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Energies, Volume 5, Issue 6 (June 2012) – 19 articles , Pages 1705-2070

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657 KiB  
Article
Factor Analysis of the Aggregated Electric Vehicle Load Based on Data Mining
by Qinglai Guo, Yao Wang, Hongbin Sun, Zhengshuo Li, Shujun Xin and Boming Zhang
Energies 2012, 5(6), 2053-2070; https://doi.org/10.3390/en5062053 - 21 Jun 2012
Cited by 33 | Viewed by 8339
Abstract
Electric vehicles (EVs) and the related infrastructure are being developed rapidly. In order to evaluate the impact of factors on the aggregated EV load and to coordinate charging, a model is established to capture the relationship between the charging load and important factors [...] Read more.
Electric vehicles (EVs) and the related infrastructure are being developed rapidly. In order to evaluate the impact of factors on the aggregated EV load and to coordinate charging, a model is established to capture the relationship between the charging load and important factors based on data mining. The factors can be categorized as internal and external. The internal factors include the EV battery size, charging rate at different places, penetration of the charging infrastructure, and charging habits. The external factor is the time-of-use pricing (TOU) policy. As a massive input data is necessary for data mining, an algorithm is implemented to generate a massive sample as input data which considers real-world travel patterns based on a historical travel dataset. With the input data, linear regression was used to build a linear model whose inputs were the internal factors. The impact of the internal factors on the EV load can be quantified by analyzing the sign, value, and temporal distribution of the model coefficients. The results showed that when no TOU policy is implemented, the rate of charging at home and range anxiety exerts the greatest influence on EV load. For the external factor, a support vector regression technique was used to build a relationship between the TOU policy and EV load. Then, an optimization model based on the relationship was proposed to devise a TOU policy that levels the load. The results suggest that implementing a TOU policy reduces the difference between the peak and valley loads remarkably. Full article
(This article belongs to the Special Issue Electrical Power and Energy Systems)
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3336 KiB  
Article
Design, Construction and Testing of a Hydraulic Power Take-Off for Wave Energy Converters
by Joseba Lasa, Juan Carlos Antolin, Carlos Angulo, Patxi Estensoro, Maider Santos and Pierpaolo Ricci
Energies 2012, 5(6), 2030-2052; https://doi.org/10.3390/en5062030 - 20 Jun 2012
Cited by 43 | Viewed by 8515
Abstract
This paper presents the construction, mathematical modeling and testing of a scaled universal hydraulic Power Take-Off (PTO) device for Wave Energy Converters (WECs). A specific prototype and test bench were designed and built to carry out the tests. The results obtained from these [...] Read more.
This paper presents the construction, mathematical modeling and testing of a scaled universal hydraulic Power Take-Off (PTO) device for Wave Energy Converters (WECs). A specific prototype and test bench were designed and built to carry out the tests. The results obtained from these tests were used to adjust an in-house mathematical model. The PTO was initially designed to be coupled to a scaled wave energy capture device with a low speed and high torque oscillating motion and high power fluctuations. Any Energy Capture Device (ECD) that fulfils these requirements can be coupled to this PTO, provided that its scale is adequately defined depending on the rated power of the full scale prototype. The initial calibration included estimation of the pressure drops in the different components, the pressurization time of the oil inside the hydraulic cylinders and the volumetric efficiency of the complete circuit. Since the overall efficiency measured during the tests ranged from 0.69 to 0.8 and the dynamic performance of the PTO was satisfactory, the results are really promising and it is believed that this solution might prove effective in real devices. Full article
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2714 KiB  
Article
An Overview of Two Years of Continuous Energy Optimization at the Velenje Coal Mine
by Milan Medved, Ivica Ristovic, Janez Roser and Milivoj Vulic
Energies 2012, 5(6), 2017-2029; https://doi.org/10.3390/en5062017 - 20 Jun 2012
Cited by 14 | Viewed by 7185
Abstract
The Velenje Coal Mine (VCM) is one of the largest and the most modern underground coal mines in Europe. Although the coal mining industry produces coal as an energy source, it is also uses a lot of energy for its own operation and [...] Read more.
