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Energies, Volume 7, Issue 2 (February 2014), Pages 498-1097

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Open AccessEditorial Energies Best Paper Award 2014
Energies 2014, 7(2), 1095-1097; https://doi.org/10.3390/en7021095
Received: 13 February 2014 / Accepted: 19 February 2014 / Published: 24 February 2014
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Abstract
Last year, Energies (ISSN 1996-1073) decided to award a prize to outstanding papers in the area of energy technologies and applications published in Energies. In 2014, the Prize Awarding Committee has decided to also grant awards in the category of “best review
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Last year, Energies (ISSN 1996-1073) decided to award a prize to outstanding papers in the area of energy technologies and applications published in Energies. In 2014, the Prize Awarding Committee has decided to also grant awards in the category of “best review papers”. [...] Full article
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Open AccessArticle Development and Improvement of an Intelligent Cable Monitoring System for Underground Distribution Networks Using Distributed Temperature Sensing
Energies 2014, 7(2), 1076-1094; https://doi.org/10.3390/en7021076
Received: 15 November 2013 / Revised: 4 February 2014 / Accepted: 11 February 2014 / Published: 24 February 2014
Cited by 6 | PDF Full-text (2063 KB) | HTML Full-text | XML Full-text
Abstract
With power systems switching to smart grids, real-time and on-line monitoring technologies for underground distribution power cables have become a priority. Most distribution components have been developed with self-diagnostic sensors to realize self-healing, one of the smart grid functions in a distribution network.
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With power systems switching to smart grids, real-time and on-line monitoring technologies for underground distribution power cables have become a priority. Most distribution components have been developed with self-diagnostic sensors to realize self-healing, one of the smart grid functions in a distribution network. Nonetheless, implementing a real-time and on-line monitoring system for underground distribution cables has been difficult because of high cost and low sensitivity. Nowadays, optical fiber composite power cables (OFCPCs) are being considered for communication and power delivery to cope with the increasing communication load in a distribution network. Therefore, the application of distributed temperature sensing (DTS) technology on OFCPCs used as underground distribution lines is studied for the real-time and on-line monitoring of the underground distribution power cables. Faults can be reduced and operating ampacity of the underground distribution system can be increased. This paper presents the development and improvement of an intelligent cable monitoring system for the underground distribution power system, using DTS technology and OFCPCs as the underground distribution lines in the field. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessEditorial Acknowledgement to Reviewers of Energies in 2013
Energies 2014, 7(2), 1066-1075; https://doi.org/10.3390/en7021066
Received: 24 February 2014 / Accepted: 24 February 2014 / Published: 24 February 2014
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Abstract
The editors of Energies would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...] Full article
Open AccessArticle Influence of Prewhirl Regulation by Inlet Guide Vanes on Cavitation Performance of a Centrifugal Pump
Energies 2014, 7(2), 1050-1065; https://doi.org/10.3390/en7021050
Received: 30 November 2013 / Revised: 17 January 2014 / Accepted: 10 February 2014 / Published: 24 February 2014
Cited by 24 | PDF Full-text (1969 KB) | HTML Full-text | XML Full-text
Abstract
The influence of prewhirl regulation by inlet guide vanes (IGVs) on a centrifugal pump performance is investigated experimentally and numerically. The experimental results show that IGVs can obviously change the head and increase the efficiency of the tested centrifugal pump over a wide
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The influence of prewhirl regulation by inlet guide vanes (IGVs) on a centrifugal pump performance is investigated experimentally and numerically. The experimental results show that IGVs can obviously change the head and increase the efficiency of the tested centrifugal pump over a wide range of flow rates. Although the cavitation performance is degraded, the variation of the cavitation critical point is less than 0.5 m. Movement of the computed three-dimensional streamlines in suction pipe and impeller are analyzed in order to reveal the mechanism how the IGVs realize the prewhirl regulation. The calculated results show that the influence of IGVs on the cavitation performance of centrifugal pump is limited by a maximum total pressure drop of 1777 Pa, about 7.6% of the total pressure at the suction pipe inlet for a prewhirl angle of 24°. Full article
