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Energies, Volume 5, Issue 1 (January 2012), Pages 1-180

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Research

Open AccessArticle Mid-Term Energy Demand Forecasting by Hybrid Neuro-Fuzzy Models
Energies 2012, 5(1), 1-21; doi:10.3390/en5010001
Received: 29 September 2011 / Revised: 8 November 2011 / Accepted: 7 December 2011 / Published: 22 December 2011
Cited by 11 | PDF Full-text (2330 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a structure for long-term energy demand forecasting. The proposed hybrid approach, called HPLLNF, uses the local linear neuro-fuzzy (LLNF) model as the forecaster and utilizes the Hodrick–Prescott (HP) filter for extraction of the trend and cyclic components of the [...] Read more.
This paper proposes a structure for long-term energy demand forecasting. The proposed hybrid approach, called HPLLNF, uses the local linear neuro-fuzzy (LLNF) model as the forecaster and utilizes the Hodrick–Prescott (HP) filter for extraction of the trend and cyclic components of the energy demand series. Besides, the sophisticated technique of mutual information (MI) is employed to select the most relevant input features with least possible redundancies for the forecast model. Each generated component by the HP filter is then modeled through an LLNF model. Starting from an optimal least square estimation, the local linear model tree (LOLIMOT) learning algorithm increases the complexity of the LLNF model as long as its performance is improved. The proposed HPLLNF model with MI-based input selection is applied to the problem of long-term energy forecasting in three different case studies, including forecasting of the gasoline, crude oil and natural gas demand over the next 12 months. The obtained forecasting results reveal the noteworthy performance of the proposed approach for long-term energy demand forecasting applications. Full article
(This article belongs to the Special Issue Intelligent Energy Demand Forecasting)
Open AccessArticle Changing Lifestyles Towards a Low Carbon Economy: An IPAT Analysis for China
Energies 2012, 5(1), 22-31; doi:10.3390/en5010022
Received: 20 October 2011 / Revised: 9 December 2011 / Accepted: 20 December 2011 / Published: 27 December 2011
Cited by 23 | PDF Full-text (277 KB) | HTML Full-text | XML Full-text
Abstract
China has achieved notable success in developing its economy with approximate 10 percent average annual GDP growth over the last two decades. At the same time, energy consumption and CO2 emissions almost doubled every five years, which led China to be [...] Read more.
China has achieved notable success in developing its economy with approximate 10 percent average annual GDP growth over the last two decades. At the same time, energy consumption and CO2 emissions almost doubled every five years, which led China to be the world top emitter in 2007. In response, China’s government has put forward a carbon mitigation target of 40%–45% reduction of CO2 emission intensity by 2020. To better understand the potential for success or failure of such a policy, it is essential to assess different driving forces such as population, lifestyle and technology and their associated CO2 emissions. This study confirms that increase of affluence has been the main driving force for China’s CO2 emissions since the late 1970s, which outweighs reductions achieved through technical progress. Meanwhile, the contribution of population growth to CO2 emissions was relatively small. We also found a huge disparity between urban and rural households in terms of changes of lifestyle and consumption patterns. Lifestyles in urban China are beginning to resemble Western lifestyles, and approaching their level of CO2 emissions. Therefore, in addition to the apparent inefficiencies in terms of production technologies there is also a lot of room for improvement on the consumption side especially in interaction of current infrastructure investments and future consumption. Full article
(This article belongs to the Special Issue Low Carbon Transitions Worldwide)
Open AccessArticle On the Establishment of Climatic Zones in Europe with Regard to the Energy Performance of Buildings
Energies 2012, 5(1), 32-44; doi:10.3390/en5010032
Received: 7 December 2011 / Revised: 23 December 2011 / Accepted: 26 December 2011 / Published: 29 December 2011
Cited by 11 | PDF Full-text (1114 KB) | HTML Full-text | XML Full-text
Abstract
Nowadays, subjects such as eco-design requirements, product rating or code compliance with regard to energy efficiency are expanding towards a pan-European level. This leads to the necessity of defining zones within the European region, which share common climatic characteristics and will further [...] Read more.
