高频震实台在消失模铸造生产线上的应用

介绍消失模铸造工艺对震实台的要求,高性能的震实台在消失模铸造中的重要性,并介绍美国GK公司的HDCT型重型高频震实台基本组成、性能特点以及在消失模铸造生产线的应用情况.     

简单模式的一种匹配方法

模式匹配是包括LFC在内的大多数函数式语言都具有的特点。文章在LFC语言现有的模式匹配实现方法的基础上,结合常用的模式匹配树的构造思想,设计了一种模式匹配方法。这种模式匹配方法通过计算给定模式集合的扩展集合来构造模式匹配树。虽然在最坏情况下,该方法与LFC现有实现的空间复杂度一样,但当函数定义是部分构造式,而定义中的非项模式覆盖了较多项时,这种模式匹配方法可以避免LFC语言现有实现中较大的编码空间。这个方法略作修改即可用于复杂的嵌套模式,是一种通用的模式匹配方法。     

A novel adaptive deadbeat- based control for load frequency control of low inertia system in interconnected zones north and south of Scotland

An adaptive deadbeat (ADB) controller was developed to investigate its capability in providing a fast frequency response to an electrical power system. This controller was developed to meet the requirements of the National Grid System Operability Framework (SOF), which requires frequency to be accelerated in line with a fast rate of change of frequency (RoCoF) when a high rate of nonsynchronous machines are presented. The controller’s parameters were optimized using particle swarm optimization (PSO) to ensure a robust operation and to maintain the proper operation of the power system. The design of the ADB controller was then integrated with the multiarea model of the north and south zones of Scotland. This model was developed in order to conform to the future energy requirements scenario stated by National Grid whereby regional control can be provided in both the north and south of Scotland. In comparison with the standard PI and Fuzzy-PI controllers used in the four highlighted case studies, it was shown that the ADB controller was able to significantly reduce the RoCoF and deviation of frequency when a sudden loss of generation occurred in a low inertia zone. The ADB also showed high robustness against a wide range of operating conditions.     

Multi objective load frequency control using hybrid bacterial foraging and particle swarm optimized PI controller

Excessive load demand with reliability in power availability, demands for interconnection of large number of generating units over existing tie lines. Due to sudden change in demand, the power transfer over existing tie lines working close to their thermal limits results in low frequency power oscillations. Thus, in modern power systems the study of mitigation of these frequency oscillations is more involved and formulates the area of Load Frequency Control (LFC). Many conventional and heuristic control techniques have been recently applied to address the issue of LFC. This paper investigates load frequency control of large interconnected power system consisting of conventional and renewable energy sources, using hybrid heuristic approach. The proposed strategy is shown to result in improved system damping resulting in faster mitigation of low frequency oscillations.     

The strength of coating in the lost foam casting process

The functions of the coating in the lost foam casting (LFC) process include developing the strength to support unbonded sand and providing permeable channels to permeate the decomposed expandable polystyrene pattern in-mould. The strengths of coatings developed at room temperature differ from those at a high temperature owing to the heat effect introduced by the filling metal. In this study, we examine the effect of shape and size of refractory particle, and type and added weight per cent of binder in the coating on the strength of the coating.

Experimental results indicate that for either a given particle size or a given wt% of a binder, the coating using flaky alumina and acrylic resin (binder B) develops the greatest strength at room temperature and the greatest hot strength. If a polyvinyl acetate (binder A) is used, the coating generally develops an inferior strength to that of acrylic resin (binder B). For a given resin used in the coating, angular silica used as the refractory particle decreases the strength of the coating at room temperature and its hot strength. In addition, pouring trials demonstrate that if alumina particles (74 μm, mesh No. 200) are added to the coating, the optimum wt% of acrylic resin is 0.25% to 1%. Those coatings produce sound and smooth grey iron plate castings, (5 mm in thickness). Moreover, the optimum wt% of acrylic resin is 0.25% for those producing sound and smooth thick plate castings, (20 mm in thickness).     

Numerical simulation of heat transfer and fluid flow of molten metal in MMA–St copolymer lost foam casting process

In this study, a computational fluid dynamics (CFD) code was developed to calculate the filling pattern using volume of fluid (VOF) algorithm with donor–acceptor method for free surface simulation. This algorithm has been modified to include the pressure of the gas produced from foam degradation. For this purpose a heat transfer model and 2D foam degradation model were developed. In heat transfer model, radiation and conduction between foam and molten metal; and convection between gas and molten metal were considered. In order to evaluate the results of simulation, a bench scale casting apparatus was assembled and the casting was conducted in a transparent mold. The effect of several parameters such as coating thickness, foam density and vacuum level on the gap temperature, gap pressure and filling speed was studied with the developed software. It was found that the simulated results are in good agreement with experimental results.     

自动发电控制研究综述

随着能源危机和环境污染的问题越来越严重,以风电和光伏为代表的可再生能源被大规模地开发利用,电力系统运行稳定性也成为了国内外广泛关注的问题之一。本文首先阐述了自动发电控制(Automatic Generation Control, AGC)的控制原理和控制模式,接着讨论了负荷频率控制(Load Frequency Control, LFC)和经济调度控制(Economic Dispatch Control, EDC)策略的研究现状,通过分析各类方法的优缺点,指出了目前AGC研究存在的一些问题。针对这些问题,进一步阐述了动态AGC控制策略的研究情况,最后对未来AGC领域的发展方向进行了讨论。     

美国低阶煤提质技术发展概述

回顾了美国低阶煤提质技术的发展历程;重点介绍了LFC技术和ACCP技术的工艺流程、技术特点、开发历程和商业化示范装置运行概况;综合分析认为,LFC技术和ACCP技术已具备商业化应用的技术基础,建议我国可适时引进美国低阶煤提质技术,以提升我国低阶煤加工技术的进步。     

负荷频率系统的LFC模糊监控器设计

应用在LFC控制中常规的模糊调整增益PI控制器和I控制器,只针对单一区域的负荷频率进行控制,并不考虑实际模型中的互相扰动.其中最突出的问题是由于不限制联络线上的功率流动,电能总是从频率高区域流向频率低区域,加剧了频率高区域的控制负担,再加上各区域控制动作的不协调,使得当扰动在不同的时间和幅值时引起系统调节过程的急剧恶化,导致整个系统不稳定.提出一种基于模糊MAMDANI推理算法的模糊监督控制器,采用各个区域的频率偏差作为控制器的输入,监督控制器作为一种前馈补偿,设计输出为一个ACE的倍数,加快调节过程,到达稳态.经过实验仿真数据对比,说明提出的监督控制器能有效提高系统的稳定性.     

Simulation based neuro-fuzzy hybrid intelligent PI control approach in four-area load frequency control of interconnected power system

This paper presents a novel control approach of hybrid neuro-fuzzy (HNF) for load frequency control (LFC) of four-area power system. The advantage of this controller is that it can handle the non-linearities, and at the same time it is faster than other existing controllers. The effectiveness of proposed controller in increasing the damping of local and inter area modes of oscillation is demonstrated in four area interconnected power system. Area-1 and area-2 consist of thermal reheat power plant whereas area-3 and area-4 consist of hydro power plant. Performance evaluation is carried out by using fuzzy, ANN, ANFIS and conventional PI and PID control approaches. The performances of the controllers are simulated using MATLAB/Simulink package. The result shows that intelligent HNF controller is having improved dynamic response and at the same time faster than ANN, fuzzy and conventional PI and PID controllers.