The Velenje Coal Mine (VCM) is one of the largest and the most modern underground coal mines in Europe. Although the coal mining industry produces coal as an energy source, it is also uses a lot of energy for its own operation and support processes. At this time of volatile energy prices and more and more strict environmental emission requirements, optimizing energy consumption plays an important role in good business performance. To track the consumption of electricity, district heating, drinking water and compressed air at the VCM a detailed energy monitoring methodology was developed and established in July 2010. The essential element of the presented monitoring system is a software application named “Central System for Regulation of Energy” (CSRE). The purpose of the CSRE is to control energy processes from a distance, take measures for economical and efficient use of energy, as well as to assist in maintenance. Such monitoring allows extensive comparisons between different energy sources consumption and enables correct measures to be taken to reduce the difference between the target and actual consumption of energy in VCM. With established real-time monitoring system, it is possible to look at mining processes and see where energy is being used inefficiently. Full article
(This article belongs to the Special Issue Selected Papers from the 24th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS2011))
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372 KiB  
Article
Two LQRI based Blade Pitch Controls for Wind Turbines
by Sungsu Park and Yoonsu Nam
Energies 2012, 5(6), 1998-2016; https://doi.org/10.3390/en5061998 - 20 Jun 2012
Cited by 20 | Viewed by 7930
Abstract
As the wind turbine size has been increasing and their mechanical components are built lighter, the reduction of the structural loads becomes a very important task of wind turbine control in addition to maximum wind power capture. In this paper, we present a [...] Read more.
As the wind turbine size has been increasing and their mechanical components are built lighter, the reduction of the structural loads becomes a very important task of wind turbine control in addition to maximum wind power capture. In this paper, we present a separate set of collective and individual pitch control algorithms. Both pitch control algorithms use the LQR control technique with integral action (LQRI), and utilize Kalman filters to estimate system states and wind speed. Compared to previous works in this area, our pitch control algorithms can control rotor speed and blade bending moments at the same time to improve the trade-off between rotor speed regulation and load reduction, while both collective and individual pitch controls can be designed separately. Simulation results show that the proposed collective and individual pitch controllers achieve very good rotor speed regulation and significant reduction of blade bending moments. Full article
(This article belongs to the Special Issue Wind Turbines)
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785 KiB  
Article
Double-Linear Approximation Algorithm to Achieve Maximum-Power-Point Tracking for Photovoltaic Arrays
by Chih-Lung Shen and Cheng-Tao Tsai
Energies 2012, 5(6), 1982-1997; https://doi.org/10.3390/en5061982 - 20 Jun 2012
Cited by 24 | Viewed by 6556
Abstract
In this paper, a double-linear approximation algorithm (DLAA) to achieve maximum-power-point tracking (MPPT) for photovoltaic (PV) arrays is proposed. The DLAA is based on the approximation that the maximum power point varies linearly with irradiation and temperature. With the DLAA, a maximum power [...] Read more.
In this paper, a double-linear approximation algorithm (DLAA) to achieve maximum-power-point tracking (MPPT) for photovoltaic (PV) arrays is proposed. The DLAA is based on the approximation that the maximum power point varies linearly with irradiation and temperature. With the DLAA, a maximum power point can be determined instantaneously. Moreover, complicated calculations and perturbations about an optimal point can be avoided. The paper also proposes a corresponding circuit to realize the DLAA. The configuration of the DLAA circuit is simple such that it is cost-effective and can be embedded into PV arrays easily. An example of implementation of a PV power supply system with the proposed MPPT is designed and the DLAA is compared with the perturb-and-observe method. Simulated and experimental results have demonstrated the feasibility of the PV power system and verified the advantages of the proposed DLAA. Full article
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821 KiB  
Article
Comprehensive Evaluation of Algal Biofuel Production: Experimental and Target Results
by Colin M. Beal, Robert E. Hebner, Michael E. Webber, Rodney S. Ruoff, A. Frank Seibert and Carey W. King
Energies 2012, 5(6), 1943-1981; https://doi.org/10.3390/en5061943 - 20 Jun 2012
Cited by 43 | Viewed by 11434
Abstract
Worldwide, algal biofuel research and development efforts have focused on increasing the competitiveness of algal biofuels by increasing the energy and financial return on investments, reducing water intensity and resource requirements, and increasing algal productivity. In this study, analyses are presented in each [...] Read more.
