Energies

28 pages, 5159 KiB

Open AccessArticle

Thermodynamic Evaluation of LiCl-H₂O and LiBr-H₂O Absorption Refrigeration Systems Based on a Novel Model and Algorithm

by Jie Ren, Zuoqin Qian, Zhimin Yao, Nianzhong Gan and Yujia Zhang

Energies 2019, 12(15), 3037; https://doi.org/10.3390/en12153037 - 6 Aug 2019

Cited by 34 | Viewed by 5924

An absorption refrigeration system (ARS) is an alternative to the conventional mechanical compression system for cold production. This study developed a novel calculation model using the Matlab language for the thermodynamic analysis of ARS. It was found to be reliable in LiCl-H₂ [...] Read more.

An absorption refrigeration system (ARS) is an alternative to the conventional mechanical compression system for cold production. This study developed a novel calculation model using the Matlab language for the thermodynamic analysis of ARS. It was found to be reliable in LiCl-H₂O and LiBr-H₂O ARS simulations and the parametric study was performed in detail. Moreover, two 50 kW water-cooled single effect absorption chillers were simply designed to analyze their off-design behaviors. The results indicate that LiCl-H₂O ARS had a higher coefficient of performance (COP) and exergetic efficiency, particularly in the lower generator or higher condenser temperature conditions, but it operated more restrictively due to crystallization. The off-design analyses revealed that the preponderant performance of LiCl-H₂O ARS was mainly due to its better solution properties because the temperature of each component was almost the same for both chillers in the operation. The optimum inlet temperature of hot water for LiCl-H₂O (83 °C) was lower than that of LiBr-H₂O (98 °C). The cooling water inlet temperature should be controlled within 41 °C, otherwise the performances are discounted heavily. The COP and cooling capacity could be improved by increasing the temperature of hot water or chilled water properly, contrary to the exergetic efficiency. Full article

(This article belongs to the Special Issue Refrigeration Systems and Applications 2019)

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15 pages, 3194 KiB

Open AccessArticle

Experimental Testing of Hydrophobic Microchannels, with and without Nanofluids, for Solar PV/T Collectors

by Mahdi Motamedi, Chia-Yang Chung, Mehdi Rafeie, Natasha Hjerrild, Fan Jiang, Haoran Qu and Robert A. Taylor

Energies 2019, 12(15), 3036; https://doi.org/10.3390/en12153036 - 6 Aug 2019

Cited by 14 | Viewed by 4198

Abstract

Solar energy can be converted into useful energy via photovoltaic cells or with a photothermal absorber. While these technologies are well-developed and commercially viable, significant benefits can be realised by pulling these two technologies together in photovoltaic/thermal (PV/T) systems which can provide both [...] Read more.

Solar energy can be converted into useful energy via photovoltaic cells or with a photothermal absorber. While these technologies are well-developed and commercially viable, significant benefits can be realised by pulling these two technologies together in photovoltaic/thermal (PV/T) systems which can provide both heat and electricity from a single collector. Emerging configurations in the PV/T field aim to incorporate micro and/or nanotechnology to boost total solar utilisation even further. One example of this is the nanofluid-based PV/T collector. This type of solar collector utilises nanofluids—suspensions of nanoparticles in traditional heat transfer fluids—as both an optical filter and as a thermal absorber. This concept seeks to harvest the whole solar spectrum at its highest thermodynamic potential through specially engineered nanofluids which transmit the portion of solar spectrum corresponding to the PV response curve while absorbing the rest as heat. Depending on the nanoparticle concentration, employing nanofluids in a flowing system may come with a price—an efficiency penalty in the form of increased pumping power (due to increased viscosity). Similarly, microchannel-based heat exchangers have been shown to increase heat transfer, but they may also pay the price of high pumping power due to additional wall-shear-related pressure drop (i.e., more no-slip boundary area). To develop a novel PV/T configuration which pulls together the advantages of these micro and nanotechnologies with minimal pumping power requirements, the present study experimentally investigated the use of nanofluids in patterned hydrophobic microchannels. It was found that slip with the walls reduced the impact of the increased viscosity of nanofluids by reducing the pressure drop on average 17% relative to a smooth channel. In addition, flowing a selective Ag/SiO₂ core–shell nanofluid over a silicon surface (simulating a PV cell underneath the fluid) provided a 20% increase in solar thermal conversion efficiency and ~3% higher stagnation temperature than using pure water. This demonstrates the potential of this proposed system for extracting more useful energy from the same incident flux. Although no electrical energy was extracted from the underlying patterned silicon, this study highlights potential a new development path for micro and nanotechnology to be integrated into next-generation PV/T solar collectors. Full article

(This article belongs to the Special Issue Hybrid Solar Photovoltaic / Thermal (PVT) Collectors)

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19 pages, 7398 KiB

Open AccessArticle

Effects of Blade Fillet Structures on Flow Field and Surface Heat Transfer in a Large Meridional Expansion Turbine

by Fusheng Meng, Qun Zheng and Jian Zhang

Energies 2019, 12(15), 3035; https://doi.org/10.3390/en12153035 - 6 Aug 2019

Cited by 4 | Viewed by 3807

Abstract

This paper is a continuation of the previous work, aiming to explore the influence of fillet configurations on flow and heat transfer in a large meridional expansion turbine. The endwall of large meridional expansion turbine stator has a large expansion angle, which leads [...] Read more.

This paper is a continuation of the previous work, aiming to explore the influence of fillet configurations on flow and heat transfer in a large meridional expansion turbine. The endwall of large meridional expansion turbine stator has a large expansion angle, which leads to early separation of the endwall boundary layer, resulting in excessive aerodynamic loss and local thermal load. In order to improve the flow state and reduce the local high thermal load, five typical fillet distribution rules are designed. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solver for viscous turbulent flows was used to investigate the different fillet configurations of the second stage stator blades of a 1.5-stage turbine, and which fillet distribution is suitable for large meridional expansion turbines. The influence of fillet structures on the vortex system and loss characteristics was analyzed, and its impact on wall thermal load was studied in detail. The fillet structure mainly affects the formation of horseshoe vortexes at the leading edge of the blade so as to reduce the loss caused by horseshoe vortexes and passage vortexes. The fillet structure suitable for the large meridional expansion turbine was obtained through the research. Reasonable fillet structure distribution can not only improve the flow state but also reduce the high thermal load on the wall surface of the meridional expansion turbine. It has a positive engineering guiding value. Full article

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26 pages, 33473 KiB

Open AccessArticle

A Monocular Vision-Based Framework for Power Cable Cross-Section Measurement

by Xiaoming Zhang and Hui Yin

Energies 2019, 12(15), 3034; https://doi.org/10.3390/en12153034 - 6 Aug 2019

Cited by 2 | Viewed by 4102

Abstract

The measurements of the diameter of different layers, the thickness of different layers and the eccentricity of insulation layer in the cross-section of power cables are important items of power cable test, which currently depend on labor-intensive manual operations. To improve efficiency, automatic [...] Read more.

