Optimization of equipment capacity and an operational method based on cost analysis of a fuel cell microgrid

A microgrid requires a stable supply of electric power and heat, which is achieved by the cooperative operation of two or more pieces of equipment. The equipment capacity and the operational method of the equipment were optimized using a newly developed orthogonal array-GA (genetic algorithm) hybrid method for an independent microgrid accompanied by a fuel cell cascade system, solar water electrolysis, battery, and heat storage. This type of system had not been hardly developed until now. The objective function of the proposed system was the minimization of the total amount of equipment and fuel cost over ten years. For the first step in the proposed analysis method, the capacity of each piece of equipment and the operational method, which are considered to be close to the optimal solution of the system, are combined using the orthogonal array and factorial-effect chart, which are an experimental design technique. In the next step, the combination described above provides the initial values to the GA, and the GA searches for the optimal capacity and operational method for each piece of equipment in question. Compared with a simple GA, the convergence characteristic improves greatly using the proposed analysis method developed in this study.     

一种新型分布式供能系统的研究

本文在介绍了生物质能的利用方式以及分布式供能系统的基础上,介绍了一种以生物质能为原料的可再生能源的分布式供能方式,详细介绍了系统中各设备的运行情况,并分析了这种分布式供能系统的经济效益和社会效益。     

Simplified fitness-for-service assessment of pressure vessels and piping systems containing thermal hot spots and corrosion damage

Fitness-for-service (FFS) assessment is a quantitative engineering evaluation of operational components. In the context of pressure vessels and piping systems FFS assessment is performed periodically to ensure the operational safety and structural integrity. In this paper, a simplified method is developed for Level 2 FFS assessment (as described in API 579) of pressure vessels and piping systems containing thermal hot spots or corrosion damage. The method is based upon variational principles in plasticity, the m_α-tangent method (an extension of the m_α method), the concept of decay length and reference volume. The use of the m_α-tangent method extends the range of applicability to components and structures experiencing significant stress gradients in and around the damaged spot. The method is shown to provide a reasonably accurate estimate of the remaining strength of ageing pressure components. The method is demonstrated through an example, and the results are compared with Level 3 inelastic finite element analyses.     

Procedure for probabilistic safety assessment of leaks and breaks of piping systems

The estimation of leak and break frequencies in piping systems is part of the probabilistic safety assessment of technical plants. In this paper, a statistical method based on the evaluation of German operational experience for piping systems with different diameters is described because an earlier estimation has been updated and extended introducing new methodical aspects and data. A major point is the inclusion of structural reliability models based on fracture mechanics calculation procedures. As an example of application the statistical estimation method for leak and break frequencies of piping systems with a nominal diameter of 50 mm (the volume control system of a German pressurized water reactor) was updated. Moreover, the evaluation of the operational experience was extended to 341 years with respect to cracks, leaks and breaks in the volume control system of German pressurized water reactors (PWR). Using the actual database, new calculations of leak and break frequencies have been performed and the results have been compared with previous values.     

Lead-acid batteries for remote photovoltaic applications

The various load profile characteristics most commonly encountered in photovoltaic installations are analyzed in conjunction with solar array and battery performance data and used to generate battery specifications with particular respect to operating characteristics and cycle life requirements.The design of lead-acid batteries for photovoltaic applications is discussed and illustrated with both operating, maintenance, and cycle life data. Other performance characteristics of lead-acid photovoltaic batteries are described including the effects of operating temperature and the correct choice of charging method for various operational requirements.     

基于属性模糊聚类和关联规则的锅炉异常工况分析

针对火电厂锅炉运行过程复杂,而且异常工况难以分析的状况,提出了一种新的分析方法.该方法融合属性模糊聚类和关联规则算法两种数据挖掘技术,利用属性模糊聚类方法建立锅炉各运行参数对类别的不确定性描述,选择出代表性分析参数;利用经典的Apriori算法和改进的关联规则找出这些参数的关系.通过2个超温的实例对该方法进行分析考核.结果表明:它不仅充分利用了电厂DCS系统存储的海量数据,而且可实现故障诊断、运行指导等,并可满足诊断的实时性要求,从而可保证锅炉乃至整个机组的安全运行.     

Research on twin trawling charging-discharging experimental method for the magnetically suspended flywheel-based dynamic UPS system

首先介绍飞轮动态UPS系统组成及工作原理,并对飞轮交流并网拓扑及阵列结构进行分析。在此基础上,针对电网容量受限和电能浪费问题,开展基于飞轮阵列对拖充放电实验方法研究。通过搭建飞轮阵列硬件平台,给出飞轮UPS的直流母线并网逻辑、软件控制架构和实际对拖实验运行过程。最后给出了磁悬浮飞轮动态UPS实验装置和系统参数。     

Operational costs induced by fluctuating wind power production in Germany and Scandinavia