Open AccessCorrection Li, R.; Ma, H.; Wang, F.; Wang, Y.; Liu, Y.; Li, Z. Game Optimization Theory and Application in Distribution System Expansion Planning, Including Distributed Generation. Energies 2013, 6, 1101–1124
Energies 2014, 7(2), 1048-1049; https://doi.org/10.3390/en7021048
Received: 5 February 2014 / Accepted: 11 February 2014 / Published: 24 February 2014
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Abstract
The authors wish to make the following corrections to this paper [1]. [...] Full article
Open AccessArticle Anticipating and Coordinating Voltage Control for Interconnected Power Systems
Energies 2014, 7(2), 1027-1047; https://doi.org/10.3390/en7021027
Received: 19 November 2013 / Revised: 27 January 2014 / Accepted: 20 February 2014 / Published: 24 February 2014
Cited by 7 | PDF Full-text (544 KB) | HTML Full-text | XML Full-text
Abstract
This paper deals with the application of an anticipating and coordinating feedback control scheme in order to mitigate the long-term voltage instability of multi-area power systems. Each local area is uniquely controlled by a control agent (CA) selecting control values based on model
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This paper deals with the application of an anticipating and coordinating feedback control scheme in order to mitigate the long-term voltage instability of multi-area power systems. Each local area is uniquely controlled by a control agent (CA) selecting control values based on model predictive control (MPC) and is possibly operated by an independent transmission system operator (TSO). Each MPC-based CA only knows a detailed local hybrid system model of its own area, employing reduced-order quasi steady-state (QSS) hybrid models of its neighboring areas and even simpler PV models for remote areas, to anticipate (and then optimize) the future behavior of its own area. Moreover, the neighboring CAs agree on communicating their planned future control input sequence in order to coordinate their own control actions. The feasibility of the proposed method for real-time applications is explained, and some practical implementation issues are also discussed. The performance of the method, using time-domain simulation of the Nordic32 test system, is compared with the uncoordinated decentralized MPC (no information exchange among CAs), demonstrating the improved behavior achieved by combining anticipation and coordination. The robustness of the control scheme against modeling uncertainties is also illustrated. Full article
Open AccessArticle Voltage Support Provided by STATCOM in Unbalanced Power Systems
Energies 2014, 7(2), 1003-1026; https://doi.org/10.3390/en7021003
Received: 5 December 2013 / Revised: 6 February 2014 / Accepted: 19 February 2014 / Published: 24 February 2014
Cited by 7 | PDF Full-text (647 KB) | HTML Full-text | XML Full-text
Abstract
The presence of an unbalanced voltage at the point of common coupling (PCC) results in the appearance of a negative sequence current component that deteriorates the control performance. Static synchronous compensators (STATCOMs) are well-known to be a power application capable of carrying out
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The presence of an unbalanced voltage at the point of common coupling (PCC) results in the appearance of a negative sequence current component that deteriorates the control performance. Static synchronous compensators (STATCOMs) are well-known to be a power application capable of carrying out the regulation of the PCC voltage in distribution lines that can suffer from grid disturbances. This article proposes a novel PCC voltage controller in synchronous reference frame to compensate an unbalanced PCC voltage by means of a STATCOM, allowing an independent control of both positive and negative voltage sequences. Several works have been proposed in this line but they were not able to compensate an unbalance in the PCC voltage. Furthermore, this controller includes aspects as antiwindup and droop control to improve the control system performance. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Multi-Objective Structural Optimization Design of Horizontal-Axis Wind Turbine Blades Using the Non-Dominated Sorting Genetic Algorithm II and Finite Element Method
Energies 2014, 7(2), 988-1002; https://doi.org/10.3390/en7020988
Received: 26 December 2013 / Revised: 30 January 2014 / Accepted: 10 February 2014 / Published: 24 February 2014
Cited by 9 | PDF Full-text (564 KB) | HTML Full-text | XML Full-text
Abstract
