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Energies, Volume 14, Issue 7 (April-1 2021) – 238 articles

Cover Story (view full-size image): Power converters in wind turbines exhibit frequent failures—the causes of which have remained unexplained for years. Pronounced seasonal failure patterns point to environmental influences, in particular to humidity, as a critical stressor and likely driver of converter failure. This paper summarizes the results of field-measurement campaigns in 31 wind turbines of seven different manufacturers spread over three continents. The temperature and humidity conditions inside the converter cabinets are characterized, related to the environmental conditions and the operation of the turbines. Their analysis reveals remarkable relations with the failure behavior. View this paper.
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Open AccessArticle
A Computationally Efficient Framework for Modelling Energy Consumption of ICE and Electric Vehicles
Energies 2021, 14(7), 2031; https://doi.org/10.3390/en14072031 - 06 Apr 2021
Viewed by 293
Abstract
This article proposes a novel framework to develop computationally efficient energy consumption models of electric and internal combustion engine vehicles. The number of calculations in a conventional energy consumption model prevents the model’s usage in applications where time is limited. As many fleet [...] Read more.
This article proposes a novel framework to develop computationally efficient energy consumption models of electric and internal combustion engine vehicles. The number of calculations in a conventional energy consumption model prevents the model’s usage in applications where time is limited. As many fleet operators around the world are in the process of transitioning towards electric vehicles, a computationally efficient energy consumption model will be valuable to analyse the vehicles they trial. A vehicle’s energy consumption depends on the vehicle characteristics, drive cycles and vehicle mass. The proposed modelling framework considers these aspects, is computationally efficient, and can be run using open source software packages. The framework is validated through two use cases: an electric bus and a diesel truck. The model error’s standard deviation is less 5% and its mean is less than 2%. The proposed model’s mean computation time is less than 20 ms, which is two orders of magnitude lower than that of the baseline model. Finally, a case study was performed to illustrate the usefulness of the modelling framework for a fleet operator. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle
Scenario Analyses of Exhaust Emissions Reduction through the Introduction of Electric Vehicles into the City
Energies 2021, 14(7), 2030; https://doi.org/10.3390/en14072030 - 06 Apr 2021
Viewed by 267
Abstract
In recent years, policymakers of urban agglomerations in various regions of the world have been striving to reduce environmental pollution from harmful exhaust and noise emissions. Restrictions on conventional vehicles entering the inner city are being introduced and the introduction of low-emission measures, [...] Read more.
In recent years, policymakers of urban agglomerations in various regions of the world have been striving to reduce environmental pollution from harmful exhaust and noise emissions. Restrictions on conventional vehicles entering the inner city are being introduced and the introduction of low-emission measures, including electric ones, is being promoted. This paper presents a method for scenario analysis applied to study the reduction of exhaust emissions by introducing electric vehicles in a selected city. The original scenario analyses relating to real problems faced by contemporary metropolitan areas are based on the VISUM tool (PTV Headquarters for Europe: PTV Planung Transport Verkehr AG, 76131 Karlsruhe, Germany). For the case study, the transport model of the city of Bielsko-Biala (Poland) was used to conduct experiments with different forms of participation of electric vehicles on the one hand and traffic restrictions for high emission vehicles on the other hand. Scenario analyses were conducted for various constraint options including inbound, outbound, and through traffic. Travel time for specific transport relations and the volume of harmful emissions were used as criteria for evaluating scenarios of limited accessibility to city zones for selected types of vehicles. The comparative analyses carried out showed that the introduction of electric vehicles in the inner city resulted in a significant reduction in the emission of harmful exhaust compounds and, consequently, in an increase in the area of clean air in the city. The case study and its results provide some valuable insights and may guide decision-makers in their actions to introduce both driving ban restrictions for high-emission vehicles and incentives for the use of electric vehicles for city residents. Full article
(This article belongs to the Special Issue Exhaust Emissions from Passenger Cars)
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Open AccessArticle
Environment Management of Hydropower Development: A Case Study
Energies 2021, 14(7), 2029; https://doi.org/10.3390/en14072029 - 06 Apr 2021
Viewed by 250
Abstract
Environment management is one of the key aspects of hydropower development in acquiring sustainable energy. However, there has been limited research demonstrating the overall aspects of environment management of hydropower development with support of sound empirical evidence. In present study, the status of [...] Read more.
Environment management is one of the key aspects of hydropower development in acquiring sustainable energy. However, there has been limited research demonstrating the overall aspects of environment management of hydropower development with support of sound empirical evidence. In present study, the status of environment management in hydropower development was comprehensively investigated by conducting a case study based on the data collected from a field survey. The results show that, as environment management is largely subject to legal requirements, the environment management system needs to be established by integrating the legal requirements and needs of project implementation. This could potentially reduce the influence of legal restrictions on hydropower development. The main hydropower project environment management processes include identifying key environmental factors, implementation, monitoring, and performance measurement, which deal with environmental issues such as terrestrial and aquatic ecology protection, wastewater treatment, solid waste disposal, and acoustic-environment protection. Project participants should establish partnering relationships to cooperatively deal with environmental impacts of hydropower project development, in which public participation and sufficient resources input into environmental protection are essential for project success. The results of this study provide a sound basis for participants to deal with the key issues of environmental protection such as meeting legal requirements, training for improving environment management process, cost control, and cooperative environment management. The results of this study could help practitioners to tackle the interactions among project delivery, environmental protection, and engagement of local communities in an optimized way with the aim of maximizing effectiveness of the resources of all participants. Full article
(This article belongs to the Special Issue A New Water-Energy Nexus: The Transition to Sustainable Energy)
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Open AccessArticle
Integrated Risk Assessment for Robustness Evaluation and Resilience Optimisation of Power Systems after Cascading Failures
by and
Energies 2021, 14(7), 2028; https://doi.org/10.3390/en14072028 - 06 Apr 2021
Viewed by 272
Abstract
Power systems face failures, attacks and natural disasters on a daily basis, making robustness and resilience an important topic. In an electrical network, robustness is a network’s ability to withstand and fully operate under the effects of failures, while resilience is the ability [...] Read more.
