A Novel Serial Hybrid Three-level NPC Topology for Multi-MW Medium Voltage Wind Power Converters

提出一种新型的串联混合三电平中点钳位（neutralpoint clamped,NPC）拓扑,该拓扑是基于传统三电平NPC拓扑的改进和优化,引入大功率IGBT的串联应用。该新型拓扑中,桥臂的两个外管分别用两个低压IGBT串联,两个内管均用高压IGBT。在多兆瓦级中压风电变流器中,大功率IGBT的开关损耗很大,从而限制了开关频率。提出的新型拓扑通过低压IGBT的串联来减小功率器件的损耗,从而提高开关频率,同时可减小输出滤波器的尺寸。通过传统三电平拓扑和新型串联混合三电平拓扑IGBT损耗的对比,说明新拓扑的优势。通过改变门极驱动电阻实现串联IGBT的均压,对新拓扑的应用具有重大意义。最后通过新拓扑的单相样机验证新拓扑的正确性和可行性。

Mathematical Modeling of Porous Medium for Sound Absorption Simulations: Application of Multi-Scales and Homogenization

The modeling of porous medium has many applications whose techniques can be used in the fields of automotive, aerospace, oil exploration, and biomedical. This work concentrates on the Noise and Vibration (NV) development of automotive interiors but the ideas can be translated to the aforementioned areas. The NV development requires the setting of NV targets at dif-ferent levels. These targets are then translated to TL (Transmission Loss), IL (Insertion Loss), and Alpha (absorption) performance. Therefore, the ability to manage an efficient product development cycle, that entails analyzing vibro-acoustic environments, hinges on the premise that accurate TL, IL, or Alpha values pertaining to the different multi-layered porous materials can be calculated. Thus, there is a need to have a thorough understanding of the physics behind the energy dissipating mechanism that includes the effects of the fluid meandering through the pores of the material. The goal of this series is to model the acoustic and dynamic coupling via multi-scale and homogenizations techniques, thus subsequently understand where to incorporate the concepts of dynamic tortuosity, viscous and thermal permeability, as well as viscous and thermal lengths. This study will allow the ability to get a better understanding of the underlying processes and also provides tools to create practical concepts for determining the coefficients of the macroscopic equations. This will assist in attaining novel ideas for NV absorption and insulation.

PARAMETRIC MATCHING SELECTION OF MULTI-MEDIUM COUPLING SHOCK ABSORBER

To achieve the dual demand of resisting violent impact and attenuating vibration in vibration-impact-safety of protection for precision equipment such as MEMS packaging system, a theo- retical mathematical model of multi-medium coupling shock absorber is presented. The coupling of quadratic damping, linear damping, Coulomb damping and nonlinear spring are considered in the model. The approximate theoretical calculating formulae are deduced by introducing transformation-tactics. The contrasts between the analytical results and numerical integration results are developed. The resisting impact characteristics of the model are also analyzed in progress. In the meantime, the optimum model of the parameters matching selection for design of the shock absorber is built. The example design is illustrated to confirm the validity of the modeling method and the theoretical solution.

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component （such as carbon, nitrogen, sulphur and oxygen, etc） thermo-chemical treatment（LTGMTT） can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 （0.48%C） steel prepared by low temperature gas multi-component thermo-chemical treatment （LTGMTT） technology. The fretting wear tests of the modified layer flat specimens and its substrate （LZ50 steel） against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope（SEM）, optical microscope（OM）, X-ray diffraction（XRD） and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime（MFR） of the LTGMTT modified layer diminished, and the slip regime（SR） of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction（COF） of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime（PSR） was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.