Worldwide, algal biofuel research and development efforts have focused on increasing the competitiveness of algal biofuels by increasing the energy and financial return on investments, reducing water intensity and resource requirements, and increasing algal productivity. In this study, analyses are presented in each of these areas—costs, resource needs, and productivity—for two cases: (1) an Experimental Case, using mostly measured data for a lab-scale system, and (2) a theorized Highly Productive Case that represents an optimized commercial-scale production system, albeit one that relies on full-price water, nutrients, and carbon dioxide. For both cases, the analysis described herein concludes that the energy and financial return on investments are less than 1, the water intensity is greater than that for conventional fuels, and the amounts of required resources at a meaningful scale of production amount to significant fractions of current consumption (e.g., nitrogen). The analysis and presentation of results highlight critical areas for advancement and innovation that must occur for sustainable and profitable algal biofuel production can occur at a scale that yields significant petroleum displacement. To this end, targets for energy consumption, production cost, water consumption, and nutrient consumption are presented that would promote sustainable algal biofuel production. Furthermore, this work demonstrates a procedure and method by which subsequent advances in technology and biotechnology can be framed to track progress. Full article
(This article belongs to the Special Issue Algae Fuel)
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784 KiB  
Article
Field Measurements of Residential Energy Consumption and Indoor Thermal Environment in Six Chinese Cities
by Tianchi Hu, Hiroshi Yoshino and Jie Zhou
Energies 2012, 5(6), 1927-1942; https://doi.org/10.3390/en5061927 - 19 Jun 2012
Cited by 8 | Viewed by 5214
Abstract
The purpose of this study was to reveal the energy use and indoor environment characteristics of twelve households located in six cities in China, including daily use of gas and electricity, temperature and humidity throughout a year. The energy uses for district heating [...] Read more.
The purpose of this study was to reveal the energy use and indoor environment characteristics of twelve households located in six cities in China, including daily use of gas and electricity, temperature and humidity throughout a year. The energy uses for district heating and hot water were not included. The investigated houses were separated into two groups, namely Group 1 with domestic heating, and Group 2 with district heating. The analysis showed that the energy use of Lighting and Audio visual & information for each house is not very different during the four seasons. Annual energy use varied from 13.3 to 32.4 GJ in Group 1. The energy use of House 05 was 32.4 GJ/year, which is the highest in Group 1, the space heating reached 18.5 GJ/year, accounting for 57% of the total. Energy use of House 01 increased in winter and summer, which is attributed to the use of heating in winter and cooling in summer, respectively. Annual energy use varied from 2.9 to 17.0 GJ in Group 2. Almost no change of energy use was found for the houses in Group 2 during the four seasons, but a big difference of average indoor temperature was found in the coldest days between the houses in Group 1 (around 10 °C) and Group 2 (around 20 °C), while the difference was small in summer. Full article
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3562 KiB  
Article
Modeling of Step-up Grid-Connected Photovoltaic Systems for Control Purposes
by Adriana Trejos, Daniel Gonzalez and Carlos Andres Ramos-Paja
Energies 2012, 5(6), 1900-1926; https://doi.org/10.3390/en5061900 - 18 Jun 2012
Cited by 44 | Viewed by 8220
Abstract
This paper presents modeling approaches for step-up grid-connected photovoltaic systems intended to provide analytical tools for control design. The first approach is based on a voltage source representation of the bulk capacitor interacting with the grid-connected inverter, which is a common model for [...] Read more.
This paper presents modeling approaches for step-up grid-connected photovoltaic systems intended to provide analytical tools for control design. The first approach is based on a voltage source representation of the bulk capacitor interacting with the grid-connected inverter, which is a common model for large DC buses and closed-loop inverters. The second approach considers the inverter of a double-stage PV system as a Norton equivalent, which is widely accepted for open-loop inverters. In addition, the paper considers both ideal and realistic models for the DC/DC converter that interacts with the PV module, providing four mathematical models to cover a wide range of applications. The models are expressed in state space representation to simplify its use in analysis and control design, and also to be easily implemented in simulation software, e.g., Matlab. The PV system was analyzed to demonstrate the non-minimum phase condition for all the models, which is an important aspect to select the control technique. Moreover, the system observability and controllability were studied to define design criteria. Finally, the analytical results are illustrated by means of detailed simulations, and the paper results are validated in an experimental test bench. Full article
(This article belongs to the Special Issue Solar Energy Systems and Materials)
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3213 KiB  
Article
Electric Vehicle Scenario Simulator Tool for Smart Grid Operators
by João Soares, Bruno Canizes, Cristina Lobo, Zita Vale and Hugo Morais
Energies 2012, 5(6), 1881-1899; https://doi.org/10.3390/en5061881 - 15 Jun 2012
Cited by 93 | Viewed by 12640
Abstract
This paper presents a simulator for electric vehicles in the context of smart grids and distribution networks. It aims to support network operators’ planning and operations but can be used by other entities for related studies. The paper describes the parameters supported by [...] Read more.