Power systems face failures, attacks and natural disasters on a daily basis, making robustness and resilience an important topic. In an electrical network, robustness is a network’s ability to withstand and fully operate under the effects of failures, while resilience is the ability to rapidly recover from such disruptive events and adapt its structure to mitigate the impact of similar events in the future. This paper presents an integrated framework for jointly assessing these concepts using two complementary algorithms. The robustness model, which is based on a cascading failure algorithm, quantifies the degradation of the power network due to a cascading event, incorporating the circuit breaker protection mechanisms of the power lines. The resilience model is posed as a mixed-integer optimisation problem and uses the previous disintegration state to determine both the optimal dispatch and topology at each restoration stage. To demonstrate the applicability of the proposed framework, the IEEE 118-bus test network is used as a case study. Analyses of the impact of variations in both generation and load are provided for 10 simulation scenarios to illustrate different network operating conditions. The results indicate that a network’s recovery could be related to the overload capacity of the power lines. In other words, a power system with high overload capacity can withstand higher operational stresses, which is related to increased robustness and a faster recovery process. Full article
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Open AccessArticle
Novel Intelligent Control Technology for Enhanced Stability Performance of an Ocean Wave Energy Conversion System
Energies 2021, 14(7), 2027; https://doi.org/10.3390/en14072027 - 06 Apr 2021
Viewed by 238
Abstract
In this article, a novelty control structure of grid-connected doubly-fed induction generator (DFIG) based on a function link (FL)-based Wilcoxon radial basis function network (FLWRBFN) controller is proposed. The back-propagation (BP) method is used online to train the node connecting weights of the [...] Read more.
In this article, a novelty control structure of grid-connected doubly-fed induction generator (DFIG) based on a function link (FL)-based Wilcoxon radial basis function network (FLWRBFN) controller is proposed. The back-propagation (BP) method is used online to train the node connecting weights of the FLWRBFN. To improve the online learning capability of FLWBFN, differential evolution with particle swarm optimization (DEPSO) is used to tune the learning rates of FLWRBFN. For high randomness of wave energy generation, the transmission power between generators and electrical grids is easy to unstable and AC bus voltage and DC voltage will also lose constant under the conditions of variable generator speed and variable load. Therefore, the proposed intelligent controller can maintain the above power balance and voltage constant and reduce fluctuation. Finally, PSCAD/EMTDC software is used to simulate and study various cases to confirm the robustness and usefulness of the proposed intelligent control technology applied to an ocean wave energy conversion system. Full article
(This article belongs to the Special Issue Wave Energy Conversion 2021)
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Open AccessArticle
Households’ Energy Autonomy: Risks or Benefits for a State?
Energies 2021, 14(7), 2026; https://doi.org/10.3390/en14072026 - 06 Apr 2021
Viewed by 237
Abstract
The purpose of this study is to determine the impact of households’ energy autonomy on a country’s energy independence level, to identify prospects and risks. To assess the economic efficiency of households’ energy autonomy, the study used a modeling method based on maximizing [...] Read more.
The purpose of this study is to determine the impact of households’ energy autonomy on a country’s energy independence level, to identify prospects and risks. To assess the economic efficiency of households’ energy autonomy, the study used a modeling method based on maximizing the net present value, determining the average notional cost of energy efficiency and the level of energy independence in 20 countries. Based on the analysis of the volumes of electricity consumption by households in the studied countries for the period 2000–2018, it was revealed that in developed and developing countries there is an increase in this indicator. Diagnostics of the investment attractiveness of the installation and operation of energy systems for households makes it possible to determine the boundaries of a possible increase in the level of their energy autonomy. The scientific novelty of the research is represented by the proposed methodological approach, which makes it possible to assess the level of energy dependence of countries, possible deviations, and an increase in households’ energy autonomy in relation to the risk limit of energy dependence. The proposed methodological approach allowed the authors to prove the positive impact of increasing households’ energy autonomy for most developed countries. The most positive effect is characteristic of the leading countries in fossil energy market. Full article
(This article belongs to the Special Issue Innovation in Energy Security and Long-Term Energy Efficiency Ⅱ)
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Open AccessArticle
Towards Understanding Interactions between Sustainable Development Goals: The Role of Climate-Well-Being Linkages. Experiences of EU Countries
Energies 2021, 14(7), 2025; https://doi.org/10.3390/en14072025 - 06 Apr 2021
Viewed by 250
Abstract
The 2030 Agenda with 17 Sustainable Development Goals (SDGs) is a challenge for all countries in the world. Their implementation may turn out to be a compromise or the creation of effective interactions that dynamize sustainable development. To achieve the SDGs, it is [...] Read more.
The 2030 Agenda with 17 Sustainable Development Goals (SDGs) is a challenge for all countries in the world. Their implementation may turn out to be a compromise or the creation of effective interactions that dynamize sustainable development. To achieve the SDGs, it is essential to understand how they interact with each other. It seems that in the times of the climate and health crisis caused by the COVID-19 pandemic, caring for the environment and ensuring a healthy life and promoting well-being at all ages is the basis for environmental, economic and social sustainable development. The aim of the study is to compare the degree of implementation of the goals of sustainable development in the scope of goal 13 “Climate action” and goal 3 “Good health and well-being” in the EU countries. In addition, we analyze how trade-offs and synergies between these goals have developed. Data from the Eurostat database were used to achieve the goal. The study used the method of multivariate comparative analysis—linear ordering of objects. The technique for order preference by similarity to an ideal solution (TOPSIS) method was used to measure the studied phenomenon. The results indicate a different degree of implementation of the sustainable development goals related to climate change and the improvement of health and social well-being. Only a few countries have synergy in achieving these goals, most of them compromise, manifesting themselves in improving one goal over another. In the group of analyzed EU countries, a simultaneous deterioration in the effectiveness of achieving both objectives were also noted. Our research also shows that energy policy is an important attribute in improving the achievement of these goals. The conducted analysis fills the gap in the research on the implementation of selected sustainable development goals and their interactions. It contributes to the discussion on increasing the links between them, in particular with regard to emerging compromises. This research can provide a basis for re-prioritizing and intensifying the actions where individual EU countries are lagging most behind. Full article
(This article belongs to the Collection Feature Papers in Energy, Environment and Well-Being)
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Open AccessReview
Metadata Schemas and Ontologies for Building Energy Applications: A Critical Review and Use Case Analysis
Energies 2021, 14(7), 2024; https://doi.org/10.3390/en14072024 - 06 Apr 2021
Viewed by 877
Abstract
Digital and intelligent buildings are critical to realizing efficient building energy operations and a smart grid. With the increasing digitalization of processes throughout the life cycle of buildings, data exchanged between stakeholders and between building systems have grown significantly. However, a lack of [...] Read more.