The measurements of the diameter of different layers, the thickness of different layers and the eccentricity of insulation layer in the cross-section of power cables are important items of power cable test, which currently depend on labor-intensive manual operations. To improve efficiency, automatic measurement methods are in urgent need. In this paper, a monocular vision-based framework for automatic measurement of the diameter, thickness, and eccentricity of interest in the cross-section of power cables is proposed. The proposed framework mainly consists of three steps. In the first step, the images of cable cross-section are captured and undistorted with the camera calibration parameters. In the second step, the contours of each layer are detected in the cable cross-section image. In order to detect the complete and accurate contours of each layer, the structural edges in the cross-section image are firstly detected and divided into individual layers, then unconnected edges are connected by arc-based method, and finally contours are refined by the proposed break detection and grouping (BDG) and linear trend-based correction (LTBC) algorithm. In the third step, the monocular vision-based cross-section dimension measurement is accomplished by placing a chessboard coplanar with the power cable cross-section plane. The homography matrix mapping pixel coordinates to chessboard world coordinates is estimated, and the diameter, thickness and eccentricity of specific layers are calculated by homography matrix-based measurement method. Simulated data and actual cable data are both used to validate the proposed method. The experimental results show that diameter, minimum thickness, mean thickness and insulation eccentricity of simulated image without additive noise are measured with root mean squared error (RMSE) of 0.424, 0.103 and 0.063 mm, and 0.002, respectively, those of simulated image with additive Gaussian noise and salt and pepper noise are measured with RMSE of 0.502, 0.243 and 0.058 mm and 0.001. Diameter, minimum thickness and mean thickness of actual cable images are measured with average RMSE of 0.768, 0.308 and 0.327 mm. The measurement error of insulation eccentricity of actual cable image is comparatively large, and the measurement accuracy should be improved. Full article

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14 pages, 2681 KiB

Open AccessArticle

Improved Performance of a PV Integrated Ventilated Façade at an Existing nZEB

by Ana Tejero-González, Dorota Anna Krawczyk, José Ramón Martín-Sanz García, Francisco Javier Rey-Martínez and Eloy Velasco-Gómez

Energies 2019, 12(15), 3033; https://doi.org/10.3390/en12153033 - 6 Aug 2019

Cited by 5 | Viewed by 3498

Abstract

Ventilated façades are among the existing measures to reduce the energy demand in buildings. The combination of this passive heating and cooling strategy with photovoltaics (PV) can drive new buildings towards the current European targets near or even to net zero energy Buildings [...] Read more.

Ventilated façades are among the existing measures to reduce the energy demand in buildings. The combination of this passive heating and cooling strategy with photovoltaics (PV) can drive new buildings towards the current European targets near or even to net zero energy Buildings (nZEB). The present work studies the thermal behavior of the PV integrated ventilated façade applied in the nZEB known as “LUCIA” (acronym in Spanish for “University Centre to Launch Applied Research”) at the University of Valladolid, Spain. The aim is to evaluate the interest of recirculating indoor air within the façade during winter, as an alternative to the present preferred operating mode during the target season, in which the façade acts as further insulation. First, the radiant properties of the PV façade are measured to use the values in a mathematical model that describes the behavior of the ventilated façade in its current operating mode in winter. Then, the solar radiation available, the air-dry bulb temperatures indoors, outdoors and inside the ventilated façade are monitored to obtain experimental data to validate the model. The results show that air recirculation can entail favorable heat gains during 10% of winter, being this alternative preferable to the present operating mode when outdoor temperatures are over 18.4 °C. Full article

(This article belongs to the Special Issue Innovations-Sustainability-Modernity-Openness in Energy Research 2019)

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13 pages, 3740 KiB

Open AccessArticle

High Step-up Coupled Inductor Inverters Based on qSBIs

by Hongchen Liu, Xi Su and Junxiong Wang

Energies 2019, 12(15), 3032; https://doi.org/10.3390/en12153032 - 6 Aug 2019

Cited by 4 | Viewed by 3202

Abstract

In this paper, two types of high step-up coupled inductor inverters based on qSBIs (quasi- switched boost inverters) are proposed. By applying the coupled inductor to the qSBIs, the voltage gain of the proposed inverter is regulated by turn ratio and duty ratio. [...] Read more.

In this paper, two types of high step-up coupled inductor inverters based on qSBIs (quasi- switched boost inverters) are proposed. By applying the coupled inductor to the qSBIs, the voltage gain of the proposed inverter is regulated by turn ratio and duty ratio. Thus, a high voltage gain can be achieved without the circuits operating at the extreme duty cycle by choosing a suitable turn ratio of the coupled inductor. In addition, the proposed circuits have the characteristics of continuous input current and low voltage stress across the passive components. A boost unit can be added to the proposed inverters for further improvement of the voltage gain. In this paper, the working principle, steady state analysis, and the comparisons of the proposed inverter with other impedance-source inverters are described. A 200 W prototype was created and the experimental results confirm the correctness of the analysis in this paper. Full article

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24 pages, 5463 KiB

Open AccessArticle

Life Cycle Assessment of Fuel Cell Vehicles Considering the Detailed Vehicle Components: Comparison and Scenario Analysis in China Based on Different Hydrogen Production Schemes

by Yisong Chen, Xu Hu and Jiahui Liu

Energies 2019, 12(15), 3031; https://doi.org/10.3390/en12153031 - 6 Aug 2019

Cited by 32 | Viewed by 9444

Abstract

Numerous studies concerning the life cycle assessment of fuel cell vehicles (FCVs) have been conducted. However, little attention has been paid to the life cycle assessment of an FCV from the perspective of the detailed vehicle components. This work conducts the life cycle [...] Read more.

