Sliding mode control of three-phase AC/DC converters using exponential rate reaching law

Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are involved in the SMC operation, namely reaching mode and sliding mode.In the reaching mode, the system state is forced to reach the sliding surface in a finite time.The major drawback of the SMC approach is the occurrence of chattering in the sliding mode, which is undesirable in most applications.Generally, the trade-off between chattering reduction and fast reaching time must be considered in the conventional SMC design.This paper proposes SMC design with a novel reaching law called the exponential rate reaching law(ERRL) to reduce chattering, and the control structure of the converter is designed based on the multiinput SMC that is applied to a three-phase AC/DC power converter.The simulation and experimental results show the effectiveness of the proposed technique.

FCS-MPC for four-switch three-phase AC-DC converters with DC-link capacitor voltage balancing

Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.

High Power Density Three-Level Three-Phase AC-DC 48 V Power Supply

International standards impose several constraints concerning the electric power quality and require that the harmonic content of the line current of grid connected equipment is below assigned limits; for this reason, operating of AC-DC converters with high power factor and low line current distortion has become essential. In this paper, the prototypal realization of a three-phase AC-DC 48 V power electronic converter for telecom system supplying is described and experimental testing results are discussed. The main constraints in the power supply design are the required power density of about 900 W per dm3 as well as the absence of the neutral wire in the supply grid. The carried out investigation is focused on three-level power converter configurations which are considered in order to reduce voltage rating of power switches. As a result of the reduced voltage, low on-resistance metal-oxide-semiconductor field effect transistors can be used in the power stage, solution which allows to achieve improved efficiency as well as increased switching frequency with respect to the insulated gate bipolar transistors based two-level topologies.

Electrical characteristics of new three-phase traction power supply system for rail transit

A novel three-phase traction power supply system is proposed to eliminate the adverse effects caused by electric phase separation in catenary and accomplish a unifying manner of traction power supply for rail transit.With the application of two-stage three-phase continuous power supply structure,the electrical characteristics exhibit new features differing from the existing traction system.In this work,the principle for voltage levels determining two-stage network is dissected in accordance with the requirements of traction network and electric locomotive.The equivalent model of three-phase traction system is built for deducing the formula of current distribution and voltage losses.Based on the chain network model of the traction network,a simulation model is established to analyze the electrical characteristics such as traction current distribution,voltage losses,system equivalent impedance,voltage distribution,voltage unbalance and regenerative energy utilization.In a few words,quite a lot traction current of about 99%is undertaken by long-section cable network.The proportion of system voltage losses is small attributed to the two-stage three-phase power supply structure,and the voltage unbal-ance caused by impedance asymmetry of traction network is less than 1‰.In addition,the utilization rate of regenerative energy for locomotive achieves a significant promotion of over 97%.

Three-phase AC-DC Converter for Direct-drive PMSG-based Wind Energy Conversion System

In this paper,a wind energy conversion system(WECS)is presented for the electrification of rural areas with wind energy availability.A three-phase AC-DC converter based on a bridgeless Cuk converter is used for power extraction from the permanent magnet synchronous generator(PMSG).The bridgeless topology enables the elimination of the front-end diode bridge rectifier(DBR).Moreover,the converter has fewer components,simple control,and high efficiency,making it suitable for a small-scale WECS.A squirrel cage induction motor(SCIM)is used to emulate a MOD-2 wind turbine to implement the PMSG-based WECS.A direct-drive eight-pole PMSG is used in this study;thus,a low-input-voltage system is designed.The converter is designed to operate in the discontinuous inductor current mode(DICM)for inherent power factor correction(PFC)and the maximum power point tracking(MPPT)is achieved through the tip-speed ratio(TSR)following.The performance of the developed system is analyzed through simulation,and a 500 W hardware prototype is developed and tested in different wind speed conditions.

Current optimization-based control of dual three-phase PMSM for low-frequency temperature swing reduction

In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.

Deciphering engineering principle of three-phase interface for advanced gas-involved electrochemical reactions

As an alternative to conventional energy conversion and storage reactions,gas-involved electrochemical reactions,including the carbon dioxide reduction reaction(CO_(2)RR),nitrogen reduction reaction(NRR)and hydrogen evolution reaction(HER),have become an emerging research direction and have gained increasing attention due to their advantages of environmental friendliness and sustainability.Various studies have been designed to accelerate sluggish kinetics but with limited results.Most of them promote the reaction by modulating the intrinsic properties of the catalyst,ignoring the synergistic effect of the reaction as a whole.Due to the introduction of gas,traditional liquid-solid two-phase reactions are no longer applicable to future research.Since gas-involved electrochemical reactions mostly occur at the junctions of gaseous reactants,liquid electrolytes and solid catalysts,the focus of future research on reaction kinetics should gradually shift to three-phase reaction interfaces.In this review,we briefly introduce the formation and constraints of the three-phase interface and propose three criteria to judge its merit,namely,the active site,mass diffusion and electron mass transfer.Subsequently,a series of modulation methods and relevant works are discussed in detail from the three improvement directions of‘exposing more active sites,promoting mass diffusion and accelerating electron transfer’.Definitively,we provide farsighted insights into the understanding and research of three-phase interfaces in the future and point out the possible development direction of future regulatory methods,hoping that this review can broaden the future applications of the three-phase interface,including but not limited to gas-involved electrochemical reactions.