Digital and intelligent buildings are critical to realizing efficient building energy operations and a smart grid. With the increasing digitalization of processes throughout the life cycle of buildings, data exchanged between stakeholders and between building systems have grown significantly. However, a lack of semantic interoperability between data in different systems is still prevalent and hinders the development of energy-oriented applications that can be reused across buildings, limiting the scalability of innovative solutions. Addressing this challenge, our review paper systematically reviews metadata schemas and ontologies that are at the foundation of semantic interoperability necessary to move toward improved building energy operations. The review finds 40 schemas that span different phases of the building life cycle, most of which cover commercial building operations and, in particular, control and monitoring systems. The paper’s deeper review and analysis of five popular schemas identify several gaps in their ability to fully facilitate the work of a building modeler attempting to support three use cases: energy audits, automated fault detection and diagnosis, and optimal control. Our findings demonstrate that building modelers focused on energy use cases will find it difficult, labor intensive, and costly to create, sustain, and use semantic models with existing ontologies. This underscores the significant work still to be done to enable interoperable, usable, and maintainable building models. We make three recommendations for future work by the building modeling and energy communities: a centralized repository with a search engine for relevant schemas, the development of more use cases, and better harmonization and standardization of schemas in collaboration with industry to facilitate their adoption by stakeholders addressing varied energy-focused use cases. Full article
(This article belongs to the Special Issue Data Modeling and Analytics Applied to Buildings)
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Open AccessArticle
Thermal Performance Analysis of Heat Collection Wall in High-Rise Building Based on the Measurement of Near-Wall Microclimate
Energies 2021, 14(7), 2023; https://doi.org/10.3390/en14072023 - 06 Apr 2021
Viewed by 212
Abstract
Near-wall microenvironment of a building refers to parameters such as wind speed, temperature, relative humidity, solar radiation near the building’s façade, etc. The distribution of these parameters on the building façade shows a certain variation based on changes in height. As a technology [...] Read more.
Near-wall microenvironment of a building refers to parameters such as wind speed, temperature, relative humidity, solar radiation near the building’s façade, etc. The distribution of these parameters on the building façade shows a certain variation based on changes in height. As a technology of passive heating and ventilation, the effectiveness of this application on heat collection wall is significantly affected by the near-wall microclimate, which is manifested by the differences, and rules of the thermal process of the components present at different elevations. To explore the feasibility and specificity of this application of heat collection wall in high-rise buildings, this study uses three typical high-rise buildings from Zhengzhou, China, as research buildings. Periodic measurements of the near-wall microclimate during winter and summer were carried out, and the changing rules of vertical and horizontal microclimate were discussed in detail. Later, by combining these measured data with numerical method, thermal process and performance of heat collection wall based on increasing altitude were quantitatively analyzed through numerical calculations, and the optimum scheme for heat collection wall components was summarized to provide a theoretical basis for the structural design of heat-collecting wall in high-rise buildings. Full article
(This article belongs to the Section Energy and Environment)
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Open AccessArticle
Development of New Mean of Individual Transport for Application in Underground Coal Mines
Energies 2021, 14(7), 2022; https://doi.org/10.3390/en14072022 - 06 Apr 2021
Viewed by 345
Abstract
Development of underground coal mines is reflected in increasing lengths of transport routes between shafts and workplaces. This is not an issue in terms of transportation of materials or groups of people, because suspended railways are efficient, safe, and fast mean of transport. [...] Read more.
Development of underground coal mines is reflected in increasing lengths of transport routes between shafts and workplaces. This is not an issue in terms of transportation of materials or groups of people, because suspended railways are efficient, safe, and fast mean of transport. However, transportation of individual people or small loads is an issue because of the lack of a means of individual transport and the high cost of transport using suspended railways. The development of individual means of transport, based on historical solutions, utilizes existing equipment of mine workings. This paper presents the stages of development of an underground bike, from the original idea to tests and analysis. The development process consists of simulations of different parameters of the bike using Working Model software and real-life tests conducted in an underground mine. The paper also presents analysis of the legal background of this new means of individual transport. Full article
(This article belongs to the Special Issue The IMTech 2021 Innovative Mining Technologies)
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Open AccessArticle
Will the Management Structure of Energy Administrators Affect the Achievement of the Electrical Efficiency Mandatory Target for Taiwan Factories?
Energies 2021, 14(7), 2021; https://doi.org/10.3390/en14072021 - 06 Apr 2021
Viewed by 246
Abstract
Since 2014, Taiwan has promoted a 1% annual electricity saving target to promote electrical efficiency efforts. As the industrial sector accounts for approximately 60% of the overall electricity consumption of Taiwan, this sector presents the greatest opportunity for improving Taiwan’s overall energy efficiency. [...] Read more.