A multi-objective optimization method for the structural design of horizontal-axis wind turbine (HAWT) blades is presented. The main goal is to minimize the weight and cost of the blade which uses glass fiber reinforced plastic (GFRP) coupled with carbon fiber reinforced plastic (CFRP)
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A multi-objective optimization method for the structural design of horizontal-axis wind turbine (HAWT) blades is presented. The main goal is to minimize the weight and cost of the blade which uses glass fiber reinforced plastic (GFRP) coupled with carbon fiber reinforced plastic (CFRP) materials. The number and the location of layers in the spar cap, the width of the spar cap and the position of the shear webs are employed as the design variables, while the strain limit, blade/tower clearance limit and vibration limit are taken into account as the constraint conditions. The optimization of the design of a commercial 1.5 MW HAWT blade is carried out by combining FEM analysis and a multi-objective evolutionary algorithm under ultimate (extreme) flap-wise load and edge-wise load conditions. The best solutions are described and the comparison of the obtained results with the original design is performed to prove the efficiency and applicability of the method. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle Temperatures and Heat Flows in a Soil Enclosing a Slinky Horizontal Heat Exchanger
Energies 2014, 7(2), 972-987; https://doi.org/10.3390/en7020972
Received: 20 November 2013 / Revised: 22 January 2014 / Accepted: 12 February 2014 / Published: 24 February 2014
Cited by 15 | PDF Full-text (558 KB) | HTML Full-text | XML Full-text
Abstract
Temperature changes and heat flows in soils that host “slinky”-type horizontal heat exchangers are complex, but need to be understood if robust quantification of the thermal energy available to a ground-source heat pump is to be achieved. Of particular interest is the capacity
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Temperature changes and heat flows in soils that host “slinky”-type horizontal heat exchangers are complex, but need to be understood if robust quantification of the thermal energy available to a ground-source heat pump is to be achieved. Of particular interest is the capacity of the thermal energy content of the soil to regenerate when the heat exchangers are not operating. Analysis of specific heat flows and the specific thermal energy regime within the soil, including that captured by the heat-exchangers, has been characterised by meticulous measurements. These reveal that high concentrations of antifreeze mix in the heat-transfer fluid of the heat exchanger have an adverse impact on heat flows discharged into the soil. Full article
Open AccessArticle Performance Evaluation of an In-Wheel Motor Cooling System in an Electric Vehicle/Hybrid Electric Vehicle
Energies 2014, 7(2), 961-971; https://doi.org/10.3390/en7020961
Received: 6 November 2013 / Revised: 22 January 2014 / Accepted: 14 February 2014 / Published: 21 February 2014
Cited by 4 | PDF Full-text (526 KB) | HTML Full-text | XML Full-text
Abstract
High power and miniaturization of motors in an in-wheel drive system, which is installed inside the wheels of a vehicle, are required for directly driving the wheels. In addition, an efficient cooling system is required to ensure high driving performance and durability. This
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High power and miniaturization of motors in an in-wheel drive system, which is installed inside the wheels of a vehicle, are required for directly driving the wheels. In addition, an efficient cooling system is required to ensure high driving performance and durability. This study experimentally evaluated the heat dissipation performance of a 35-kW-class large-capacity in-wheel motor equipped with an internal-circulation-type oil-cooling system that exhibits high cooling performance and can be easily miniaturized to this motor. Temperatures of the coil and stator core of cooling systems with and without a radiator were measured in real time under in-wheel motor driving conditions. It was found that operating the cooling system at a continuous-rating maximum speed without the radiator was difficult. We confirmed that under continuous-rating base speed and continuous-rating maximum speed driving conditions, the cooling system with the radiator showed thermally stable operation. Furthermore, under maximum-rating base speed and maximum-rating maximum speed driving conditions, the cooling system with the radiator provided additional driving times of approximately 22 s and 2 s, respectively. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
Open AccessArticle Research on the Power Management Strategy of Hybrid Electric Vehicles Based on Electric Variable Transmissions
Energies 2014, 7(2), 934-960; https://doi.org/10.3390/en7020934
