基于容性能量转移原理的高压大容量DC/DC变换器

随着基于电压源型换流器的柔性直流输电(voltage source converter based high voltage direct current,VSC-HVDC)技术的快速发展,十几年间世界范围内已建成数十个各种不同电压等级的VSC-HVDC工程。根据交流电网的发展历史,未来构建大规模直流电网是必然趋势。然而直流电网必须采用DC/DC变换器来充当直流变压器的角色,因此高效率、低成本的高压大容量DC/DC变换器是直流电网技术中亟待攻克的关键基础性课题。该文针对不同电压等级直流输电线路互联的技术需求,对经典低压DC/DC拓扑进行改造,推演出一系列基于容性能量转移原理的高压大容量DC/DC变换器拓扑,并揭示此类拓扑的演化规律和换流原理。相比传统变换器方案,该拓扑可降低器件数量,提升拓扑转换效率以及减小变换器体积重量。最后,通过仿真和实验验证基于容性能量转移原理的DC/DC变换器的可行性。

基于容性能量转移变化的高压真空断路器故障智能诊断

高压断路器作为电力系统中最重要的承载、保护与控制单元之一,其绝缘与开断依赖SF6气体。由于常规高压真空断路器存在自然电流零点和电能谷底干扰,其故障检测的核心过程为:电流零区弧隙之间SF6气体介质强度变化引起的信号瞬时启动。为了减低故障漏检情况,结合神经网络+混合布谷鸟算法,设计一种高精度的高压真空断路器故障智能诊断方法。首先,分析故障发生后容性能量转移过程,归纳故障发生后容性能量转移的空间特征和时间特征。其次,构建基于PNN神经网络的高压真空断路器机械故障诊断模型,将容性能量转移特征向量作为训练样本输入到模型中展开训练,完成故障智能诊断。最后,利用混合布谷鸟算法对模型中的参数展开寻优,以此得到高精度诊断结果。实验结果表明:所提方法在高压真空断路器诊断过程中的精度和稳定性具有较高优势。

Electrochemical performances of AB_5-type hydrogen storage alloy modified with Co_3O_4

Anodic electrodes with the mixture of hydrogen storage alloys and different contents of Co3O4（2%,4%,6% and 8%,mass fraction） powders were made.The effects of Co3O4 on the electrochemical performance of the alloy electrodes were studied.The constant charge-discharge tests show that the discharge capacity of alloy electrodes with Co3O4 significantly increases,and the maximum discharge capacities of electrodes with 2%,4%,6% and 8% Co3O4 are higher than the electrode with no Co3O4 by 0.83%,4.86%,7.18% and 9.21%,accordingly.Linear polarization（LP） and electrochemical impedance spectroscopy（EIS） tests suggest that charge-transfer resistance decreases by the addition of Co3O4.Cyclic voltammogram（CV）,scanning electron microscopy（SEM） and energy dispersive spectrum（EDS） tests indicate that Co3O4 can partly dissolve and experience a reversible oxidation-reduction process of Co to Co（OH）2,leading to the improvement in the electrochemical performance of hydrogen storage alloy.

Interference analysis and improvement of capacity reduction for FHSS networks in WPAN application environment

The coexistence between Bluetooth system and IEEE 802.11 frequency hoppingspread spectrum (FHSS) equipment is analyzed. Based on the capacity formulae and system simulation,the inter-affection between these networks is compared. A fragment adaptive solution of packetpayload length is presented, which can be used to improve the capacity reduction of IEEE 802.11 FHSSnetwork. Analysis results show that the IEEE 802.11 WLAN standard with its inherent mechanismsupports this fragment length adaptive algorithm. With the increasing of Bluetooth interferingnetworks, this adaptive solution can effectively relieve capacity decreasing of IEEE 802.11 FHSSnetwork. The capacity analysis method and adaptive algorithm adopted in this paper can also begeneralized into other FHSS networks.

Mechanism for capacity fading of 18650 cylindrical lithium ion batteries

The mechanism for capacity fading of18650lithium ion full cells under room-temperature(RT)is discussedsystematically.The capacity loss of18650cells is about12.91%after500cycles.The cells after cycles are analyzed by XRD,SEM,EIS and CV.Impedance measurement shows an overall increase in the cell resistance upon cycling.Moreover,it also presents anincreased charge-transfer resistance(Rct)for the cell cycled at RT.CV test shows that the reversibility of lithium ioninsertion/extraction reaction is reduced.The capacity fading for the cells cycled can be explained by taking into account the repeatedfilm formation over the surface of anode and the side reactions.The products of side reactions deposited on separator are able toreduce the porosity of separator.As a result,the migration resistance of lithium ion between the cathode and anode would beincreased,leading the fading of capacity and potential.

