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Energies, Volume 11, Issue 9 (September 2018) – 313 articles

Cover Story (view full-size image): The article investigates the performance of cooling systems in the Polish hard-coal mining industry. A study conducted in six hard-coal mines revealed that despite implementing air conditioning systems, the permitted air temperature value of 28 °C was exceeded. The article mainly presents the cooling performance of movable spot air-coolers. The obtained results have allowed identifying the factors that diminish the efficiency of cooling under analysis. These factors can be treated on equal terms with key performance indicators, which can be used to monitor the performance of cooling system components and provide managers with high-level indicators on which decisions can be based. View this paper.
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14 pages, 2628 KiB  
Article
Environmentally Friendly Compact Air-Insulated High-Voltage Substations
by Maurizio Albano, A. Manu Haddad, Huw Griffiths and Paul Coventry
Energies 2018, 11(9), 2492; https://doi.org/10.3390/en11092492 - 19 Sep 2018
Cited by 12 | Viewed by 6259
Abstract
This paper investigates the possible options for achieving a substantial reduction in a substation footprint using air-insulated switchgear as a more environmentally-friendly alternative to gas-insulated substations that use SF6 gas. Adopting a new approach to surge arrester location and numbers, International Electrotechnical [...] Read more.
This paper investigates the possible options for achieving a substantial reduction in a substation footprint using air-insulated switchgear as a more environmentally-friendly alternative to gas-insulated substations that use SF6 gas. Adopting a new approach to surge arrester location and numbers, International Electrotechnical Commission (IEC) minimum clearances can be successfully selected instead of the maximum clearances as currently adopted by many utilities, as is the case in the UK. In addition, innovative alternative compact busbar arrangements using vertical and delta configurations have been proposed by the authors. A further opportunity for compaction is offered by the application of compact and integrated technology offered from several manufacturers. The full overvoltage control within the entire substation under any surge condition is a key aspect of the feasibility of this type of substation. This work demonstrates that the new design option can be an attractive alternative for future substation configuration with minimum footprint. Full article
(This article belongs to the Special Issue 10 Years Energies - Horizon 2028)
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16 pages, 3632 KiB  
Article
Impact of Forest Fuels on Gas Emissions in Coal Slurry Fuel Combustion
by Galina Nyashina and Pavel Strizhak
Energies 2018, 11(9), 2491; https://doi.org/10.3390/en11092491 - 19 Sep 2018
Cited by 17 | Viewed by 3677
Abstract
Anthropogenic emissions from coal combustion pose a serious threat to human wellbeing. One prospective way to solve this problem is by using slurry fuels instead of coal. The problem is especially pressing in China and Russia, so these countries need reliable experimental data [...] Read more.
Anthropogenic emissions from coal combustion pose a serious threat to human wellbeing. One prospective way to solve this problem is by using slurry fuels instead of coal. The problem is especially pressing in China and Russia, so these countries need reliable experimental data on the SOx and NOx emissions reduction range more than others do. The experiments in this research are based on the components that are typical of Russia. Experimental research was conducted on the way typical forest fuels (ground pine needles, leaves and their mixtures, bark, sawdust, and charcoal) affect the gas emissions from the combustion of slurry fuels based on the wastes. It was established that using forest fuels as additives to coal-water slurries reduces SOx and NOx emissions by 5–91% as compared to coal or to slurries based on used turbine oil. It was revealed that even small concentrations of such additives (7–15%) could result in a several-fold reduction in SOx and NOx. The higher the temperature, the more prominent the role of forest biomass. The calculated complex criterion illustrates that forest fuels increase the performance indicator of fuel suspensions by 1.2–10 times. Full article
(This article belongs to the Special Issue Sustainability of Fossil Fuels)
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22 pages, 8679 KiB  
Article
A Novel Robust Model Predictive Controller for Aerospace Three-Phase PWM Rectifiers
by Tao Lei, Weiwei Tan, Guangsi Chen and Delin Kong
Energies 2018, 11(9), 2490; https://doi.org/10.3390/en11092490 - 19 Sep 2018
Cited by 2 | Viewed by 4252
Abstract
This paper presents a novel Model Predictive Direct Power Control (MPDPC) approach for the pulse width modulation (PWM) rectifiers in the Aircraft Alternating Current Variable Frequency (ACVF) power system. The control performance of rectifiers may be largely affected by variations in the AC [...] Read more.
This paper presents a novel Model Predictive Direct Power Control (MPDPC) approach for the pulse width modulation (PWM) rectifiers in the Aircraft Alternating Current Variable Frequency (ACVF) power system. The control performance of rectifiers may be largely affected by variations in the AC side impedance, especially for systems with limited power volume system. A novel idea for estimating the impedance variation based on the Bayesian estimation, using an algorithm embedded in MPDPC is presented in this paper. The input filter inductance and its equivalent series resistance (ESR) of PWM rectifiers are estimated in this algorithm by measuring the input current and input voltage in each cycle with the probability Bayesian estimation theory. This novel estimation method can overcome the shortcomings of traditional data based estimation methods such as least square estimation (LSE), which achieves poor estimation results with the small samples data set. In ACVF systems, the effect on the parameters estimation accuracy caused by the number of sampling points in one cycle is also analyzed in detail by simulation. The validity of this method is verified by the digital and Hard-in-loop simulation compared with other estimation methods such as the least square estimation method. The experimental testing results show that the proposed estimation algorithm can improve the robustness and the control performance of the MPDPC under the condition of the uncertainty of the AC side parameters of the three-phase PWM rectifiers in aircraft electrical power system. Full article
(This article belongs to the Section F: Electrical Engineering)
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25 pages, 1803 KiB  
Article
A Novel Approach for the Selection of Power-Generation Technology Using a Linguistic Neutrosophic CODAS Method: A Case Study in Libya
by Dragan Pamučar, Ibrahim Badi, Korica Sanja and Radojko Obradović
Energies 2018, 11(9), 2489; https://doi.org/10.3390/en11092489 - 19 Sep 2018
Cited by 87 | Viewed by 5170
Abstract
Rapid increases in energy demand and international drive to reduce carbon emissions from fossil fuels have led many oil-rich countries to diversify their energy portfolio and resources. Libya is one of these countries, and it has recently become interested in utilizing its renewable-energy [...] Read more.