Since 2014, Taiwan has promoted a 1% annual electricity saving target to promote electrical efficiency efforts. As the industrial sector accounts for approximately 60% of the overall electricity consumption of Taiwan, this sector presents the greatest opportunity for improving Taiwan’s overall energy efficiency. Here, the energy audit data of industrial energy users are analyzed via logistic regression to understand the factors impacting their likelihood of achieving the targeted 1% electricity saving. Of the variables under study, the number of employees and the rank of the energy administrator were significantly correlated with the likelihood of reaching the electricity saving target. Within the management structure of the factory, energy users with higher-ranking energy administrators are more likely to achieve the targeted 1% electricity saving. As it is impractical to rapidly increase the number of employees, higher-ranking employees, i.e., factory executives, should be appointed as energy administrators to improve users’ electrical efficiency and thus reach the targeted 1% annual electricity saving. Based on the findings of our research, we put forward a point of view that in addition to the introduction of new technologies to improve energy efficiency, it can also be achieved through adjustments to the management structure of energy administration. Full article
(This article belongs to the Special Issue Energy Management and Energy Efficiency in Industry)
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Open AccessArticle
Experimental Investigation of the Movement of an Offshore Floating Platform in Straight Wind, Tornadic Wind, and Downburst Conditions
Energies 2021, 14(7), 2020; https://doi.org/10.3390/en14072020 - 06 Apr 2021
Viewed by 326
Abstract
There is growing interest in multi-purpose offshore floating platforms that: harvest energy from the sun, wind, water, and waves; desalinize water; host agriculture and aquaculture; and house residents. While there are some basic commonalities with well established, oil and gas platforms, lighter variants [...] Read more.
There is growing interest in multi-purpose offshore floating platforms that: harvest energy from the sun, wind, water, and waves; desalinize water; host agriculture and aquaculture; and house residents. While there are some basic commonalities with well established, oil and gas platforms, lighter variants are functionally different with little wind research coverage. Here, we investigate a floating, multi-purpose, light duty platform under 1:150 scaled straight atmospheric boundary layer wind (ABL), tornado like vortices (TLV), and downburst (DB) conditions. The experiments examined the movement of a 1:150 geometrically scaled platform with six degrees of freedom and two mooring Configurations. Four Configurations are studied, (1) Loosely moored platform, (2) Tightly moored platform, (3) Platform with ballast, and (4) Platform with ballast and weight on the deck. DB winds produced the greatest movement, followed by the TLV winds. Little movement was seen under the ABL winds. Loosely moored platforms moved more than tightly moored. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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Open AccessArticle
Analysis of the Possibility of Disinfecting Surfaces Using Portable Foggers in the Era of the SARS-CoV-2 Epidemic
Energies 2021, 14(7), 2019; https://doi.org/10.3390/en14072019 - 06 Apr 2021
Viewed by 269
Abstract
The SARS-CoV-2 pandemic has resulted in the need for increased surface disinfection. For this purpose, biocides, UV-C radiation, or ozonation can be used. The most commonly used are biocides that can be deposited on the surface with the use of various devices, including [...] Read more.
The SARS-CoV-2 pandemic has resulted in the need for increased surface disinfection. For this purpose, biocides, UV-C radiation, or ozonation can be used. The most commonly used are biocides that can be deposited on the surface with the use of various devices, including foggers. The disinfection efficiency is related to the size of the aerosol droplets formed and their distribution. This paper specifies the distribution of droplet diameters and mean droplet diameters obtained during the use of a commercial fogger. It was shown that the droplet diameters formed were mainly in the range of up to 30–40 μm. A ceramic filter allowed for a larger number of smaller droplets and a limitation in the number of droplets with larger diameters. The results are important in the context of fighting the virus in hard-to-reach places where battery devices can be used. Full article
(This article belongs to the Special Issue Bioeconomy for Resilient Post-COVID Economies)
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Open AccessReview
Cleaning of Floating Photovoltaic Systems: A Critical Review on Approaches from Technical and Economic Perspectives
Energies 2021, 14(7), 2018; https://doi.org/10.3390/en14072018 - 06 Apr 2021
Viewed by 329
Abstract
There are some environmental factors, such as ambient temperature, dust, etc., which cause a reduction in the efficiency of Photovoltaic (PV) systems. Installation of PV panels on the water surface, commonly known as Floating Photovoltaic (FPV) systems, is one solution to employ PV [...] Read more.
There are some environmental factors, such as ambient temperature, dust, etc., which cause a reduction in the efficiency of Photovoltaic (PV) systems. Installation of PV panels on the water surface, commonly known as Floating Photovoltaic (FPV) systems, is one solution to employ PV panels in a cooler environment, achieve higher efficiency, and reduce water evaporation. FPV systems open up new opportunities for scaling up solar generating capacity, especially in countries with high population density and valuable lands, as well as countries with high evaporation rates and water resources deficiency. Since the FPV system is an almost new concept, its cleaning techniques have not been comprehensively studied. While FPV systems are located on the surface of water resources and reservoirs, the water quality can limit the application of different cleaning techniques. Therefore, this paper investigates different techniques of FPV systems cleaning and categorizes them into water-based and water-free approaches. In addition, their cleaning frequencies, as well as economic aspects, are presented and discussed to determine their merits and demerits for using them in FPV systems. Full article
(This article belongs to the Special Issue Optimization and Control of Renewable Energy Sources in Smart Grid)
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Open AccessArticle
Component-in-the-Loop Testing of Automotive Powertrains Featuring All-Wheel-Drive
Energies 2021, 14(7), 2017; https://doi.org/10.3390/en14072017 - 06 Apr 2021
Viewed by 284
Abstract
The article is dedicated to the methodology of designing component-in-the-loop (CiL) testing systems for automotive powertrains featuring several drivelines, including variants with individually driven axles or wheels. The methodical part begins with descriptions of operating and control loops of CiL systems having various [...] Read more.