Numerous studies concerning the life cycle assessment of fuel cell vehicles (FCVs) have been conducted. However, little attention has been paid to the life cycle assessment of an FCV from the perspective of the detailed vehicle components. This work conducts the life cycle assessment of Toyota Mirai with all major components considered in a Chinese context. Both the vehicle cycle and the fuel cycle are included. Both comprehensive resources and energy consumption and comprehensive environmental emissions of the life cycles are investigated. Potential environmental impacts are further explored based on CML 2001 method. Then different hydrogen production schemes are compared to obtain the most favorable solution. To explore the potential of the electrolysis, the scenario analysis of the power structure is conducted. The results show that the most mineral resources are consumed in the raw material acquisition stage, the most fossil energy is consumed in the use stage and global warming potential (GWP) value is fairly high in all life cycle stages of Toyota Mirai using electrolyzed hydrogen. For hydrogen production schemes, the scenario analysis indicates that simply by optimizing the power structure, the environmental impact of the electrolysis remains higher than other schemes. When using the electricity from hydropower or wind power, the best choice will be the electrolysis. Full article

(This article belongs to the Section B: Energy and Environment)

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26 pages, 1438 KiB

Open AccessArticle

Load Areas in Radial Unbalanced Distribution Systems

by Giovanni M. Casolino and Arturo Losi

Energies 2019, 12(15), 3030; https://doi.org/10.3390/en12153030 - 6 Aug 2019

Cited by 8 | Viewed by 3096

Abstract

The demand becoming flexible is a requirement for the full exploitation of renewable energy sources. Aggregation may foster the provision of flexibility by small-scale providers connected to distribution grids, since it allows offering significant flexibility volumes to the market. The aggregation of flexibility [...] Read more.

The demand becoming flexible is a requirement for the full exploitation of renewable energy sources. Aggregation may foster the provision of flexibility by small-scale providers connected to distribution grids, since it allows offering significant flexibility volumes to the market. The aggregation of flexibility providers is carried out by the aggregator, a new market role and possibly a new market player. Location information of individual flexibility providers is necessary for both the aggregator and the system operators, in particular, the Distribution System Operator (DSO). For the former, information should allow treating a high number of individual flexibility providers as a single provider to offer significant flexibility volumes to the markets; for the latter, the information should ensure an adequate visibility of the connection of the individual providers to the grid. In the paper, the concept of Load Area (LA) is recalled, which combines the needs of location information of the aggregator and of the DSO. A method for the identification and modeling of LAs for the general case of unbalanced radial systems is proposed. The results of the methods’ application to two studied unbalanced networks are presented, showing the effectiveness and viability of the proposed approach. Full article

(This article belongs to the Special Issue Distribution System Optimization)

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20 pages, 9481 KiB

Open AccessArticle

Reduction of Prediction Errors for the Matrix Converter with an Improved Model Predictive Control

by Shuang Feng, Chaofan Wei and Jiaxing Lei

Energies 2019, 12(15), 3029; https://doi.org/10.3390/en12153029 - 6 Aug 2019

Cited by 10 | Viewed by 2490

Abstract

In this paper, an improved model predictive control (MPC) is proposed for the matrix converter (MC). First, the conventional MPC which adopts the separately discretized prediction models is discussed. It shows that the conventional MPC ignores the input–output interaction in every sampling period. [...] Read more.

In this paper, an improved model predictive control (MPC) is proposed for the matrix converter (MC). First, the conventional MPC which adopts the separately discretized prediction models is discussed. It shows that the conventional MPC ignores the input–output interaction in every sampling period. Consequently, additional prediction errors arise, resulting in more current harmonics. Second, the principle of the improved MPC is presented. With the interaction considered, the integral state-space equation of the whole MC system is constructed and discretized to obtain the precise model. The eigenvalue analysis shows that the proposed prediction model has the same eigenvalues with the continuous model, and thus is more accurate than the conventional one to describe the MC’s behavior in every sampling period. Finally, experimental results under various working conditions prove that the proposed approach can always increase the control accuracy and reduce the harmonic distortions, which in turn requires smaller filter components. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 1586 KiB

Open AccessArticle

Using Biofuels for Highly Renewable Electricity Systems: A Case Study of the Jatropha curcas

by Petr Procházka, Luboš Smutka and Vladimír Hönig

Energies 2019, 12(15), 3028; https://doi.org/10.3390/en12153028 - 6 Aug 2019

Cited by 3 | Viewed by 3904

Abstract

Recent movements for the decarbonization of the electricity sector have become a priority for many countries around the world and will inevitably lead to the sharp decline of fossil-fuel-based energy. Energy from fossil fuels is to be replaced by renewable energy sources (RES), [...] Read more.

Recent movements for the decarbonization of the electricity sector have become a priority for many countries around the world and will inevitably lead to the sharp decline of fossil-fuel-based energy. Energy from fossil fuels is to be replaced by renewable energy sources (RES), although the transition will neither be cheap nor smooth. One sustainable and environmentally friendly alternative to fossil fuels and which will take a considerable share in the increasing supply of renewable energy resources is biofuels. There are various types of biofuels used in practice; however, biodiesels represent one of the most popular and widespread ones. This paper focuses as a case study on the byproducts of Jatropha curcas, a crop and a plant that is already used for biofuel production and which is subsequently employed in electricity generation in Jatropha curcas producing regions. This paper identifies the limitations and prospects of Jatropha curcas utilization. Also, Jatropha curcas is compared to other materials suitable for biomass generation. An economic analysis for a 2 MW biofuel powerplant was conducted incorporating various market-related risks. The study shows that at current prices, net profitability can be achieved using Jatropha curcas byproducts for producing electricity. Full article

(This article belongs to the Special Issue Market Design for a High-Renewables Electricity System)

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13 pages, 2598 KiB

Open AccessArticle

Potential of District Cooling Systems: A Case Study on Recovering Cold Energy from Liquefied Natural Gas Vaporization

by Alice Mugnini, Gianluca Coccia, Fabio Polonara and Alessia Arteconi

Energies 2019, 12(15), 3027; https://doi.org/10.3390/en12153027 - 6 Aug 2019

Cited by 11 | Viewed by 5525

Abstract

District cooling systems (DCSs) are networks able to distribute thermal energy, usually as chilled water, from a central source to industrial, commercial, and residential consumers, to be used for space cooling/dehumidification. As cooling demand will increase significantly in the next decades, DCSs can [...] Read more.

District cooling systems (DCSs) are networks able to distribute thermal energy, usually as chilled water, from a central source to industrial, commercial, and residential consumers, to be used for space cooling/dehumidification. As cooling demand will increase significantly in the next decades, DCSs can be seen as efficient solutions to improve sustainability. Although DCSs are considered so relevant for new city developments, there are still many technical, economic, and social issues to be overcome to let such systems to spread out. Thus, this paper aims to highlight the advantages and issues linked to the adoption of DCSs for building cooling when cold is recovered from a specific application. A case study based on liquified natural gas (LNG) cold energy recovery from the transport sector is presented. Starting from the estimation of the free cooling availability, a DCS design method is proposed and the potential energy saving is investigated. Results show that a DCS using the cold waste derived from LNG can provide a relevant amount of electricity saving (about 60%) for space cooling compared to traditional solutions, in which standard air conditioning systems are installed in every building. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues)

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25 pages, 6872 KiB

Open AccessArticle

Multi-Objective Optimization of Off-Grid Hybrid Renewable Energy Systems in Buildings with Prior Design-Variable Screening

by Paolo Conti, Giovanni Lutzemberger, Eva Schito, Davide Poli and Daniele Testi

Energies 2019, 12(15), 3026; https://doi.org/10.3390/en12153026 - 6 Aug 2019

Cited by 18 | Viewed by 3887

Abstract

This work presents an optimization strategy and the cost-optimal design of an off-grid building served by an energy system involving solar technologies, thermal and electrochemical storages. Independently from the multi-objective method (e.g., utility function) and algorithm used (e.g., genetic algorithms), the optimization of [...] Read more.