Adding wind power generation in a power system changes the operational patterns of the existing units due to the variability and partial predictability of wind power production. For large amounts of wind power production, the expectation is that the specific operational costs (fuel costs, start-up costs, variable operation and maintenance costs, costs of consuming CO2 emission permits) of the other power plants will increase due to more operation time in part-load and more start-ups. The change in operational costs induced by the wind power production can only be calculated by comparing the operational costs in two power system configurations: with wind power production and with alternative wind production having properties such as conventional production, that is, being predictable and less variable. The choice of the characteristics of the alternative production is not straightforward and will therefore influence the operational costs induced by wind power production. A method is applied for calculating the change in operational costs due to wind power production using a stochastic optimisation model covering the power systems in Germany and the Nordic countries. Two cases of alternative production are used to calculate the change in operational costs, namely perfectly predictable wind power production enabling the calculation of the costs connected to partial predictability and constant wind power production enabling the calculation of the operational costs connected to variability of wind power production. A 2010 case with three different wind power production penetration levels is analysed.     

基于复杂性理论的水资源配置框架及方法体系

鉴于以特定需求驱动的传统水资源配置模型缺乏可操作性、集成性、动态性的问题日益凸显,在分析水资源配置系统具有复杂大系统特点的基础上,采用复杂性理论,建立具有复杂配水网络图、动力学配水模型、模拟仿真演化、预测分析模块的复杂水资源配置框架,并对利用知识图概化配水网络图、多目标动态配水行为构建和综合集成预测等方法体系进行详细说明。同时,综合采用WebService技术、知识可视化技术、组件化技术进行实现。实例应用表明,基于复杂性理论的水资源配置框架体系具有可操作性和实用性,能够满足合理、有效、动态的水资源配置要求,辅助配水决策。     

Ringhals No. 2—Steam generator repair/replacement options

This paper reports on steam generator operational experience in Ringhals No. 2 PWR nuclear power plant. A study carried out to find the cause of corrosion and to make a steam generator performance prognosis is presented. The screening of different remedies and the final selection of options is described.

After taking into account technical aspects and evaluating operational economy and radiation exposure during the remaining life of the unit, the replacement of the steam generators in Ringhals No. 2 was found to be the optimum solution.     

A numerical solution for a stochastic beam equation exhibiting purely viscous behavior

The deflection of Euler–Bernoulli beams under stochastic dynamic loading, exhibiting purely viscous behavior, is characterized by partial differential equations of the fourth order. This paper proposes a computational method to determine the approximate solution to such equations. The functions are approximated using two-dimensional shifted Legendre polynomials. An operational matrix of integration and an operational matrix of stochastic integration are derived. The operational matrices assist in breaking down the problem under consideration into a set of algebraic equations that may be solved using any known numerical technique that leads to the solution of the stochastic beam equation. The well-posedness of the problem is studied. The proposed methodology is demonstrated to be practical for addressing the novel stochastic dynamic loading problem by confirming the outcome using a few numerical examples. Thus the effectiveness and applicability of the technique are ensured. The solution quality is explored through diagrams. The accuracy of the method is substantiated by comparing it with the Runge–Kutta method of order 1.5 (R–K 1.5). The absolute error caused by the proposed technique is comparably much less than R–K 1.5. A simulation analysis is carried out with MATLAB, and an algorithm is developed.     

Optimal operational strategy for a future electricity and hydrogen supply system in a residential area

This study introduces a novel framework of an electricity and hydrogen supply system integrating with a photovoltaic power station for a residential area. The non-residential parts including the power grid and non-residential vehicles are added to ensure power balance and bring benefits, respectively. The optimal operational strategy of the proposed framework with considering uncertainties is proposed. The objective function minimizes the expected operational cost (EOC) by reducing the imported electricity from the power grid and increasing exported electricity/hydrogen to non-residential vehicles. Additionally, the demand response program (DRP) is applied in the residential load to achieve operational cost reduction. The uncertainties are modeled via various scenarios by using scenario-based stochastic optimization method. Notably, existing research for similar frameworks both lacks the consideration of uncertainties and DRP, and fails to distinguish the residential and non-residential vehicles with different charging behaviors. The results indicate that 1) The feasibility of the proposed framework is validated which can ensure the power balance of the residential area and reduce the operational cost. 2) The EOC is reduced when considering DRP.     

The performance of a remote wind–diesel power system

The collection and analysis of 6 months of continuously recorded field data from a small remote wind–diesel power system at a coastal farm site is reported. The power system and the data acquisition unit are described and the performance characteristics of the major components discussed. Analysis of the field data has led to a number of recommendations for possible improvement in component sizing and control strategy. The siting of the turbine is excellent by international standards and the annual wind energy produced is greater than the demand. However, almost a fifth of the wind energy generated has to be dumped due to the short-term oversupply of power and over one-quarter of the total energy supplied still comes from the diesel generator as a result of transient energy deficits. An operational strategy that can deal with this paradox of alternating supply and demand excesses could lead to further operational improvements.     

