Comparative analysis of different grid-independent hybrid power generation systems for a residential load

Demand of electricity is rising all over the world, both in developing and developed countries due to escalation in world population and economic growth. The exploitation of renewable energy is imperative to mitigate energy crisis and to avoid the environmental downfall. The stochastic nature of many renewable energy sources sets techno-economic and functional limitations in their application for covering most types of energy needs. These limitations can be surmounted if a renewable and a conventional energy source are combined to formulate a hybrid generation power system.This paper examines the techno-economic feasibility of four hybrid power generation systems applied to cover the demand of a typical off-grid residence for a 20 years period. Each one of these hybrid power solutions should involve at least one renewable energy source technology and be able to cover all load needs. Four applications are investigated for each hybrid system, accounting to different geographical areas in Greece with diverse solar and aeolic profile. A comparative analysis is followed to set off the optimal solution based on a minimal total cost criterion.     

Incorporation of a new wind turbine generating system model into distribution systems load flow analysis

This paper describes a new model for wind turbine generating systems (WTGSs) that is widely used as distributed generation sources. The model is developed by using the bi‐quadratic equation, which is generally used for the calculation of the line voltages in distribution systems' load flow analysis, and facilitates computation of real and reactive power outputs of the WTGSs for a specified wind speed and terminal voltage. The developed model is validated with an experimental setup composed by an induction generator coupled with an induction motor as a prime mover. In addition to that, measured values are also compared with the calculated values, obtained by using the turbine models found in the literature. The incorporation of the developed model into some well‐known distribution systems' load flow algorithms is detailed. The effect of WTGSs on the power losses, voltage profile of radial distribution systems are evaluated for the sample test systems. Additionally, the performance of the load flow algorithms with the new model are examined and found to be robust and reliable. Copyright © 2008 John Wiley & Sons, Ltd.     

一种配电变压器型式及容量选择的新方法

以负荷密度为突破口，提出了一种新的配电变压器型式及容量选择思路，并系统地归纳了配电变压器选择问题的数学模型及相应的选择方法。其中特别引入了潜在损失费用、区域形状系数等概念，进一步完善了数学模型。该方法简单实用，过程清晰明了，通过实际算例验证了该方法的有效性。同时还利用该方法系统分析了负荷特性及相关参数在配电变压器选择问题上所起的重要影响。     

Design of a tower and drive train damping controller for the three‐bladed controls advanced research turbine operating in design‐driving load cases

Wind turbines experience both fatigue and extreme loading, and individual components of a wind turbine are affected differently by these loads. The current practice to achieve the typical 20 year design life is to build a turbine with robust components that can withstand fatigue and extreme loads for this duration. Unfortunately, overbuilding of components may lead to higher‐than‐necessary initial capital costs. In this research, we studied design‐driving load cases and designed advanced control algorithms aimed at enabling a decrease in initial capital cost. Our approach used a subset of a full International Electrotechnical Commission loads case analysis and selected major components experiencing design‐driving extreme loads that can be alleviated using advanced control. We first describe the results from the loads case analysis and then discuss the components on which we focused the advanced control design. We next describe the controller design and finally compare the results from the advanced controller simulations with those using a baseline controller. The baseline consists of a nonlinear torque controller below rated wind speed and a proportional‐integral‐derivative‐like controller above rated and the advanced controller uses proportional feedback and state‐space design to reduce tower bending and drive train torsional loads. Copyright © 2011 John Wiley & Sons, Ltd.     

Cooling load and coefficient of performance optimizations for real air-refrigerators

Based on a simple irreversible variable-temperature heat reservoir air (Brayton) refrigeration cycle model, a performance analysis and optimization of a real air refrigerator is carried out using finite-time thermodynamics. To maximize the cooling load and the coefficient of performance (COP) of the cycle, the allocation of a fixed total heat-exchanger inventory and thermal-capacity rate matching between the working fluid and heat reservoirs are optimized, respectively. The influences of pressure ratio, the total heat-exchanger inventory, the efficiencies of the compressor and expander, the thermal capacity rate of the working fluid and the ratio of the thermal-capacity rates of the heat reservoirs on the performance of the cycle are shown by numerical examples. The results obtained provide guidances for the design of practical air-refrigeration plants.     