This work presents an optimization strategy and the cost-optimal design of an off-grid building served by an energy system involving solar technologies, thermal and electrochemical storages. Independently from the multi-objective method (e.g., utility function) and algorithm used (e.g., genetic algorithms), the optimization of this kind of systems is typically characterized by a high-dimensional variables space, computational effort and results uncertainty (e.g., local minimum solutions). Instead of focusing on advanced optimization tools to handle the design problem, the dimension of the full problem has been reduced, only considering the design variables with a high “effect” on the objective functions. An off-grid accommodation building is presented as test case: the original six-variable design problem consisting of about 300,000 possible configurations is reduced to a two-variable problem, after the analysis of 870 Monte Carlo simulations. The new problem includes only 220 possible design alternatives with a clear benefit for the multi-objective optimization algorithm. The energy-economy Pareto frontiers obtained by the original and the reduced problems overlap, showing the validity of the proposed methodology. The No-RES (no renewable energy sources) primary energy consumption can be reduced up to almost 0 kWh/(m²yr) and the net present value (NPV) after 20 years can reach 70 k€ depending on the number of photovoltaic panels and electrochemical storage size. The reduction of the problem also allows for a plain analysis of the results and the drawing of handy decision charts to help the investor/designer in finding the best design according to the specific investment availability and target performances. The configurations on the Pareto frontier are characterized by a notable electrical overproduction and a ratio between the two main design variables that goes from 4 to 8 h. A sensitivity analysis to the unitary price of the electrochemical storage reveals the robustness of the sizing criterion. Full article

(This article belongs to the Special Issue Solar Thermal Energy Storage and Conversion)

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17 pages, 10414 KiB

Open AccessArticle

Electric Vehicle Battery Simulation System for Mobile Field Test of Off-Board Charger

by Xiangwu Yan, Ling Wang, Zhichao Chai, Shuaishuai Zhao, Zisheng Liu and Xuewei Sun

Energies 2019, 12(15), 3025; https://doi.org/10.3390/en12153025 - 6 Aug 2019

Cited by 3 | Viewed by 3314

Abstract

An electric vehicle power battery simulation system simulating different power battery packs for the field test of the off-board charger is designed, which can be used to test the performance of an off-board charger. Specifically, the improved power battery model is combined with [...] Read more.

An electric vehicle power battery simulation system simulating different power battery packs for the field test of the off-board charger is designed, which can be used to test the performance of an off-board charger. Specifically, the improved power battery model is combined with the improved lightweight charging load and the online estimation of the state of charge as well as the electromotive force of the battery model are used to adjust charging load parameters in real time to simulate the charging response. An acceleration coefficient is introduced into the traditional battery model to improve test efficiency, and the type, specification, temperature and voltage parameters of the battery can be set online according to the test requirements. An improved charging load scheme is proposed, in which a DC converter cascaded power battery pack of the mobile test vehicle is used to form a lightweight charging load with the mode of constant voltage, constant current, constant power and constant resistance and the ability to be adjusted continuously within the rated range. As a result, the size and weight of the charging load are reduced and the autonomous test of the off-board charger is realized. The performances of the proposed battery simulation system are validated through the various experimental results. Full article

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24 pages, 8807 KiB

Open AccessArticle

A Control Strategy for Smooth Power Tracking of a Grid-Connected Virtual Synchronous Generator Based on Linear Active Disturbance Rejection Control

by Yaya Zhang, Jianzhong Zhu, Xueyu Dong, Pinchao Zhao, Peng Ge and Xiaolian Zhang

Energies 2019, 12(15), 3024; https://doi.org/10.3390/en12153024 - 6 Aug 2019

Cited by 8 | Viewed by 3525

Abstract

The power quality of new energy resources has received tremendous attention recently. The control approach for the inverter, an interface between the new energy resources, and the infinite bus system is of vital importance. For the virtual synchronous generator (VSG), one of the [...] Read more.

The power quality of new energy resources has received tremendous attention recently. The control approach for the inverter, an interface between the new energy resources, and the infinite bus system is of vital importance. For the virtual synchronous generator (VSG), one of the research hotspots in the inverter control field, there are some challenges remaining to be dealt with. First is the contradiction between the rapid response and overshoot of active power output if VSG is connected to the grid. Secondly, the active power is deeply influenced by the fluctuation of gird frequency and this may bring power oscillation to VSG in weak grids. In this article, an active power controller for power tracking of grid-connected VSG is designed based on linear active disturbance rejection control (LADRC) by compensating for the lumped disturbance in a feedforward fashion. The parameters of the controller are analyzed and tuned in the frequency domain to acquire a desirable control performance. Moreover, the robustness of the control system is also considered. Simulation results show that the designed control system can transmit active power to the grid in a timely manner with no overshoot, as demanded. Additionally, it can output active power steadily according to the power reference without using a phase-locked loop (PLL) when the grid frequency has different features of fluctuation. In addition, the simulation results demonstrate that the improved VSG has strong robustness to the model parameter perturbation and mismatch. Full article

(This article belongs to the Special Issue Control Strategies for Power Conversion Systems)

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11 pages, 3774 KiB

Open AccessArticle

Analysis of the Effect of the Variable Charging Current Control Method on Cycle Life of Li-ion Batteries

by In-Ho Cho, Pyeong-Yeon Lee and Jong-Hoon Kim

Energies 2019, 12(15), 3023; https://doi.org/10.3390/en12153023 - 6 Aug 2019

Cited by 42 | Viewed by 7931

Abstract

Applications of rechargeable batteries have recently expanded from small information technology (IT) devices to a wide range of other industrial sectors, including vehicles, rolling stocks, and energy storage system (ESS), as a part of efforts to reduce greenhouse gas emissions and enhance convenience. [...] Read more.