铁线莲品种‘Multi-Blue’不定根的诱导培养及其发生过程的解剖学观察

对适宜于铁线莲品种‘Multi-Blue’(Clematis‘Multi-Blue’)不定芽生根培养的基本培养基进行了筛选,并采用L9(32)正交实验设计对生根培养基中NAA和IBA质量浓度进行了比较分析,对不定根形成过程中解剖结构的变化也进行了观察。接种在1/2MS培养基上的铁线莲品种‘Multi-Blue’不定芽的生根率极显著高于改良1/2MS、MS和WPM培养基(P<0.01),生根率达66.97%;在1/2MS培养基中添加0.05 mg.L-1NAA,不定芽的生根效果最好,生根率达69.34%,极显著高于其他处理组(P<0.01)。研究结果表明,添加0.05 mg.L-1NAA的1/2MS培养基(含30 g.L-1蔗糖和8 g.L-1琼脂,pH5.8)为铁线莲品种‘Multi-Blue’不定芽生根培养的最佳培养基。在不定芽的茎横切面上未见潜伏根原基存在;而在接种约1周后,不定芽茎基部皮层的薄壁细胞逐渐恢复分生能力,出现胞质变浓、核质增加、液泡缩小及细胞排列紧密等变化,细胞开始分裂并形成分生细胞团;接种后约2周,根原基发端细胞不断分裂并逐渐形成体积较小、染色较深的一群分生细胞,并出现明显的分层结构;接种后约3周,细胞继续进行平周分裂和垂周分裂,并分化出球形或楔形的不定根根原基;根原基在皮层中常发生弯曲或分支,且皮层处的不定根加粗生长,最终突破皮孔并形成独立的不定根。观察结果表明,铁线莲品种‘Multi-Blue’不定芽基部形成的不定根根原基为诱生根原基。

面向服务的Multi-Agent系统

本文以服务为中心,从面向服务的系统架构、中介服务协作机制、理性化的协商机制和智能交互等四个方面去建立开放、动态、面向服务的多Agent系统,以提高Agent的社会性智能。

Performance Evaluation for Medium Voltage MIMO-OFDM Power Line Communication System

Power line communication(PLC)provides intelligent electrical functions such as power quality measurement,fault surveys,and remote control of electrical network.Most of research works have been done in low voltage(LV)scenario due to the fast development of in-home PLC.The aim of this paper is to evaluate the link-level performance of a medium voltage(MV)MIMO-OFDM communication system based on transmission link under underground power line channel.The MIMO channel is modeled as a modified multipath model in the presence of impulsive noise and background noise.We first perform a measurement on the practical MV MIMO channel parameters for a section of buried cable of 1 km long in Ganzhou city,Jiangxi province,China.Based on the measured channel,we design the frame structure based on an IEEE standard for broadband over power line networks[1]to support MV MIMO-OFDM transmission.According to designed frame structure,we design an encoder and a decoder for a dual binary tail-biting turbo code and optimize some key decoder parameters for low bit error rate performance.Finally,the link-level performance for both spatial multiplexing and spatial diversity are evaluated.Numeral results show that MV MIMO-OFDM is a promising approach to provide both high data rate and link reliability for PLC.

RECONSTRUCTION OF ONE DIMENSIONAL MULTI-LAYERED MEDIA BY USING A TIME DOMAIN SIGNAL FLOW GRAPH TECHNIQUE

A novel inverse scattering method to reconstruct the permittivity profile of one-dimensional multi-layered media is proposed in this paper.Based on the equivalent network ofthe medium,a concept of time domain signal flow graph and its basic principles are introduced,from which the reflection coefficient of the medium in time domain can be shown to be a series ofDirac δ-functions(pulse responses).In terms of the pulse responses,we will reconstruct both thepermittivity and the thickness of each layer will accurately be reconstructed.Numerical examplesverify the applicability of this

In-plane dynamic Green's functions for inclined and uniformly distributed loads in a multi-layered transversely isotropic half-space