Preparation and characterization of spinel LiMn_2O_4 nanorods as lithium-ion battery cathodes

The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of producing pure,single-phase and crystalline nanorods.The LiMn2O4 nanorods have an diameter of about 300 nm.The discharge capacity and cyclic performance of the batteries were investigated.The LiMn2O4 nanorods show better cyclic performance with a capacity retention ratio of 86.2% after 100 cycles.Battery cyclic studies reveal that the prepared LiMn2O4 nanorods have high capacity with a first discharge capacity of 128.7 mA·h/g.

Thermodynamic properties and heat capacity of Ru metal in HCP,FCC,BCC and liquid state

Isometric heat capacity cv and isobar heat capacity cp of Ru metal in HCP,FCC,BCC and liquid state were calculated by using pure element systematic theory.The results are in good agreement with joint army-navy-air force(JANAF) experimental value and the calculation result by first-principle(FP) method.But the results have great differences in contrast to Scientific Group Thermodata Europe(SGTE) database.The cause is found that it cannot neglect the electron devotion to heat capacity to adjust cp in one-atom(OA) method.The disparity between OA method and SGTE database was discussed.The main cause is that OA method adopts the crosspoint with iso-Ec-line and iso-a-line in hybritriangle to determine the properties,but SGTE database is obtained by extrapolation from activity measurements and critical assessment of data from a large number of binary system.Thermodynamic properties of Ru metal in HCP,FCC,BCC and liquid state,such as entropy S,enthalpy H and Gibbs energy G were calculated.Therefore,the full description of thermodynamic properties from 0 K to random temperature is implemented.

An iterative computation method for interpreting and extending an analytical battery model

Battery models are of great importance to develop portable computing systems,for whether the design of low power hardware architecture or the design of battery-aware scheduling policies.In this paper,we present a physically justified iterative computing method to illustrate the discharge,recovery and charge process of Li/Li-ion batteries.The discharge and recovery processes correspond well to an existing accurate analytical battery model:R-V-W's analytical model,and thus interpret this model algorithmically.Our method can also extend R-V-W's model easily to accommodate the charge process.The work will help the system designers to grasp the characteristics of R-V-W's battery model and also,enable to predict the battery behavior in the charge process in a uniform way as the discharge process and the recovery process.Experiments are performed to show the ac-curacy of the extended model by comparing the predicted charge times with those derived from the DUALFOIL simulations.Various profiles with different combinations of battery modes were tested.The experimental results show that the extended battery model preserves high accuracy in predicting the charge behavior.

Commercial Applications of Paraxylene Adsorbents RAX-2000A and RAX-3000

The RAX series paraxylene （PX） adsorbents RAX-2000A and RAX-3000, are developed by the Sinopec Re- search Institute of Petroleum Processing （RIPP） and manufactured by the Sinopec Catalyst Company. Performance test of RAX-2000A showed that the average purity of the PX product reached 99.81%, with an average PX yield of 98.6% per pass. The new generation of PX adsorbents, RAX-3000 not only retains most advantages of the adsorbent RAX-2000A, but also has higher selective adsorption capacity by at least 8%. The actual unit production capability of the adsorbent RAX- 3000 was increased by about 18%. The RAX series PX adsorbents exhibited good adaptability to unfavorable feedstock containing high ethyl benzene （EB） fraction besides their better mechanical strength. Preliminary test results indicated that compared to the adsorbent RAX-2000A, the A/Fa and D/F relating to the adsorbent RAX-3000 were notably decreased due to the hi^her selective adsorotion canacitv of the adsorbent RAX-3000.

Algebraic algorithm for reliability index weighted capacity of communication network

Communication network has communication capacity and connection reliability of the links. They canbe independently defined and can be used separately, and when the reliability of a communication network isanalyzed from a macroscopical angle of view, it is more objective to express the performance index of a commu-nication network as a whole. The reliability index weighted capacity is just obtained by integrating these two pa-rameters. It is necessary to further study the algorithm to calculate the reliability index of the communicationnetwork with a complicated topologic structure and a whole algebraic algorithm is therefore proposed for calcula-tion of the reliability index weighted capacity of a communication network with a topologic structure. The wholecomputational procedure of the algorithm is illustrated with a typical example.

