Modified Single Phase SRF d-q Theory Based Controller for DVR Mitigating Voltage Sag in Case of Nonlinear Load

This paper mainly concentrates on design of improved controller and its implementation based on single phase synchronous reference frame theory (SRFT) for Dynamic Voltage Restorer (DVR) compensating voltage sag particularly for nonlinear load. In case of single phase distribution line with nonlinear load, the complexity of controller’s design becomes more serious issue. The present single phase and/or three phase theories applicable to DVR shows poor response to restore voltage sag in case of nonlinear load due to presence of harmonics. Hence restoration of voltage sag in single phase nonlinear load connected system has been a serious concern. Therefore, new controller for DVR has been proposed incorporating effective design concept for fundamental component extraction in case of nonlinear load. The single phase SRFT based main controller for DVR works on two separate closed path viz. feed forward path for quick transient response and feedback path for reducing the steady state error. Moreover, pre-sag mitigation strategy of DVR has been adapted through these two aforementioned paths. Complete design of proposed controller is based on phasor analysis. It also consist of proportional integral (PI) controller to reduce the error in the DC-link voltage during compensation time. The controller performance has been verified in MATLAB Simulink for both types (linear and nonlinear) of load. The results obtained indicates that the proposed controller is effective in its performance.

Isolated Area Load Forecasting using Linear Regression Analysis: Practical Approach

This paper presents an analysis to forecast the loads of an isolated area where the history of load is not available or the history may not represent the realistic demand of electricity. The analysis is done through linear regression and based on the identification of factors on which electrical load growth depends. To determine the identification factors, areas are selected whose histories of load growth rate known and the load growth deciding factors are similar to those of the isolated area. The proposed analysis is applied to an isolated area of Bangladesh, called Swandip where a past history of electrical load demand is not available and also there is no possibility of connecting the area with the main land grid system.

Load Frequency Control of Small Hydropower Plants Using One-Input Fuzzy PI Controller with Linear and Non-Linear Plant Model

This study presents an intelligent approach for load frequency control (LFC) of small hydropower plants (SHPs). The approach which is based on fuzzy logic (FL), takes into account the non-linearity of SHPs—something which is not possible using traditional controllers. Most intelligent methods use two- input fuzzy controllers, but because such controllers are expensive, there is economic interest in the relatively cheaper single-input controllers. A non- linear control model based on one-input fuzzy logic PI (FLPI) controller was developed and applied to control the non-linear SHP. Using MATLAB/Si- mulink SimScape, the SHP was simulated with linear and non-linear plant models. The performance of the FLPI controller was investigated and compared with that of the conventional PI/PID controller. Results show that the settling time for the FLPI controller is about 8 times shorter;while the overshoot is about 15 times smaller compared to the conventional PI/PID controller. Therefore, the FLPI controller performs better than the conventional PI/PID controller not only in meeting the LFC control objective but also in ensuring increased dynamic stability of SHPs.

AN ANALYSIS oF THE SHEAR FAILURE OF RIGID-LINEAR HARDENING BEAMS UNDER IMPULSIVE LOADING

A theoretical rigid-plastic analysis for the dynamic shear failure of beams under impulsive loading is presented when using a travelling plastic shear hinge model which tabes into account material strain hardening. The maximum dynamic shear strain and shear strain-rate can be predicted in addition to the permanent transverse deflections and other parameters. The conditions for the three modes of shear failure, i.e., excess deflection failure, excess shear strain failure and adiabatic shear failure are analyzed. The special case of an infinitesimally small plastic zone is discussed and compared with Nonaka's solution for a rigid, perfectly plastic material. The results can also be generalized to examine the dynamic response of fibre-reinforced beams.