Nowadays, subjects such as eco-design requirements, product rating or code compliance with regard to energy efficiency are expanding towards a pan-European level. This leads to the necessity of defining zones within the European region, which share common climatic characteristics and will further facilitate the quick estimation of building energy performance. Towards this direction stands the current paper; it presents an approach for defining climatic zones in Europe on the basis of the amount of heating and cooling degree days. It is applied for the climate classification of selected European cities and is compared with the conventional scheme based solely on heating degree days. Since the approach is orientated mainly towards the assessment of building energy performance, its outcomes are evaluated with regard to the actual heating and cooling energy needs of a reference building unit with office use located in representative cities of the proposed climatic zones and facing the four cardinal orientations. The classification of climatic zones on the basis of both heating and cooling degree days leads to more realistic results, since nowadays cooling needs form a substantial part of the energy balance of the building, especially in the Mediterranean regions. Full article
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Open AccessArticle Modeling and Control of a Flux-Modulated Compound-Structure Permanent-Magnet Synchronous Machine for Hybrid Electric Vehicles
Energies 2012, 5(1), 45-57; doi:10.3390/en5010045
Received: 9 September 2011 / Revised: 29 December 2011 / Accepted: 29 December 2011 / Published: 5 January 2012
Cited by 2 | PDF Full-text (721 KB) | HTML Full-text | XML Full-text
Abstract
The compound-structure permanent-magnet synchronous machine (CS-PMSM), comprising a double rotor machine (DRM) and a permanent-magnet (PM) motor, is a promising electronic-continuously variable transmission (e-CVT) concept for hybrid electric vehicles (HEVs). By CS-PMSM, independent speed and torque control of the vehicle engine is [...] Read more.
The compound-structure permanent-magnet synchronous machine (CS-PMSM), comprising a double rotor machine (DRM) and a permanent-magnet (PM) motor, is a promising electronic-continuously variable transmission (e-CVT) concept for hybrid electric vehicles (HEVs). By CS-PMSM, independent speed and torque control of the vehicle engine is realized without a planetary gear unit. However, the slip rings and brushes of the conventional CS-PMSM are considered a major drawback for vehicle application. In this paper, a brushless flux-modulated CS-PMSM is investigated. The operating principle and basic working modes of the CS-PMSM are discussed. Mathematical models of the CS-PMSM system are given, and joint control of the two integrated machines is proposed. As one rotor of the DRM is mechanically connected with the rotor of the PM motor, special rotor position detection and torque allocation methods are required. Simulation is carried out by Matlab/Simulink, and the feasibility of the control system is proven. Considering the complexity of the controller, a single digital signal processor (DSP) is used to perform the interconnected control of dual machines instead of two separate ones, and a typical hardware implementation is proposed. Full article
(This article belongs to the Special Issue Electric and Hybrid Vehicles)
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Open AccessArticle The Potential of a Surfactant/Polymer Flood in a Middle Eastern Reservoir
Energies 2012, 5(1), 58-70; doi:10.3390/en5010058
Received: 8 August 2011 / Revised: 4 January 2012 / Accepted: 5 January 2012 / Published: 11 January 2012
Cited by 1 | PDF Full-text (593 KB) | HTML Full-text | XML Full-text
Abstract
An integrated full-field reservoir simulation study has been performed to determine the reservoir management and production strategies in a mature sandstone reservoir. The reservoir is a candidate for an enhanced oil recovery process or otherwise subject to abandonment. Based on its charateristics, [...] Read more.