A novel power system reconfiguration for a distribution system with minimum load balancing index using bacterial foraging optimization algorithm

In this paper, the objective of minimum load balancing index (LBI) for the 16-bus distribution system is achieved using bacterial foraging optimization algorithm (BFOA). The feeder reconfiguration problem is formulated as a non-linear optimization problem and the optimal solution is obtained using BFOA. With the proposed reconfiguration method, the radial structure of the distribution system is retained and the burden on the optimization technique is reduced. Test results are presented for the 16-bus sample network, the proposed reconfiguration method has effectively decreased the LBI, and the BFOA technique is efficient in searching for the optimal solution.     

机车驱动系统联轴器参数优化及轴承载荷分析

使用有限元软件ANSYS对联轴器的性能及机车驱动系统的轴承载荷进行分析。根据驱动系统的特点及联轴器的工作特点对联轴器进行优化,以联轴器的弯曲刚度为目标函数,分别计算分析了优化前、后联轴器的性能特征以及对轴承载荷的影响。结果表明：通过优化联轴器结构,能够提高联轴器承受系统安装误差引起的附加力和力矩等载荷作用的能力,并且能够显著降低驱动系统轴承载荷的增载率,提高机车驱动系统中轴承的性能。     

Spatially resolved current density measurements and real-time modelling as a tool for the determination of local operating conditions in polymer electrolyte fuel cells

In this contribution a simplified, isothermal, two-phase, one-dimensional model for the calculation of the cathodic gas flow along the flow field channels of a polymer electrolyte fuel cell (PEFC) is presented. The composition of the humidified oxidant gas, average gas velocity, pressure drop, and other quantities can be calculated for any gas distributor structures with one channel. Thereby, the model requires several input parameters which have to be determined solely by experiment and pre-defined operation conditions, e.g. the water content of the feed gas, local current densities, and gas flow rates. In contrast to other models, the cross-section reduction has been taken into account which results from the penetration of the gas diffusion layer into the flow field channels due to the mounting pressure. Beyond this, the model needs no fit-parameters for further adjustment.For close examination of the factors limiting the performance of a PEFC, the DLR has developed several techniques for measuring the current density distribution with spatial resolution. In order to investigate the origin of the corresponding effects, one of these techniques has been improved by implementing the model of the cathodic gas flow as an on-line feature.The combination of a spatially resolved measurement technique with a real-time simulation gives a better understanding of the local processes within the cell and represents a helpful tool for the development of fuel cell components as well as for the optimization of the operating conditions. Exemplarily, the presentation the results for a 25 cm² serpentine flow field at different operation modes are shown in this paper.     

Sensitivity analysis and component modelling of a packed-type liquid desiccant system at partial load operating conditions

Prediction of annual energy consumption requires the partial load performance evaluation of each component in an air conditioning system. A packed-type or a coil-type liquid desiccant apparatus is an essential component of a hybrid liquid desiccant system. Therefore, predicting the hour by hour performance of a packed-type hybrid liquid desiccant system to estimate its annual energy consumption requires that the performance of a packed-type system be known at partial load conditions. For this purpose a detailed sensitivity analysis of heat and mass transfer performance of a packed-type liquid desiccant system is carried out to identify important performance parameters. Two output parameters — enthalpy effectiveness and humidity effectiveness — are defined to present the results. Based on the conclusions drawn from the detailed sensitivity analysis, a simple model is developed to predict the performance of an absorber and a regenerator at partial load operating conditions. Performance predictions using the simple model are compared with the predictions from the detailed analysis along with another existing model which is available in the literature. The simple model is in excellent agreement with the predictions of other two models.     

A two-stage modelling and optimization of biohydrogen production from a mixture of agro-municipal waste

A two-stage modelling and optimization of biohydrogen production is reported. A mixture design was used to determine the optimum proportions of bean husk (BH), corn stalk (CS), and organic fraction of solid municipal waste (OFSMW). The optimum operational setpoints for substrate concentration, pH, temperature and hydraulic retention time (HRT) were further investigated using the box-behnken design. The quadratic polynomial model from the mixture design had a coefficient of determination (R²) of 0.9427 and the optimized mixtures were in the ratio of OFSMW:BH:CS = 30:0:0 and OFSMW:BH:CS = 15:15:0 with yields of 56.47 ml H₂/g TVS and 41.16 ml H₂/g TVS respectively. Optimization on physico-chemical process parameters on the improved substrate gave the setpoints of 40.45 g/l, 7.9, 30.29 °C, 86.28 h for substrate concentration, pH, temperature and HRT respectively having a predicted H₂ yield of 57.73 ml H₂/g TVS. Model validation gave 58.62 ml H₂/g TVS, thus an improvement of 3.8% on the optimized mixture. Biohydrogen production can be significantly enhanced by a suitable mixture of agro-municipal waste and operational optimal setpoints.     