Rapid increases in energy demand and international drive to reduce carbon emissions from fossil fuels have led many oil-rich countries to diversify their energy portfolio and resources. Libya is one of these countries, and it has recently become interested in utilizing its renewable-energy resources in order to reduce financial and energy dependency on oil reserves. This paper introduces an original multicriteria decision-making Pairwise-CODAS model in which the modification of the CODAS method was made using Linguistic Neutrosophic Numbers (LNN). The paper also suggests a new LNN Pairwise (LNN PW) model for determining the weight coefficients of the criteria developed by the authors. By integrating these models with linguistic neutrosophic numbers, it was shown that it is possible to a significant extent to eliminate subjective qualitative assessments and assumptions by decision makers in complex decision-making conditions. The LNN PW-CODAS model was tested and validated in a case study of the selection of optimal Power-Generation Technology (PGT) in Libya. Testing of the model showed that the proposed model based on linguistic neutrosophic numbers provides objective expert evaluation by eliminating subjective assessments when determining the numerical values of criteria. A sensitivity analysis of the LNN PW-CODAS model, carried out through 68 scenarios of changes in the weight coefficients, showed a high degree of stability of the solutions obtained in the ranking of the alternatives. The results were validated by comparison with LNN extensions of four multicriteria decision-making models. Full article
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12 pages, 5151 KiB  
Article
Pseudo-Elastic Response of Gas Bearing Clastic Formations: An Italian Case Study
by Christian Coti, Vera Rocca and Quinto Sacchi
Energies 2018, 11(9), 2488; https://doi.org/10.3390/en11092488 - 19 Sep 2018
Cited by 14 | Viewed by 3082
Abstract
The research presented in this paper focuses on the analysis of land movements induced by underground gas storage operations in a depleted reservoir in Northern Italy with the aim of increasing the understanding of the deformation response of deep formations via a real [...] Read more.
The research presented in this paper focuses on the analysis of land movements induced by underground gas storage operations in a depleted reservoir in Northern Italy with the aim of increasing the understanding of the deformation response of deep formations via a real case study. The a priori knowledge of the pseudo-elastic parameters showed a substantial discrepancy between static values from triaxial lab tests and dynamic values obtained via the interpretation of sonic data at wellbore scale. The discrepancy is not surprising for the formations under investigation: a thousand meters of a silty to shaly sequence intercalated with arenaceous banks above a reservoir formation, which is basically made up of sandstone intercalated with shale intervals and conglomerates. Information collected for over more than ten years of seasonal production/injection cycles (i.e., time and space evolution of the reservoir fluid pressure and of the induced land surface movements) was then combined in a 3D numerical geomechanical model to constrain and update the a priori knowledge on the pseudo elastic model parameters via a back analysis approach. The obtained calibrated model will then be used for reliable prediction of system safety analyses, for example in terms of induced ground movements. Full article
(This article belongs to the Section D: Energy Storage and Application)
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16 pages, 4651 KiB  
Article
Modified High Back-Pressure Heating System Integrated with Raw Coal Pre-Drying in Combined Heat and Power Unit
by Heng Chen, Zhen Qi, Qiao Chen, Yunyun Wu, Gang Xu and Yongping Yang
Energies 2018, 11(9), 2487; https://doi.org/10.3390/en11092487 - 19 Sep 2018
Cited by 15 | Viewed by 3806
Abstract
A conceptual high-back pressure (HBP) heating system cooperating raw coal pre-drying for combined heat and power (CHP) was proposed to improve the performance of the HBP-CHP unit. In the new design, besides of heating the supply-water of the heating network, a portion of [...] Read more.
A conceptual high-back pressure (HBP) heating system cooperating raw coal pre-drying for combined heat and power (CHP) was proposed to improve the performance of the HBP-CHP unit. In the new design, besides of heating the supply-water of the heating network, a portion of the exhaust steam from the turbine is employed to desiccate the raw coal prior to the coal pulverizer, which further recovers the waste heat of the exhaust steam and contributes to raising the overall efficiency of the unit. Thermodynamic and economic analyzes were conducted based on a typical 300 MW coal-fired HBP-CHP unit with the application of the modified configuration. The results showed that the power generation thermal efficiency promotion of the unit reaches 1.7% (absolute value) owing to suggested retrofitting, and meanwhile, the power generation standard coal consumption rate is diminished by 5.8 g/kWh. Due to the raw coal pre-drying, the energy loss of the exhaust flue gas of the boiler is reduced by 19.1% and the boiler efficiency increases from 92.7% to 95.4%. The impacts of the water content of the dried coal and the unit heating capacity on the energy-saving effect of the new concept were also examined. Full article
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15 pages, 7460 KiB  
Article
A Compensation Control Scheme of Voltage Unbalance Using a Combined Three-Phase Inverter in an Islanded Microgrid
by Biying Ren, Xiangdong Sun, Shasha Chen and Huan Liu
Energies 2018, 11(9), 2486; https://doi.org/10.3390/en11092486 - 18 Sep 2018
Cited by 17 | Viewed by 4588
Abstract
A large number of single-phase loads in an islanded microgrid have a bad influence on the alternating current (AC) bus voltage symmetry, which will further impact the power supply for the other loads. In this paper, the combined three-phase inverter is adopted as [...] Read more.
A large number of single-phase loads in an islanded microgrid have a bad influence on the alternating current (AC) bus voltage symmetry, which will further impact the power supply for the other loads. In this paper, the combined three-phase inverter is adopted as the distributed generation (DG) interface circuit for its independent control of each bridge. However, the combined three-phase inverter will generate an asymmetrical voltage with the traditional droop control. Moreover, the system impedance also effects the voltage symmetry. Therefore, the improved droop control method based on the self-adjusting P-f and Q-U droop curves and the system impedance voltage drop compensation are proposed. The system control scheme is also designed in detail. A simulation and an experiment under the conditions of the balanced, unbalanced loads are carried out, and the results verify the feasibility and effectiveness of the control strategy. Full article
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10 pages, 2532 KiB  
Article
Improved Current Doubler Rectifier
by Mihail Antchev
Energies 2018, 11(9), 2485; https://doi.org/10.3390/en11092485 - 18 Sep 2018
Cited by 3 | Viewed by 5682
Abstract
It is widely accepted to examine and explain the functioning of the standard “Current Doubler Rectifier” as strictly symmetrical according to the electrical current through the two inductances. The present work challenges this consideration and proposes a new version of the electrical circuit [...] Read more.
