Tuning and Assessment of Proportional–Integral–Derivative Controller for an Automatic Voltage Regulator System Employing Local Unimodal Sampling Algorithm

Abstract—This article presents an approach for obtaining proportional–integral–derivative controller parameters for an automatic voltage regulator system based on a local unimodal sampling optimization algorithm. A conventional integral time of squared error objective function and modified objective functions in terms of integral time of absolute error, integral of absolute error, integral of squared error, peak overshoot, and settling time with appropriate weighting factors are employed to tune the controller parameters. Different objective functions are employed to obtain optimized proportional–integral–derivative controller gains. Superiority of proposed technique over some recently published modern heuristic optimization techniques, such as artificial bee colony algorithm, particle swarm optimization algorithm, and differential evolution algorithm, for the same automatic voltage regulator system is demonstrated. Simulation results reveal that the proposed proportional–integral–derivative controlled automatic voltage regulator system tuned by the local unimodal sampling algorithm with modified objective function exhibits better performance in terms of settling time, peak overshoot, and stability. The robustness of the system tuned by the proposed algorithm is also studied satisfactorily by varying the time constants of the automatic voltage regulator system in the range of –50% to +50% in steps of 25%.     

用于人脸识别的相对梯度直方图特征描述

由于方向边缘幅值模式(POEM)在剧烈光照变化情况下无法获得足够的特征描述信息,本文分析了相对梯度幅值图像特点,提出了相对梯度直方图特征描述方法。该方法根据图像的梯度方向对相对梯度幅值图像进行分解、滤波、局部二值模式编码和特征降维,形成了对光照变化,尤其是非均匀光照变化具有健壮性的低维直方图特征。在FERET和YaleB子集上的人脸识别实验证实:在光照变化较小时,相对梯度直方图特征描述方法与方向边缘幅值模式的性能相当,均显著优于经典的局部二值模式特征;在光照剧烈变化时,前者的识别精度比方向边缘幅值模式至少高5%,性能显著优于方向边缘幅值模式和局部二值模式,展示了相对梯度直方图特征描述方法的有效性和对光照变化的良好健壮性。     

竖直矩形窄通道内水流动沸腾换热特性的研究

建立单面加热垂直矩形窄通道流动沸腾换热试验装置,针对截面250mm×3.5mm的窄缝通道,对水流动沸腾换热特性进行试验研究。通过试验分析可知:(1)随着干度的增加,局部换热系数先增加后减小,有一个最大值,此时处于饱和核沸腾区域,其蒸汽干度也接近于0,同时也接近于沸腾起始点。相应地流体从单相流-泡状-块状流-搅拌-环状流转变。(2)在流动沸腾换热中,热流密度对核态沸腾换热有明显影响,而对流动沸腾液膜蒸发的影响甚小,所以可以认为由热流密度的变化而引起的换热变化,主要表现在核态沸腾。(3)入口温度的变化对单相流动的换热系数有影响,而沸腾换热系数与流型及汽泡的产生及扰动有极大关系,入口温度对流动沸腾局部换热系数基本没有影响。     

地方本科高校转型发展：可能效应与主要问题

目前我国正在实施新建地方本科高校转型发展政策,这项政策将会产生巨大的政策效应,对我国高等教育结构、大学教育理念以及专科层次高职院校改革发展均会产生重大影响。地方本科院校转型发展必须解决好现有教师队伍向“双师型”教师队伍转型、教学体系由知识教学体系向实训教学体系转型,以及如何更好实现校企深度合作等三方面的问题。     

Fatigue crack initiation potential from defects in terms of local stress analysis

The competition of surface and subsurface crack initiation induced failure is critical to understand very high cycle fatigue（VHCF） behavior, which necessitates the elucidation of the underlying mechanisms for the transition of crack initiation from surface to interior defects. Crack initiation potential in materials containing defects is investigated numerically by focusing on defect types, size, shape, location, and residual stress influences. Results show that the crack initiation potency is higher in case of serious property mismatching between matrix and defects, and higher strength materials are more sensitive to soft inclusions（elastic modulus lower than the matrix）. The stress localization around inclusions are correlated to interior crack initiation mechanisms in the VHCF regime such as inclusion-matrix debonding at soft inclusions and inclusion-cracking for hard inclusions（elastic modulus higher than the matrix）. It is easier to emanate cracks from the subsurface pores with the depth 0.7 times as large as their diameter. There exists an inclusion size independent region for crack incubation, outside which crack initiation will transfer from the subsurface soft inclusion to the interior larger one. As for elliptical inclusions, reducing the short-axis length can decrease the crack nucleation potential and promote the interior crack formation, whereas the long-axis length controls the site of peak stress concentration. The compressive residual stress at surface is helpful to shift crack initiation from surface to interior inclusions. Some relaxation of residual stress can not change the inherent crack initiation from interior inclusions in the VHCF regime. The work reveals the crack initiation potential and the transition among various defects under the influences of both intrinsic and extrinsic factors in the VHCF regime, and is helpful to understand the failure mechanism of materials containing defects under long-term cyclic loadings.     