This paper presents a simulator for electric vehicles in the context of smart grids and distribution networks. It aims to support network operators’ planning and operations but can be used by other entities for related studies. The paper describes the parameters supported by the current version of the Electric Vehicle Scenario Simulator (EVeSSi) tool and its current algorithm. EVeSSi enables the definition of electric vehicles scenarios on distribution networks using a built-in movement engine. The scenarios created with EVeSSi can be used by external tools (e.g., power flow) for specific analysis, for instance grid impacts. Two scenarios are briefly presented for illustration of the simulator capabilities. Full article
(This article belongs to the Special Issue Vehicle to Grid)
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1202 KiB  
Article
On the Evaluation of Solar Greenhouse Efficiency in Building Simulation during the Heating Period
by Francesco Asdrubali, Franco Cotana and Antonio Messineo
Energies 2012, 5(6), 1864-1880; https://doi.org/10.3390/en5061864 - 15 Jun 2012
Cited by 58 | Viewed by 7622
Abstract
Among solar passive systems integrated in buildings, sunspaces or solar greenhouses represent a very interesting solution. A sunspace is a closed, southbound volume, constituted by transparent surfaces, adjacent to a building, which reduces winter energy demand thanks to the use of solar gains. [...] Read more.
Among solar passive systems integrated in buildings, sunspaces or solar greenhouses represent a very interesting solution. A sunspace is a closed, southbound volume, constituted by transparent surfaces, adjacent to a building, which reduces winter energy demand thanks to the use of solar gains. The effect of a typical solar greenhouse on the energy balance of a building was evaluated during the heating period with two stationary procedures (Method 5000 and EN ISO 13790) and with a dynamic tool (TRNSYS). After the analysis of the greenhouse alone, the behavior of an entire house was simulated; a flat equipped with a sunspace, recently built thanks to public contributions provided by the Umbria Region in Italy to widespread bio-climatic architecture, was used as case-study. Simulations were carried out for the examined flat, both with a steady-state tool and with a dynamic one; the contribution of the sunspace was estimated thanks to the various methods previously mentioned. Finally, the simulated data were satisfactorily compared with the real energy consumptions (natural gas for heating) of the flat; the sunspace allows a reduction of winter energy demand of the flat of about 20%. Full article
(This article belongs to the Special Issue Solar Energy Systems and Materials)
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268 KiB  
Article
Advanced Thermodynamic Analysis and Evaluation of a Supercritical Power Plant
by Ligang Wang, Yongping Yang, Tatiana Morosuk and George Tsatsaronis
Energies 2012, 5(6), 1850-1863; https://doi.org/10.3390/en5061850 - 15 Jun 2012
Cited by 103 | Viewed by 8286
Abstract
A conventional exergy analysis can highlight the main components having high thermodynamic inefficiencies, but cannot consider the interactions among components or the true potential for the improvement of each component. By splitting the exergy destruction into endogenous/exogenous and avoidable/unavoidable parts, the advanced exergy [...] Read more.