Applications of rechargeable batteries have recently expanded from small information technology (IT) devices to a wide range of other industrial sectors, including vehicles, rolling stocks, and energy storage system (ESS), as a part of efforts to reduce greenhouse gas emissions and enhance convenience. The capacity of rechargeable batteries adopted in individual products is meanwhile increasing and the price of the batteries in such products has become an important factor in determining the product price. In the case of electric vehicles, the price of batteries has increased to more than 40% of the total product cost. In response, various battery management technologies are being studied to increase the service life of products with large-capacity batteries and reduce maintenance costs. In this paper, a charging algorithm to increase the service life of batteries is proposed. The proposed charging algorithm controls charging current in anticipation of heating inside the battery while the battery is being charged. The validity of the proposed charging algorithm is verified through an experiment to compare charging cycles using high-capacity type lithium-ion cells and high-power type lithium-ion cells. Full article

(This article belongs to the Special Issue Energy Storage and Management for Electric Vehicles)

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16 pages, 2875 KiB

Open AccessArticle

A Voltage-Based Approach for Series High Impedance Fault Detection and Location in Distribution Systems Using Smart Meters

by Francinei L. Vieira, Pedro H. M. Santos, José M. Carvalho Filho, Roberto C. Leborgne and Marino P. Leite

Energies 2019, 12(15), 3022; https://doi.org/10.3390/en12153022 - 6 Aug 2019

Cited by 15 | Viewed by 5124

Abstract

High impedance faults (HIFs) have been a major concern for protecting distribution systems and public safety hazards when involving downed conductors. The deployment of smarter grids brings new technologies for smart monitoring, automation, and protection of distribution networks. This paper presents a new [...] Read more.

High impedance faults (HIFs) have been a major concern for protecting distribution systems and public safety hazards when involving downed conductors. The deployment of smarter grids brings new technologies for smart monitoring, automation, and protection of distribution networks. This paper presents a new method for a series of HIF detection and location in primary distribution feeders, using voltage unbalance measurements collected from smart meters (SMs) installed at low-voltage end-users. The methodology was tested in MATLAB and Simulink through steady-state simulations of a typical 13.8 kV distribution system, under load unbalance and different fault scenarios. Results show that the proposed method is robust and accurate for the detection of blown fuses and broken conductors, with or without ground faults, located either at the source or the load-side. The ease of implementation in SM design, formulation of parameters, and reliable simulation results show potential real-life applications. Full article

(This article belongs to the Special Issue Fault Diagnosis on MV and HV Transmission Lines)

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18 pages, 2283 KiB

Open AccessArticle

Resource Security Strategies and Their Environmental and Economic Implications: A Case Study of Copper Production in Japan

by Ran Motoori, Benjamin McLellan, Andrew Chapman and Tetsuo Tezuka

Energies 2019, 12(15), 3021; https://doi.org/10.3390/en12153021 - 6 Aug 2019

Cited by 8 | Viewed by 4166

Abstract

Japan is a nation which is highly dependent on the import of raw materials to supply its manufacturing industry, notable among them copper. When extracting copper from ore, a large amount of energy is required, typically leading to high levels of CO₂ [...] Read more.

Japan is a nation which is highly dependent on the import of raw materials to supply its manufacturing industry, notable among them copper. When extracting copper from ore, a large amount of energy is required, typically leading to high levels of CO₂ emissions due to the fossil fuel-dominated energy mix. Moreover, maintaining security of raw material supply is difficult if imports are the only source utilized. This study examines the environmental and economic impacts of domestic mineral production from the recycling of end-of-life products and deep ocean mining as strategies to reduce CO₂ emissions and enhance security of raw material supplies. The results indicate that under the given assumptions, recycling, which is typically considered to be less CO₂ intensive, produces higher domestic emissions than current copper processing, although across the whole supply chain shows promise. As the total quantity of domestic resources from deep ocean ores are much smaller than the potential from recycling, it is possible that recycling could become a mainstream supply alternative, while deep ocean mining is more likely to be a niche supply source. Implications of a progressively aging society and flow-on impacts for the recycling sector are discussed. Full article

(This article belongs to the Special Issue Advances in Low Carbon Technologies and Transition)

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22 pages, 1285 KiB

Open AccessReview

Green, Yellow, and Woody Biomass Supply-Chain Management: A Review

by Efthymios Rodias, Remigio Berruto, Dionysis Bochtis, Alessandro Sopegno and Patrizia Busato

Energies 2019, 12(15), 3020; https://doi.org/10.3390/en12153020 - 6 Aug 2019

Cited by 13 | Viewed by 3909

Abstract

Various sources of biomass contribute significantly in energy production globally given a series of constraints in its primary production. Green biomass sources (such as perennial grasses), yellow biomass sources (such as crop residues), and woody biomass sources (such as willow) represent the three [...] Read more.

Various sources of biomass contribute significantly in energy production globally given a series of constraints in its primary production. Green biomass sources (such as perennial grasses), yellow biomass sources (such as crop residues), and woody biomass sources (such as willow) represent the three pillars in biomass production by crops. In this paper, we conducted a comprehensive review on research studies targeted to advancements at biomass supply-chain management in connection to these three types of biomass sources. A framework that classifies the works in problem-based and methodology-based approaches was followed. Results show the use of modern technological means and tools in current management-related problems. From the review, it is evident that the presented up-to-date trends on biomass supply-chain management and the potential for future advanced approach applications play a crucial role on business and sustainability efficiency of biomass supply chain. Full article

(This article belongs to the Special Issue Supply Chain Management for Bioenergy and Bioresources)

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27 pages, 54641 KiB

Open AccessFeature PaperArticle

A Multi-Agent Social Gamification Model to Guide Sustainable Urban Photovoltaic Panels Installation Policies

by Robert Olszewski, Piotr Pałka, Agnieszka Wendland and Jacek Kamiński

Energies 2019, 12(15), 3019; https://doi.org/10.3390/en12153019 - 6 Aug 2019

Cited by 8 | Viewed by 3736

Abstract

The paper presents a holistic and quantitative model of social gamification in a smart city, which is likely to stimulate the photovoltaic panels installation. The coupling of multi-agent systems, GIS tools, demographic data, and a spatial knowledge base made it possible to develop [...] Read more.