It is widely accepted to examine and explain the functioning of the standard “Current Doubler Rectifier” as strictly symmetrical according to the electrical current through the two inductances. The present work challenges this consideration and proposes a new version of the electrical circuit diagram where the current symmetry is improved. The proposed circuit is called the “Improved Current Doubler Rectifier”. Full article
(This article belongs to the Section F: Electrical Engineering)
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13 pages, 2097 KiB  
Article
Using Multiple Fidelity Numerical Models for Floating Offshore Wind Turbine Advanced Control Design
by Joannes Olondriz, Wei Yu, Josu Jugo, Frank Lemmer, Iker Elorza, Santiago Alonso-Quesada and Aron Pujana-Arrese
Energies 2018, 11(9), 2484; https://doi.org/10.3390/en11092484 - 18 Sep 2018
Cited by 5 | Viewed by 4630
Abstract
This paper summarises the tuning process of the Aerodynamic Platform Stabiliser control loop and its performance with Floating Offshore Wind Turbine model. Simplified Low-Order Wind turbine numerical models have been used for the system identification and control tuning process. Denmark Technical University’s 10 [...] Read more.
This paper summarises the tuning process of the Aerodynamic Platform Stabiliser control loop and its performance with Floating Offshore Wind Turbine model. Simplified Low-Order Wind turbine numerical models have been used for the system identification and control tuning process. Denmark Technical University’s 10 MW wind turbine model mounted on the TripleSpar platform concept was used for this study. Time-domain simulations were carried out in a fully coupled non-linear aero-hydro-elastic simulation tool FAST, in which wind and wave disturbances were modelled. This testing yielded significant improvements in the overall Floating Offshore Wind Turbine performance and load reduction, validating the control technique presented in this work. Full article
(This article belongs to the Collection Wind Turbines)
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15 pages, 1561 KiB  
Article
Comparative Analysis of CO2, N2, and Gas Mixture Injection on Asphaltene Deposition Pressure in Reservoir Conditions
by Peng Wang, Fenglan Zhao, Jirui Hou, Guoyong Lu, Meng Zhang and Zhixing Wang
Energies 2018, 11(9), 2483; https://doi.org/10.3390/en11092483 - 18 Sep 2018
Cited by 25 | Viewed by 3540
Abstract
CO2 and N2 injection is an effective enhanced oil recovery technology in the oilfield especially for low-permeability and extra low-permeability reservoirs. However, these processes can induce an asphaltene deposition during oil production. Asphaltene-deposition-induced formation damage is a fairly severe problem. Therefore, [...] Read more.
CO2 and N2 injection is an effective enhanced oil recovery technology in the oilfield especially for low-permeability and extra low-permeability reservoirs. However, these processes can induce an asphaltene deposition during oil production. Asphaltene-deposition-induced formation damage is a fairly severe problem. Therefore, predicting the likelihood of asphaltene deposition in reservoir conditions is crucial. This paper presents the results of flash separation experiments used to investigate the composition of crude oil in shallow and buried-hill reservoirs. Then, PVTsim Nova is used to simulate the composition change and asphaltene deposition of crude oil. Simulation tests indicate that the content of light components C1-C4 and heavy components C36+ decrease with increasing CO2 and N2 injection volumes. However, the extraction of CO2 is significantly stronger than that of N2. In shallow reservoirs, as the CO2 injection volume increases, the deposition pressure range decreases and asphaltenes are easily deposited. Conversely, the asphaltene deposition pressure of crude oil injected with N2 is higher and will not cause serious asphaltene deposition. When the CO2-N2 injection ratio reaches 1:1, the deposition pressure range shows a significant transition. In buried-hill reservoirs, asphaltene deposition is unlikely to occur with CO2, N2, and a gas mixture injection. Full article
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14 pages, 2477 KiB  
Article
Laboratory Test Bed for Analyzing Fault-Detection Reaction Times of Protection Relays in Different Substation Topologies
by Goran Jurišić, Juraj Havelka, Tomislav Capuder and Stjepan Sučić
Energies 2018, 11(9), 2482; https://doi.org/10.3390/en11092482 - 18 Sep 2018
Cited by 12 | Viewed by 5480
Abstract
Visions of energy transition focus on activating end users, meaning that numerous flexible-distribution network-level devices become active participants in power-system operations. This implies a fast, reliable, and secure exchange of data, enabling the distribution-system operators to maintain, or even improve, the quality and [...] Read more.
Visions of energy transition focus on activating end users, meaning that numerous flexible-distribution network-level devices become active participants in power-system operations. This implies a fast, reliable, and secure exchange of data, enabling the distribution-system operators to maintain, or even improve, the quality and delivery of service. With the introduction of the International Electrotechnical Commission (IEC) 61850 standard, the path is set for a single communication topology covering all substation levels. The standard has the potential to change the way substations are designed, built, tested, and maintained. This means that the key segment of the substation, its protection system, will go through a transition period with the end goal of having a digitized substation where all information exchange is performed over an Ethernet communication bus. This paper analyzes the performance impact of the IEC 61850-9-2LE on the protection system. To do this, a laboratory hardware-in-the-loop test setup was developed representing traditional-, hybrid-, and digital-substation topology. The setup serves to simulate faults and create transient waveforms in an extended IEEE 123-node test system, which is then used to detect the reaction times of protection relay devices. To verify the results, a significant number of tests was performed clearly showing the benefits of digitalizing the distribution system. Full article
(This article belongs to the Section F: Electrical Engineering)
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17 pages, 4697 KiB  
Article
Kinetic Study on the Pyrolysis of Medium Density Fiberboard: Effects of Secondary Charring Reactions
by Longwei Pan, Yong Jiang, Lei Wang and Wu Xu
Energies 2018, 11(9), 2481; https://doi.org/10.3390/en11092481 - 18 Sep 2018
Cited by 13 | Viewed by 3640
Abstract
The reaction models employed in the kinetic studies of biomass pyrolysis generally do not include the secondary charring reactions. The aim of this work is to propose an applicable kinetic model to characterize the pyrolysis mechanism of medium density fiberboard (MDF) and to [...] Read more.