A conventional exergy analysis can highlight the main components having high thermodynamic inefficiencies, but cannot consider the interactions among components or the true potential for the improvement of each component. By splitting the exergy destruction into endogenous/exogenous and avoidable/unavoidable parts, the advanced exergy analysis is capable of providing additional information to conventional exergy analysis for improving the design and operation of energy conversion systems. This paper presents the application of both a conventional and an advanced exergy analysis to a supercritical coal-fired power plant. The results show that the ratio of exogenous exergy destruction differs quite a lot from component to component. In general, almost 90% of the total exergy destruction within turbines comes from their endogenous parts, while that of feedwater preheaters contributes more or less 70% to their total exergy destruction. Moreover, the boiler subsystem is proven to have a large amount of exergy destruction caused by the irreversibilities within the remaining components of the overall system. It is also found that the boiler subsystem still has the largest avoidable exergy destruction; however, the enhancement efforts should focus not only on its inherent irreversibilities but also on the inefficiencies within the remaining components. A large part of the avoidable exergy destruction within feedwater preheaters is exogenous; while that of the remaining components is mostly endogenous indicating that the improvements mainly depend on advances in design and operation of the component itself. Full article
(This article belongs to the Special Issue Exergy Analysis of Energy Systems)
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825 KiB  
Article
Microalgae Isolation and Selection for Prospective Biodiesel Production
by Van Thang Duong, Yan Li, Ekaterina Nowak and Peer M. Schenk
Energies 2012, 5(6), 1835-1849; https://doi.org/10.3390/en5061835 - 15 Jun 2012
Cited by 142 | Viewed by 16311
Abstract
Biodiesel production from microalgae is being widely developed at different scales as a potential source of renewable energy with both economic and environmental benefits. Although many microalgae species have been identified and isolated for lipid production, there is currently no consensus as to [...] Read more.
Biodiesel production from microalgae is being widely developed at different scales as a potential source of renewable energy with both economic and environmental benefits. Although many microalgae species have been identified and isolated for lipid production, there is currently no consensus as to which species provide the highest productivity. Different species are expected to function best at different aquatic, geographical and climatic conditions. In addition, other value-added products are now being considered for commercial production which necessitates the selection of the most capable algae strains suitable for multiple-product algae biorefineries. Here we present and review practical issues of several simple and robust methods for microalgae isolation and selection for traits that maybe most relevant for commercial biodiesel production. A combination of conventional and modern techniques is likely to be the most efficient route from isolation to large-scale cultivation. Full article
(This article belongs to the Special Issue Algae Fuel)
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392 KiB  
Article
Fatigue Reliability and Calibration of Fatigue Design Factors for Offshore Wind Turbines
by Sergio Márquez-Domínguez and John D. Sørensen
Energies 2012, 5(6), 1816-1834; https://doi.org/10.3390/en5061816 - 15 Jun 2012
Cited by 67 | Viewed by 8390 | Correction
Abstract
Consequences of failure of offshore wind turbines (OWTs) is in general lower than consequences of failure of, e.g., oil & gas platforms. It is reasonable that lower fatigue design factors can be applied for fatigue design of OWTs when compared to other fixed [...] Read more.
Consequences of failure of offshore wind turbines (OWTs) is in general lower than consequences of failure of, e.g., oil & gas platforms. It is reasonable that lower fatigue design factors can be applied for fatigue design of OWTs when compared to other fixed offshore structures. Calibration of appropriate partial safety factors/Fatigue Design Factors (FDF) for steel substructures for OWTs is the scope of this paper. A reliability-based approach is used and a probabilistic model has been developed, where design and limit state equations are established for fatigue failure. The strength and load uncertainties are described by stochastic variables. SN and fracture mechanics approaches are considered for to model the fatigue life. Further, both linear and bi-linear SN-curves are formulated and various approximations are investigated. The acceptable reliability level for fatigue failure of OWTs is discussed and results are presented for calibrated optimal fatigue design factors. Further, the influence of inspections is considered in order to extend and maintain a given target safety level. Full article
(This article belongs to the Special Issue Wind Turbines)
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690 KiB  
Article
Dynamic Output Feedback Power-Level Control for the MHTGR Based On Iterative Damping Assignment
by Zhe Dong
Energies 2012, 5(6), 1782-1815; https://doi.org/10.3390/en5061782 - 13 Jun 2012
Cited by 19 | Viewed by 5911
Abstract
Because of its strong inherent safety features and high outlet temperature, the modular high temperature gas-cooled nuclear reactor (MHTGR) is already seen as the central part of the next generation of nuclear plants. Such power plants are being considered for industrial applications with [...] Read more.