Received: 12 December 2013 / Revised: 26 January 2014 / Accepted: 14 February 2014 / Published: 21 February 2014
Cited by 6 | PDF Full-text (1208 KB) | HTML Full-text | XML Full-text
Abstract
Electric variable transmission is a new electromechanical energy conversion device structure, which is especially suitable as the driving force distribution device for hybrid electric vehicles. This paper focuses on the power management strategy of hybrid electric vehicles based on an electric variable transmission,
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Electric variable transmission is a new electromechanical energy conversion device structure, which is especially suitable as the driving force distribution device for hybrid electric vehicles. This paper focuses on the power management strategy of hybrid electric vehicles based on an electric variable transmission, and a kind of hierarchical control ideology is proposed. The control strategy is composed of four control levels, namely analysis of force requirement, operation mode switching, force distribution and coordinate control, which are designed respectively in this paper. Then a simulation model is built based on the notion of energetic macroscopic representation, and an experimental test bench is built. The simulation and experiment results demonstrate the feasibility of the proposed strategy, and it can be taken as a new theory and method for the study of hybrid electric vehicle based on electric variable transmission. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
Open AccessArticle Investigation of the Wind Resource Assessment over 2D Continuous Rolling Hills Due to Tropical Cyclones in the Coastal Region of Southeastern China
Energies 2014, 7(2), 913-933; https://doi.org/10.3390/en7020913
Received: 9 December 2013 / Revised: 15 February 2014 / Accepted: 18 February 2014 / Published: 20 February 2014
Cited by 3 | PDF Full-text (2929 KB) | HTML Full-text | XML Full-text
Abstract
The effect of tropical cyclones on the turbulent flow over 2D continuous rolling hills was numerically investigated based on a field test analysis of the coastal region of Southeast China. A computational fluid dynamics (CFD) method was first developed and verified using previously
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The effect of tropical cyclones on the turbulent flow over 2D continuous rolling hills was numerically investigated based on a field test analysis of the coastal region of Southeast China. A computational fluid dynamics (CFD) method was first developed and verified using previously published experimental results. Then two typical beneficial and destructive cyclone cases were studied above different locations of the hills. Results showed that the continuous hilly flow was much more drastic and variable than previously reported normal wind; the mean and turbulent magnitudes became the strongest around the hill top, with the maximum speed-up ratio, turbulence intensity and gust-speed ratio of 1.1, 0.32 and 1.6; the flow over lower hill was greatly affected by the nearby higher hills; the mean and fluctuating quantities were mostly smaller than the corresponding single hill case. These phenomena were considered to be related with the rather strong detachment and attachment of the cyclone flow around the two hills. In addition, the mean and fluctuating wind velocities were found to be underestimated by at least 20% if the widely accepted IEC standard equations were utilized, suggesting the necessity to supplement the field test analysis in the standard for more reasonable wind resource evaluation within the Southeast China coastal area. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle Large Eddy Simulation of Vertical Axis Wind Turbine Wakes
Energies 2014, 7(2), 890-912; https://doi.org/10.3390/en7020890
Received: 11 December 2013 / Revised: 5 February 2014 / Accepted: 11 February 2014 / Published: 20 February 2014
Cited by 37 | PDF Full-text (4867 KB) | HTML Full-text | XML Full-text
Abstract
In this study, large eddy simulation (LES) is combined with a turbine model to investigate the wake behind a vertical-axis wind turbine (VAWT) in a three-dimensional turbulent flow. Two methods are used to model the subgrid-scale (SGS) stresses: (a) the Smagorinsky model; and