An integrated full-field reservoir simulation study has been performed to determine the reservoir management and production strategies in a mature sandstone reservoir. The reservoir is a candidate for an enhanced oil recovery process or otherwise subject to abandonment. Based on its charateristics, the reservoir was found to be most suited for a surfactant/polymer (SP) flood. The study started with a large data gathering and the building of a full-field three-dimensional geological model. Subsequently, a full field simulation model was built and used to history match the water flood. The history match of the water flood emphasizes the areas with remaining high oil saturations, establishes the initial condition of the reservoir for an SP flood, and generates a forecast of reserves for continued water flood operations. A sector model was constructed from the full field model and then used to study different design parameters to maximize the project profitability from the SP flood. An economic model, based on the estimated recovery, residual oil in-place, oil price, and operating costs, has been implemented in order to optimize the project profitability. The study resulted in the selection of surfactant and polymer concentrations and slug size that yielded the best economic returns when applied in this reservoir. The study shows that, in today’s oil prices, surfactant/polymer flood when applied in this reservoir has increased the ultimate oil recovery and provide a significant financial returns. Full article
(This article belongs to the Special Issue Advances in Petroleum Engineering)
Open AccessArticle Is the Electric Vehicle an Attractive Option for Customers?
Energies 2012, 5(1), 71-91; doi:10.3390/en5010071
Received: 7 November 2011 / Revised: 23 December 2011 / Accepted: 4 January 2012 / Published: 12 January 2012
Cited by 3 | PDF Full-text (575 KB) | HTML Full-text | XML Full-text
Abstract
As a new technology, electric mobility has the potential to achieve a reduction in CO2 emissions and contribute to the transition from the current transportation system to a better one, environmentally speaking. The objective of the paper is to aid the [...] Read more.
As a new technology, electric mobility has the potential to achieve a reduction in CO2 emissions and contribute to the transition from the current transportation system to a better one, environmentally speaking. The objective of the paper is to aid the necessary decision-making for the adoption and development of electric vehicles in Spain, taking the time horizon of 2020. This will be achieved by building a System Dynamics model for various scenarios that will be used for the analysis and comparison of various dynamic variables, as well as to determine how, and to what extent, they will influence the number of electric vehicles that will run on Spanish roads in the coming years, focusing on the cost variable. Full article
(This article belongs to the Special Issue Electric and Hybrid Vehicles)
Open AccessArticle Correlation of the Growth Rate of the Hydrate Layer at a Guest/Liquid-Water Interface to Mass Transfer Resistance
Energies 2012, 5(1), 92-100; doi:10.3390/en5010092
Received: 14 December 2011 / Revised: 10 January 2012 / Accepted: 11 January 2012 / Published: 18 January 2012
Cited by 6 | PDF Full-text (620 KB) | HTML Full-text | XML Full-text
Abstract
Growth rate of a hydrate layer at the guest/liquid-water interface is analyzed considering the conjugate process of the mass-transfer and hydrate crystal growth. Hydrate-layer growth rate data in the literature are often compiled according to the system subcooling (∆T T [...] Read more.
Growth rate of a hydrate layer at the guest/liquid-water interface is analyzed considering the conjugate process of the mass-transfer and hydrate crystal growth. Hydrate-layer growth rate data in the literature are often compiled according to the system subcooling (∆T TeqTex, where Teq is the equilibrium dissociation temperature of the hydrate and Tex is the system temperature), suggesting predominant heat transfer limitations. In this paper, we investigate how the existing data on hydrate-layer growth is better correlated to mass transfer of the guest species in liquid water in three-phase equilibrium with bulk guest fluid and hydrate. We have analyzed the conjugate processes of mass-transfer/hydrate-layer-growth following our previous study on the hydrate crystal growth into liquid water saturated with a guest substance. A dimensionless parameter representing the hydrate-layer growth rate is derived from the analysis. This analysis is based on the idea that the growth rate is controlled by the mass transfer of the hydrate-guest substance, dissolved in the bulk of liquid water, to the front of the growing hydrate-layer along the guest/water interface. The variations in the hydrate-layer growth rate observed in the previous studies are related to the dimensionless parameter. Full article
(This article belongs to the Special Issue Natural Gas Hydrate 2011)
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Open AccessArticle Modeling of Turbine Cycles Using a Neuro-Fuzzy Based Approach to Predict Turbine-Generator Output for Nuclear Power Plants
Energies 2012, 5(1), 101-118; doi:10.3390/en5010101
Received: 15 December 2011 / Revised: 16 January 2012 / Accepted: 16 January 2012 / Published: 19 January 2012
Cited by 5 | PDF Full-text (2587 KB) | HTML Full-text | XML Full-text
Abstract
Due to the very complex sets of component systems, interrelated thermodynamic processes and seasonal change in operating conditions, it is relatively difficult to find an accurate model for turbine cycle of nuclear power plants (NPPs). This paper deals with the modeling of [...] Read more.