Optimization of Control Loops and Operating Parameters for Three-Phase Separators Used in Oilfield Central Processing Facilities

In this study,the Stokes formula is used to analyze the separation effect of three-phase separators used in a Oilfield Central Processing Facility.The considered main influencing factors include(but are not limited to)the typical size of oil and water droplets,the residence time and temperature of fluid and the dosage of demulsifier.Using the“Specification for Oil and Gas Separators”as a basis,the control loops and operating parameters of each separator are optimized Considering the Halfaya Oilfield as a testbed,it is shown that the proposed approach can lead to good results in the production stage.

Purification of Moringa oleifera Leaves Protease by Three-Phase Partitioning and Investigation of Its Potential Antibacterial Activity

One of plant-based products for dental care is plant-based proteolytic enzymes which are principally proteases. In order not to damage the protein and bioactive content, an efficient method should be employed for their purifications. As such, three-phase partitioning (TPP) was used to purify protease from moringa (Moringa oleifera). TPP is an emerging, promising, non-chromatographic and economical technology which is simple, quick, efficient and often one-step process for the separation and purification of bioactive molecules from natural sources. It involves the addition of salt (ammonium sulphate) to the crude extract followed by the addition of an organic solvent (butanol). The protein appears as an interfacial precipitate between upper organic solvent and lower aqueous phases. The various conditions such as ammonium sulphate, ratio of crude extract to t-butanol and pH which are required for attaining efficient purification of the protease fractions were optimized. Under optimized conditions, it was seen that, 35% of ammonium sulphate saturation with 1:0.75 ratio of crude extract to t-butanol at pH 7 gave 4.94-fold purification with 96.20% activity yield of protease in the middle phase of the TPP system. The purified enzyme from Moringa oleifera has no antimicrobial effect on the pathogenic bacteria tested. However, this purified enzyme, can be considered as a promising agent, cheap, and safe source which is suitable for using in various industries.

Vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers under blast load

In this article,vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers subjected to blast load are studied.Higher-order ES-MITC3 element based on higher-order shear deformation theory(HSDT)to achieve the governing equations.The sandwich plates with the ultra-light feature of the auxetic honeycomb core layer(negative Poisson’s ratio)and reinforced by two laminated three-phase skin layers.The obtained results in our work are compared with other previously published to confirm accuracy and reliability.In addition,the effects of parameters such as geometrical and material parameters on the vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers are fully investigated.

Enhancing ammonia production rates from electrochemical nitrogen reduction by engineering three-phase boundary with phosphorus-activated Cu catalysts

Electrochemical N_(2) reduction reaction(eNRR) over Cu-based catalysts suffers from an intrinsically low activity of Cu for activation of stable N_(2) molecules and the limited supply of N_(2) to the catalyst due to its low solubility in aqueous electrolytes.Herein,we propose phosphorus-activated Cu electrocatalysts to generate electron-deficient Cu sites on the catalyst surface to promote the adsorption of N_(2) molecules.The eNRR system is further modified using a gas diffusion electrode(GDE) coated with polytetrafluoroethylene(PTFE) to form an effective three-phase boundary of liquid water-gas N_(2)-solid catalyst to facilitate easy access of N_(2) to the catalytic sites.As a result,the new catalyst in the flow-type cell records a Faradaic efficiency of 13.15% and an NH_(3) production rate of 7.69 μg h^(-1) cm^(-2) at-0.2 V_(RHE),which represent 3.56 and 59.2 times increases from those obtained with a pristine Cu electrode in a typical electrolytic cell.This work represents a successful demonstration of dual modification strategies;catalyst modification and N_(2) supplying system engineering,and the results would provide a useful platform for further developments of electrocatalysts and reaction systems.