A review of modelling and optimisation techniques for district heating systems

This article provides an extensive survey on the modelling and optimisation of district heating systems (DHSs) focused on the heat distribution network. For this purpose, the major components of a DHS have been described and discussed, and their modelling has been briefly reviewed, including numerical simulation models for heat sources, end‐users, and especially the distribution network. The main deterministic and heuristic optimisation techniques are briefly described. Additionally, a single‐objective and multiobjective optimisation problem is generally formulated, and the main optimisation criteria for the design and operation of the distribution network are synthesised and analysed. The state of the art in DHS optimisation has been also reviewed and categorised. Finally, some recommendations for future developments were included.     

A review of limit load solutions for cylinders with axial cracks and development of new solutions

Limit load solutions for axially cracked cylinders are reviewed and compared with available finite element (FE) results. New limit solutions for thick-walled cylinders with axial cracks under internal pressure are developed to overcome problems in the existing solutions. The newly developed limit load solutions are a global solution for through-wall cracks, global solutions for internal/external surface cracks and local solutions for internal/external surface cracks. The newly developed limit pressure solutions are compared with available FE data and the results show that the predictions agree well with the FE results and are generally conservative.     

Comparison of particle swarm optimization and dynamic programming for large scale hydro unit load dispatch

Dynamic programming (DP) is one of classic and sophisticated optimization methods that have successfully been applied to solve the problem of hydro unit load dispatch (HULD). However, DP will be faced with the curse of dimensionality with the increase of unit number and installed generating capacity of hydropower station. With the appearance of the huge hydropower station similar to the Three George with 26 generators of 700 MW, it is hard to apply the DP to large scale HULD problem. It is crucial to seek for other optimization techniques in order to improve the operation quality and efficiency. Different with the most of literature about power generation scheduling that focused on the comparisons of novel PSO algorithms with other techniques, the paper will pay emphasis on comparison study of PSO with DP based on a case hydropower station. The objective of study is to seek for an effective and feasible method for the large scale of hydropower station of the current and future in China. This paper first compares the performance of PSO and DP using a sample load curve of the Wujiangdu hydropower plant located in the upper stream of the Yangtze River in China and contained five units with the installed capacity of 1250 MW. Next, the effect of different load interval and unit number on the optimal results and efficiency of two methods has also been implemented. The comparison results show that the PSO is feasible for HULD. Furthermore, we simulated the effect of the magnitude of unit number and load capacity on the optimal results and cost time. The simulation comparisons show that PSO has a great advantage over DP in the efficiency and will be one of effective methods for HULD problem of huge hydropower stations.     

Characterisation and modelling of a 5 kW PEMFC for transportation applications

In the framework of the French inter lab SPACT project (fuel cell systems for transportation applications), a 10 kW PEM fuel cell testing bench has been installed in 2002 in the national fuel cell test platform located in Belfort, France. The behaviour of a 5 kW fuel cell, fed with humidified pure hydrogen gas and compressed air, has been investigated by the Laboratory of Electrical Engineering and Systems (L2ES) in association with the French National Institute for Transport and Safety Research (INRETS).     

Mathematical modelling of a hydrocracking reactor for triglyceride conversion to biofuel: model establishment and validation

In the study, a 2D, non‐isothermal, heterogeneous model of a triglyceride hydrocracking reactor is investigated. The internal heat and mass transfer within the phases in the reactor were considered using the film theory. The conservation equations for energy and mass were solved simultaneously using appropriate numerical techniques whose reliability was assessed by comparison of the results with previously reported experimental data. The modelling was performed with consideration of two proposed hydrocracking kinetic models. The model predictions showed reasonable correlation with published experimental data and conversion rates. The calculations indicated that at feed temperature of 380 °C, liquid hourly space velocity of 8 h^?1 and hydrogen : feed ratio of 1500:1, the total triglyceride conversion was 82.54% for four major classes of hydrocarbons (light, middle, heavy and oligomerised). In addition, the concentration distribution and temperature profile along the reactor were investigated. The product concentrations along the reactor show that higher rates of production at the beginning of the reactor were achieved because of high concentration of triglyceride due to the exothermic hydrocracking reactions and counter‐current flow modes of triglyceride and hydrogen; a jump of 90 °C was shown at the beginning of the reactor temperature profile. Copyright © 2014 John Wiley & Sons, Ltd.     