The reaction models employed in the kinetic studies of biomass pyrolysis generally do not include the secondary charring reactions. The aim of this work is to propose an applicable kinetic model to characterize the pyrolysis mechanism of medium density fiberboard (MDF) and to evaluate the effects of secondary charring reactions on estimated products yields. The kinetic study for pyrolysis of MDF was performed by a thermogravimetric analyzer over a heating rate range from 10 to 40 °C/min in a nitrogen atmosphere. Four stages related to the degradation of resin, hemicellulose, cellulose, and lignin could be distinguished from the thermogravimetric analyses (TGA). Based on the four components and multi-component parallel reaction scheme, a kinetic model considering secondary charring reactions was proposed. A comparison model was also provided. An efficient optimization algorithm, differential evolution (DE), was coupled with the two models to determine the kinetic parameters. Comparisons of the results of the two models to experiment showed that the mass fraction (TG) and mass loss rate (DTG) calculated by the model considering secondary charring reactions were in better agreement with the experimental data. Furthermore, higher product yields than the experimental values will be obtained if secondary charring reactions were not considered in the kinetic study of MDF pyrolysis. On the contrary, with the consideration of secondary charring reactions, the estimated product yield had little error with the experimental data. Full article
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12 pages, 6110 KiB  
Article
Experimental Research on the Thermal Performance and Semi-Visualization of Rectangular Flat Micro-Grooved Gravity Heat Pipes
by Xiang Gou, Qiyan Zhang, Yamei Li, Yingfan Liu, Shian Liu and Saima Iram
Energies 2018, 11(9), 2480; https://doi.org/10.3390/en11092480 - 18 Sep 2018
Cited by 9 | Viewed by 3203
Abstract
To strengthen the heat dissipating capacity of a heat pipe used for integrated insulated gate bipolar transistors, as an extension of our earlier work, the effect of micro-groove dimension on the thermal performance of flat micro-grooved gravity heat pipe was studied. Nine pipes [...] Read more.
To strengthen the heat dissipating capacity of a heat pipe used for integrated insulated gate bipolar transistors, as an extension of our earlier work, the effect of micro-groove dimension on the thermal performance of flat micro-grooved gravity heat pipe was studied. Nine pipes with different depths (0.4 mm, 0.8 mm, 1.2 mm) and widths (0.4 mm, 0.8 mm, 1.2 mm) were fabricated and tested under a heating load range from 80 W to 180 W. The start-up time, temperature difference, relative thermal resistance and equivalent thermal conductivity were presented as performance indicators by comparison of flat gravity heat pipes with and without micro-grooves. Results reveal that the highest equivalent thermal conductivity of the flat micro-grooved gravity heat pipes is 2.55 times as that of the flat gravity heat pipe without micro-grooves. The flat gravity heat pipes with deeper and narrower micro-grooves show better thermal performance and the optimal rectangular micro-groove dimension among the selected options is determined to be 1.2 mm (depth) × 0.4 mm (width). Furthermore, the liquid–vapor phase behaviors were observed to verify the heat transfer effects and analyze the heat transfer mechanism of the flat micro-grooved heat pipes. Full article
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21 pages, 5893 KiB  
Article
Joint Optimal Policy for Subsidy on Electric Vehicles and Infrastructure Construction in Highway Network
by Yue Wang, Zhong Liu, Jianmai Shi, Guohua Wu and Rui Wang
Energies 2018, 11(9), 2479; https://doi.org/10.3390/en11092479 - 18 Sep 2018
Cited by 8 | Viewed by 3378
Abstract
The promotion of the battery electric vehicle has become a worldwide problem for governments due to its short endurance range and slow charging rate. Besides an appropriate network of charging facilities, a subsidy has proved to be an effective way to increase the [...] Read more.
The promotion of the battery electric vehicle has become a worldwide problem for governments due to its short endurance range and slow charging rate. Besides an appropriate network of charging facilities, a subsidy has proved to be an effective way to increase the market share of battery electric vehicles. In this paper, we investigate the joint optimal policy for a subsidy on electric vehicles and infrastructure construction in a highway network, where the impact of siting and sizing of fast charging stations and the impact of subsidy on the potential electric vehicle flows is considered. A new specified local search (LS)-based algorithm is developed to maximize the overall number of available battery electric vehicles in the network, which can get provide better solutions in most situations when compared with existed algorithms. Moreover, we firstly combined the existing algorithms to establish a multi-stage optimization method, which can obtain better solutions than all existed algorithms. A practical case from the highway network in Hunan, China, is studied to analyze the factors that impact the choice of subsidy and the deployment of charging stations. The results prove that the joint policy for subsidy and infrastructure construction can be effectively improved with the optimization model and the algorithms we developed. The managerial analysis indicates that the improvement on the capacity of charging facility can increase the proportion of construction fees in the total budget, while the improvement in the endurance range of battery electric vehicles is more efficient in expanding battery electric vehicle adoption in the highway network. A more detailed formulation of the battery electric vehicle flow demand and equilibrium situation will be studied in the future. Full article
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17 pages, 2407 KiB  
Article
Improved Data Center Energy Efficiency and Availability with Multilayer Node Event Processing
by Vojko Matko and Barbara Brezovec
Energies 2018, 11(9), 2478; https://doi.org/10.3390/en11092478 - 18 Sep 2018
Cited by 18 | Viewed by 3899
Abstract
This article presents an overview of a new multilayer node event processing (MNEP) method for improved data center energy efficiency and event management monitoring in its physical infrastructure. Event management is essential for the provision and maintenance of the reliability and functionality of [...] Read more.
This article presents an overview of a new multilayer node event processing (MNEP) method for improved data center energy efficiency and event management monitoring in its physical infrastructure. Event management is essential for the provision and maintenance of the reliability and functionality of the physical infrastructure. For effective maintenance, action preventing any downtime accurate event information as well as appropriate energy support is of outmost importance. The novelty of this approach lies in the enhanced availability and reliability of the physical infrastructure, improved data center infrastructure energy efficiency, as well as lower costs when designing a new physical infrastructure system. The MNEP method presents a data model based on the node tree processing. The experimental results show that the number of all potential unexpected events is reduced significantly as a result of the accurate identification of the alarm root cause. The comparison of time parameters required to evaluate the maintenance factors shows that the time needed to detect, identify, and react to alarm events decreases and has a significant impact on maintaining a defined high level of availability and energy efficiency in a data center physical infrastructure. Full article
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17 pages, 1788 KiB  
Article
Pelleting Vineyard Pruning at Low Cost with a Mobile Technology
by Giuseppe Toscano, Vincenzo Alfano, Antonio Scarfone and Luigi Pari
Energies 2018, 11(9), 2477; https://doi.org/10.3390/en11092477 - 18 Sep 2018
Cited by 34 | Viewed by 3672
Abstract
The goal of this work was to test a patented pruning harvester and a mobile pelleting system specifically designed for the vineyard agripellet chain. Biomass was characterized before and after storage and after the pelleting stage. The performance, the fuel consumption, and the [...] Read more.