NON-LINEAR DYNAMIC BEHAVIOR OF THERMOELASTIC CIRCULAR PLATE WITH VARYING THICKNESS SUBJECTED TO NONCONSERVATIVE LOADING

The non-linear dynamic behaviors of thermoelastic circular plate with varying thickness subjected to radially uniformly distributed follower forces are considered. Two coupled non-linear differential equations of motion for this problem are derived in terms of the transverse deflection and radial displacement component of the mid-plane of the plate. Using the Kantorovich averaging method, the differential equation of mode shape of the plate is derived, and the eigenvalue problem is solved by using shooting method. The eigencurves for frequencies and critical loads of the circular plate with unmovable simply supported edge and clamped edge are obtained. The effects of the variation of thickness and temperature on the frequencies and critical loads of the thermoelastic circular plate subjected to radially uniformly distributed follower forces are then discussed.

考虑加载历史的小半径曲线桥梁梁轨相互作用分析

目前,大部分考虑加载历史的梁轨相互作用研究都集中在直线桥梁上,针对曲线桥梁,尤其是小半径曲线桥梁,梁轨相互作用的研究相对较少。采用理想弹塑性滞回阻力模型模拟扣件纵向阻力,运用有限元软件,建立以城东特大桥为研究对象的钢轨-桥梁-墩台三维有限元空间力学计算模型,研究曲线半径对于梁轨相互作用的影响,探究了多荷载耦合作用、往复荷载作用以及循环荷载作用下考虑加载历史效应的曲线桥梁梁轨相互作用情况,并提出“拉力百分比”以及“压力百分比”的概念以便分析曲线半径对传统线性叠加法误差的影响。结果表明,曲线桥梁中梁轨纵、横向相互作用分别与曲线半径成正、反比,相关数据改变幅度与曲线半径成反比且当曲线半径超过800 m时基本收敛,此时可采用“以直代曲”的简化算法;曲线半径对于横向梁轨相互作用影响程度大于纵向,相较于挠曲、制动工况,伸缩工况受曲线半径影响更加显著;多荷载耦合作用下,采用传统线性叠加法相较于考虑加载历史更为保守且温度荷载起主要贡献;考虑加载历史时钢轨在往复荷载作用下会产生不可忽视的残余内力,且在循环荷载作用下将会产生收敛于第1次往复荷载下的残余内力,这是扣件纵向阻力的弹塑性滞回特性决定的;线性叠加法误差与曲线半径具有相关性,相较于挠曲、制动工况,伸缩工况下对其更为敏感。研究结果可为考虑加载历史下曲线桥梁结构设计提供参考。

基于希尔伯特变换的电网络约束关系研究

为了研究电压波动条件下的电网络约束关系,文章基于希尔伯特变换,构建了供电电压存在波动下线性时不变负载上电压、电流的解析信号模型,推导出了以解析信号表征线性时不变电网络的拓扑约束和元件约束关系,将相量法思想拓展至对供电电压波动下线性时不变电网络响应特性的分析与求解。仿真验证结果表明,供电电压存在波动条件下,文中所建立的基于希尔伯特变换的电网络约束关系,不仅物理意义清晰、表征简明,而且正确、好用。文章所建立的电网络约束关系,能够为供电电压波动条件下电网络中线性时不变负载上电压电流关系的建模、仿真分析与计算提供指导。

民用飞机高平尾侧向载荷传递结构有限元建模及仿真分析

民用飞机高平尾结构的平尾置于垂尾上方,平尾与垂尾都承受侧向载荷。为研究平尾的侧向载荷如何传到垂尾,提出一套关于高平尾侧向载荷传递结构的优化设计、有限元建模、仿真分析(涉及linear gap接触设置)的完整方法。该方法已成功应用于某型号民用飞机的研制,可推广到类似飞机结构的设计中。