The dynamic stiffness method combined with the Fourier transform is utilized to derive the in-plane Green’s functions for inclined and uniformly distributed loads in a multi-layered transversely isotropic（TI）half-space.The loaded layer is fixed to obtain solutions restricted in it and the corresponding reactions forces,which are then applied to the total system with the opposite sign.By adding solutions restricted in the loaded layer to solutions from the reaction forces,the global solutions in the wavenumber domain are obtained,and the dynamic Green’s functions in the space domain are recovered by the inverse Fourier transform.The presented formulations can be reduced to the isotropic case developed by Wolf（1985）,and are further verified by comparisons with existing solutions in a uniform isotropic as well as a layered TI halfspace subjected to horizontally distributed loads which are special cases of the more general problem addressed.The deduced Green’s functions,in conjunction with boundary element methods,will lead to significant advances in the investigation of a variety of wave scattering,wave radiation and soil-structure interaction problems in a layered TI site.Selected numerical results are given to investigate the influence of material anisotropy,frequency of excitation,inclination angle and layered on the responses of displacement and stress,and some conclusions are drawn.

Grid-connected Multilevel Topology for HVDC Offshore Wind Farm Based on MFT

This paper presents a new topology to connect high voltage direct current(HVDC) offshore wind farm into the grid.The offshore part consists of five units,each unit contains permanent magnet synchronous generator(PMSG) connected to three-phase/three-phase matrix converter to control the generator speed by using a maximum power point tracking(MPPT) control.The offshore platform consists of a three-phase medium frequency transformer(MFT) and a modular multi-level converter(MMC).The primary of each phase of the transformer connected to one phase from each unit.The secondary of the transformer connected to MMC to get HVDC.The HVDC cable will be used to transfer power from the offshore side to the on-shore side.Five-level MMC is used in the onshore side to control the DC voltage and to connect the offshore wind farm into the grid by converting the HVDC to high voltage alternative current(HVAC).

Mathematical Modeling of Porous Medium for Sound Absorption Simulations II: Wave Propagation and Interface Conditions

The application of porous medium has a myriad of applications in different industries: automotive, aerospace, civil (commercial, residential), environmental noise control, and biomedical. In the past, design questions involving porous material were addressed with seat-of-the-pants decisions that led to multiple/iterative prototypes and experiments that were costly and time consuming. The objective, in this series of publications pertaining to porous medium, is to establish tools that will lead to effective and accurate simulations involving porous medium. In this third installment of this series the focus is on establishing the constitutive equations using tensors and then applying Transfer Matrix Method (TMM) to calculate diffuse field Transmission Loss (TL) across structures that comprises of layers of different porous medium. The constitutive equations are obtained by relating information regarding the micro-structure make-up to macro level properties. In order to apply the TMM, the equations for wave propagation across different mediums need to be developed and in turn represent these propagation properties in a matrix format. Additionally, the boundary condition between each layer type is defined in order to ensure numerical stability. The author’s current research effort is running simulations for the automotive industry to predict NVH environments. Therefore, TL calculations pertaining to the materials that are utilized in the interior of automobiles are used, in this paper, as a test bed for the developed analytical tools. Case in point, the TL for a multi-layered material consisting of one panel and two different layers of foam is calculated and compared to experimental data. Future publication goals will be to apply these tools in the biomedical field;an example will be to model and run simulations of different organs like the liver and lungs that are po-rous in nature.

MEDIUM-RANGE OSCILLATION OF METEOROLOGICAL ELEMENTS AT GREAT WALL STATION,ANTARCTICA

A method of multi-spectral analysis is used to study the spectral characteristics of surface and upper-level meteorological elements over the Great Wall Station (62°12'S, 58°57'W), Antarctica and their phasecorrelation, propagation of mean oscillation at 500hPa level in the Southern Hemisphere and their corresponding synoptic sense. the results are summed up as follows: 1. Over the sub-Antatctic zone, as in the Northern Hemisphere there generally exist quasi-weekly oscillation and quasi-biweekly oscillation. In different seasons the oscillations of meteorological elements are different: in winter season quasi-biweekly oscillation is dominant, while in summer season quasi-weekly oscillation is dominant. 2. From the Earth's surface to the lower stratosphere there is a distinct quasi-weekly oscillation at each isobaric surface, but the most intense oscillation appears at 200-300hPa, and the oscillations of height and temperature are propagated downward. 3. Both in winter and summer seasons the quasi-biweekly oscillation are propagated from west to east, and the mean velocity of its propagation is about 7-17 longtitude / day. 4. The quasi-biweekly oscillation and the quasi-weekly oscillation over the sub - Antarctic zone are closely related to the activity and intensity variation of polar vortex at 500hPa, while at 1000hPa they reflect an interaction between the circumpolar depression and the sub-tropical high. The quasi-biweekly oscillation may be a reflection of inherent oscillation of the polar vortex, where as the quasi-weekly oscillation is a result of forced oscillation by external disturbance.A large number of calculations and analysis made reveals the features of medium-range oscillation over the sub-Antarctic zone. The results are of significance for understanding the behaviour of synoptic dynamics and making the weather forecast.This work is supported by National Committee for Antarctic Research.

