied by employing a NACA0012 model, and influences of the tip speed ratio, pitch angle, chord length, rotor radius, incoming wind speed and rotational speed on the performance of the blade are discussed. Furthermore, the optimi... [more]

Latent heat stored in phase change materials (PCM) can greatly improve energy efficiency in indoor heating/cooling applications. This study presents the materials and methods for the formation and characterization of a PCM layer for a latent heat thermal energy storage (LHTES) application. Four commercially available PCMs comprising the classes of organic paraffins and organic non-paraffins were selected for thermal storage application. Pure organic PCM and PCM in water emulsions were experimentally investigated. PCM electrospun microfibers were produced by a co-axial electrospinning technique, where solutions of Polycaprolactone (PCL) 9% w/v and 12% w/v in dichloromethane (DCM) were used as the fiber shell materials. PCM emulsified with sodium dodecyl sulfate (SDS), and Polyvinylalcohol 10% w/v (PVA) constituted the core of the fibers. The thermal behavior of the PCM, PCM emulsions, and PCM electrospun fibers were analyzed with differential scanning calorimetry (DSC). A commercial org... [more]

Connecting a large number of distributed sources to the medium and low voltage grid poses many problems. The most important of these are the voltage changes inside the network, what can be observed when the power flow from these sources towards the HV/MV (High Voltage/Medium Voltage) transformer station. In particular, if the power consumption in nodes of the MV network is small and the distance between the place of installation of the source and the substation is large, increases and changes in voltage may be dangerous for the insulation of the network and burdensome for the consumers connected to it. The solution most frequently used to control voltage increases is the appropriate setting of the controller that affects the on-load tap changer of the MV/HV or even MV/LV (Medium Voltage/Low Voltage) transformer. It is also possible to regulate the reactive power of the sources and, of course, to limit their generated active power (curtailment of generation). The development of energy s... [more]

Tariff subsidies are beneficial to the further development of the microgrid market. In response to the reduction of the power generation costs of microgrids, the energy storage subsidy for microgrids has become a key factor affecting their further development. Therefore, it is essential to explore and establish a government subsidy mechanism for the energy storage price of microgrids. In this paper, we consider the incentive compatibility constraints and participation constraints of both the government and the microgrid energy storage subsidy. The cases of hidden information and no hidden information are investigated. A microgrid energy storage subsidy model of the incentive compatibility constraint was established to analyze the efficiency of the government subsidy and the microgrid energy storage in the “self-generation + energy storage” mode. The results show that there is an adverse selection problem between the government and energy storage subsidies for microgrid users. In the ca... [more]

Distributed energy resources (DERs), including renewable energy resources (RESs) and electric vehicles (EVs), have a significant impact on distribution systems because they can cause bi-directional power flow in the distribution lines. Thus, the voltage regulation and thermal limits of the distribution system to mitigate from the excessive power generation or consumption should be considered. The focus of this study is on a control strategy for DERs in low-voltage DC microgrids to minimize the operating costs and maintain the distribution voltage within the normal range based on intelligent scheduling of the charging and discharging of EVs, and to take advantage of RESs such as photovoltaic (PV) plants. By considering the time-of-use electricity rates, we also propose a 24-h sliding window to mitigate uncertainties in loads and PV plants in which the output is time-varied and the EV arrival cannot be predicted. After obtaining a request from the EV owner, the proposed optimal DER contr... [more]

A welding power source is commonly assimilated to a non-linear load. Arc welding market being in full growth, the resulting harmonic pollution is becoming an increasingly difficult problem to ignore. Therefore, the main purpose of this work is to define and implement the most suitable solution for power factor correction in a welding power source. Due to the high non-linearity of the electric arc, the current controller used to control grid current need to show high robustness. Consequently, this paper focuses on the digitization of a very robust Phase-Shift Self-Oscillating Current Controller (PSSOCC), which only exists in its analog version until then, to carry out this task. After quick descriptions of the entire energy conversion chain and the PSSOCC operation principle, a model of the digital PSSOCC is proposed. Then, the quality and the accuracy of the aforementioned model are evaluated and its operating limits are identified. Afterwards, the behavior of the digital controller is... [more]

Understanding to what extent the emergence of prosumers and prosumagers organized in energy communities can impact the organization and operation of power grids has been one of the major recent research avenues at the European level. In renewable-based communities aiming to reach some level of energy self-sufficiency, a key issue to be addressed is assessing how the presence of end-users playing different roles in the system (self-consuming, producing and trading, performing demand management, etc.) can influence the overall system performance. In this setting, this paper combines Distributed Artificial Intelligence and optimization approaches to assess how prosumagers and consumers pursuing different goals can influence the energy self-sufficiency of a local energy community. The residential demand is accurately modeled, and the agents’ preferences are considered in the modeling to represent a smart community. The results show that although energy community members may have conflictin... [more]