The goal of this work was to test a patented pruning harvester and a mobile pelleting system specifically designed for the vineyard agripellet chain. Biomass was characterized before and after storage and after the pelleting stage. The performance, the fuel consumption, and the work quality of the harvester were assessed together with the productivity and the power consumption of the mobile pelleting system. Production costs of pellet were estimated for the whole logistic chain, considering two scenarios: Storage and pelleting directly at the farm site or at a dedicated location at variable distance from the fields. For comparison, the direct production of chips without pelleting was considered. Results indicate that harvester performance was quite good and comparable with commercial solutions; the chips produced exhibited excellent storage performance, allowing direct pelleting without forced drying; the pellet quality was good comparable with that produced from forestry biomass. From an economic point of view, in-field pelleting was the most cost-effective solution, with a good margin of profit up to 57€ t−1; on the other hand, when transport to an intermediate storage center is necessary, profit margin reduces gradually and fades off at an average 50 km distance from the fields. Full article
(This article belongs to the Section A: Sustainable Energy)
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16 pages, 656 KiB  
Article
SwarmGrid: Demand-Side Management with Distributed Energy Resources Based on Multifrequency Agent Coordination
by Manuel Castillo-Cagigal, Eduardo Matallanas, Estefanía Caamaño-Martín and Álvaro Gutiérrez Martín
Energies 2018, 11(9), 2476; https://doi.org/10.3390/en11092476 - 18 Sep 2018
Cited by 8 | Viewed by 2793
Abstract
This paper focuses on a multi-agent coordination for demand-side management in electrical grids with high penetration rates of distributed generation, in particular photovoltaic generation. This coordination is done by the use of swarm intelligence and coupled oscillators, proposing a novel methodology, which is [...] Read more.
This paper focuses on a multi-agent coordination for demand-side management in electrical grids with high penetration rates of distributed generation, in particular photovoltaic generation. This coordination is done by the use of swarm intelligence and coupled oscillators, proposing a novel methodology, which is implemented by the so-call SwarmGrid algorithm. SwarmGrid seeks to smooth the aggregated consumption by considering distributed and local generation by the development of a self-organized algorithm based on multifrequency agent coordination. The objective of this algorithm is to increase stability and reduce stress of the electrical grid by the aggregated consumption smoothing based on a frequency domain approach. The algorithm allows not only improvements in the electrical grid, but also increases the penetration of distributed and renewable sources. Contrary to other approaches, this objective is achieved anonymously without the need for information exchange between the users; it only takes into account the aggregated consumption of the whole grid. Full article
(This article belongs to the Special Issue Distributed Energy Resources Management 2018)
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15 pages, 3362 KiB  
Article
Forecasting Carbon Emissions Related to Energy Consumption in Beijing-Tianjin-Hebei Region Based on Grey Prediction Theory and Extreme Learning Machine Optimized by Support Vector Machine Algorithm
by Menglu Li, Wei Wang, Gejirifu De, Xionghua Ji and Zhongfu Tan
Energies 2018, 11(9), 2475; https://doi.org/10.3390/en11092475 - 18 Sep 2018
Cited by 56 | Viewed by 5308
Abstract
Carbon emissions and environmental protection issues have brought pressure from the international community during Chinese economic development. Recently, Chinese Government announced that carbon emissions per unit of GDP would fall by 60–65% compared with 2005 and non-fossil fuel energy would account for 20% [...] Read more.
Carbon emissions and environmental protection issues have brought pressure from the international community during Chinese economic development. Recently, Chinese Government announced that carbon emissions per unit of GDP would fall by 60–65% compared with 2005 and non-fossil fuel energy would account for 20% of primary energy consumption by 2030. The Beijing-Tianjin-Hebei region is an important regional energy consumption center in China, and its energy structure is typically coal-based which is similar to the whole country. Therefore, forecasting energy consumption related carbon emissions is of great significance to emissions reduction and upgrading of energy supply in the Beijing-Tianjin-Hebei region. Thus, this study thoroughly analyzed the main energy sources of carbon emissions including coal, petrol, natural gas, and coal power in this region. Secondly, the kernel function of the support vector machine was applied to the extreme learning machine algorithm to optimize the connection weight matrix between the original hidden layer and the output layer. Thirdly, the grey prediction theory was used to predict major energy consumption in the region from 2017 to 2030. Then, the energy consumption and carbon emissions data for 2000–2016 were used as the training and test sets for the SVM-ELM (Support Vector Machine-Extreme Learning Machine) model. The result of SVM-ELM model was compared with the forecasting results of SVM (Support Vector Machine Algorithm) and ELM (Extreme Learning Machine) algorithm. The accuracy of SVM-ELM was shown to be higher. Finally, we used forecasting output of GM (Grey Prediction Theory) (1, 1) as the input of the SVM-ELM model to predict carbon emissions in the region from 2017 to 2030. The results showed that the proportion of energy consumption seriously affects the amount of carbon emissions. We found that the energy consumption of electricity and natural gas will reach 45% by 2030 and carbon emissions in the region can be controlled below 96.9 million tons. Therefore, accelerating the upgradation of industrial structure will be the key task for the government in controlling the amount of carbon emissions in the next step. Full article
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18 pages, 4573 KiB  
Article
An Irregular Current Injection Islanding Detection Method Based on an Improved Impedance Measurement Scheme
by Menghua Liu, Wei Zhao, Qing Wang, Songling Huang and Kunpeng Shi
Energies 2018, 11(9), 2474; https://doi.org/10.3390/en11092474 - 17 Sep 2018
Cited by 9 | Viewed by 3160
Abstract
One class of islanding detection methods, known as impedance measurement-based methods and voltage change monitoring-based methods, are implemented through injecting irregular currents into the network, for which reason they are defined in this paper as irregular current injection methods. This paper indicates that [...] Read more.