The paper presents a holistic and quantitative model of social gamification in a smart city, which is likely to stimulate the photovoltaic panels installation. The coupling of multi-agent systems, GIS tools, demographic data, and a spatial knowledge base made it possible to develop and calibrate a computable model of social interaction in a “model smart city,” as well as to quantitatively evaluate the deployment of photovoltaic panels. It also enabled the analysis of factors affecting the efficiency of this process, e.g., the photovoltaic potential of solar roofs, the ownership of buildings, the type of building development, the level of social trust, institutional and social incentives, and the development of an information society. The devised model is tested on the city of Warsaw, utilizing spatial and descriptive data provided by city authorities. Full article

(This article belongs to the Special Issue Approaches, Advances and Applications in Sustainable Development of Smart Cities )

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14 pages, 2954 KiB

Open AccessArticle

Empirical Conductivity Equation for the Simulation of the Stationary Space Charge Distribution in Polymeric HVDC Cable Insulations

by Christoph Jörgens and Markus Clemens

Energies 2019, 12(15), 3018; https://doi.org/10.3390/en12153018 - 5 Aug 2019

Cited by 2 | Viewed by 3518

Abstract

Many processes are involved in the accumulation of space charges within the insulation materials of high voltage direct current (HVDC) cables, e.g., the local electric field, a conductivity gradient inside the insulation, and the injection of charges at both electrodes. An accurate description [...] Read more.

Many processes are involved in the accumulation of space charges within the insulation materials of high voltage direct current (HVDC) cables, e.g., the local electric field, a conductivity gradient inside the insulation, and the injection of charges at both electrodes. An accurate description of the time dependent charge distribution needs to include these effects. Furthermore, using an explicit Euler method for the time integration of a suitably formulated transient model, low time steps are used to resolve fast charge dynamics and to satisfy the Courant–Friedrichs–Lewy (CFL) stability condition. The long lifetime of power cables makes the use of a final stationary charge distribution necessary to assess the reliability of the cable insulations. For an accurate description of the stationary space charge and electric field distribution, an empirical conductivity equation is developed. The bulk conductivity, found in literature, is extended with two sigmoid functions to represent a conductivity gradient near the electrodes. With this extended conductivity equation, accumulated bulk space charges and hetero charges are simulated. New introduced constants to specify the sigmoid functions are determined by space charge measurements, taken from the literature. The measurements indicate accumulated hetero charges in about one quarter of the insulation thickness in the vicinity of both electrodes. The simulation results conform well to published measurements and show an improvement to previously published models, i.e., the developed model shows a good approximation to simulate the stationary bulk and hetero charge distribution. Full article

(This article belongs to the Special Issue Selected Papers from 2018 IEEE International Conference on High Voltage Engineering (ICHVE 2018))

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9 pages, 202 KiB

Open AccessEditorial

Special Issue “Intelligent Control in Energy Systems”

by Anastasios Dounis

Energies 2019, 12(15), 3017; https://doi.org/10.3390/en12153017 - 5 Aug 2019

Cited by 5 | Viewed by 3327

Abstract

The editor of this special issue on “Intelligent Control in Energy Systems” have made an attempt to publish a book containing original technical articles addressing various elements of intelligent control in energy systems. The response to our call had 60 submissions, of which [...] Read more.

The editor of this special issue on “Intelligent Control in Energy Systems” have made an attempt to publish a book containing original technical articles addressing various elements of intelligent control in energy systems. The response to our call had 60 submissions, of which 27 were published submissions and 33 were rejections. This book contains 27 technical articles and one editorial. All have been written by authors from 15 countries (China, Netherlands, Spain, Tunisia, United States of America, Korea, Brazil, Egypt, Denmark, Indonesia, Oman, Canada, Algeria, Mexico, and Czech Republic), which elaborated several aspects of intelligent control in energy systems. It covers a broad range of topics including fuzzy PID in automotive fuel cell and MPPT tracking, neural network for fuel cell control and dynamic optimization of energy management, adaptive control on power systems, hierarchical Petri Nets in microgrid management, model predictive control for electric vehicle battery and frequency regulation in HVAC systems, deep learning for power consumption forecasting, decision tree for wind systems, risk analysis for demand side management, finite state automata for HVAC control, robust μ-synthesis for microgrid, and neuro-fuzzy systems in energy storage. Full article

(This article belongs to the Special Issue Intelligent Control in Energy Systems)

17 pages, 4515 KiB

Open AccessArticle

Mining-Induced Failure Criteria of Interactional Hard Roof Structures: A Case Study

by Wenlong Shen, Meng Wang, Zhengzheng Cao, Faqiang Su, Hua Nan and Xuelong Li

Energies 2019, 12(15), 3016; https://doi.org/10.3390/en12153016 - 5 Aug 2019

Cited by 18 | Viewed by 3317

Abstract

Due to the additional abutment stress, interactional hard roof structures (IHRS) affect the normal operation of the coal production system in underground mining. The movement of IHRS may result in security problems, such as the failure of supporting body, large deformation, and even [...] Read more.

Due to the additional abutment stress, interactional hard roof structures (IHRS) affect the normal operation of the coal production system in underground mining. The movement of IHRS may result in security problems, such as the failure of supporting body, large deformation, and even roof caving for nearby openings. According to the physical configuration and loading conditions of IHRS in a simple two-dimensional physical model under the plane stress condition, mining-induced failure criteria were proposed and validated by the mechanical behavior of IHRS in a mechanical analysis model. The results indicate that IHRS, consisting of three interactional parts—the lower key structure, the middle soft interlayer, and the upper key structure—are governed by the additional abutment stress induced by the longwall mining working face. The fracture of the upper key structure in IHRS can be explained as follows: Due to the crushing failure, lower key structure, and middle soft interlayer yield, the action force between the upper and lower key structures vanishes, resulting in fracture of the upper key structure in IHRS. In a field case, when additional abutment stress reaches 7.37 MPa, the energy of 2.35 × 10⁵ J is generated by the fracture of the upper key structure in IHRS. Under the same geological and engineering conditions, the energy generated by IHRS is much larger than that generated by a single hard roof. The mining-induced failure criteria are successfully applied in a field case. The in-situ mechanical behavior of the openings nearby IHRS under the mining abutment stress can be clearly explained by the proposed criteria. Full article

(This article belongs to the Section L: Energy Sources)

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21 pages, 1269 KiB

Open AccessArticle

Economic Health-Aware LPV-MPC Based on System Reliability Assessment for Water Transport Network

by Fatemeh Karimi Pour, Vicenç Puig and Gabriela Cembrano

Energies 2019, 12(15), 3015; https://doi.org/10.3390/en12153015 - 5 Aug 2019

Cited by 10 | Viewed by 3578

Abstract

This paper proposes a health-aware control approach for drinking water transport networks. This approach is based on an economic model predictive control (MPC) that considers an additional goal with the aim of extending the components and system reliability. The components and system reliability [...] Read more.