Due to the very complex sets of component systems, interrelated thermodynamic processes and seasonal change in operating conditions, it is relatively difficult to find an accurate model for turbine cycle of nuclear power plants (NPPs). This paper deals with the modeling of turbine cycles to predict turbine-generator output using an adaptive neuro-fuzzy inference system (ANFIS) for Unit 1 of the Kuosheng NPP in Taiwan. Plant operation data obtained from Kuosheng NPP between 2006 and 2011 were verified using a linear regression model with a 95% confidence interval. The key parameters of turbine cycle, including turbine throttle pressure, condenser backpressure, feedwater flow rate and final feedwater temperature are selected as inputs for the ANFIS based turbine cycle model. In addition, a thermodynamic turbine cycle model was developed using the commercial software PEPSE® to compare the performance of the ANFIS based turbine cycle model. The results show that the proposed ANFIS based turbine cycle model is capable of accurately estimating turbine-generator output and providing more reliable results than the PEPSE® based turbine cycle models. Moreover, test results show that the ANFIS performed better than the artificial neural network (ANN), which has also being tried to model the turbine cycle. The effectiveness of the proposed neuro-fuzzy based turbine cycle model was demonstrated using the actual operating data of Kuosheng NPP. Furthermore, the results also provide an alternative approach to evaluate the thermal performance of nuclear power plants. Full article
(This article belongs to the Special Issue Intelligent Energy Demand Forecasting)
Open AccessArticle Performance Analysis and Simulation of a Novel Brushless Double Rotor Machine for Power-Split HEV Applications
Energies 2012, 5(1), 119-137; doi:10.3390/en5010119
Received: 8 September 2011 / Revised: 4 January 2012 / Accepted: 13 January 2012 / Published: 19 January 2012
Cited by 4 | PDF Full-text (526 KB) | HTML Full-text | XML Full-text
Abstract
A new type of brushless double rotor machine (BDRM) is proposed in this paper. The BDRM is an important component in compound-structure permanent-magnet synchronous machine (CS-PMSM) systems, which are promising for power-split hybrid electric vehicle (HEV) applications. The BDRM can realize the [...] Read more.
A new type of brushless double rotor machine (BDRM) is proposed in this paper. The BDRM is an important component in compound-structure permanent-magnet synchronous machine (CS-PMSM) systems, which are promising for power-split hybrid electric vehicle (HEV) applications. The BDRM can realize the speed adjustment between claw-pole rotor and permanent-magnet rotor without brushes and slip rings. The structural characteristics of the BDRM are described and its magnetic circuit model is built. Reactance parameters of the BDRM are deduced by an analytical method. It is found that the size characteristics of the BDRM are different from those of conventional machines. The new sizing and torque equations are analyzed and the theoretical results are used in the optimization process. Studies of the analytical magnetic circuit and finite element method (FEM) model show that the BDRM tends to have high leakage flux and low power factor, and then the method to obtain high power factor is discussed. Furthermore, a practical methodology of the BDRM design is developed, which includes an analytical tool, 2D field calculation and performance evaluation by 3D field calculation. Finally, different topologies of the BDRM are compared and an optimum prototype is designed. Full article
(This article belongs to the Special Issue Electric and Hybrid Vehicles)
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Open AccessArticle Standardization Work for BEV and HEV Applications: Critical Appraisal of Recent Traction Battery Documents
Energies 2012, 5(1), 138-156; doi:10.3390/en5010138
Received: 30 September 2011 / Revised: 16 January 2012 / Accepted: 16 January 2012 / Published: 19 January 2012
Cited by 19 | PDF Full-text (1622 KB) | HTML Full-text | XML Full-text
Abstract
The increased activity in the field of Battery Electric Vehicles (BEVs) and Hybrid Electric Vehicles (HEVs) have led to an increase in standardization work, performed by both world-wide organizations like the IEC or the ISO, as by regional and national bodies such [...] Read more.