One class of islanding detection methods, known as impedance measurement-based methods and voltage change monitoring-based methods, are implemented through injecting irregular currents into the network, for which reason they are defined in this paper as irregular current injection methods. This paper indicates that such methods may be affected by distributed generation (DG) unit cut-in events. Although the network impedance change can still be used as a judgment basis for islanding detection, the general impedance measurement scheme cannot separate island events from DG unit cut-in events in multi-DG operation. In view of this, this paper proposes a new islanding detection method based on an improved impedance measurement scheme, i.e., dynamic impedance measurement, which will not be affected by DG unit cut-in events and can further assist some other equipment in islanding detection. The simulations and experiments verify the stated advantages of the new islanding detection method. Full article
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15 pages, 2454 KiB  
Article
A Study on the Strategy for Departure Aircraft Pushback Control from the Perspective of Reducing Carbon Emissions
by Xinhua Zhu, Nan Li, Yu Sun, Hongfei Zhang, Kai Wang and Sang-Bing Tsai
Energies 2018, 11(9), 2473; https://doi.org/10.3390/en11092473 - 17 Sep 2018
Cited by 9 | Viewed by 3855
Abstract
In order to reduce the taxiing time of departing aircraft and reduce the fuel consumption and exhaust emissions of the aircraft, Shanghai Hongqiao Airport was taken as an example to study the control strategy for aircraft departure. In this paper, the influence of [...] Read more.
In order to reduce the taxiing time of departing aircraft and reduce the fuel consumption and exhaust emissions of the aircraft, Shanghai Hongqiao Airport was taken as an example to study the control strategy for aircraft departure. In this paper, the influence of the number of departure aircraft on the runway utilization rate, the takeoff rate, and the departure rate of flight departures under the conditions of airport runway capacity constraints are studied. The influence of factors, such as the number of departure aircraft, the gate position of the aircraft, and the configuration of airport arrival and departure runways, on the aircraft taxiing time for departure is analyzed. Based on a multivariate linear regression equation, a time prediction model of aircraft departure taxiing time is established. The fuel consumption and pollutant emissions of aircraft are calculated. The experimental results show that, without reducing the utilization rate of the runway and the departure rate of flights, implementing a reasonable pushback number for control of departing aircraft during busy hours can reduce the departure taxiing time of aircraft by nearly 32%, effectively reducing the fuel consumption and pollutant emissions during taxiing on the airport surface. Full article
(This article belongs to the Special Issue Modeling and Simulation of Carbon Emission Related Issues)
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19 pages, 12292 KiB  
Article
Leveraging Hybrid Filter for Improving Quasi-Type-1 Phase Locked Loop Targeting Fast Transient Response
by Yunlu Li, Junyou Yang, Haixin Wang, Weichun Ge and Yiming Ma
Energies 2018, 11(9), 2472; https://doi.org/10.3390/en11092472 - 17 Sep 2018
Cited by 8 | Viewed by 3246
Abstract
In renewable energy generation applications, phase locked loop (PLL) is one of the most popular grid synchronization technique. The main objective of PLL is to rapidly and precisely extract phase and frequency especially when the grid voltage is under non-ideal conditions. This motivates [...] Read more.
In renewable energy generation applications, phase locked loop (PLL) is one of the most popular grid synchronization technique. The main objective of PLL is to rapidly and precisely extract phase and frequency especially when the grid voltage is under non-ideal conditions. This motivates the recent development of moving average filters (MAFs) based PLL in a quasi-type-1 system (i.e., QT1-PLL). Despite its success in certain applications, the transient response is still unsatisfactory, mainly due to the fact that the time delay caused by MAFs is still large. This has significantly limited the utilization of QT1-PLL, according to common grid codes such as German and Spanish grid codes. This challenge has been tackled in this paper. The basic idea is to develop a new hybrid filtering stage, consisting of adaptive notch filters (ANFs) and MAFs, arranged at the inner loop of QT1-PLL. Such an idea can greatly improve the transient response of QT1-PLL, owing to the fact that ANFs are utilized to remove the fundamental frequency negative voltage sequence (FFNS) component while other dominant harmonics can be removed by MAFs with a small time delay. By applying the proposed technique, the settling time is reduced to less than one cycle of grid frequency without any degradation in filtering capability. Moreover, the proposed PLL can be easily expanded to handle dc offset rejection. The effectiveness is validated by comprehensive experiments. Full article
(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems)
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23 pages, 4390 KiB  
Article
Short-Circuit Current Calculation and Harmonic Characteristic Analysis for a Doubly-Fed Induction Generator Wind Turbine under Converter Control
by Jing Li, Tao Zheng and Zengping Wang
Energies 2018, 11(9), 2471; https://doi.org/10.3390/en11092471 - 17 Sep 2018
Cited by 13 | Viewed by 4842
Abstract
An accurate calculation of short-circuit current (SCC) is very important for relay protection setting and optimization design of electrical equipment. The short-circuit current for a doubly-fed induction generator wind turbine (DFIG-WT) under excitation regulation of a converter contains the stator current and grid-side [...] Read more.
An accurate calculation of short-circuit current (SCC) is very important for relay protection setting and optimization design of electrical equipment. The short-circuit current for a doubly-fed induction generator wind turbine (DFIG-WT) under excitation regulation of a converter contains the stator current and grid-side converter (GSC) current. The transient characteristics of GSC current are controlled by double closed-loops of the converter and influenced by fluctuations of direct current (DC) bus voltage, which is characterized as high order, multiple variables, and strong coupling, resulting in great difficulty with analysis. Existing studies are mainly focused on the stator current, neglecting or only considering the steady-state short-circuit current of GSC, resulting in errors in the short-circuit calculation of DFIG-WT. This paper constructs a DFIG-WT total current analytical model involving GSC current. Based on Fourier decomposition of switch functions and the frequency domain analytical method, the fluctuation of DC bus voltage is considered and described in detail. With the proposed DFIG-WT short-circuit current analytical model, the generation mechanism and evolution law of harmonic components are revealed quantitatively, especially the second harmonic component, which has a great influence on transformer protection. The accuracies of the theoretical analysis and mathematical model are verified by comparing calculation results with simulation results and low-voltage ride-through (LVRT) field test data of a real DFIG. Full article
(This article belongs to the Special Issue Modeling of Wind Turbines and Wind Farms)
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10 pages, 4087 KiB  
Article
In Situ Studies on the Characteristics of Strata Structures and Behaviors in Mining of a Thick Coal Seam with Hard Roofs
by Yiwen Lan, Rui Gao, Bin Yu and Xiangbin Meng
Energies 2018, 11(9), 2470; https://doi.org/10.3390/en11092470 - 17 Sep 2018
Cited by 29 | Viewed by 3189
Abstract
The movements of overburden induced by mining a thick coal seam with a hard roof extend widely. The effects of breakages in the hard strata on the strata behaviors might vary with the overlying strata layers. For this reason, we applied a test [...] Read more.
