Improved synergetic excitation control for transient stability enhancement and voltage regulation of power systems

This paper proposes decentralized improved synergetic excitation controllers (ISEC) for synchronous generators to enhance transient stability and obtain satisfactory voltage regulation performance of power systems. Each generator is considered as a subsystem, for which an ISEC is designed. According to the control objectives, a manifold, which is a linear combination of the deviation of generator terminal voltage, rotor speed and active power, is chosen for the design of ISEC. Compared with the conventional synergetic excitation controller (CSEC), a parameter adaptation scheme is proposed for updating the controller parameter online in order to improve the transient stability and voltage regulation performance simultaneously under various operating conditions. Case studies are undertaken on a single-machine infinite-bus power system and a two-area four-machine power system, respectively. Simulation results show the ISEC can provide better damping and voltage regulation performance, compared with the CSEC without parameter adaptation scheme and the conventional power system stabilizer.     

Optimised phase compositions and improved microwave dielectric properties based on calcium tin silicates

The Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) low-permittivity microwave dielectric ceramics were prepared through solid-state reaction at 1350–1450 °C for 5 h. The relations between microwave dielectric properties and phase compositions for non-stoichiometric Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) ceramics have been investigated. A single CaSnSiO₅ phase with abnormally positive temperature coefficient of resonant frequency (τ_f = + 62.5 ppm/°C) was synthesised at 1450 °C. This composition was an effective τ_f compensator of CaSiO₃ and Ca₃SnSi₂O₉ phases with typically negative τ_f value. The CaSiO₃ second phase was related to the Sn deficiency in the CaSn_(1-x)SiO_(5-2x) (0 < x < 1.0) composition, whereas the Ca₃SnSi₂O₉ second phase was obtained by controlling the Ca:Sn:Si ratios on the basis of the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (0 < y < 1.0) composition. A promising low-permittivity millimetre-wave ceramic with most excellent microwave dielectric properties (ε_r = 10.2, Q×f = 81,000 GHz and τ_f = −4.8 ppm/°C) was produced from the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (y = 0.4) ceramic.     

葛洲坝水力发电厂自动化技术应用概述

以葛洲坝水力发电厂主要自动化技术应用与设备改造为线索，重点回顾 了该厂实现计算机实时监控、全面提高综合自动化水平的历程；全面总结了该厂为实现“无 人值班”（少人值守）而进行的自动化设备换型改造情况和自动化新技术的应用情况；简要 阐述了自动化技术应用给该厂在运行和管理方面带来的深刻变化；展望了该厂未来自动化技 术应用的前景。     

三峡三期大坝工程大体积温控技术综述

葛洲坝集团公司在三峡三期大坝工程大体积混凝土施工中加强过程控制，采用优化减水剂参量、采用低热水泥和高效减水剂控制出机口温度，供料浅降温、仓面降温和保温，通冷水等。并应用新材料、新工艺，实行精细化管理，从2003年8月开工至今，浇筑了200万m^3大体积混凝土术出现一条裂缝，保证了施工质量。     

Papermaking characteristics of three Populus clones grown in the north-central United States

The papermaking properties of 22 pure and hybrid poplars are being evaluated in an on-going investigation. Twenty of the poplars were harvested after 7.5 years from three different sites in the Midwestern and North Central US. The other 2 poplars survived at only two of three sites (64 total samples). The Crandon hybrid had the highest growth rate (t ha⁻¹ y⁻¹) and wood density (both averaged across the 3 sites). This poplar had a high cellulose content (compared to the average), a low lignin content and produced bleached kraft fibers at a high yield (wt.% on wood chips). Further, this poplar responded very well to kraft pulping and oxygen delignification and bleached to the highest final brightness ever observed in our laboratory (94.5% Elrepho). It also produced an 18 kappa number unbleached pulp with <0.5% rejects in only two-thirds the time required for sugar maple (Acer saccharum).We also report on clone 220-5 that had the highest area-weighted average microfibril angle. Pulps from this poplar had excellent tensile properties and further improvements are expected with 1–2 years of additional growth that should result in a small, but significant increase in average fiber length. Some results are also presented for clone 313.55 and aspen (Populus tremuloides) to demonstrate the many substantial benefits that can be accrued from proper wood selection.     

视错觉及其应用

视觉足人类获取外部信息的最重要方式。但由于人类自身的生理、心理因素以及外界光、形、色等因素的干扰,会产生视觉误差,即视错觉。本章系统的分析了视错觉产生原因,按不同的现象和成因把视错觉分成病理视错觉、动态视错觉、几何视错觉、颜色视错觉、轮廓错觉等5类。在此基础上介绍了视错觉的应用,特别介绍了其在图像融合中的应用,并用matlab实现了图像的融合。     

带平衡约束矩形布局优化问题的深度强化学习算法

带平衡约束的矩形布局问题源于卫星舱设备布局设计,属于组合优化问题。深度强化学习利用奖赏机制,通过数据训练实现高性能决策优化。针对布局优化问题,提出一种基于深度强化学习的新算法DAR及其扩展算法IDAR。DAR用指针网络输出定位顺序,再利用定位机制给出布局结果,算法的时间复杂度是O（n³）;IDAR算法在DAR的基础上引入迭代机制,算法时间复杂度是O（n⁴）,但能给出更好的结果。测试表明DAR算法具有较好的学习能力,用小型布局问题进行求解训练所获得的模型,能有效应用在大型问题上。在两个大规模典型算例的对照实验中,提出算法分别超出和接近目前最优解,具有时间和质量上的优势。     

组合隔板式鱼道水力特性数值模拟研究

鱼道是为鱼类提供洄游通道的一种重要的工程措施。基于Flow-3D采用标准RNG k-ε紊流模型和Tru-VOF追踪自由液面方法,对鱼道池室内流场进行三维紊流数值模拟,研究池室内水流流速、流态空间分布,分析鱼道的水力特性对目标鱼类洄游上溯的影响。结果表明:溢流堰与竖缝组合隔板式鱼道在设计流速v=0.75 m/s条件下,竖缝处平均流速为0.83 m/s,竖缝处流速分布范围为0.76~0.89 m/s;堰上流速为0.90~1.12 m/s,回流区流速分布范围为0.09~0.25 m/s,流速大小在鱼类的克流能力范围之内,但靠竖缝隔板处存在明显的主流贴壁现象。为此开展了池室优化方案设计,使鱼道池室流态满足鱼类上溯要求。     

真三轴应力下混凝土的动态力学性能及破坏准则

为研究混凝土结构处于复杂应力状态下的静动态力学特性,进行了不同应力比及加载速率下的真三轴压缩试验。对混凝土的强度特性和变形特性展开了深入分析,并基于八面体应力空间建立了考虑应变速率效应的真三轴动态破坏准则。结果表明:真三轴受压下的混凝土极限抗压强度随着应力比的增大而增大。随着应变速率的增加,应力比较低时,混凝土的极限抗压强度逐渐增大;应力比较高时,极限抗压强度先减小后增加。随着应变速率的增加,侧向变形曲线的破坏峰值点更明显;随着应力比的增大,侧应力较大方向上的变形越来越小。基于八面体应力空间建立的真三轴动态破坏准则表达式中包含3个率效应参数,经验证与试验数据吻合较好。