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In this study, large eddy simulation (LES) is combined with a turbine model to investigate the wake behind a vertical-axis wind turbine (VAWT) in a three-dimensional turbulent flow. Two methods are used to model the subgrid-scale (SGS) stresses: (a) the Smagorinsky model; and (b) the modulated gradient model. To parameterize the effects of the VAWT on the flow, two VAWT models are developed: (a) the actuator swept-surface model (ASSM), in which the time-averaged turbine-induced forces are distributed on a surface swept by the turbine blades, i.e., the actuator swept surface; and (b) the actuator line model (ALM), in which the instantaneous blade forces are only spatially distributed on lines representing the blades, i.e., the actuator lines. This is the first time that LES has been applied and validated for the simulation of VAWT wakes by using either the ASSM or the ALM techniques. In both models, blade-element theory is used to calculate the lift and drag forces on the blades. The results are compared with flow measurements in the wake of a model straight-bladed VAWT, carried out in the Institute de Méchanique et Statistique de la Turbulence (IMST) water channel. Different combinations of SGS models with VAWT models are studied, and a fairly good overall agreement between simulation results and measurement data is observed. In general, the ALM is found to better capture the unsteady-periodic nature of the wake and shows a better agreement with the experimental data compared with the ASSM. The modulated gradient model is also found to be a more reliable SGS stress modeling technique, compared with the Smagorinsky model, and it yields reasonable predictions of the mean flow and turbulence characteristics of a VAWT wake using its theoretically-determined model coefficient. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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Open AccessArticle Modelling and Internal Fuzzy Model Power Control of a Francis Water Turbine
Energies 2014, 7(2), 874-889; https://doi.org/10.3390/en7020874
Received: 17 November 2013 / Revised: 6 February 2014 / Accepted: 8 February 2014 / Published: 19 February 2014
Cited by 17 | PDF Full-text (1082 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents dynamic modelling of a Francis turbine with a surge tank and the control of a hydro power plant (HPP). Non-linear and linear models include technical parameters and show high similarity to measurement data. Turbine power control with an internal model
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This paper presents dynamic modelling of a Francis turbine with a surge tank and the control of a hydro power plant (HPP). Non-linear and linear models include technical parameters and show high similarity to measurement data. Turbine power control with an internal model control (IMC) is proposed, based on a turbine fuzzy model. Considering appropriate control responses in the entire area of turbine power, the model parameters of the process are determined from a fuzzy model, which are further included in the internal model controller. The results are compared to a proportional-integral (PI) controller tuned with an integral absolute error (IAE) objective function, and show an improved response of internal model control. Full article
Open AccessArticle Impact of Hot-Water Extraction on Acetone-Water Oxygen Delignification of Paulownia Spp. and Lignin Recovery
Energies 2014, 7(2), 857-873; https://doi.org/10.3390/en7020857
Received: 9 December 2013 / Revised: 7 February 2014 / Accepted: 17 February 2014 / Published: 19 February 2014
Cited by 6 | PDF Full-text (606 KB) | HTML Full-text | XML Full-text
Abstract
A hardwood-based biorefinery process starting with hot-water extraction (HWE) is recommended in order to remove most of the hemicelluloses/xylans before further processing. HWE may be followed by delignification in acetone/water in the presence of oxygen (AWO) for the production of cellulose and lignin.
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A hardwood-based biorefinery process starting with hot-water extraction (HWE) is recommended in order to remove most of the hemicelluloses/xylans before further processing. HWE may be followed by delignification in acetone/water in the presence of oxygen (AWO) for the production of cellulose and lignin. In this study, the HWE-AWO sequence was evaluated for its effectiveness at removing lignin from the fast-growing species Paulownia tomentosa (PT) and Paulownia elongata (PE), in comparison with the reference species, sugar maple (Acer saccharum, SM). HWE might lead to a remarkable increase in lignin accessibility, and as a result, a greater AWO delignification degree was observed for extracted PT, PE, and SM than for unextracted ones. Organosolv lignin was recovered from the spent liquor of AWO delignification of PT with/without prior HWE and characterized to evaluate the benefits of HWE on the lignin structure and purity. The lignin recovered from the spent liquor of HWE-AWO sequence is of higher purity and lighter color than that recovered from the AWO spent liquor. These properties along with low sulfur content are desirable for lignin high-value applications. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
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