Overcharge performance of LiMn_2O_4/graphite battery with large capacity

The LiMn2O4/grapbite battery was fabricated and its 3 C/10 V overcharge performance was studied. Spinel LiMn2O4 was synthesized by solid-state method and 325680-type size full battery was fabricated. The structure and morphology of the powders were characterized by XRD and SEM technique, respectively. The battery explodes after 3 C/10 V overcharged test, and surface temperature of the battery case arrives at 290 ℃ in 12 s after exploding. Black air is given out with blast. Carbon, MnO, and Li2CO3 are observed in the exploded powders. The cathode electrode remains spinel structure with 5.0 V charged. Cracks in the cathode electrode particles are detected with the increase of voltage by SEM technique. The 5.0 V charged electrode can decompose into Mn3O4 at 400 ℃. It is demonstrated that the decomposition of 5.0 V charged electrode can be promoted and Mn^4＋ can be deoxidized to Mn^2＋ by carbon and electrolyte through the simulation of blast process.

Hydrothermal Synthesis and Electrochemical Properties of Amorphous LiMoS2 as a High Capacity Anode Material for Lithium Ion Batteries

The LiMoS： anode material for lithium ion rechargeable batteries were synthesized by a hydrothermal method at 150 ℃. According to our measurements with X-ray diffraction, LiMoS2 was amorphous structure. Electrochemical measurements results showed that LiMoS2 exhibited large lithium storage capacities.

Performance of Micelle-Clay Filters for Removing Pollutants and Bacteria from Tertiary Treated Wastewater

Filters filled with a micelle-clay complex mixed with sand were employed to investigate their purification capability of tertiary treated wastewater with loose UF-membranes. The UF membrane was hollow fiber with a molecular weight cutoff of 100 kD. The complex was prepared from the organic cation octadecyltrimethylammonium （ODTMA） and the negatively charged clay-mineral, montmoriIIonite. This complex has a very large surface area, which includes large hydrophobic domains and is positively charged, about half of the cation exchange capacity of the clay. Two sets of filtration experiments were carried out at flow rates of 1.2 and 50 mL/min, which correspond to flow velocities of 3.7 and 153 cm/h, respectively. In the first case, after a passage of 1 L, the turbidity, total suspended solids （TSS）, fecal coliforms （FC）, and total coliforms （TC） were reduced to zero from 14 NTU, 6 ppm, 350 and 10,000 counts per 100 mL, respectively. In the second case, the numbers of FC and TC were reduced from 50,000/100 mL to zero after the passage of 14 L. The values of COD and BOD were reduced several-fold. The conclusion is that the incorporation of micelle-clay filters in the sewage treatment system with loose tertiary capability is promising and warrants larger scale experiments for optimization of the overall system.

Electrochemical Behavior of Electrodeposited Sn Films： Possible Negative Electrode for Na^＋ Rechargeable Batteries

Tin films on copper substrate, obtained by electrodeposition procedure, were structural and electrochemical characterized. In particular to investigate the possibility to use such metal as possible negative electrode in Na＋ rechargeable batteries, EPS （electrochemical potential spectroscopy） and galvanostatic charge/discharge cycling of the electrodes were investigated, at room temperature in organic electrolyte. Three crystalline and one amorphous phases were identified as well as high discharge capacity （738 mAb/g） was obtained after 4 cycles. Unfortunately material fading, due to the internal stress during sodiation/desodiation process, causes poor cyclability.

Investigation on specific heat capacity and thermal behavior of sodium hydroxyethyl sulfonate

The thermal decomposition process was studied by the TG–DTA analyzer. The results show that the decomposition process of sodium hydroxyethyl sulfonate consisted of three stages: the mass loss for the first, the second and third stages may be about the groups of CH_3CH_2OH, CH_3CHO and SO_2 volatilized, respectively. The decomposition residuum of three stages was analyzed by FT-IR, and the results of FT-IR agreed with the decomposition process predicted by theoretical weight loss. The specific heat capacity of sodium hydroxyethyl sulfonate was determined by differential scanning calorimetry(DSC). The melting temperature and melting enthalpy were obtained to be 465.41 K and 25.69 kJ·mol^(-1), respectively. The molar specific heat capacity of sodium hydroxyethyl sulfonate was determinated from 310.15 K to 365.15 K and expressed as a function of temperature.