Because of its strong inherent safety features and high outlet temperature, the modular high temperature gas-cooled nuclear reactor (MHTGR) is already seen as the central part of the next generation of nuclear plants. Such power plants are being considered for industrial applications with a wide range of power levels, and thus power-level control is an important technique for their efficient and stable operation. Stimulated by the high regulation performance provided by nonlinear controllers, a novel dynamic output-feedback nonlinear power-level regulator is developed in this paper based on the technique of iterative damping assignment (IDA). This control strategy can provide the L2 disturbance attenuation performance under modeling uncertainty or exterior disturbance, and can also guarantee the globally asymptotic closed-loop stability without uncertainty and disturbance. This newly built control strategy is then applied to the power-level regulation of the HTR-PM plant, and numerical simulation results show both the feasibility and high performance of this newly-built control strategy. Furthermore, the relationship between the values of the parameters and the performance of this controller is not only illustrated numerically but also analyzed theoretically. Full article
(This article belongs to the Special Issue Electrical Power and Energy Systems)
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472 KiB  
Article
An Optimization Model of Carbon Sinks in CDM Forestry Projects Based on Interval Linear Programming
by Dufeng Li, Yang Zhang, Xianen Wang, Yu Li and Wenjin Zhao
Energies 2012, 5(6), 1766-1781; https://doi.org/10.3390/en5061766 - 13 Jun 2012
Cited by 2 | Viewed by 6002
Abstract
This study describes the first general optimization model for complex systems with uncertain parameters and decision variables represented as intervals in CDM forestry projects. We work through a specific example of the optimization method developed for a Clean Development Mechanism (CDM) forestry project [...] Read more.
This study describes the first general optimization model for complex systems with uncertain parameters and decision variables represented as intervals in CDM forestry projects. We work through a specific example of the optimization method developed for a Clean Development Mechanism (CDM) forestry project in Inner Mongolia, China. This model is designed to optimize the carbon sink capacity of the new forests, and can deal with uncertainties in the carbon sink capacity, average annual rainfall, ecological parameters, and biological characteristics of tree species. The uncertain inputs are presented in the form of intervals, as are several of the optimized output variables. Compared with the project’s originally recommended scheme, the optimized model will absorb and fix between 1,142 and 885,762 tonnes of extra carbon dioxide. Moreover, the ecological and environmental benefits of the project are also raised to various extents. Full article
(This article belongs to the Special Issue Low Carbon Transitions Worldwide)
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247 KiB  
Article
Reciprocating Expander for an Exhaust Heat Recovery Rankine Cycle for a Passenger Car Application
by Yulia Glavatskaya, Pierre Podevin, Vincent Lemort, Osoko Shonda and Georges Descombes
Energies 2012, 5(6), 1751-1765; https://doi.org/10.3390/en5061751 - 5 Jun 2012
Cited by 80 | Viewed by 11196
Abstract
Nowadays, on average, two thirds of the fuel energy consumed by an engine is wasted through the exhaust gases and the cooling liquid. The recovery of this energy would enable a substantial reduction in fuel consumption. One solution is to integrate a heat [...] Read more.
Nowadays, on average, two thirds of the fuel energy consumed by an engine is wasted through the exhaust gases and the cooling liquid. The recovery of this energy would enable a substantial reduction in fuel consumption. One solution is to integrate a heat recovery system based on a steam Rankine cycle. The key component in such a system is the expander, which has a strong impact on the system’s performance. A survey of different expander technologies leads us to select the reciprocating expander as the most promising one for an automotive application. This paper therefore proposes a steady-state semi-empirical model of the expander device developed under the Engineering Equation Solver (EES) environment. The ambient and mechanical losses as well as internal leakage were taken into account by the model. By exploiting the expander manufacturer’s data, all the parameters of the expander model were identified. The model computes the mass flow rate, the power output delivered and the exhaust enthalpy of the steam. The maximum deviation between predictions and measurement data is 4.7%. A performance study of the expander is carried out and shows that the isentropic efficiency is quite high and increases with the expander rotary speed. The mechanical efficiency depends on mechanical losses which are quite high, approximately 90%. The volumetric efficiency was also evaluated. Full article
(This article belongs to the Special Issue Waste to Energy Technologies)
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238 KiB  
Article
A Closed-Form Technique for the Reliability and Risk Assessment of Wind Turbine Systems
by Akwasi F. Mensah and Leonardo Dueñas-Osorio
Energies 2012, 5(6), 1734-1750; https://doi.org/10.3390/en5061734 - 4 Jun 2012
Cited by 17 | Viewed by 6917
Abstract
This paper proposes a closed-form method to evaluate wind turbine system reliability and associated failure consequences. Monte Carlo simulation, a widely used approach for system reliability assessment, usually requires large numbers of computational experiments, while existing analytical methods are limited to simple system [...] Read more.