The movements of overburden induced by mining a thick coal seam with a hard roof extend widely. The effects of breakages in the hard strata on the strata behaviors might vary with the overlying strata layers. For this reason, we applied a test method that integrated a borehole TV tester, borehole-based monitoring of strata movement, and monitoring of support resistance for an in situ investigation of a super-thick, 14–20 m coal seam mining in the Datong mining area in China. The results showed that the range of the overburden movement was significantly high, which could reach to more than 300 m. The key strata (KS) in the lower layer main roof were broken into a ‘cantilever beam and voussoir beam’ structure. This structure accounted for the ‘long duration and short duration’ strata behaviors in the working face. On the other hand, the hard KS in the upper layer broke into a ‘high layer structure’. The structural instability induced intensive and wide-ranging strata behaviors that lasted for a long time (two to three days). Support in the working face were over-pressured by large dynamic factors and were widely crushed, while the roadways were violently deformed. Hence, the structure of a thick coal seam with a hard roof after mining will form a ‘cantilever beam and voussoir beam and high layer structure’, which is unique to a large space stope. Full article
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18 pages, 5046 KiB  
Article
Synchronous Resonant Control Technique to Address Power Grid Instability Problems Due to High Renewables Penetration
by Majid Mehrasa, Edris Pouresmaeil, Bahram Pournazarian, Amir Sepehr, Mousa Marzband and João P. S. Catalão
Energies 2018, 11(9), 2469; https://doi.org/10.3390/en11092469 - 17 Sep 2018
Cited by 19 | Viewed by 4939
Abstract
This paper presents a synchronous resonant control strategy based on the inherent characteristics of permanent magnet synchronous generators (PMSG) for the control of power converters to provide stable operating conditions for the power grid under high penetration of renewable energy resources (RERs). The [...] Read more.
This paper presents a synchronous resonant control strategy based on the inherent characteristics of permanent magnet synchronous generators (PMSG) for the control of power converters to provide stable operating conditions for the power grid under high penetration of renewable energy resources (RERs). The proposed control technique is based on the small signal linearization of a dynamic model with grid specifications, load-current-based voltages, and power converter currents. A combination of the linearized dynamic model with the PMSG swing equation and resonant controller leads to a control technique with synchronous features and appropriate inertia for the control of converter-based power generators. As the main contribution of this work, an extra functionality is proposed in the control loop of the proposed model to solve the inherent inconveniences of conventional synchronous generators. Also, a comprehensive collaboration between interfaced converter specifications and PMSG features is achieved as another contribution of the proposed control technique, and this can guarantee accurate performance under various conditions. A current perturbation curve is introduced to assess the variations of the grid frequency and voltage magnitude under operation of the interfaced converters controlled by the proposed control technique. Moreover, by taking into account the load-based voltages, the effects of the current perturbation components are investigated. The proposed model is simulated in MATLAB/Simulink environment to verify the high performance of the proposed control technique over the other existing control methods. Full article
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13 pages, 2295 KiB  
Article
Using Piecewise Linearization Method to PCS Input/Output-Efficiency Curve for a Stand-Alone Microgrid Unit Commitment
by Ha-Lim Lee and Yeong-Han Chun
Energies 2018, 11(9), 2468; https://doi.org/10.3390/en11092468 - 17 Sep 2018
Cited by 4 | Viewed by 3417
Abstract
When operating a stand-alone micro grid, the battery energy storage system (BESS) and a diesel generator are key components needed in order to maintain demand-supply balance. Using Unit Commitment (UC) to calculate the optimal operation schedule of a BESS and diesel generator helps [...] Read more.
When operating a stand-alone micro grid, the battery energy storage system (BESS) and a diesel generator are key components needed in order to maintain demand-supply balance. Using Unit Commitment (UC) to calculate the optimal operation schedule of a BESS and diesel generator helps minimize the operation cost of the micro grid. While calculating the optimal operation schedule for the microgrid, it is important that it reflects the actual characteristics of the implanted devices, in order to increase the schedule result accuracy. In this paper, a piecewise linearization, on the actual power conditioning system (PCS) input/output-efficiency characteristic curve, has been considered while calculating the optimal operation schedule using UC. The optimal schedule result calculated by the proposed method has been examined by comparing the schedule calculated by a fixed input/output-efficiency case, which is conventionally used while solving UC for a stand-alone microgrid. Full article
(This article belongs to the Special Issue Optimization Methods Applied to Power Systems)
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28 pages, 14272 KiB  
Article
Nonlinear Temperature-Dependent State Model of Cylindrical LiFePO4 Battery for Open-Circuit Voltage, Terminal Voltage and State-of-Charge Estimation with Extended Kalman Filter
by Cheng Siong Chin, Zuchang Gao, Joel Hay King Chiew and Caizhi Zhang
Energies 2018, 11(9), 2467; https://doi.org/10.3390/en11092467 - 17 Sep 2018
Cited by 28 | Viewed by 5386
Abstract
Ambient temperature affects the performance of a battery power system and its accuracy in state-of-charge (SOC) estimation for electric vehicles and smart grid systems. This paper proposes a battery model that considered ambient temperature, cell temperature, hysteresis voltage and thermal aging [...] Read more.
Ambient temperature affects the performance of a battery power system and its accuracy in state-of-charge (SOC) estimation for electric vehicles and smart grid systems. This paper proposes a battery model that considered ambient temperature, cell temperature, hysteresis voltage and thermal aging on capacity due to multiple charging and discharging. The SOC is then estimated using an extended Kalman filter. Several forms of validation were tested on an actual cell battery under specific ambient temperatures to verify the battery cell model, terminal voltage and SOC estimation performance. The SOC estimation results show an improvement in root-mean-squared error as compared to Extended Kalman Filter (EKF) without considering the temperature dependency. The proposed battery temperature-dependent model gave a smaller root-mean square error in SOC and terminal voltage at 5 °C, 15 °C and 45 °C. Full article
(This article belongs to the Special Issue 10 Years Energies - Horizon 2028)
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17 pages, 5765 KiB  
Article
An Adaptive Weighted Pearson Similarity Measurement Method for Load Curve Clustering
by Rongheng Lin, Budan Wu and Yun Su
Energies 2018, 11(9), 2466; https://doi.org/10.3390/en11092466 - 17 Sep 2018
Cited by 16 | Viewed by 3910
Abstract
Load curve data from advanced metering infrastructure record the consumers’ behavior. User consumption models help one understand a more intelligent power provisioning and clustering the load data is one of the popular approaches for building these models. Similarity measurements are important in the [...] Read more.
