Damping forced oscillations in power system via interline power flow controller with additional repetitive control

With the continuous expansion of power systems and the application of power electronic equipment, forced oscillation has become one of the key problems in terms of system safety and stability. In this paper, an interline power flow controller (IPFC) is used as a power suppression carrier and its mechanism is analyzed using the linearized state-space method to improve the system damping ratio. It is shown that although the IPFC can suppress forced oscillation with well-designed parameters, its capability of improving the system damping ratio is limited. Thus, combined with the repetitive control method, an additional repetitive controller (ARC) is proposed to further dampen the forced power oscillation. The ARC control scheme is characterized by outstanding tracking performance to a system steady reference value, and the main IPFC controller with the ARC can provide higher damping, and further reduce the amplitude of oscillations to zero compared with a supplementary damping controller (SDC). Simulation results show that the IPFC with an ARC can not only greatly reduce the oscillation amplitude, but also actively output the compensation power according to the reference value of the ARC tracking system.     

一种基于四变量模型的系统安全性建模与分析方法

近年来,基于模型的系统安全性分析与验证方法是安全关键系统工程领域中的一个重要研究方向。提出了一种基于四变量模型的系统安全性建模与分析验证方法,该方法利用AltaRica建模语言对系统进行建模。通过对四变量模型及AltaRica进行语义研究构建二者之间的映射规则,以民用飞机中机轮刹车系统(Wheel Brake System,WBS)为例来说明整个验证过程,即首先利用四变量模型从系统的需求层次上对WBS进行需求分析并根据映射关系构建AltaRica模型,接着利用故障树分析方法对WBS进行安全性研究,最后基于AltaRica配套工具ARC对系统的安全性属性进行验证。验证结果表明了该方法在系统安全工程领域中的实用性。     

分布式环境下的并行处理ARC／INFO飞行动画生成技术

针对ARC／INFO系统中飞行动画生成速度慢的问题,分析了速度慢的原因,提出了用并行处理技术来加速的思想,设计了相应的并行算法,并在cluster结构上实现了飞行动画生成并行处理,经实际应用达到了提高计算速度,满足实时性要求的目的。     

ROBUST CONTROL OF GAS TUNGSTEN ARC WELDING SYSTEM

The robust control law for gas tungsten arc welding dynamic process, which is a typical sampled-data system and full of uncertainties, is presented. By using the Lyapunov second method, the robust control and robust optimal control for a class of sampled-data systems whose underlying continuous-time systems are subjected to structured uncertainties are discussed in time-domain. As a result, some sufficient conditions of robust stability and the corresponding robust control laws are derived. All these results are designed by solving a class of linear matrix inequalities (LMIs) and a class of dynamic optimization problem with LMIs constraints respectively. An example adapted under some experimental conditions in the dynamic process of gas tungsten arc welding system in which the controlled variable is the backside width of weld pool and controlling variable pulse duty ratio, is worked out to illustrate the proposed results, it is shown that the sampling period is the crucial design parameter.     

Thermal and Spectroscopic Analyses of Caustic Side Solvent Extraction Solvent Contacted with 16 Molar and 8 Molar Nitric Acid

Abstract

Thermal and spectroscopic analyses were performed on multiple layers formed when Caustic Side Solvent Extraction (CSSX) solvent was contacted with 16 M or 8 M nitric acid. A rapid (i.e., minutes to hours) chemical reaction occurs between the solvent and 16 M or 8 M nitric acid as evidenced by color changes and the detection of nitro groups in the infrared spectrum of the aged samples. Thermal analysis revealed that decomposition of the resulting mixture does not meet the definition of explosive or deflagrating material.     

A way to reduce environmental impact of ladle furnace slag

Abstract

In the last decades the European steel industry has made continuous efforts to reduce residues and byproducts and to increase recycling in order to reduce its environmental impact. While some steelmaking slags have been widely characterised and, to a certain extent reused, ladle furnace (LF) slag is used in different applications because of its specific properties. The main purpose of the case study presented in this paper concerns the reduction of potential LF slag environmental impacts, because of its intrinsic physicochemical properties. During the handling and cooling of LF slag, it disintegrates into a powder due to instability of the dicalcium silicate, causing an increase in dust emissions to the environment. The approach presented in this paper aims to reduce this phenomenon in order to achieve a more sustainable solution in term of reduction of powder dispersion in the environment, of costs saving and of nuisance reduction in the surroundings areas.     