The outbreak and rapid spread of the COVID-19 pandemic has hit the global financial markets, including the energy sector. Alternative energy belongs to the economy’s key sectors concerning environmental issues and seems to be a full-fledged alternative for fossil-based conventional energy. This paper aims to assess the impact of COVID-19 on the stock market indices related to the alternative and conventional energy sector. We use daily data on the Morgan Stanley Capital International (MSCI) Global Alternative Energy Index, the MSCI All Country World Index (ACWI) Energy Index, and self-developed Average-49 COVID-19 New Cases Index and Average-49 Stringency Index. The research covers the period January−October 2020. The average level of the MSCI Global Alternative Energy Index in COVID-19 year was more than a quarter higher than in 2019 while the MSCI ACWI Energy fell almost one-third in the same period. Based on the Markov-switching model, we show that both the MSCI Global Alternative E... [more]

The geometrical and mechanical properties of non-persistent joints as well as the mechanical behavior of intact rock (rock bridges) are significantly effective in the shear strength of weakness planes containing non-persistent joints. Therefore, comprehensive knowledge of the shear mechanism of both joints and rock bridges is required to assess the shear strength of the planes. In this study, the shear behavior of specimens containing a single non-persistent rough joint is investigated. A novel procedure was used to prepare cast specimens embedding a non-persistent (disc-shaped) rough joint using 3D printing and casting technology, and the shear strength of the specimens was examined through an extensive direct shear testing program under constant normal load (CNL) condition. Three levels for three different variables of the joint roughness, rock bridge ratio, and normal stress were considered, and the effects of these factors on the shear behavior of prepared samples were tested. The... [more]

Carbon quantum dots (CQDs) are nanomaterials with a particle size range of 2 to 10 nm. CQDs have a wide range of applications such as medical diagnostics, bio-imaging, biosensors, coatings, solar cells, and photocatalysis. Although the effect of various experimental parameters, such as the synthesis method, reaction time, etc., have been investigated, the effect of different feedstocks on CQDs has not been studied yet. In this study, CQDs were synthesized from hydroxymethylfurfural, furfural, and microcrystalline cellulose via hydrothermal carbonization at 220 °C for 30 min of residence time. The produced CQDs showed green luminescence behavior under the short-wavelength UV light. Furthermore, the optical properties of CQDs were investigated using ultraviolet-visible spectroscopy and emission spectrophotometer, while the morphology and chemical bonds of CQDs were investigated using transmission electron microscopy and Fourier-transform infrared spectroscopy, respectively. Results showe... [more]

The aim of this paper is to present a methodology for dimensioning an energy storage system (ESS) to the generation data measured in an operating wave energy generation plant connected to the electric grid in the north of Spain. The selection criterion for the ESS is the compliance of the power injected into the grid with a specific active-power ramp-rate limit. Due to its electrical characteristics, supercapacitor (SC) technology is especially suitable for this application. The ESS dimensioning methodology is based on a mathematical model, which takes into account the power generation system, the chosen ramp-rate limit, the ESS efficiency maps and electrical characteristics. It allows one to evaluate the number of storage cabinets required to satisfy the needs described, considering a compromise between the number of units, which means cost, and the reliability of the storage system to ensure the grid codes compliance. Power and energy parameters for the ESS are obtained from the calc... [more]

The new generation of capsules that circulate through vacuum tubes at speeds up to 1200 km/h, which is being developed, demands communication systems that can operate at these speeds with high capacity and quality of service. Currently, the two technologies available are the new generation of 802.11ax networks and 5G NR. Using these technologies at such high speeds in a confined environment requires a careful study and design of the configuration of the network and optimization of the physical interface. This paper describes the requirements for critical and business communications, proposing a WLAN and 5G network design based on the analysis of the propagation characteristics and constraints of vacuum tubes and using propagation measurements and simulations made in similar environments at frequencies of 2.5/5.7/24 GHz. These measurements and simulations show that propagation losses in this environment are low (4−5 dB/100 m), as a consequence of the guided propagation, so that the use... [more]

The behaviours of individual flow structures have become a relevant matter of study in turbulent flows as the computational power to allow their study feasible has become available. Especially, high instantaneous Reynolds Stress events have been found to dominate the behaviour of the logarithmic layer. In this work, we present a viability study where two machine learning solutions are proposed to reduce the computational cost of tracking such structures in large domains. The first one is a Multi-Layer Perceptron. The second one uses Long Short-Term Memory (LSTM). Both of the methods are developed with the objective of taking the the structures’ geometrical features as inputs from which to predict the structures’ geometrical features in future time steps. Some of the tested Multi-Layer Perceptron architectures proved to perform better and achieve higher accuracy than the LSTM architectures tested, providing lower errors on the predictions and achieving higher accuracy in relating the st... [more]