Load curve data from advanced metering infrastructure record the consumers’ behavior. User consumption models help one understand a more intelligent power provisioning and clustering the load data is one of the popular approaches for building these models. Similarity measurements are important in the clustering model, but, load curve data is a time series style data, and traditional measurement methods are not suitable for load curve data. To cluster the load curve data more accurately, this paper applied an enhanced Pearson similarity for load curve data clustering. Our method introduces the ‘trend alteration point’ concept and integrates it with the Pearson similarity. By introducing a weight for Pearson distance, this method helps to keep the whole contour of the load data and the partial similarity. Based on the weighed Pearson distance, a weighed Pearson-based hierarchy clustering algorithm is proposed. Years of load curve data are used for evaluation. Several user consumption models are found and analyzed. Results show that the proposed method improves the accuracy of load data clustering. Full article
(This article belongs to the Collection Smart Grid)
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14 pages, 2972 KiB  
Article
Enhancing Green Building Rating of a School under the Hot Climate of UAE; Renewable Energy Application and System Integration
by Joud Al Dakheel, Kheira Tabet Aoul and Ahmed Hassan
Energies 2018, 11(9), 2465; https://doi.org/10.3390/en11092465 - 17 Sep 2018
Cited by 20 | Viewed by 4678
Abstract
Similar to many fast growing countries, the United Arab Emirates (UAE) witnessed fast population and urbanization growth. The building sector accounts for a major share of its electricity consumption, reaching up to 70%. To encourage sustainable development and reduce energy consumption and emissions, [...] Read more.
Similar to many fast growing countries, the United Arab Emirates (UAE) witnessed fast population and urbanization growth. The building sector accounts for a major share of its electricity consumption, reaching up to 70%. To encourage sustainable development and reduce energy consumption and emissions, the government introduced a sustainability initiative called “Estidama”, which employs the use of the Pearl Building Rating System (PBRS). Government buildings, which constitute 20% of the built environment, aim to lead the way, and are therefore required to attain a high level of achievement, based on their PBRS ranking (minimum of two out of five pearls). Schools, led by Abu Dhabi Educational Council (ADEC), are governmental buildings and aim to attain a higher level of achievement (three out of five pearls). The ADEC plans to build one hundred schools to be built by 2020, through its Future Schools Program. Over half of the schools have been completed, but only 20% reached the targeted rating (of three out of five pearls). The Renewable Energy (RE) application in the UAE is minimal, although it represents 25% of the local rating code. The objective of this paper is to explore the sustainable performance of one representative school that did not reach the desired green rating level, with the objective to assess opportunities for an enhanced performance. This is done through testing the performance and the application of three RE systems comprising of photovoltaics (PV) array, an absorption cooling system and a geothermal cooling system through Transient Systems Simulation (TRNSYS) software. Cumulatively, implementation of these options results in RE potentially contributing to 19% of the school’s annual energy consumption, enhancing the school’s performance by up to 14 additional credit points, and reaching the target level of achievement (a three pearl rating). Furthermore, system integration of RE into the existing school were also considered. Results indicate the significant potential of integrating RE systems in future schools in hot climatic contexts, for an improved energy performance. Full article
(This article belongs to the Section A: Sustainable Energy)
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20 pages, 6418 KiB  
Article
Prediction of Combustion and Heat Release Rates in Non-Premixed Syngas Jet Flames Using Finite-Rate Scale Similarity Based Combustion Models
by Ali Shamooni, Alberto Cuoci, Tiziano Faravelli and Amsini Sadiki
Energies 2018, 11(9), 2464; https://doi.org/10.3390/en11092464 - 17 Sep 2018
Cited by 6 | Viewed by 4449
Abstract
Generating energy from combustion is prone to pollutant formation. In energy systems working under non-premixed combustion mode, rapid mixing is required to increase the heat release rates. However, local extinction and re-ignition may occur, resulting from strong turbulence–chemistry interaction, especially when rates of [...] Read more.
Generating energy from combustion is prone to pollutant formation. In energy systems working under non-premixed combustion mode, rapid mixing is required to increase the heat release rates. However, local extinction and re-ignition may occur, resulting from strong turbulence–chemistry interaction, especially when rates of mixing exceed combustion rates, causing harmful emissions and flame instability. Since the physical mechanisms for such processes are not well understood, there are not yet combustion models in large eddy simulation (LES) context capable of accurately predicting them. In the present study, finite-rate scale similarity (SS) combustion models were applied to evaluate both heat release and combustion rates. The performance of three SS models was a priori assessed based on the direct numerical simulation of a temporally evolving syngas jet flame experiencing high level of local extinction and re-ignition. The results show that SS models following the Bardina’s “grid filtering” approach (A and B) have lower errors than the model based on the Germano’s “test filtering” approach (C), in terms of mean, root mean square (RMS), and local errors. In mean, both Bardina’s based models capture well the filtered combustion and heat release rates. Locally, Model A captures better major species, while Model B retrieves radicals more accurately. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)
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20 pages, 2892 KiB  
Review
An Overview of Direct Current Distribution System Architectures & Benefits
by Venkata Anand Prabhala, Bhanu Prashant Baddipadiga, Poria Fajri and Mehdi Ferdowsi
Energies 2018, 11(9), 2463; https://doi.org/10.3390/en11092463 - 17 Sep 2018
Cited by 64 | Viewed by 9707
Abstract
This paper examines existing and future direct current (DC) distribution systems with a wide range of applications in data centers, telecommunication systems, commercial buildings, residential homes, electric vehicles, spacecraft, and aircrafts. DC distribution systems have many advantages and disadvantages over their alternating current [...] Read more.
This paper examines existing and future direct current (DC) distribution systems with a wide range of applications in data centers, telecommunication systems, commercial buildings, residential homes, electric vehicles, spacecraft, and aircrafts. DC distribution systems have many advantages and disadvantages over their alternating current (AC) counterparts. There are a few surviving examples of DC distribution systems; among them are the telecommunication systems and data centers that use the low-voltage 48 Vdc systems. However, recently, there has been a move towards higher DC bus voltages. In this paper, a comparative study of different DC distribution architectures and bus structures is presented and voltage level selection is discussed for maximizing system efficiency and reliability, reducing system costs, and increasing the flexibility of the system for future expansion. Furthermore, DC distribution systems are investigated from a safety standpoint and the current global market for these distribution systems is also discussed. Full article
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