基于RLLE算法的脑力负荷分类

近年来,随着人工智能领域技术的不断发展,脑机接口(brain-computer interface,BCI)吸引了更多学者的关注。实时监测高强度脑力工作者的脑力负荷水平并根据其任务做出动态调整是保护国家财产和操作人员安全的重要手段。研究表明由脑电图(electroencephalogram,EEG)提取的特征功率谱密度对于脑力负荷的变化比较敏感,但由于其维数过高,容易造成数据灾难。传统的主成分分析降维(principal component analysis,PCA)算法会损失数据的部分非线性特征。局部线性嵌入(locally linear embedding,LLE)是常用的非线性降维算法,但该算法对噪声的敏感性高,降维结果受参数影响较大。稳健局部线性嵌入算法RLLE(robust locally linear embedding),在LLE优化权重矩阵时添加了正则项优化,不仅增强了模型的抗噪能力,也解决了解模型过程中可能会出现的矩阵病态和奇异性问题。实验结果表明,经过RLLE降维后的数据使用支持向量机(support vector machine,SVM)分类精度普遍高于经过PCA和LLE的降维方式,具有更强的抗干扰能力。

一种高载荷燃气轮机高压透平可控扩散叶型开发

文章针对某燃气轮机高压透平,开发了一种高载荷叶型,其叶型Zweifel载荷系数达到1.2,对该叶型在典型的燃机叶片运行压比下进行平面叶栅吹风试验验证,试验结果显示气动载荷分布与设计值匹配较好,在设计工况下叶型能量损失系数为1.4%;在1.1到1.7的压比之间叶型损失系数都小于1.7%,出口气流角的变化在1°以内;在-10°到20°的攻角变化范围内表现出优异的气动性能;不同的安装角下叶型损失系数都在1.5%以内。

游离氧化铁对崩岗不同土层土壤胀缩特性的影响

【目的】研究游离氧化铁对崩岗不同土层土壤胀缩特性的影响。【方法】利用无荷膨胀试验、线性收缩试验和计算土壤胶体扩散双电层中滑动层厚度,分析游离氧化铁对崩岗不同土层土壤胀缩特性的影响。【结果】游离氧化铁含量与崩岗土壤无荷膨胀率呈线性递增关系(P<0.01),与土壤线性收缩率呈线性递减关系(P<0.05);在电解质浓度相同的条件下,崩岗土壤滑动层厚度随着游离氧化铁含量的提高而增大;游离氧化铁含量不同的红土层、砂土层的土壤滑动层厚度与无荷膨胀率均呈显著正相关(P<0.05),与线性收缩率呈显著负相关(P<0.05)。【结论】游离氧化铁含量影响土壤滑动层厚度,进而影响土壤的胀缩性能。

基于装卸顺序的中型机多航段协同配载优化

多航段、多经停的航空货运航班,飞行过程中需要合理控制飞机的重心(CG)位置,保持平衡状态,中转站装卸操作过程中需要避免额外装卸操作,减少时间和劳力浪费,因此,研究多航段航班的协同配载问题具有重要现实意义。根据航空器自身特点与集装器(ULD)装卸顺序,结合各航段飞机装载平衡与过站机场ULD装卸操作要求,通过协调分配各航段ULD和散货位置,建立了中型机联程航班多目标整数线性规划模型。模型考虑了ULD和散货的质量、体积及与舱位的匹配限制,航空器限重、舱位限重、舱位及区域累积限重、上下舱联合限重和CG位置的平衡限制,以及前后航段ULD和散货的连接性约束。根据造成中间机场额外装卸操作的2种原因,基于装卸顺序,提出装卸优化模型,通过ULD的舱内平移,优化了CG,减少了装卸次数。以B757-200F机型为例,在两装一卸、一装两卸和两装两卸3种场景下,采用商用求解器Gurobi,分别针对3种不同目标函数组合进行求解和分析对比。实验表明:所提模型可以有效协调过站货物的额外装卸次数,优化前后两航段的CG位置。

基于高电负荷直线电机的电磁输弹技术研究

为实现大口径火炮输弹机构的轻量化和小型化,根据惯性输弹工作原理,采用以直线电机为核心的电磁输弹方式进行弹丸装填。针对短时间歇式的输弹工作特点,开展适用于输弹的高电负荷直线电机设计,以降低输弹机构的质量和体积。基于虚拟样机仿真建立电磁输弹机构动力学模型,并结合电机参数进行输弹动力学仿真,结果表明,在最大射角下以直线电机为核心的电磁输弹机构可使弹丸具备可靠的卡膛速度,且相比于常规电负荷输弹机构,高电负荷输弹机构的质量降低了58.9%,体积降低了53.6%。基于高电负荷直线电机的电磁输弹方式可为输弹机构轻量化和小型化设计提供参考。