The determination of natural gas content in coal seams is essential to safe mining activities and to estimate gas resources. It is used to estimate methane emissions into workings, which is very important when using preventive measures of methane ignition and explosion. Methane content in a coal seam is mostly determined using a direct method. However, a problem with estimation of gas loss during collecting a sample in a mine occurs in each method. That gas loss is estimated using different procedures. In the Polish mining industry, methane content in a coal seam is mostly determined during roadway advancing faces in coal seams. The differences in procedures for determining methane content in coal in various laboratories gave rise to starting research into developing a new method. This article presents results of study of gas loss unification for the determination of methane content in coal seams. The research focused mainly on determining a uniform method for estimating gas loss using... [more]

More than 150 municipal utilities (so-called Stadtwerke) were established in Germany from the beginning of the millennium, bringing the total number of Stadtwerke currently established within the country to approximately 900. With responsibility for more than half of the supply of electricity, gas and heat in Germany, these Stadtwerke play a central role in the transformation of the energy sector, or Energiewende. In addition, due to their local and regional ties, Stadtwerke have a particular role to play in energy politics, the economy and across society. This article focuses on the motives behind, and grounds for, the current wave of newly established Stadtwerke. Further, it discusses the factors that were critical to the successful formation of new Stadtwerke in recent years. The results of our survey indicate that the establishment of municipal Stadtwerke is a suitable measure to implement the energy transition at the local level, whereby the concept of public value has a high leve... [more]

The COVID-19 pandemic and the associated lockdown can be regarded as a forced social experiment, the results of which show how to use energy under specific conditions. During this period, there was a reduction in electricity consumption at the level of the power system, but a different specificity distinguishes the group of household users. The article aims at presenting and analysing the identified issues concerning residential electricity users based on the experience from the COVID-19 pandemic lockdown. Data from energy meters from almost 7000 flats in Warsaw’s housing estates during the lockdown in 2020 and the analogous period before the pandemic were used. The analysis showed that, on average, residential users staying practically the whole day in their flats increased their energy consumption, but without increasing their average daily peak power, smoothing the profile in the morning hours to the level reaching the peak power that had occurred in the analogous period before the... [more]

Lithium-ion capacitors (LICs) have gained significant attention in recent years for their increased energy density without altering their power density. LICs achieve higher capacitance than traditional supercapacitors due to their hybrid battery electrode and subsequent higher voltage. This is due to the asymmetric action of LICs, which serves as an enhancer of traditional supercapacitors. This culminates in the potential for pollution-free, long-lasting, and efficient energy-storing that is required to realise a renewable energy future. This review article offers an analysis of recent progress in the production of LIC electrode active materials, requirements and performance. In-situ hybridisation and ex-situ recombination of composite materials comprising a wide variety of active constituents is also addressed. The possible challenges and opportunities for future research based on LICs in energy applications are also discussed.

In recent years, the dynamic development of renewable energy has been visible all over the world, including Poland. Wind energy is one of the most used renewable energy sources. In Poland, by 2030, it is planned to commission at least six offshore wind farms with a total capacity of 3.8 GW. It is estimated that these investments will increase Poland’s GDP by approximately PLN 60 billion and increase tax revenues by PLN 15 billion. Therefore, they could be a strong stimulus for the development of the Polish economy and may be of great importance in recovering from the crisis caused by the economic constraints related to the COVID-19 pandemic. The aim of the article is a multi-criteria evaluation of the investments planned in Poland in offshore wind farms and identification of potentially the most economically effective investments. To account for the uncertainty in this decision problem, a modified fuzzy Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method w... [more]

In this paper, we apply the Failure Modes, Effects, and Criticality Analysis (FMECA) approach to the criticality and risk analysis of the efficiency, safety/reliability, environment, and financial criteria of the high voltage transmission line. In the efficiency analysis, the weighting-scoring method and analytical hierarchy process are applied to obtain the line renovation index, which is interpreted as efficiency severity. The safety/reliability severity relates to the system impacts are caused by failure of the equipment and the system. The environmental severity takes social impacts and pollution into consideration. The financial severity involves the cost of spare parts and maintenance costs, which are interpreted as the financial severity of the lines. Twenty practical transmission lines in Thailand with actual data for 115, 230, and 500 kV were studied. The transmission line components are divided into eight components including the conductor, conductor accessories, insulator, s... [more]

This century registers a significant expansion in the wind power market. However, the vast majority of these investments are concentrated in large wind turbines. The century begins with an installed capacity of about 20 GW, which reaches 650 GW in 2019. On the other hand, it is important to highlight that small wind turbines have not followed this virtuous path, a fact that is evident in Brazil’s reality. In this context, the article aims at evaluating the current situation of the wind energy market for Small Wind Turbines in Brazil (SWT) and its future perspectives, identifying the main characteristics of the sector, its challenges, and opportunities. It is an exploratory−explanatory research study that investigates the theme, generating knowledge that turns to practical application, as it seeks answers to solve local interests. This methodological approach provides objective evidence that the production of knowledge about the use of SWT in Brazil still remains embryonic, shaded by th... [more]