Automatic measurement of three-phase contact angles in pore throats based on digital images

With the help of digital image processing technology, an automatic measurement method for the three-phase contact angles in the pore throats of the microfluidic model was established using the microfluidic water flooding experiment videos as the data source. The results of the new method were verified through comparing with the manual measurement data.On this basis, the dynamic changes of the three-phase contact angles under flow conditions were clarified by the contact angles probability density curve and mean value change curve. The results show that, for water-wetting rocks, the mean value of the contact angles is acute angle during the early stage of the water flooding process, and it increases with the displacement time and becomes obtuse angle in the middle-late stage of displacement as the dominant force of oil phase gradually changes from viscous force to capillary force. The droplet flow in the remaining oil occurs in the central part of the pore throats, without three-phase contact angle. The contact angles for the porous flow and the columnar flow change slightly during the displacement and present as obtuse angles in view of mean values, which makes the remaining oil poorly movable and thus hard to be recovered. The mean value of the contact angle for the cluster flow tends to increase in the flooding process, which makes the remaining oil more difficult to be recovered. The contact angles for the membrane flow are mainly obtuse angles and reach the highest mean value in the late stage of displacement, which makes the remaining oil most difficult to be recovered. After displacement, the remaining oils under different flow regimes are just subjected to capillary force, with obtuse contact angles, and the wettability of the pore throat walls in the microfluidic model tends to be oil-wet under the action of crude oil.

单级三相谐波电流注入可升降压AC/DC变换器

为适应电动车充电电压宽范围变化需求,本文针对传统充电桩前级整流器拓扑开展研究,提出一种新式单级三相AC/DC变换器。该变换器集成了三相桥式不控整流电路与Cuk模块,为降低输入侧电流谐波分量,选用双向开关管构建谐波电流回馈通路,整体构造成单级式拓扑结构。文章阐述了变换器的电路结构及工作模态,通过建立变换器的等效模型推导出电压增益。变换器通过简单的控制逻辑即可实现正弦输入电流并拥有高功率因数。最后通过搭建变换器数字控制实验平台验证了所提变换器的可行性。

COMPARISON AND EVALUATION OF CURRENT REFERENCE GENERATION STRATEGIES FOR ACTIVE POWER FILTERS IN THREE-PHASE FOUR-WIRE SYSTEMS

For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous active current （IAC） methods are analyzed and compared with each other. The interpretation of active and reactive currents in non-sinusoidal and unbalanced three-phase four-wire systems is given based on the generalized instantaneous reactive power theory. The performance and the characteristic are evaluated, and the application conditions of current reference generation strategies are concluded. Simulation results under different source voltages and loads verify the evaluation result.

长链非编码RNA AC004920.3在胃腺癌癌栓和细胞中的作用

目的探寻AC004920.3在胃腺癌患者血清中的表达和细胞中的作用。方法收集胃腺癌患者血清标本和病历资料。PCR扩增AC004920.3的表达。慢病毒过表达AC004920.3转染AGS细胞后进行凋亡、CCK增殖和划痕实验。结果胃腺癌脉管癌栓患者血清AC004920.3表达ΔCt值12.06±3.33明显高于无脉管癌栓ΔCt值的10.05±3.32,差异有统计学意义(P=0.003),与D-二聚体呈正相关(r=0.679,P<0.001)。AC004920.3过表达组AGS细胞早期凋亡率为(33.45±3.90)%,高于未转染组[(12.13±1.54)%,P<0.001]和空载体组[(13.18±1.55)%,P<0.001];CCK增殖实验AC004920.3过表达组的A值为2.89±0.17,低于未转染组的3.20±0.21,差异有统计学意义(P=0.003);也低于空载体组3.28±0.18,差异有统计学意义(P=0.001);AC004920.3过表达组的划痕面积(3.54±0.12)灰度值,明显大于未转染组和空载体组(2.43±0.34)灰度值,差异有统计学意义(P=0.001);也大于空载体组(2.60±0.39)灰度值,差异有统计学意义(P=0.004)。结论胃腺癌脉管癌栓患者血清AC004920.3高表达,且与D-二聚体正相关。AC004920.3促进AGS细胞凋亡以及抑制AGS细胞增殖和迁移。

线性型霍尔电流传感器ACS730在电流测量中的应用研究

针对科研和工业生产中对电流测量的需求,提出了一种基于单片机、线性型霍尔电流传感器ACS730的电流测量的设计方案及实现方法。文中比较详细地介绍了对ACS730输出信号的预处理、单片机与A/D转换器ADC0831的接口方法等,并给出了完整的电路图和程序流程图。