This paper proposes a health-aware control approach for drinking water transport networks. This approach is based on an economic model predictive control (MPC) that considers an additional goal with the aim of extending the components and system reliability. The components and system reliability are incorporated into the MPC model using a Linear Parameter Varying (LPV) modeling approach. The MPC controller uses additionally an economic objective function that determines the optimal filling/emptying sequence of the tanks considering that electricity price varies between day and night and that the demand also follows a 24-h repetitive pattern. The proposed LPV-MPC control approach allows considering the model nonlinearities by embedding them in the parameters. The values of these varying parameters are updated at each iteration taking into account the new values of the scheduling variables. In this way, the optimization problem associated with the MPC problem is solved by means of Quadratic Programming (QP) to avoid the use of nonlinear programming. This iterative approach reduces the computational load compared to the solution of a nonlinear optimization problem. A case study based on the Barcelona water transport network is used for assessing the proposed approach performance. Full article

(This article belongs to the Special Issue Approaches, Advances and Applications in Sustainable Development of Smart Cities )

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22 pages, 9008 KiB

Open AccessArticle

Impact of Electrically Assisted Turbocharger on the Intake Oxygen Concentration and Its Disturbance Rejection Control for a Heavy-duty Diesel Engine

by Chao Wu, Kang Song, Shaohua Li and Hui Xie

Energies 2019, 12(15), 3014; https://doi.org/10.3390/en12153014 - 5 Aug 2019

Cited by 7 | Viewed by 4256

Abstract

The electrically assisted turbocharger (EAT) shows promise in simultaneously improving the boost response and reducing the fuel consumption of engines with assist. In this paper, experimental results show that 7.8% fuel economy (FE) benefit and 52.1% improvement in transient boost response can be [...] Read more.

The electrically assisted turbocharger (EAT) shows promise in simultaneously improving the boost response and reducing the fuel consumption of engines with assist. In this paper, experimental results show that 7.8% fuel economy (FE) benefit and 52.1% improvement in transient boost response can be achieved with EAT assist. EAT also drives the need for a new feedback variable for the air system control, instead of the exhaust recirculation gas (EGR) rate that is widely used in conventional turbocharged engines (nominal system). Steady-state results show that EAT assist allows wider turbine vane open and reduces pre-turbine pressure, which in turn elevates the engine volumetric efficiency hence the engine air flow rate at fixed boost pressure. Increased engine air flow rate, together with the reduced fuel amount necessary to meet the torque demand with assist, leads to the increase of the oxygen concentration in the exhaust gas (EGR gas dilution). Additionally, transient results demonstrate that the enhanced air supply from the compressor and the diluted EGR gas result in a spike in the oxygen concentration in the intake manifold (X_oim) during tip-in, even though there is no spike in the EGR rate response profile. Consequently, there is Nitrogen Oxides (NOx) emission spike, although the response of boost pressure and EGR rate is smooth (no spike is seen). Therefore, in contrast to EGR rate, X_oim is found to be a better choice for the feedback variable. Additionally, a disturbance observer-based X_oim controller is developed to attenuate the disturbances from the turbine vane position variation. Simulation results on a high-fidelity GT-SUTIE model show over 43% improvement in disturbance rejection capability in terms of recovery time, relative to the conventional proportional-integral-differential (PID) controller. This X_oim-based disturbance rejection control solution is beneficial in the practical application of the EAT system. Full article

(This article belongs to the Special Issue Internal Combustion Engines Improving Performance, Fuel Economy and Emissions)

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21 pages, 8310 KiB

Open AccessArticle

Simultaneous Inertia Contribution and Optimal Grid Utilization with Wind Turbines

by Clemens Jauch and Arne Gloe

Energies 2019, 12(15), 3013; https://doi.org/10.3390/en12153013 - 5 Aug 2019

Cited by 7 | Viewed by 3751

Abstract

This paper presents findings of a study on continuous feed-in management and continuous synthetic inertia contribution with wind turbines. A realistic case study, based on real measurements, is outlined. A wind turbine feeds into a weak feeder, such that its power has to [...] Read more.

This paper presents findings of a study on continuous feed-in management and continuous synthetic inertia contribution with wind turbines. A realistic case study, based on real measurements, is outlined. A wind turbine feeds into a weak feeder, such that its power has to be adapted to the permissible loading of this feeder. At the same time the wind turbine is to provide inertia to the grid by applying the previously published variable inertia constant controller. It is discussed that optimal grid utilization and simultaneous inertia contribution are mandatory for the frequency control in power systems that are heavily penetrated with renewable energies. The study shows that continuous feed-in management can be combined well with continuous inertia provision. There are hardly any negative consequences for the wind turbine. The benefits for the grid are convincing, both in terms of increased system utilization and in terms of provided inertia. It is concluded that wind turbines can enhance angular stability in a power system to a larger extent than conventional power plants. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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20 pages, 5510 KiB

Open AccessArticle

Island DC Microgrid Hierarchical Coordinated Multi-Mode Control Strategy

by Zhongbin Zhao, Jing Zhang, Yu He and Ying Zhang

Energies 2019, 12(15), 3012; https://doi.org/10.3390/en12153012 - 5 Aug 2019

Cited by 8 | Viewed by 3905

Abstract

As renewable energy sources connecting to power systems continue to improve and new-type loads, such as electric vehicles, grow rapidly, direct current (DC) microgrids are attracting great attention in distribution networks. In order to satisfy the voltage stability requirements of island DC microgrids, [...] Read more.

As renewable energy sources connecting to power systems continue to improve and new-type loads, such as electric vehicles, grow rapidly, direct current (DC) microgrids are attracting great attention in distribution networks. In order to satisfy the voltage stability requirements of island DC microgrids, the problem of inaccurate load power dispatch caused by line resistance must be solved and the defects of centralized communication and control must be overcome. A hierarchical, coordinated, multiple-mode control strategy based on the switch of different operation modes is proposed in this paper and a three-layer control structure is designed for the control strategy. Based on conventional droop control, a current-sharing layer and a multi-mode switching layer are used to ensure the stable operation of the DC microgrid. Accurate load power dispatch is satisfied using a difference discrete consensus algorithm. Furthermore, virtual bus voltage information is applied to guarantee smooth switching between various modes, which safeguards voltage stability. Simulation verification is carried out for the proposed control strategy by power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC). The results indicate that the proposed control strategy guarantees the voltage stability of island DC microgrids and accurate load power dispatch under different operation modes. Full article

(This article belongs to the Special Issue Clean Energy Microgrids)

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22 pages, 2423 KiB

Open AccessReview

Mapping Knowledge in the Economic Areas of Green Building Using Scientometric Analysis

by Xue Xiao, Martin Skitmore, Heng Li and Bo Xia

Energies 2019, 12(15), 3011; https://doi.org/10.3390/en12153011 - 5 Aug 2019

Cited by 39 | Viewed by 4541

Abstract

This paper presents the first inclusive scientometric review of the economic areas of green building (GBE). The aim is to methodically examine and summarize the state-of-the-art of the GBE body of knowledge. To this end, this study analyses 1713 GBE-related bibliographic records retrieved [...] Read more.