基于多目标优化的跨介质航行体水面滑跳初始运动参数设计

基于耦合欧拉-拉格朗日方法,开展了初始运动参数对带滑板跨介质航行体近水面滑跳过程的影响规律研究。采用参数回归方法分别建立最大浸深、最大过载和俯仰角变化3个变量随航行体初始速度、入水角、滑板倾角变化的关系式,得到了跨介质航行体稳定滑跳的参数包络,在入水角2°~5°、滑板倾角10°~25°、速度60~80 m/s范围之间,且在范围内各参数之间会相互制约。在此基础上,基于多目标优化算法获得了最适宜航行体稳定滑跳的初始参数为入水速度60.1 m/s、滑板倾角18.8°、入水角2°,在此参数范围内,跨介质航行体的水面滑跳过程可以在不超过航行体过载要求的条件下获得相对最小的入水浸深和俯仰角变化。

Further Stabilization and Power Density Improvement of Stack-Type Thermoelectric Power Generating Module with Biphasic Medium by Using Various Flexible Metals as Electrodes

In order to realize further stability of a stack-type thermoelectric power generating module (i.e. no electrical connections inside), flexible materials of metal springs and/or rods having restoring forces were installed between lower-temperature-sides of thermoelectric elements. These flexible materials were expected to play three important roles of interpolating different thermal expansions of the module components, enlarging heat removal area and penetration of any media through themselves. Then, a low-boiling-point medium (i.e. NOVEC manufactured by 3M Japan Ltd.) was also applied for a high-speed direct heat removal via its phase change from the lower-temperature-sides of the thermoelectric elements in the proposing stack-type thermoelectric power generating module. No electrical disconnections inside the module were confirmed for more than 9 years of use, indicating further module stability. The power generating density was improved to about 120 mW·m-2 with SUS304 springs having 0.7 mm diameter. Increasing power generating density can be expected in terms of suitable selection of flexible metal with high Vickers hardness, cavities control on the spring surface, more vigorous multiphase flow with adding powders to the medium and optimization of the module configurations according to numerical simulations.

多介质过滤处理农村灰水影响因素实验研究

为寻求多介质过滤技术处理农村灰水的可行性及最佳运行条件,以内蒙古呼和浩特市某村生活灰水为研究对象,选择玉米茎、陶粒、活性炭作为过滤介质构建多介质过滤系统处理农村灰水,研究滤速、介质配比、进水LAS、COD、SS浓度和温度等影响因素对多介质过滤系统处理效果的影响。结果表明多介质过滤处理农村灰水的最佳滤速为0.26 m/h;介质配比玉米茎∶陶粒∶活性炭为1.5∶2∶0.5;多介质过滤系统处理灰水中LAS、COD、SS的浓度限值为30、300、300 mg/L;温度为2℃时,系统出水仍满足农田灌溉水质标准(GB 5084-2021)。研究表明,多介质过滤技术对农村灰水有较好的处理效果,降低农村灰水处理设备建设和运行成本,有利于农村污水就地回用资源化利用。

Peristaltic Blood Flow with Gold Nanoparticles on a Carreau Nanofluid through a Non-Darcian Porous Medium