利用A2C-ac的城轨车车通信资源分配算法

在城市轨道交通列车控制系统中,车车(T2T)通信作为新一代列车通信模式,利用列车间直接通信来降低通信时延,提高列车运行效率。在T2T通信与车地(T2G)通信并存场景下,针对复用T2G链路产生的干扰问题,在保证用户通信质量的前提下,该文提出一种基于多智能体深度强化学习(MADRL)的改进优势演员-评论家(A2C-ac)资源分配算法。首先以系统吞吐量为优化目标,以T2T通信发送端为智能体,策略网络采用分层输出结构指导智能体选择需复用的频谱资源和功率水平,然后智能体做出相应动作并与T2T通信环境交互,得到该时隙下T2G用户和T2T用户吞吐量,价值网络对两者分别评价,利用权重因子β为每个智能体定制化加权时序差分(TD)误差,以此来灵活优化神经网络参数。最后,智能体根据训练好的模型联合选出最佳的频谱资源和功率水平。仿真结果表明,该算法相较于A2C算法和深度Q网络(DQN)算法,在收敛速度、T2T成功接入率、吞吐量等方面均有明显提升。

基于ACE/AngⅡ/AT1R通路探讨补肾降压方对盐敏感性高血压大鼠肾纤维化的作用机制

目的:探讨补肾降压方对盐敏感性高血压DS大鼠肾纤维化及肾素血管紧张素转换酶-血管紧张素Ⅱ-血管紧张素Ⅱ1型受体(ACE-AngⅡ-AT1R)信号通路的调节作用,探讨其防治高血压肾损害的作用机制。方法:选用盐敏感性高血压大鼠(Dahl salt-sensitve,DS)48只,随机数字表法分为低盐组、高盐组、缬沙坦组和补肾降压组,喂食以不同浓度钠盐饲料造模后,予药物干预8周。于干预前后测量血压。干预后酶联免疫吸附测定(ELISA)血清中血肌酐(Cr)、尿素氮(BUN)、血管紧张素Ⅱ(AngⅡ)及转化生长因子-β_(1)(TGF-β_(1))的含量。苏木精-伊红(HE)染色观察肾组织病理学改变情况,Masson染色观察肾纤维化程度。反转录PCR(RT-PCR)及蛋白质印迹法分别检测肾脏血管紧张素转化酶(ACE)及血管紧张素Ⅱ1型受体(AT1R)mRNA及蛋白表达水平。结果:喂食3周不同浓度盐后,喂食高盐各组收缩压均较低盐组升高(P<0.01)。干预后,与低盐组比较,高盐组收缩压升高,Cr、BUN升高,血清AngⅡ及TGF-β_(1)水平升高,HE及Masson染色显示肾脏纤维化程度加重,肾脏ACE及AT1R蛋白及mRNA表达升高(P<0.01)。与高盐组比较,缬沙坦组及补肾降压组收缩压降低,Cr、BUN降低,血清AngⅡ及TGF-β_(1)水平降低,肾脏纤维化程度减轻,肾脏ACE及AT1R蛋白及mRNA表达降低(P<0.05,P<0.01)。结论:补肾降压方有平稳降压,改善肾功能的作用,其作用机制可能与调节ACE/AngⅡ/AT1R轴进而抑制TGF-β_(1)达到延缓肾纤维化相关。

用于恶性肿瘤治疗的^(225)Ac放射性药物的研究现状与展望

^(225)Ac具有半衰期较长(10 d)、射程短(<100μm)和高能量沉积(80~100 keV/μm)等优点,是重要的医用α核素之一。^(225)Ac衰变产生的高传能线密度α粒子可以导致肿瘤细胞的DNA双链断裂,具有重要的临床应用价值。本文综述了^(225)Ac的衰变特性、生产来源以及^(225)Ac与靶向配体偶联的螯合剂,总结了^(225)Ac-前列腺特异性膜抗原(PSMA)-617、^(225)Ac-PMSA-I&T、^(225)Ac-1,4,7,10-四氮杂环十二烷-1,4,7,10-四羧酸(DOTA)-SP和^(225)Ac-1,4,7,10-四氮杂环十二烷-N,N′,N″,N-四乙酸d-苯丙氨酸1-酪氨酸3-奥曲肽(DOTATE)等药物在前列腺癌、脑胶质瘤、乳腺癌和肺癌治疗中的研究及临床应用进展,展望了^(225)Ac治疗药物研发面临的困难与挑战,以期为^(225)Ac放射性药物在恶性肿瘤治疗中的研究与应用提供参考。

基于双模式变频移相调制的单级式双有源桥型DC-AC变换器

针对单级式双有源桥(DAB)型DC-AC变换器关断电流较大和软开关范围有限的问题,该文提出一种双模式变频移相调制策略。首先,对DAB变换器的单移相(SPS)调制和扩展移相(EPS)调制进行时域分析,得到其功率传输特性;然后,分析变换器的关断电流与软开关条件,得到移相比和开关频率约束方程;在此基础上,分析双模式间的移相比边界条件,提出变换器运行模式的切换机制,从而在实现变换器单级功率变换的同时,保证全范围软开关并降低低压侧的关断电流;最后,通过仿真和实验验证了所提调制策略的有效性与可行性。