This paper presents the first inclusive scientometric review of the economic areas of green building (GBE). The aim is to methodically examine and summarize the state-of-the-art of the GBE body of knowledge. To this end, this study analyses 1713 GBE-related bibliographic records retrieved from the Web of Science by using the quantitative method of knowledge mapping. The knowledge base, knowledge domain, and knowledge evolution of how they interacted with each other are explored using document co-citation analysis and keywords co-citation analysis of the existing body of literature. The research findings are informative in recognizing and interpreting the underlying structure and trends in GBE. A knowledge map provides a valuable and instructive understanding of the evolution and status quo of the GBE knowledge body, as well as assisting in recognizing the gaps and deficiencies involved. The results will help in understanding how GBE knowledge is evolving and its role played in green building, and thus provide suggestions of how academic research can enhance sustainability practices in terms of economic area in the future. Full article

(This article belongs to the Special Issue Economic Development and Energy Policy)

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15 pages, 3881 KiB

Open AccessArticle

Distribution of the Strip Tensions with Slip Control in Strip Processing Lines

by Daniel Magura, Karol Kyslan, Sanjeevikumar Padmanaban and Viliam Fedák

Energies 2019, 12(15), 3010; https://doi.org/10.3390/en12153010 - 4 Aug 2019

Cited by 5 | Viewed by 4984

Abstract

The control of tension in processing lines for metal strips tackles several problems. The process of achieving high tension driven by a multi-motor drive system, where the motors are mechanically coupled by a strip, is affected by the maximal torque of each drive, [...] Read more.

The control of tension in processing lines for metal strips tackles several problems. The process of achieving high tension driven by a multi-motor drive system, where the motors are mechanically coupled by a strip, is affected by the maximal torque of each drive, by friction between the strip and the surface of the tension roll, and by the wrap angle. The friction itself and the wrap angle are described by the e^µα factor, which can be also calculated as the ratio of tensions in the strip in the previous section and subsequent section of the multi-motor drive. In this paper, an algorithm for the proper distribution of tensions in the strip for a multi-motor drive system of a continuous processing line is revealed. The algorithm ensures the tension distribution among particular drives of the tension leveler while respecting the physical limits of the drives and also preserving the desired conditions of a constant ratio between the input and output tensions for all drives in the leveler. The algorithm also prevents overloading of the drives. Finally, the algorithm was implemented in a control system of a strip processing line, and the obtained results correspond with the simulations. This, in turn, confirms the correctness of the algorithm design. Full article

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21 pages, 13054 KiB

Open AccessArticle

Control Technology of Soft Rock Floor in Mining Roadway with Coal Pillar Protection: A case study

by Housheng Jia, Luyao Wang, Kai Fan, Bo Peng and Kun Pan

Energies 2019, 12(15), 3009; https://doi.org/10.3390/en12153009 - 4 Aug 2019

Cited by 23 | Viewed by 3124

Abstract

This study considered the mining roadway with coal pillar protection in the fully mechanized caving face of the Dananhu No.1 Coal Mine, China. Theoretical analysis, numerical simulation, and field tests were conducted, and the stress environment, deformation, and failure characteristics of the mining [...] Read more.

This study considered the mining roadway with coal pillar protection in the fully mechanized caving face of the Dananhu No.1 Coal Mine, China. Theoretical analysis, numerical simulation, and field tests were conducted, and the stress environment, deformation, and failure characteristics of the mining roadway in the fully mechanized caving face were analyzed. The results revealed that the intrinsic cause for the large asymmetrical floor deformation in the mining roadway is the asymmetrical phenomenon of the surrounding rock’s stress environment, caused by mining. This also results in the non-uniform distribution of the mining roadway floor’s plastic zone. The degree of asymmetrical floor heave is internally related to the thickness of the caving coal. When the thickness of the caving coal was in the range of 5.9 m, the deformation of the asymmetrical floor heave, caused by the plastic failure in the floor, became more obvious as certain parameters increased. As the rotation angle of the principal stress direction increased, the maximum plastic failure depth position of the floor gradually moved toward the middle of the roadway. This caused a different distribution for the maximum deformation position. The control of the floor heave deformation was poor, and it was not feasible to use high-strength support under the existing engineering conditions. Hence, the control should mainly be applied to the floor heave deformation. When the thickness of the caving coal was more than 5.9 m, the main roof strata was prone to instability and being cut along the edge of the coal pillar; the rock stress environment surrounding the roadway tended to revert back to the initial geostress state. The proposed floor heave control strategy achieved good results, and as the deformation of the floor heave decreased, the workload of the floor heave was also greatly reduced. Full article

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27 pages, 3037 KiB

Open AccessArticle

Smart Meter Data-Based Three-Stage Algorithm to Calculate Power and Energy Losses in Low Voltage Distribution Networks

by Gheorghe Grigoras and Bogdan-Constantin Neagu

Energies 2019, 12(15), 3008; https://doi.org/10.3390/en12153008 - 4 Aug 2019

Cited by 21 | Viewed by 4127

Abstract

In this paper, an improved smart meter data-based three-stage algorithm to calculate the power/energy losses in three-phase networks with the voltage level below 0.4 kV (low voltage—LV) is presented. In the first stage, the input data regarding the hourly active and reactive powers [...] Read more.

In this paper, an improved smart meter data-based three-stage algorithm to calculate the power/energy losses in three-phase networks with the voltage level below 0.4 kV (low voltage—LV) is presented. In the first stage, the input data regarding the hourly active and reactive powers of the consumers and producers are introduced. The powers are loaded from the database of the smart metering system (SMS) for the consumers and producers integrated in this system or files containing the characteristic load profiles established by the Distribution Network Operator for the consumers, which have installed the conventional meters non-integrated in the SMS. In the second stage, a function, which is based on the work with the structure vectors, was implemented to easily identify the configuration of analysed networks. In the third stage, an improved version of a forward/backward sweep-based algorithm was proposed to quickly calculate the power/energy losses to three-phase LV distribution networks in a balanced and unbalanced regime. A real LV rural distribution network from a pilot zone belonging to a Distribution Network Operator from Romania was used to confirm the accuracy of the proposed algorithm. The comparison with the results obtained using the DigSilent PowerFactory Simulation Package certified the performance of the algorithm, with the mean absolute percentage error (MAPE) being 0.94%. Full article

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Energies, Volume 12, Issue 15 (August-1 2019) – 197 articles

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