基于电容序列近似熵的消弧线圈接地选线方法

针对零序电流互感器极性不明确导致选线失败的问题,分析了选线失败的原因,提出一种基于对地电容近似熵的选线方法。提出利用差分方法改进矩阵束,解决分量湮没问题,从而准确提取复频域极点信息。分别求取每条线路对地电容序列,由于消弧线圈补偿作用故障线路电容序列近似熵将超过阈值,则判断该条线路为故障线路。仿真实验结果验证:该方法摆脱了由于零序互感器极性不同而导致选线错误的限制,且适用于两出线系统,适应性强,选线准确率高。     

基于物元可拓模型的光伏发电综合效益评价研究

为避免人为主观因素的影响,运用熵权法对层次分析确定描述指标体系各层级指标相对重要程度的权重进行修正;通过物元可拓模型从经济效益、技术效益、社会效益和环境效益4个方面,全面系统分析新能源光伏发电项目综合效益,并对蒙阴光伏发电项目进行综合效益评价,得出了相应结论,为客观评价光伏发电综合效益提供方法。     

配电网多级继电保护配合的关键技术研究

为了更好地进行配电网继电保护配合设计,推导了实现多级3段式过流保护配合所需要的条件,提出一种区分两相短路和三相短路故障配置差异化定值的改进方法。以环状配电网为例,探讨了相互联络的配电网多级3段式过流保护的配置方法。在此基础上,综合时间级差配合方式,提出了4种配电网多级继电保护配合模式,分别分析了其特点。结合实例对所建议的方法进行了详细分析,结果表明差异化定值的改进方法能够有效增大保护范围,所建议的多级保护配合模式、配置和参数整定方法是可行的。     

新型多端高压变换器拓扑构造和分析

提出一族多端高压变换器拓扑,分别为多端高压AC-DC变换器、多端高压DC-DC变换器、多端高压DCAC变换器和多端高压AC-AC变换器。论述了多端高压变换器拓扑的构造原理和主要拓扑结构。研究表明,所提拓扑的显著优点是一个拓扑即可实现多路输入或多路输出,大大减少了开关器件、降低了变换器成本,且输出多电平电压、谐波含量少,适用于多端高压直流输电、多端交流输电、多电机高压变频驱动、电力电子变压器、电能质量补偿装置等工业场合。     

级联式多电平无桥整流器的研究

针对传统中高压变频器中采用笨重复杂的移相变压器构成整流环节的问题,提出了一种新型的级联式多电平无桥整流电路拓扑。该拓扑采用级联的无桥整流模块单元结构,无需采用多重化工频移相变压器,通过一定的控制策略,可实现交流网侧较高的功率因数;同时可使每个模块单元输出稳定均衡的直流电压,从而为后级DCDC以及DC-AC变换器的构成与实现提供良好的条件;对该新型电路拓扑的基本工作原理、稳态数学模型、输入功率因数以及控制策略进行了详细讨论。最后通过仿真与实验验证了所提电路的可行性和正确性。     

Origin of the High Permittivity and Varistor Behavior in SnO2–Zn2SnO4 Composite Ceramics

SnO₂–Zn₂SnO₄ composite ceramics with a colossal dielectric permittivity and varistor behavior are prepared by traditional ceramic processing. By increasing bias voltage from 0 to 10 V at a low frequency (~10³ Hz) and at room temperature, the relative permittivity decreased rapidly from about 20 000 to several thousand, whereas the radius of the semicircle in the complex impedance decreased and the tail gradually disappeared. However, the peak height and the position of the imaginary part of the complex modulus in the spectra were independent of the applied DC voltage. The slope deduced from the bias voltage‐dependent straight lines of the double‐logarithmic imaginary permittivity spectra were constant with a value of ?0.63 at high frequencies and they decreased to ?1 at low frequencies. The results strongly indicate that a number of weekly trapped charges existed in the ceramic bulk. From the temperature‐dependent dielectric and electric modulus spectra, the trapped charge activation energy was about 0.32 eV, which may be associated with the oxygen vacancies. Based on the results, a modified equivalent circuit related to the colossal dielectric permittivity and varistor properties was proposed, in which a Warburg impedance was added in parallel with the resistance and capacitance.     