The article is dedicated to the methodology of designing component-in-the-loop (CiL) testing systems for automotive powertrains featuring several drivelines, including variants with individually driven axles or wheels. The methodical part begins with descriptions of operating and control loops of CiL systems having various simulating functionality—from a “lumped” vehicle for driving cycle tests to vehicles with independently rotating drivelines for simulating dynamic maneuvers. The sequel contains an analysis that eliminates a lack of clarity observed in the existing literature regarding the principles of building a “virtual inertia” and synchronization of loading regimes between individual drivelines of the tested powertrain. In addition, a contribution to the CiL methodology is offered by analyzing the options of simulating tire slip taking into account a limited accuracy of measurement equipment and a limited performance of actuating devices. The methodical part concludes with two examples of mathematical models that can be employed in CiL systems to simulate vehicle dynamics. The first one describes linear motion of a “lumped” vehicle, while the second one simulates vehicle’s trajectory motion taking into account tire slip in both the longitudinal and lateral directions. The practical part of the article presents a case study showing an implementation of the CiL design principles in a laboratory testing facility intended for an all-wheel-drive hybrid powertrain of a heavy-duty vehicle. The CiL system description is followed by the test results simulating the hybrid powertrain operation in a driving cycle and in trajectory maneuvering. The results prove the validity of the proposed methodical principles, as well as their suitability for practical implementations. Full article
(This article belongs to the Section Electric Vehicles)
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Open AccessReview
AC Microgrid Protection System Design Challenges—A Practical Experience
Energies 2021, 14(7), 2016; https://doi.org/10.3390/en14072016 - 06 Apr 2021
Viewed by 261
Abstract
Alternating current (AC) microgrids are the next step in the evolution of the electricity distribution systems. They can operate in a grid-tied or island mode. Depending on the services they are designed to offer, their grid-tied or island modes could have several sub-operational [...] Read more.
Alternating current (AC) microgrids are the next step in the evolution of the electricity distribution systems. They can operate in a grid-tied or island mode. Depending on the services they are designed to offer, their grid-tied or island modes could have several sub-operational states and or topological configurations. Short-circuit current levels and protection requirements between different microgrid modes and configurations can vary significantly. Designing a microgrid’s protection system, therefore, requires a thorough understanding of all microgrid operational modes, configurations, transitional states, and how transitions between those modes are managed. As part of the microgrid protection design, speed and reliability of information flow between the microprocessor-based relays and the microgrid controller, including during microgrid failure modes, must be considered. Furthermore, utility protection practices and customer requirements are not always inclusive of the protection schemes that are unique to microgrids. These and other aspects contribute to the overall complexity and challenge of designing effective microgrid protection systems. Following a review of microgrid protection system design challenges, this paper discusses a few real-world experiences, based on the authors’ own engineering, design, and field experience, in using several approaches to address microgrid protection system design, engineering, and implementation challenges. Full article
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Open AccessArticle
Numerical Investigation of the Influence of the Drill String Vibration Cyclic Loads on the Development of the Wellbore Natural Fracture
Energies 2021, 14(7), 2015; https://doi.org/10.3390/en14072015 - 06 Apr 2021
Viewed by 364
Abstract
Wellbore instability is one of the most serious issues faced in the drilling process. During drilling operations, the cyclic loads applied on the fractured formation progressively modify the initial parameters (i.e., length and width) of the fractured formation, thus resulting into undesirable wellbore [...] Read more.
Wellbore instability is one of the most serious issues faced in the drilling process. During drilling operations, the cyclic loads applied on the fractured formation progressively modify the initial parameters (i.e., length and width) of the fractured formation, thus resulting into undesirable wellbore instability. In this paper, using a nonlinear finite element software (ABAQUS) as the numerical simulator, a poro-elasto-plastic model has been established which aimed at analyzing the influence of drill string vibration cyclic loads on the development of the wellbore natural fracture. The numerical results showed that the fracture width as a function of time profiles followed a sinusoidal behavior similar to the drill string vibration cyclic load profiles. For different cyclic load magnitudes with constant number of cyclic loads, the highest percentage increase of the fracture width after integration of cyclic loads was 64.77%. Interestingly, the fracture width increased with the fracture length in the near wellbore region while it globally decreased in the region far away from the wellbore. But for constant cyclic load magnitude with different number of cyclic loads, the biggest percentage increase of the fracture width after integration of cyclic loads was slightly lower representing 63.12% while the oscillating period of the fracture width increased with the number of cyclic loads. The parametric study revealed that the drill string vibration cyclic loads were relatively independent of the fracture length and the bottom hole pressure. However, the fracture width and the loss circulation rates were considerably impacted by the drill string vibration and the highest percentage increase of the loss circulation rate after integration of cyclic loads was 14.3%. This study provides an insight into the coupling of the fracture rock development and the continuous cyclic loads generated by drill string vibrations which is an aspect that has been rarely discussed in the literature. Full article
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Open AccessArticle
Resonant Power Frequency Converter and Application in High-Voltage and Partial Discharge Test of a Voltage Transformer
Energies 2021, 14(7), 2014; https://doi.org/10.3390/en14072014 - 05 Apr 2021
Viewed by 331
Abstract
This paper presents application of a resonant power frequency converter for high-voltage (HV) and partial discharge (PD) test of a voltage transformer. The rating voltage, power, and frequency of the system are 70 kVrms, 40 kVA, and 200 Hz, respectively. The [...] Read more.
This paper presents application of a resonant power frequency converter for high-voltage (HV) and partial discharge (PD) test of a voltage transformer. The rating voltage, power, and frequency of the system are 70 kVrms, 40 kVA, and 200 Hz, respectively. The testing system utilized the converter feeding to an HV testing transformer connected to a conventional partial discharge detection system. The converter system comprising a rectifier and insulated-gate bipolar (IGBT) switches with the H-bridge configuration was applied as a low-voltage source instead of a conventional motor-generator test set which requires large space and high cost. The requirements of the test according to the standards are quality of the test voltage and the background noise level. The required voltage must have the different voltage (DV) and total harmonic distortion (THDv) in the acceptable values of less than 5%. The DV is defined as the difference of the root mean square and peak voltages in percent. The required background noise level must be lower than 2.5 pC. Simulations and experiments were performed for verification of the developed system performance in comparison with those of the previously developed system based on the pulse width modulation converter. It is found that the developed system can provide the testing voltage with the DV and the THDv of lower than 1% and the background noise level of lower than 1 pC. Considering this achievement of promising performance, the developed system is an attractive choice for the HV and PD testing of voltage transformers in real practice. Full article
(This article belongs to the Special Issue Simulation and Analysis of High Voltage Engineering in Power Systems)
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Open AccessArticle
Optimization and Characteristics Analysis of High Torque Density 12/8 Switched Reluctance Motor Using Metaheuristic Gray Wolf Optimization Algorithm
Energies 2021, 14(7), 2013; https://doi.org/10.3390/en14072013 - 05 Apr 2021
Viewed by 353
Abstract
In this paper, the optimization and characteristics analysis of a three-phase 12/8 switched reluctance motor (SRM) based on a Grey Wolf Optimizer (GWO) for electric vehicles (EVs) application is presented. This research aims to enhance the output torque density of the proposed SRM. [...] Read more.