基于负载追踪补偿的大电流LDO设计

提出一种有效提升大电流输出应用的低压差线性稳压器(LDO)环路稳定性的技术,采用负载追踪补偿方式消除电路输出端与负载相关的极点对环路稳定性的影响,且在维持环路低频增益不变的前提下降低高频下环路中节点阻抗,从而达到同时提升输出精度和优化瞬态响应性能的目的。采用TSMC 0.18µm BCD工艺进行仿真验证,结果表明电路最大输出电流6 A,在6 A/6μs的负载突变情况下输出电压下冲为36.6 mV,过冲为35.3 mV,稳定时间小于56.3μs。全负载电流范围内,瞬态性能大幅提升。

基于回归模型的中央监控平台设计与实现

中央监控平台是一个以数据为中心的服务器保护平台。该平台通过组合服务器上的哨兵来防止数据免受泄露和攻击,同时对系统的运行状态进行全面的监测。通过数据分析,并运用数理统计的方法,在可提供的计算力与系统资源利用率之间建立线性回归模型。该模型解释了在某一资源消耗状态下,系统可提供的计算力估算值,在可允许误差为0.1的情况下,其准确率可以达到97%以上,为当前系统运行状态做出精准的评估。

考虑负荷电压静特性和PV节点的配电网线性化潮流计算

鉴于原有的高维非线性潮流模型无法适用于配电网线性规划,而现有的线性化潮流模型存在通用性不强的问题,提出了一种考虑负荷电压静特性和PV节点的配电网线性化潮流计算方法。所提方法基于极坐标系下的潮流方程,利用配电网的特征对潮流方程的电压幅值和相角进行解耦;再根据PV节点自身的控制特性,推导出一种含PV节点的线性化潮流计算模型。所提模型不仅考虑了PV节点和负荷电压静特性,而且兼顾对过负载和弱环网的适应性,无需迭代便可求解配电网的电压分布。仿真结果表明:所提方法具有较高的精度和通用性,可用于配电网的快速分析。

某商用车钢板弹簧失效分析与结构优化

为解决某商用车钢板弹簧断裂问题,分别从板簧材质、成型工艺、结构设计强度多方面进行失效分析,考虑不同工况场景的载荷特点,建立板簧的非线性仿真模型。根据整车冲击工况加载标准,提取各工况下的板簧应力。建立板簧总成的详细模型,以提取的板簧应力为载荷,考察板簧及桥壳底板的可靠性,从而确定薄弱部位与断裂原因。以主簧的簧片厚度为设计变量,以板簧的结构应力为约束条件,以总质量最小为约束目标,对板簧进行尺寸优化,寻找满足应力要求的簧片最小厚度。对优化后的主、副簧进行疲劳耐久试验,验证仿真结果的准确性。

计及源荷相关度类线性紧缩法的配电网有功无功协同优化

随着分布式电源的高比例渗透,主动配电网的稳定性受到很大影响,因此主动配电网有功-无功协同优化至关重要。对此,提出一种计及源荷相关度类线性紧缩法(Quasi-Linear Contraction,QLC)的配电网有功无功协同优化方法。首先,基于相关性分析方法分析新能源出力以及负荷的相关度,给出源荷相关度概率约束,完善系统优化模型。然后,针对优化模型非凸非线性容易导致局部最优解问题,采用泰勒展开式求解分支电流的上下界并代入节点电压和功率流方程,完成主动配电网模型的类线性紧缩,再采用罚函数方法校正,当得出的解在缩小后的约束范围内时该解为实际最优解,当得出的解在紧缩的约束边界上时,在满足原有约束范围的前提下向外寻优,得到实际最优解。最后,通过Yalmip等仿真计算软件验证所提方法的稳定性、准确性以及有效性。