Mathematical modelling of drying based on a surface evaporation source term for coupled energy and mass transfer

A mathematical model is developed by introducing a source term and using the coupled mass and energy balances based on the Luikov's system of equations. The source term is due to the surface evaporation of many particles in a solid bed. A numerical scheme based on explicit finite difference method is applied. The prediction of bulk temperature profile and moisture content from the model shows, qualitatively, the same trend as the experimental results found in literature. Additionally, parametric studies are performed to investigate the effect of different parameters such as the porosity, the heat and mass transfer coefficients and the velocity on the overall energy efficiency of the drying process. The present model provides better approximation to an actual drying process, especially in the initial and final periods of drying. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance characteristics and modelling of a micro gas turbine for their integration with thermally activated cooling technologies

We have developed a simple model of a micro gas turbine system operating at high ambient temperatures and characterized its performance with a view to integrating this system with thermally activated cooling technologies. To develop and validate this model, we used experimental data from the micro gas turbine test facility of the CREVER research centre. The microturbine components were modelled and the thermodynamic properties of air and combustion gases were estimated using a commercial process simulator. Important information such as net output power, microturbine fuel consumption and exhaust gas mass flow rate can be obtained with the empirical correlations we have developed in this study. This information can be useful for design exhaust gas fired absorption chillers. Copyright © 2006 John Wiley & Sons, Ltd.     

输配电线路智能导航巡检系统研究与设计

针对当前巡检工作存在到达难、定位难、监督难、上报及时率低的现状,提出基于GPS/GPRS、嵌入式GIS和移动数据库技术,结合全国导航地图,研发了线路智能导航巡检系统.利用GPS实现人员、设施定位,巡检轨迹采集以及缺失路网采集,为线路抢修、巡检是否到位监督和巡检路径规划提供数据;利用GPRS实时上报发现的各种隐患,为及时派遣并解决问题提供准确信息.示范工程实例表明,该研究成果能有效解决传统输配电线路巡检中存在的问题.     

Field test validation of Flex5, MSC.Adams,alaska/Wind and SIMPACK for load calculations on wind turbines

Load calculation is a very important part in the development of wind turbines. Prototype testing over the whole product life cycle is not possible. Accurate load calculations are necessary to ensure that the wind turbine withstands the loads during the expected lifetime. During the last 20years, Flex5 developed at the Danish Technical University has been used as standard tool for load calculation. Ongoing development leads to a more detailed simulation of wind turbines. A lot of general purpose multibody programs are available providing packages for load calculation of wind turbines. Within this contribution, the multibody codes Flex5, MSC.Adams, alaska/Wind and SIMPACK are compared with measurements on a prototype of a 2.05MW wind turbine developed by W2E Wind to Energy. The aim of this work is not to set one simulation package as reference but to validate all simulation packages by measurements on a physical wind turbine. A statistical and dynamical evaluation of simulation results and measurements by means of maximum, minimum, mean value, standard deviation and rainflow matrix has been performed to compare the simulation packages. The comparison of the values of wind turbine behaviour such as generated electrical power or rotor speed shows a good agreement between simulations and measurements. This could be expected because of the use of the same controller software as used on the physical wind turbine. Considering the interface loads of the wind turbine, differences occur between the simulation packages caused by different kinds of modelling. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimum allocation of heat transfer surface area for cooling load and COP optimization of a thermoelectric refrigerator

The theory of finite time thermodynamics is applied to analyze and optimize the performance of a thermoelectric refrigerator, which is composed of multi-elements. For the fixed total heat transfer surface area of two heat exchangers, the ratio of the heat transfer surface area of the high temperature side heat exchanger to the total heat transfer surface area of the heat exchangers is optimized for maximizing the cooling load and the coefficient of performance of the thermoelectric refrigerator. The effects of various parameters on the optimum performance are analyzed. The results may provide guides for the analysis and optimization of practical thermoelectric refrigerators.