In this paper, the optimization and characteristics analysis of a three-phase 12/8 switched reluctance motor (SRM) based on a Grey Wolf Optimizer (GWO) for electric vehicles (EVs) application is presented. This research aims to enhance the output torque density of the proposed SRM. Finite element method (FEM) was used to analyze the characteristics and optimization process of the proposed motor. The proposed metaheuristic GWO combines numerous objective functions and design constraints with different weight factors. Maximum flux density, current density, and motor volume are selected as the optimization constraints, which play a significant role in the optimization process. GWO performs optimization for each iteration and sends it to FEM software to analyze the performance before starting another iteration until the optimized value is found. Simulations are employed to understand the characteristics of the proposed motor. Finally, the optimized prototype motor is manufactured and performance is verified by experiment. It is shown that the torque can be increased by 120% for the same outer volume, by using the proposed method. Full article
(This article belongs to the Special Issue Advances in Motor and Drive)
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Open AccessArticle
Harmonic Mitigation in Electric Railway Systems Using Improved Model Predictive Control
Energies 2021, 14(7), 2012; https://doi.org/10.3390/en14072012 - 05 Apr 2021
Viewed by 354
Abstract
An electric multiple unit (EMU) high-speed train is the dynamic load that degrades the power quality in an electric railway system. Therefore, a power quality improvement system using an active power filter (APF) must be considered. Due to the oscillating load current in [...] Read more.
An electric multiple unit (EMU) high-speed train is the dynamic load that degrades the power quality in an electric railway system. Therefore, a power quality improvement system using an active power filter (APF) must be considered. Due to the oscillating load current in the dynamic load condition, a fast and accurate harmonic current-tracking performance is required. As such, this paper proposes the design of a model predictive control (MPC) since the minimization of cost function in the MPC process can suitably determine APF switching states. The design technique of MPC is based on the APF mathematical model. This controller was designed to compensate the time delay in the digital control. Moreover, the synchronous detection (SD) method applied the reference current calculations, as shown in this paper. To verify the proposed MPC, the overall control of APF was implemented on a eZdsp F28335 board by using the hardware-in-the-loop technique. The testing results indicated that the proposed MPC can provide a fast and accurate harmonic current-tracking response compared with the proportional-integral controller. In the load changing condition, the MPC was still effective in providing a good result after compensation. The percentage of total harmonic distortion, the percentage current unbalance factor, and the power factor would also be kept within the IEEE Standard 519 and IEEE Standard 1459. Full article
(This article belongs to the Special Issue Power Quality in Electrified Transportation Systems)
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Open AccessArticle
Hamiltonian Modeling and Structure Modified Control of Diesel Engine
Energies 2021, 14(7), 2011; https://doi.org/10.3390/en14072011 - 05 Apr 2021
Viewed by 295
Abstract
A diesel engine is a typical dynamic system. In this paper, a dynamics method is proposed to establish the Hamiltonian model of the diesel engine, which solves the main difficulty of constructing a Hamiltonian function under the multi-field coupling condition. Furthermore, the control [...] Read more.
A diesel engine is a typical dynamic system. In this paper, a dynamics method is proposed to establish the Hamiltonian model of the diesel engine, which solves the main difficulty of constructing a Hamiltonian function under the multi-field coupling condition. Furthermore, the control method of Hamiltonian model structure modification is introduced to study the control of a diesel engine. By means of the principle of energy-shaping and Hamiltonian model structure modification theories, the modified energy function is constructed, which is proved to be a quasi-Lyapunov function of the closed-loop system. Finally, the control laws are derived, and the simulations are carried out. The study reveals the dynamic mechanism of diesel engine operation and control and provides a new way to research the modeling and control of a diesel engine system. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle
Design and Implement of Three-Phase Permanent-Magnet Synchronous Wave Generator using Taguchi Approach
Energies 2021, 14(7), 2010; https://doi.org/10.3390/en14072010 - 05 Apr 2021
Viewed by 314
Abstract
In this paper, the design and performance analysis of a high-efficiency permanent-magnet synchronous wave generator (PSWG) are presented. A systematic approach for the design of the outer rotor was proposed as a prototype model. The magnetic field, magnetic circuit characteristics, electrical characteristics of [...] Read more.
In this paper, the design and performance analysis of a high-efficiency permanent-magnet synchronous wave generator (PSWG) are presented. A systematic approach for the design of the outer rotor was proposed as a prototype model. The magnetic field, magnetic circuit characteristics, electrical characteristics of the generator, and optimal design parameters such as the pole–arc ratio and shoe outer length were determined using the Taguchi method, finite-element analysis (FEA) software, and rotor skewing techniques. The proposed six series and six parallel-connection winding configurations can provide an evenly distributed current for practical applications. A PSWG was designed and fabricated according to the proposed methodology. According to the experimental results by implementing the optimized design, the efficiencies of the proposed PSWG which used 3.6 Ω load at 300 rpm is 86.32% and the efficiency error between simulation and experiment is less than 1.8%. It verifies the feasibility of the proposed method to PSWG and the structural reliability optimization design. Full article
(This article belongs to the Special Issue New Advances in Permanent Magnet Electrical Machines)
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Open AccessArticle
Improving the Solar Reliability Factor of a Dual-Axis Solar Tracking System Using Energy-Efficient Testing Solutions
Energies 2021, 14(7), 2009; https://doi.org/10.3390/en14072009 - 05 Apr 2021
Viewed by 232
Abstract
This paper presents an improved mathematical model for calculating the solar test factor (STF) and solar reliability factor (SRF) of a photovoltaic (PV) automated equipment. By employing a unified metrics system and a combined testing suite encompassing various energy-efficient testing techniques, the aim [...] Read more.