Matching Gasoline Supply with Distribution Requirements Optimizes Depot Storage Capacity and Performance

This study was done for one of the Nigerian National Petroleum Corporation （refiner） depot supplied by a multi-product （gasoline, diesel and kerosene） pipeline. Distribution/loading facility designed for a total of six arms： two each for gasoline, kerosene and diesel （or 33.33% for each product） whereas gasoline storage capacity is 55%, diesel, 33%, kerosene 11%, and slops, 1% of the total depot capacity. The design supply to distribution chain capacity ratio showed a mismatch, which in actual operation becomes 2：1. The above design created ullage problem at sustained supplies, gross under utilization of supply chain infrastructures and poor operational performance. After a technical evaluation, a section of the depot storage to loading pipeline network was re-designed and modified to enable products supply capacity to match loading and minimize storage. Hence, the gasoline loading became 66.67%, kerosene and diesel, each of 16.67%, increasing the actual supply to distribution chain capacity ratio from 2：1 to 2：2 （and when required, can be maximized to 2：3） thereby correcting the apparent mismatch between the supply and distribution chain capacities. The modification has enabled the refiner to increase depot and upstream supply chain utilization

Electrochemical Performance and Capacity Fading Mechanism of LiFePO4 at Different pH Aqueous Electrolyte Solutions

The electrochemical stability of LiFePO4 in a Li＋-containing aqueous electrolyte solution is critically dependent on the pH value of the aqueous solution. It shows a considerable decay in capacity of LiFePO4 upon cycling when the pH value is increased to 11. The mechanism responsible for the capacity fading is extensively investigated by means of cyclic voltammogram, ac impedance, charge/discharge, ex situ X-ray diffraction, and chemical analysis. LiFePO4 is relatively electrochemically stable in LiNO3 aqueous solution with pH=7. But the electrochemical performance of LiFePO4 in aqueous electrolyte is inferior to that in organic electrolyte. It is attributed to the loss of Li and the Fe, P dissolution during prolonged charge-discharge in aqueous medium. A precipitate is formed on the surface of LiFePO4 electrodes. It results in the change of crystalline structure, a large electrode polarization, and capacity fading.

A Routing Metric Based on Available Bandwidth Routing in Wireless Mesh Networks

Wireless Mesh Network has drawn much attention due to wide area service coverage with low system cost and being easy to install.However,WMN suffers from high bit error rate,which provides different link capacity among wireless mesh routers.The conventional routing metrics select the path based on link quality.The link with the best quality is preferred as the data transmission path,and thus all nodes likely select the same link,which leads to network performance degradation.This paper proposes a routing metric that considers the available bandwidth and the number of nodes suffering congestion in the path.It is confirmed that the proposed method provides higher network performance of reduced delay,reduced packet loss and increased throughput than conventional routing metrics.

Video over IEEE802.11 Wireless LAN: A Brief Survey

With relatively high transmission capacity and usually unconstrained connections, IEEE802.11 WLANs provide the ideal infrastructure for pervasive video content sharing and communications. However, the delivery of high-performance video streams over 802.11 WLANs remains a challenging task due to the inherent characteristics of compressed video and dynamic channels. In this paper, we present a brief survey of various recent innovations that have been developed to enhance the Quality of Service (QoS) performance for video over WLANs. Based on the application scenarios, the solutions have focused mainly on three network layers, that is, Application layer (APP), Media Access Control layer (MAC), and Physical layer (PHY). After reviewing the video compression technology, we first examine various single-layer solutions for video over WLANs. We then discuss several cross-layer solutions that take advantage of mutual interactions between different network layers. Finally, several technical issues beyond QoS performance, including energy and security, are also addressed. We conclude that the application of video over WLANs will continue to increase in future.

A new capacitive borehole tiltmeter for crustal deformation measurement and its performance analysis

Borehole inclinometers are important observation instruments used to measure ground tilt movement and monitor crustal deformation of solid tides and geological landslide disasters.They are widely used in oil exploration,mineral resource drilling,well logging,exploration and other fields.There is potential for development of rock stress strain monitoring tools.Many types of tiltmeters have been installed,such as SQ-7,FSQ,VS and JB.However,these tiltmeters are generally installed in a deep cave to avoid the interference of temperature,humidity,and human activities.With the urbanization of human society,suitable installation locations are difficult to find.To solve the problem,a two-component borehole tiltmeter,named the CBT-type tiltmeter,is proposed in this paper.It can be installed in a borehole less than500 m deep to eliminate environmental influences.The tiltmeter is composed of two sophisticated gravitational swing and two capacitive transducers.From preliminary theory and experiment analysis,its linear correlation coefficient is higher than 0.99,its co-seismic response is rapid and its noise level is up to 10 4arc seconds in practice.