锂离子电池的可逆及不可逆产热测试

针对商业化的圆柱型18650锂离子电池,对其在充放电过程中的可逆及不可逆产热参数分别进行测试和计算,结合绝热加速量热仪(ARC)对电池放热的实测数据进行拟合分析,结果表明:根据该测试方法计算的可逆及不可逆产热数值与实测值具有很好的吻合性;该电池在0.3 C充放电过程中的总产热功率变化情况由可逆产热功率决定;可逆产热功率在电池荷电态为20%~60%区间内呈现出一个最高峰,对应电池发生熵变的脱嵌锂电化学主反应;不可逆产热功率在低荷电态下较高,而在其他荷电区间内变化幅度较小;电池在充放电过程中的总产热功率曲线是以不可逆产热功率曲线为对称轴,而在形状上基本呈现为上下对称。     

Neural network model of heat and fluid flow in gas metal arc fillet welding based on genetic algorithm and conjugate gradient optimisation

Abstract

Although numerical calculations of heat transfer and fluid flow can provide detailed insights into welding processes and welded materials, these calculations are complex and unsuitable in situations where rapid calculations are needed. A recourse is to train and validate a neural network, using results from a well tested heat and fluid flow model to significantly expedite calculations and ensure that the computed results conform to the basic laws of conservation of mass, momentum and energy. Seven feedforward neural networks were developed for gas metal arc (GMA) fillet welding, one each for predicting penetration, leg length, throat, weld pool length, cooling time between 800°C and 500°C, maximum velocity and peak temperature in the weld pool. Each model considered 22 inputs that included all the welding variables, such as current, voltage, welding speed, wire radius, wire feed rate, arc efficiency, arc radius, power distribution, and material properties such as thermal conductivity, specific heat and temperature coefficient of surface tension. The weights in the neural network models were calculated using the conjugate gradient (CG) method and by a hybrid optimisation scheme involving the CG method and a genetic algorithm (GA). The neural network produced by the hybrid optimisation model produced better results than the networks based on the CG method with various sets of randomised initial weights. The CG method alone was unable to find the best optimal weights for achieving low errors. The hybrid optimisation scheme helped in finding optimal weights through a global search, as evidenced by good agreement between all the outputs from the neural networks and the corresponding results from the heat and fluid flow model.     

Prediction of residual stress distributions for single weld beads deposited on to SA508 steel including phase transformation effects

Abstract

The sensitivity of residual stress distributions in bainitic–martensitic steel welds to the transformation strains that arise when austenite decomposes on cooling has been assessed by examining the predictions of three models for a simple bead-on-plate configuration. These cover the following scenarios: case I, no phase transformations; case II, transformations with volume change effects only; case III, transformations with volume change effects and associated Greenwood–Johnson transformation plasticity. Austenite decomposition was predicted by implementing Kirkaldy's reaction rate equations as a subroutine in the finite element code Sysweld, eliminating the need for a continuous cooling transformation diagram. Predicted residual stresses were then compared and rationalised alongside measurements obtained by neutron diffraction and the contour method. It was found that serious errors in predicting the location and magnitude of the peak stresses occurred if transformations were not included, while cases II and III gave similar results generally in agreement with the stress maps. Indeed, the trends in the experimental results were intermediate between cases II and III. Differences between the models and the potential for further improvements are discussed.     

多节等径直角弯头展开图的一种近似画法

本文介绍了一种用半径为R的圆弧绘制多节等径直角弯头展开曲线的方法——圆弧法。该方法能绘制任意弯头半径、管口直径、节数、剪开方位的斜口管展开图。并着重对圆弧法和精确作图的计算方法,进行了数学分析比较,其绝对误差和相对误差都较小,证明了用圆弧法绘展开图有一定的准确性,且随着节数增多、弯头半径增大,其准确度越高,因此,本方法绘图简便、灵活,有一定的实用价值。