This paper proposes a closed-form method to evaluate wind turbine system reliability and associated failure consequences. Monte Carlo simulation, a widely used approach for system reliability assessment, usually requires large numbers of computational experiments, while existing analytical methods are limited to simple system event configurations with a focus on average values of reliability metrics. By analyzing a wind turbine system and its components in a combinatorial yet computationally efficient form, the proposed approach provides an entire probability distribution of system failure that contains all possible configurations of component failure and survival events. The approach is also capable of handling unique component attributes such as downtime and repair cost needed for risk estimations, and enables sensitivity analysis for quantifying the criticality of individual components to wind turbine system reliability. Applications of the technique are illustrated by assessing the reliability of a 12-subassembly turbine system. In addition, component downtimes and repair costs of components are embedded in the formulation to compute expected annual wind turbine unavailability and repair cost probabilities, and component importance metrics useful for maintenance planning and research prioritization. Furthermore, this paper introduces a recursive solution to closed-form method and applies this to a 45-component turbine system. The proposed approach proves to be computationally efficient and yields vital reliability information that could be readily used by wind farm stakeholders for decision making and risk management. Full article
(This article belongs to the Special Issue Wind Turbines)
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2102 KiB  
Article
A High Performance Real-Time Simulator for Controllers Hardware-in-the-Loop Testing
by Mahmoud Matar, Houshang Karimi, Amir Etemadi and Reza Iravani
Energies 2012, 5(6), 1713-1733; https://doi.org/10.3390/en5061713 - 4 Jun 2012
Cited by 18 | Viewed by 8210
Abstract
This paper presents a high performance real-time simulator for power electronic systems applications and primarily intended for controller hardware-in-the-loop (CHIL) testing. The novelty of the proposed simulator resides in the massively parallel hardware architecture that efficiently exploits fine-grained parallelism without imposing severe communication [...] Read more.
This paper presents a high performance real-time simulator for power electronic systems applications and primarily intended for controller hardware-in-the-loop (CHIL) testing. The novelty of the proposed simulator resides in the massively parallel hardware architecture that efficiently exploits fine-grained parallelism without imposing severe communication overhead time that can limit the performance. The simulator enables the use of a nanosecond range simulation timestep to simulate power electronic systems. Through the use of this nanosecond range simulation timestep, the simulator minimizes the error arising from the intersimulation timestep switching phenomenon associated with CHIL. The proposed hardware architecture is realized based on the FPGA technology. The simulator is tested and its CHIL capability verified based on the closed-loop testing of a robust multivariable servomechanism controller for autonomous operation of a distributed generation unit. Full article
(This article belongs to the Special Issue Electrical Power and Energy Systems)
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378 KiB  
Article
Intermolecular Hydrogen Transfer in Isobutane Hydrate
by Naohiro Kobayashi, Takashi Minami, Atsushi Tani, Mikio Nakagoshi, Takeshi Sugahara, Kei Takeya and Kazunari Ohgaki
Energies 2012, 5(6), 1705-1712; https://doi.org/10.3390/en5061705 - 25 May 2012
Cited by 19 | Viewed by 7341
Abstract
Electron spin resonance (ESR) spectra of butyl radicals induced with γ-ray irradiation in the simple isobutane (2-methylpropane) hydrate (prepared with deuterated water) were investigated. Isothermal annealing results of the γ-ray-irradiated isobutane hydrate reveal that the isobutyl radical in a large cage withdraws a [...] Read more.
Electron spin resonance (ESR) spectra of butyl radicals induced with γ-ray irradiation in the simple isobutane (2-methylpropane) hydrate (prepared with deuterated water) were investigated. Isothermal annealing results of the γ-ray-irradiated isobutane hydrate reveal that the isobutyl radical in a large cage withdraws a hydrogen atom from the isobutane molecule through shared hexagonal-faces of adjacent large cages. During this “hydrogen picking” process, the isobutyl radical is apparently transformed into a tert-butyl radical, while the sum of isobutyl and tert-butyl radicals remains constant. The apparent transformation from isobutyl to tert-butyl radicals is an irreversible first-order reaction and the activation energy was estimated to be 35 ± 3 kJ/mol, which was in agreement with the activation energy (39 ± 5 kJ/mol) of hydrogen picking in the γ-ray-irradiated propane hydrate with deuterated water. Full article
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