This paper presents an improved mathematical model for calculating the solar test factor (STF) and solar reliability factor (SRF) of a photovoltaic (PV) automated equipment. By employing a unified metrics system and a combined testing suite encompassing various energy-efficient testing techniques, the aim of this paper is to determine a general fault coverage and improve the global SRF of a closed-loop dual-axis solar tracking system. Accelerated testing coupled with reliability analysis are essential tools for assessing the performance of modern solar tracking devices since PV system malfunctioning is directly connected to economic loss, which is an important aspect for the solar energy domain. The experimental results show that the unified metrics system is potentially suitable for assessing the reliability evaluation of many types of solar tracking systems. Additionally, the proposed combined testing platform proves efficient regarding fault coverage (overall coverage of 66.35% for all test scenarios), test time (an average of 275 min for 2864 test cycles), and power consumption (zero costs regarding electricity consumption for all considered test cases) points of view. Full article
(This article belongs to the Special Issue Analysis and Numerical Modeling in Solar Photovoltaic Systems)
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Open AccessArticle
A Multiphysics Analysis of Coupled Electromagnetic-Thermal Phenomena in Cable Lines
Energies 2021, 14(7), 2008; https://doi.org/10.3390/en14072008 - 05 Apr 2021
Viewed by 303
Abstract
The paper is focused on numerical modeling of multi-strand cable lines placed in free air. Modeling is carried out within the framework of the so-called multi-physics approach using commercial software. The paper describes in detail the steps undertaken to develop realistic, reliable numerical [...] Read more.
The paper is focused on numerical modeling of multi-strand cable lines placed in free air. Modeling is carried out within the framework of the so-called multi-physics approach using commercial software. The paper describes in detail the steps undertaken to develop realistic, reliable numerical models of power engineering cables, taking into account their geometries and heat exchange conditions. The results might be of interest to the designers of multi-strand cable systems. Full article
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System Parameter Based Performance Optimization of Solar PV Systems with Perturbation Based MPPT Algorithms
Energies 2021, 14(7), 2007; https://doi.org/10.3390/en14072007 - 05 Apr 2021
Viewed by 390
Abstract
Maximum power point tracking (MPPT) algorithms are invariably employed to utilize solar photovoltaic (PV) systems effectively. Perturbation based MPPT algorithms are popular due to their simplicity and reasonable efficiency. While novel MPPT algorithms claim increased energy utilization over classic perturbation techniques, their performance [...] Read more.
Maximum power point tracking (MPPT) algorithms are invariably employed to utilize solar photovoltaic (PV) systems effectively. Perturbation based MPPT algorithms are popular due to their simplicity and reasonable efficiency. While novel MPPT algorithms claim increased energy utilization over classic perturbation techniques, their performance is governed by the choice of optimal algorithm parameters. Existing guidelines for parameter optimization are mathematically laborious and are not generic. Hence, this paper aims to provide simple and comprehensive guidelines to ensure optimal performance from the perturbation based MPPT technique. For an illustration of proposed claims, a solar PV fed boost converter is investigated to examine the effect of input capacitor, digital filter cut-off frequency, system time constant and sampling time on implementing a classic Perturb and Observe (P and O) algorithm. The readers will be presented with two simple step tests (to determine the effective system time constant) and proposed guidelines to choose the optimal performance sampling time. Necessary laboratory experiments show that an appropriate choice of sampling time could increase efficiency and ensure system stability. This investigation’s learnings can be easily extended to any power electronics converter, loads and all perturbation-based algorithms used in solar PV systems. The results of appropriate tests on the system’s mathematical model and the laboratory prototype are presented in detail to support this research’s claims. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
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Open AccessArticle
Technological Solutions and Tools for Circular Bioeconomy in Low-Carbon Transition: Simulation Modeling of Rice Husks Gasification for CHP by Aspen PLUS V9 and Feasibility Study by Aspen Process Economic Analyzer
Energies 2021, 14(7), 2006; https://doi.org/10.3390/en14072006 - 05 Apr 2021
Viewed by 386
Abstract
This study explored the suitability of simulation tools for accurately predicting fluidized bed gasification in various scenarios without disturbing the operational system, and dedicating time to experimentation, in the aim of benefiting the decision makers and investors of the low-carbon waste-based bioenergy sector, [...] Read more.
This study explored the suitability of simulation tools for accurately predicting fluidized bed gasification in various scenarios without disturbing the operational system, and dedicating time to experimentation, in the aim of benefiting the decision makers and investors of the low-carbon waste-based bioenergy sector, in accelerating circular bioeconomy solutions. More specifically, this study aimed to offer a customized circular bioeconomy solution for a rice processing residue. The objectives were the simulation and economic assessment of an air atmospheric fluidized bed gasification system fueled with rice husk, for combined heat and power generation, by using the tools of Aspen Plus V9, and the Aspen Process Economic Analyzer. The simulation model was based on the Gibbs energy minimization concept. The technological configurations of the SMARt-CHP technology were used. A parametric study was conducted to understand the influence of process variables on product yield, while three different scenarios were compared: (1) air gasification; (2) steam gasification; and (3) oxygen-steam gasification-based scenario. Simulated results show good accuracy for the prediction of H2 in syngas from air gasification, but not for the other gas components, especially regarding CO and CH4 content. It seems that the RGIBBS and Gibbs free minimization concept is far from simulating the operation of a fluidized bed gasifier. The air gasification scenario for a capacity of 25.000 t/y rice husk was assessed for its economic viability. The economic assessment resulted in net annual earnings of EUR 5.1 million and a positive annual revenue of EUR 168/(t/y), an excellent pay out time (POT = 0.21) and return of investment (ROI = 2.8). The results are dependent on the choices and assumptions made. Full article
(This article belongs to the Special Issue Circular Economy in Low-Carbon Transition)
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Open AccessReview
Photoemission Studies on the Environmental Stability of Thermal Evaporated MAPbI3 Thin Films and MAPbBr3 Single Crystals
Energies 2021, 14(7), 2005; https://doi.org/10.3390/en14072005 - 05 Apr 2021
Viewed by 296
Abstract
Hybrid organic inorganic perovskites have been considered as a potential candidate for the next generational solar cell due to their outstanding optoelectronic properties and rapid development in recent years. However, the biggest challenge to prevent them from massive commercial use is their long-term [...] Read more.