Exploration of the oxygen transport behavior in non-precious metal catalyst-based cathode catalyst layer for proton exchange membrane fuel cells

High cost has undoubtedly become the biggest obstacle to the commercialization of proton exchange membrane fuel cells (PEMFCs), in which Pt-based catalysts employed in the cathodic catalyst layer (CCL) account for the major portion of the cost. Although non-precious metal catalysts (NPMCs) show appreciable activity and stability in the oxygen reduction reaction (ORR), the performance of fuel cells based on NPMCs remains unsatisfactory compared to those using Pt-based CCL. Therefore, most studies on NPMC-based fuel cells focus on developing highly active catalysts rather than facilitating oxygen transport. In this work, the oxygen transport behavior in CCLs based on highly active Fe-N-C catalysts is comprehensively explored through the elaborate design of two types of membrane electrode structures, one containing low-Pt-based CCL and NPMC-based dummy catalyst layer (DCL) and the other containing only the NPMC-based CCL. Using Zn-N-C based DCLs of different thickness, the bulk oxygen transport resistance at the unit thickness in NPMC-based CCL was quantified via the limiting current method combined with linear fitting analysis. Then, the local and bulk resistances in NPMC-based CCLs were quantified via the limiting current method and scanning electron microscopy, respectively. Results show that the ratios of local and bulk oxygen transport resistances in NPMC-based CCL are 80% and 20%, respectively, and that an enhancement of local oxygen transport is critical to greatly improve the performance of NPMC-based PEMFCs. Furthermore, the activity of active sites per unit in NPMC-based CCLs was determined to be lower than that in the Pt-based CCL, thus explaining worse cell performance of NPMC-based membrane electrode assemblys (MEAs). It is believed that the development of NPMC-based PEMFCs should proceed not only through the design of catalysts with higher activity but also through the improvement of oxygen transport in the CCL.     

基于边缘计算的低压智能台区应用设计

随着用电信息采集系统的大规模覆盖以及各种深化应用,为了应对新时期智能电网愈来愈丰富的发展需求,文中提出了一套低压智能台区系统设计.该系统基于边缘算法,以智能配变终端为核心,分支数据监测装置提供协助,形成低压侧智能台区系统,最终实现低压台区的本地拓扑计算识别、分支线损分析、电气量监测预警、环境异常报警、停电事件上报等功能.目前该套系统已在多地进行实地应用.     

纯Al表面局部孔蚀的电化学噪声特征分析

电化学噪声时域谱可以预测局部腐蚀的发生,定性地说明腐蚀发生的类型;电流标准偏差σ_I,噪声电阻R_n和电流白噪声水平W能表征腐蚀发展的剧烈程度,当腐蚀发生时,σ_I和W趋于增大,R_n趋于减小。     

Local error analysis of Evans–Sanugi,nonlinear one-step methods based on θ-means

A new class of weighted, homogeneous, differentiable means is introduced, referred to as θ-means, which may be extended to the whole plane. These means are applied to Evans–Sanugi nonlinear one-step methods for initial value problems of scalar differential equations. Their general local truncation error is obtained, showing the first order of these methods for θ≠1/2 and second order for θ=1/2. Numerical results for scalar DETEST problems using Arithmetic, Harmonic, Contraharmonic, Quadratic, Geometric, Heronian, Centroidal and Logarithmic θ-means are presented. Both the local error of the methods and the global error of the numerical results have the same functional dependence with the parameters of the numerical method. The results show that a comparison of different methods for scalar problems may be based on the numerical evaluation of local truncation error.     

西部地方院校成人继续教育面临的问题及对策

西部地方院校成人继续教育曾经为社会培养了大量人才,但是目前却面临许多问题。本文总结了西部地方院校成人继续教育发展面临的问题,分析其下一步发展方向,并提出对策建议,以期促进西部地方院校成人继续教育的进一步发展。