Microstructure,Thermal Conductivity,and Electrical Properties of In Situ Pressureless Densified SiC–BN Composites

The microstructure, thermal conductivity, and electrical properties of pressureless densified SiC–BN composites prepared from in situ reaction of Si₃N₄, B₄C, and C were systematically investigated, to achieve outstanding performance as substrate materials in electronic devices. The increasing BN content (0.25–8 wt%) in the composites resulted in finer microstructure, higher electrical resistivity, and lower dielectric constant and loss, at the expense of only slight degradation of thermal conductivity. The subsequently annealed composites showed more homogeneous microstructures with less crystal defects, further enhanced thermal conductivities and electrical resistivities, and reduced dielectric constants and losses, compared with the unannealed ones. The enhanced insulating performance, the weakened interface polarization, and the reduced current conduction loss were explained by the gradual equalization of dissolved B and N contents in SiC crystals and the consequent impurity compensation effect. The schottky contact between graphite and p‐type SiC grains presumably played a critical role in the formation of grain‐boundary barriers. The annealed composites doped with 8 wt% BN exhibited considerably high electrical resistivity (4.11 × 10¹¹ Ω·cm) at 100 V/cm, low dielectric constant (16.50), and dielectric loss (0.127) at 1 MHz, good thermal conductivity [66.06 W·(m·K)^?1] and relatively high strength (343 MPa) at room temperature.     

High activity and wide temperature window of Fe‐Cu‐SSZ‐13 in the selective catalytic reduction of NO with ammonia

Fe‐Cu‐SSZ‐13 catalysts were prepared by aqueous solution ion‐exchange method based on the one‐pot synthesized Cu‐SSZ‐13. The catalysts were applied to the selective catalytic reduction (SCR) of NO with NH₃ and characterized by the means of XRD, UV‐Vis, EPR, XPS, NH₃‐TPD, and so on. The selected Fe‐Cu‐SSZ‐13‐1 catalyst exhibited the high NO conversion (>90%) in the wide temperature range (225–625°C), which also showed good N₂ selectivity and excellent hydrothermal stability. The results of XPS showed that the Cu and Fe species were in the internal and outer parts of the SSZ‐13 crystals, respectively. The results of UV‐Vis and EPR indicated that the monomeric Cu²⁺ ions coordinated to three oxygen atoms on the six‐ring sites and Fe monomers are the real active species in the NH₃‐SCR reaction. Furthermore, the influence of intracrystalline mass‐transfer limitations on the Fe‐Cu‐SSZ‐13 catalysts is related to the location of active species in the SSZ‐13 crystals. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3825–3837, 2015     

Mechanistic insights into the structure‐dependent selectivity of catalytic furfural conversion on platinum catalysts

The effects of surface structures on the selectivity of catalytic furfural conversion over platinum (Pt) catalysts in the presence of hydrogen have been studied using first principles density functional theory (DFT) calculations and microkinetic modeling. Three Pt model surface structures, that is, flat Pt(111), stepped Pt(211), and Pt₅₅ cluster are chosen to represent the terrace, step, and corner sites of Pt nanoparticle. DFT results show that the dominant reaction route (hydrogenation or decarbonylation) in furfural conversion depends strongly on the structures (or reactive sites). Using the size‐dependent site distribution rule, our microkinetic modeling results indicate the decarbonylation route prevails over smaller Pt particles less than 1.4 nm while the hydrogenation is the dominant reaction route over larger Pt catalyst particles at T = 473 K and = 93 kPa. This is in good agreement with the reported experimental observations. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3812–3824, 2015     

Rare‐Earth Free Phosphors with Ultra‐Broad Band Emission Application for High Color Rendering Index Lighting Source

Rare‐earth containing phosphors have been widely applied in lighting and display fields in the past century. Lower cost rare‐earth free phosphors with high performance are highly desired driven by the exhaustion of rare earth resources and the requirement of cheaper production. Herein, Cu⁺ ions doped tetracalcium phosphate (TTCP) yellow emitting phosphors with quantum yield of 21% are exploited. Particularly, ultra‐broad band emission with a full width at half maximum (FWHM) about 200 nm throughout almost entire visible light region is observed for TTCP: Cu⁺ phosphors, evidencing its promising application in high color rendering index (CRI) lighting source. White light emission with CRI value about 94.3 is generated by combining this TTCP: Cu⁺ phosphor with commercial BaMgAl₁₀O₁₇: Eu²⁺ blue phosphor, exhibiting superiority over the traditional trichromatic phosphors. Therefore, we predict great potential application for this cheaper rare‐earth free TTCP: Cu⁺ phosphor in high CRI lighting sources.