The article investigates the influences of a variable thermal conductivity and wall slip on a peristaltic motion of Carreau nanofluid. The model is concerned with heat and mass transfer inside asymmetric channel. The blood is considered as the base Carreau non-Newtonian fluid and gold (Au) as nanoparticles stressed upon. The Fronchiener effect of the non-Darcian medium is taken in consideration. The system is stressed upon a strong magnetic field and the Hall currents are completed. The problem is modulated mathematically by a system of non-linear partial differential equations which describe the fluid velocity, temperature and concentration. The system is reformulated under the approximation of long wavelength and low Reynolds number. It is solved on using multi-step differential transform method (Ms-DTM) as a semi-analytical method. A gold nanoparticle has increased the temperature distribution which is of great importance in destroying the cancer cells.

基于斜三角形摆弧的中厚板多层单道焊接路径规划

针对中厚板结构件焊接较为复杂的问题,研究应用于中厚板焊缝的摆弧路径,提出一种基于空间直线斜三角形摆弧的轨迹算法,实现中厚板焊缝的焊接。首先,研究空间直线斜三角形摆弧轨迹算法来计算摆弧路径各插补点位置信息。然后,由插补点位置信息结合焊缝特征进行焊枪位置规划、焊道速度规划。其次,将所得到的各焊接路径算法生成的插补点输入至MATLAB进行仿真验证。最后,搭建实验平台,进行摆弧生成实验、焊接实验。实验结果表明:该算法是可行的,可以应用于实际焊接工程中。

模块化多电平中压直流变换器的高可靠自供电架构研究

随着大容量中压直流配电技术的迅速发展,模块化多电平直流变换器受到工业界和学术界的广泛关注。然而,实现高可靠的辅助供电是实现直流变换器在中压直流配电场景中应用的关键技术瓶颈之一。为此,提出一种面向模块化多电平中压直流变换器的高可靠自供电系统架构。该架构实现主控制器、子模块等辅电系统的中压直联馈电,从而无需额外低压直流电源,并且大幅提升系统启动速度。基于此架构设计,模块化多电平直流变换器的子模块控制器和旁路开关辅助供电均实现3倍冗余,提高系统容错运行的能力。在子模块电容预充电阶段,提出一种基于辅助电源自主控制的子模块电容均压方法,保证模块化多电平直流变换器可靠预充电。最终通过实验验证所提辅助供电系统架构的可行性。

提高油气田采收率技术协同方法与应用

阐述了提高油气采收率技术协同方法的内涵,研究形成了“3+2”(三次采油和二次采油)协同大幅度提高高含水老油田采收率技术,提出了“3+2”提高采收率技术政策。建立了多元热复合技术协同大幅度提高稠油采收率方法,研究提出的提高油气田采收率技术协同方法在矿场应用,难开采稠油采收率提高了21.9%。多元热复合开发与分支井技术协同应用成功将稠油黏度动用上限扩展到750000 mPa·s,储层厚度动用下限突破到1.5 m。提出了下一步技术协同发展方向:低渗透油藏压驱-注水协同开发、缝洞型油藏气-水-井网协同提高采收率、老油田油藏-井筒-地面一体化开采以及页岩气复合排水采气。

温室大棚地热能与空气能多能互补能源配比研究

“双碳”目标下采用可再生能源解决温室大棚的供冷、供暖,构建安全、绿色、智慧、高效的能源系统成为了温室大棚的发展方向。近年来,中深层地热能、浅层地热能、空气能在温室大棚供热中的应用得到快速发展。以河南省周口市扶沟县某农业产业园为例,结合区域地热资源情况,提出了中深层地热+地源热泵+水源热泵、中深层地热+地源热泵+空气源热泵、地源热泵+空气源热泵、地源热泵+水源热泵4种可再生能源配比方案。结果表明:地源热泵+水源热泵投资最高,地源热泵运行费用是中深层地热的2.01倍,空气源热泵运行费用是水源热泵1.95倍,地源热泵运行费用与水源热泵相相近。能源利用优先级排序为中深层地热能>地源热泵>水源热泵>空气源热泵,采用中深层地热+地源热泵+水源热泵方案为最优的能源搭配方式。