The increased activity in the field of Battery Electric Vehicles (BEVs) and Hybrid Electric Vehicles (HEVs) have led to an increase in standardization work, performed by both world-wide organizations like the IEC or the ISO, as by regional and national bodies such as CEN, CENELEC, SAE or JEVA. The issues of these standards cover several topics: safety, performance and operational/dimension issues. This paper reports a brief overview of current standardization activities of lithium batteries based on IEC 62660-1/2 and ISO 12405-1/2. Furthermore, in this paper, a series of innovative test procedures for lithium-ion batteries are presented. Thanks to these tests, the general characteristics of a battery such as charge and discharge capabilities, power performances and life cycle can be determined. Then, a new approach for extracting the life cycle of a battery in function of depth of discharge has been developed. Full article
(This article belongs to the Special Issue Electric and Hybrid Vehicles)
Open AccessArticle A Two-Dimensional Cloud Model for Condition Assessment of HVDC Converter Transformers
Energies 2012, 5(1), 157-167; doi:10.3390/en5010157
Received: 18 November 2011 / Revised: 17 January 2012 / Accepted: 17 January 2012 / Published: 23 January 2012
Cited by 3 | PDF Full-text (796 KB) | HTML Full-text | XML Full-text
Abstract
Converter transformers are the key and the most important components in high voltage direct current (HVDC) power transmission systems. Statistics show that the failure rate of HVDC converter transformers is approximately twice of that of transformers in AC power systems. This paper [...] Read more.
Converter transformers are the key and the most important components in high voltage direct current (HVDC) power transmission systems. Statistics show that the failure rate of HVDC converter transformers is approximately twice of that of transformers in AC power systems. This paper presents an approach integrated with a two-dimensional cloud model and an entropy-based weight model to evaluate the condition of HVDC converter transformers. The integrated approach can describe the complexity of HVDC converter transformers and achieve an effective assessment of their condition. Data from electrical testing, DGA, oil testing, and visual inspection were chosen to form the double-level assessment index system. Analysis results show that the integrated approach is capable of providing a relevant and effective assessment which in turn, provides valuable information for the maintenance of HVDC converter transformers. Full article
Open AccessArticle Steady State Assessment of Shunt Compensated EHV Insulated Cables by Means of Multiconductor Cell Analysis (MCA)
Energies 2012, 5(1), 168-180; doi:10.3390/en5010168
Received: 25 November 2011 / Revised: 17 January 2012 / Accepted: 17 January 2012 / Published: 23 January 2012
PDF Full-text (840 KB) | HTML Full-text | XML Full-text
Abstract
The author has already presented some papers which allow studying cable systems by means of the multiconductor cell analysis (MCA). This method considers the cable system in its real asymmetry without simplified and approximated hypotheses. The multiconductor matrix procedure based on the [...] Read more.
The author has already presented some papers which allow studying cable systems by means of the multiconductor cell analysis (MCA). This method considers the cable system in its real asymmetry without simplified and approximated hypotheses. The multiconductor matrix procedure based on the use of admittance matrices, which account for the line cells (with earth return currents), different types of screen bonding, possible multiple circuits (single and double circuit or more), allows predicting the steady-state regime of any cable system. In the previous papers, these matrix algorithms have been presented with reference to a short extra-high voltage (EHV) double-circuit cross-bonded (CB) underground cable (UGC) system. Since the cable link was short, the shunt reactive compensation was not necessary and consequently not considered. In this paper the procedure is generalized in order to take into account three single-phase (or also one three-phase) reactors installed at the cable ends or also at intermediate locations. Full article

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