Hybrid organic inorganic perovskites have been considered as a potential candidate for the next generational solar cell due to their outstanding optoelectronic properties and rapid development in recent years. However, the biggest challenge to prevent them from massive commercial use is their long-term stability. Photoemission spectroscopy has been widely used to investigate properties of the perovskites, which provide critical insights to better understand the degradation mechanisms. In this article, we review mainly our photoemission studies on the degradation processes of perovskite thin films and single crystals with different environmental factors, such as gases, water, and light by monitoring changes of chemical composition and electronic structure. These studies on the effects by different environmental parameters are discussed for the understanding of the stability issues and the possible solutions. Full article
(This article belongs to the Special Issue Advanced Polymer and Perovskite Solar Cells)
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Open AccessArticle
An Efficient Hybrid Algorithm for Energy Expenditure Estimation for Electric Vehicles in Urban Service Enterprises
Energies 2021, 14(7), 2004; https://doi.org/10.3390/en14072004 - 05 Apr 2021
Viewed by 320
Abstract
The article deals with the decision problems of estimating the energy expenditure of low-emission fleets in urban service companies due to environmental safety. One of the most important problems of today’s transport policy of many city authorities is the ecological safety of its [...] Read more.
The article deals with the decision problems of estimating the energy expenditure of low-emission fleets in urban service companies due to environmental safety. One of the most important problems of today’s transport policy of many city authorities is the ecological safety of its inhabitants. The basic measures are aimed at banning high-emission vehicles from city centers and promoting the introduction of zero-emission vehicles, such as electric or hybrid cars. The authors proposed an original approach to the decision model, in which the energy expenditure from the use of electric vehicles was defined as a criterion function. The boundary conditions took into account limitations typical of an electric vehicle, e.g., maximum range or battery charging time. To solve the problem, the authors proposed an efficient hybrid algorithm based on ant colony algorithm and genetic algorithm. The verification was made for the example of a utility company serving a medium-sized city in the eastern part of Poland. Full article
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Open AccessArticle
Influence of Thermal Aging on the Combustion Characteristics of Cables in Nuclear Power Plants
Energies 2021, 14(7), 2003; https://doi.org/10.3390/en14072003 - 05 Apr 2021
Viewed by 345
Abstract
In this study, the combustion characteristics and emission of toxic gases of a non-class 1E cable in a nuclear power plant were investigated with respect to the aging period. A thermal accelerated aging method was applied using the Arrhenius equation with the activation [...] Read more.
In this study, the combustion characteristics and emission of toxic gases of a non-class 1E cable in a nuclear power plant were investigated with respect to the aging period. A thermal accelerated aging method was applied using the Arrhenius equation with the activation energy of the cables and the aging periods of the cables set to zero, 10, 20, 30 and 40 years old by considering the lifetime of a nuclear power plant. According to ISO 5660-1 and ISO 19702, the cone calorimeter Fourier transform infrared spectroscopy test was performed to analyze the combustion characteristics and emission toxicity. In addition, scanning electron microscopy and an energy dispersive X-ray spectrometer were used to examine the change in the surface of the sheath and insulation of the cables according to the aging periods. To compare quantitative fire risks at an early period, the fire performance index (FPI) and fire growth index (FGI) are derived from the test results of the ignition time, peak heat release rate (PHRR) and time to PHRR (tPHRR). When comparing FPI and FGI, the fire risks decreased as the aging period increased, which means that early fire risks may be alleviated through the devolatilization of both the sheath and insulation of the cables. However, when comparing heat release and mass loss, which represent the fire risk at the mid and late period, fire intensity and severity increased with the aging period. The emission of toxic gases coincided with the results obtained from the heat release rate, which confirms that the toxicity of non-aged cables is higher than that of aged cables. From the results, it can be concluded that the aging period significantly affects both the combustion characteristics and toxicity of the emission gas. Therefore, cable degradation with aging should be considered when setting up reinforced safety codes and standards for cables and planning proper operation procedures for nuclear power plants. Full article
(This article belongs to the Section Thermal Management)
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Open AccessArticle
Tower Configuration Impacts on the Thermal and Flow Performance of Steel-Truss Natural Draft Dry Cooling System
Energies 2021, 14(7), 2002; https://doi.org/10.3390/en14072002 - 05 Apr 2021
Viewed by 259
Abstract
In recent years, the steel-truss natural draft dry cooling technique has received attention owing to its advantages in better aseismic capability, shorter construction period, and preferable recycling. For cooling towers generating the draft force of air flow, its configuration may impact the thermal [...] Read more.
In recent years, the steel-truss natural draft dry cooling technique has received attention owing to its advantages in better aseismic capability, shorter construction period, and preferable recycling. For cooling towers generating the draft force of air flow, its configuration may impact the thermal and flow performance of the steel-truss natural draft dry cooling system. With regard to the issue, this work explored the thermal and flow characteristics for the steel-truss natural draft dry cooling systems with four typical engineering tower configurations. By numerical simulation, the pressure, flow, and temperature contours were analyzed, then air mass flow rates and heat rejections were calculated and compared for the local air-cooled sectors and overall steel-truss natural draft dry cooling systems with those four tower configurations. The results present that tower 2 with the conical/cylindrical configuration had slightly lower heat rejection compared with tower 1 with the traditional hyperbolic configuration. Tower 3 with the hyperbolic/cylindrical configuration showed better thermo-flow performances than tower 1 at high crosswinds, while tower 4 with the completely cylindrical configuration appeared to have much reduced cooling capability under various crosswind conditions, along with strongly deteriorated thermal and flow behaviors. As for engineering application of the steel-truss natural draft dry cooling system, the traditional hyperbolic tower configuration is recommended for local regions with gentle wind, while for those areas with gale wind yearly, the hyperbolic/cylindrical integrated cooling tower is preferred. Full article
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