二次网定速水泵运行曲线拟合与分析

建立应用最小二乘法进行水泵运行曲线拟合的数学模型并根据工程实例求解,得到各水泵实际运行曲线和在管路中的工况点,并对不合理的运行方式提出了改进办法。     

Design of multiperiod hydrogen network with flexibilities in subperiods and redundancy control

To ensure the operational flexibility of multiperiod hydrogen network and reduce the capacity redundancy of compressors, a method for design of multiperiod hydrogen network is proposed based on flexibility analysis. In the proposed method, an initial multiperiod hydrogen network is obtained by solving the single period optimization models of hydrogen networks for each subperiod, where the minimal capacities of compressors in different subperiods are assigned. Then, the flexibility of the initial multiperiod hydrogen network is examined and improved by solving a proposed flexible design model to identify the bottlenecks of operational flexibility of each subperiod. The additional capacities of compressors and flowrates of hydrogen utility in each subperiod are then determined to finalize the design of the flexible multiperiod hydrogen network with the redundancy control of compressors capacities. The application of the proposed method are illustrated via a hydrogen network of a refinery in China.     

Considerations on the backup of wind power: Operational backup

The introduction of wind power into an electricity-generation system on a large scale brings about challenges for the evolution and operation of this system: backup for wind power becomes a necessity. This paper defines various elements that come into play when considering backup for electricity generation from wind power. The backup is split up in capacity backup and operational backup. The focus is set on the short-term, operational aspects of the backup provision. The effects of several short-term operation related parameters are defined and analysed. Most relevant parameters for the operation and needs for wind power backup are the load profiles, the wind power output profiles and the total amount of installed wind power. These are analysed by means of a Mixed Integer Linear Programming (MILP) model through two different methods for operational backup provision, comparing the incremental cost, generated by both methods. The first method applies wind power backup through a 100% provision of additional spinning reserves. The second method does not foresee any spinning reserve and relies on the balancing by the Transmission System Operator (TSO). Both methods result in different additional charges that are being affected by the said parameters. Both the wind profile and the total amount of installed wind power are positively related to the relative cost increase. The load profile is negatively correlated to this increase. The relationship between these parameters and the development of the incremental cost provides an understanding that allows finding better equilibria in the operational backup of wind power.     

基于数据包络分析法的发电商运营效率测算及影响因素

基于数据包络分析法效率评价模型,在考虑传统技术、规模因素的基础上,将影响发电商运营效率的发电可靠性和环境约束等因素纳入分析,建立了输入/输出变量体系,对发电商运营效率实施评估。算例分析表明,数据包络分析法能有效地评估发电商运营效率,并为发电企业的未来发展提供相应的决策支持。     

基于ANFIS和SOM的抽水蓄能电站主变压器健康状态监测

针对抽水蓄能电站主变压器运行工况多变、状态信息复杂,难以实现健康状态监测的问题,提出基于自适应模糊推理系统(ANFIS)和自组织映射(SOM)的主变压器健康状态监测方法。该方法充分考虑主变压器运行工况多变,健康状态特征的高维和非线性特点,采用ANFIS消除运行工况对单状态特征参数异常监测精度的影响,并在此基础上利用SOM建立多特征融合的健康状态监测模型,采用最小量化误差(MQE)作为变压器健康状态监测指标。将该方法用于某抽水蓄能电站主变压器的健康状态监测,发现该方法可提前监测到主变压器健康状态的衰退,从而实现故障的早期预警,避免严重故障发生,并为运行和检修决策提供了依据。     

A hybrid method for simultaneous optimization of DG capacity and operational strategy in microgrids considering uncertainty in electricity price forecasting

Recently, microgrids have attracted considerable attention as a high-quality and reliable source of electricity. In this work energy management in microgrids is addressed in light of economic and environmental restrictions through (a) development of an operational strategy for energy management in microgrids and (b) determination of type and capacity of distributed generation (DG) sources as well as the capacity of storage devices (SD) based on optimization. Net present value is used as an economic indicator for justification of investment in microgrids. The proposed NPV-based objective function accounts for the expenses including the initial investment costs, operational strategy costs, purchase of electricity from the utility, maintenance and operational costs, as well as revenues including those associated with reduction in non-delivered energy, the credit for reduction in levels of environmental pollution, and sales of electricity back to the utility. The optimal solution maximizing the objective function is obtained using a hybrid optimization method which combines the quadratic programming (QP) and the particle swarm optimization (PSO) algorithms to determine the optimum capacity of the sources as well as the appropriate operational strategy for the microgrid. The fuzzy set theory is employed to account for the uncertainties associated with electrical power price. Application of the proposed method under different operational scenarios serves to demonstrate the efficiency of the proposed scheme.     

An algebraic approach for identifying operating point dependentparameters of synchronous machines using orthogonal series expansions

This paper presents a method for identifying armature and field parameters of synchronous machines from digital fault recorder (DFR) data. The method uses operational properties of orthogonal series expansions such as the Hartley, Walsh and Fourier series to transform a set of differential equations into linear algebraic equations. The algebraic formulation and use of operational calculus reduce the problem of identifying parameters to the manipulation of matrices that may be easily performed in such computational packages as Matlab. The variation of machine parameters with operating point is considered