Effects of pulse parameters on arc characteristics and weld penetration in hybrid pulse VP-GTAW of aluminum alloy

A novel ultrafast-convert hybrid pulse variable polarity gas tungsten arc welding process （HPVP-GTAW） is developed. High frequency pulse square-wave current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration. The effects of pulse current parameters on arc characteristics and weld penetration have been studied during the HPVP-GTAW process using Al-5. 8 Mg alloy plates. The arc characteristics studied by arc voltage and its profile, weld penetration noted by the ratio of weld depth to width have been found to be influenced significantly by the pulse current. The experimental results show that the HPVP-GTA W process can improve the arc profile predominantly and obtain the higher weld penetration with lower heat input. The observation may help in understanding the weld characteristics with respect to variation in the pulse current parameters which may be beneficial in using the novel HPVP-GTAW process to produce the better weld quality of aluminum alloy plates.

Novel hybrid method: pulse CO_2 laser-TIG hybrid welding by coordinated control

In continuous wave CO2 laser-TlG hybrid welding process, the laser energy is not fully utilized because of the absorption and defocusing by plasma in the arc space. Therefore, the optimal welding result can only be achieved in a limited energy range. In order to improve the welding performance further, a novel hybrid welding method--pulse CO2 laser-TIG arc hybrid welding by coordinated control is proposed and investigated. The experimental results indicate that, compared with continuous wave CO2 laser-TIG hybrid welding, the absorption and defocusing of laser energy by plasma are decreased further, and at the same time, the availability ratio of laser and arc energy can be increased when a coordinated frequency is controlled. As a result, the weld appearance is also improved as well as the weld depth is deepened. Furthermore, the effect of frequency and phase of pulse laser and TIG arc on the arc images and welding characteristics is also studied. However, the novel hybrid method has great potentials in the application of industrials from views of techniques and economy.

Design and Simulation for the Pulse High-Voltage DC Power Supply (HVPS) of 1.2 MW/2.45 GHz HT-7U Lower Hybrid Current Drive System

The superconducting tokamak HT-7U [1] has been designed by the Institute of Plasma Physics since 1998 and will be set up before 2003. The 1.2 MW /2.45 GHz HT-7U LHCD (Lower hybrid current drive) system which being the most efficient non-induction device can heat the plasma and drive the plasma current has been efficiently in operation 'owl and a particular design of the 2.8 MW/-35 kV high-voltage DC power supply has been already completed and will apply to the klystron of LHCD on HT-7 and the future HT-7U, and the project of the power supply has been examined and approved professionally by an authorized group of high-level specialist in the institute of Plasma Physics. The detailed design of the power supply and the simulation results are referred in the paper.

An Improved Submodule Unified Pulse Modulation Scheme for a Hybrid Modular Multilevel Converter

This paper presents an improved submodule unified pulse width modulation(SUPWM)scheme for a hybrid modular multilevel converter(MMC)composed of half-bridge submodules(HBSMs)and full-bridge submodules(FBSMs).The proposed SUPWM scheme can achieve an output voltage of(2N+1)(where N is the number of submodules in each arm)levels,which is the same as that of the carrier-phase-shifted PWM(CPSPWM)scheme.Meanwhile,the proposed SUPWM scheme can alleviate the uneven loss distributions between the left leg and right leg in FBSMs of the hybrid MMC.Moreover,the capacitor voltages of the sub-modules can be well balanced without complicated closed-loop voltage balancing controllers.The validity of the proposed SUPWM scheme is verified by both the simulated and experimental results.

Hybrid Simulation of Duty Cycle Influences on Pulse Modulated RF SiH_4/Ar Discharge

A one-dimensional fluid/Monte-Carlo（MC）hybrid model is developed to describe capacitively coupled SiH_4/Ar discharge,in which the lower electrode is applied by a RF source and pulse modulated by a square-wave,to investigate the modulation effects of the pulse duty cycle on the discharge mechanism.An electron Monte Carlo simulation is used to calculate the electron energy distribution as a function of position and time phase.Rate coefficients in chemical reactions can then be obtained and transferred to the fluid model for the calculation of electron temperature and densities of different species,such as electrons,ions,and radicals.The simulation results show that,the electron energy distribution f（ε）is modulated evidently within a pulse cycle,with its tail extending to higher energies during the power-on period,while shrinking back promptly in the afterglow period.Thus,the rate coefficients could be controlled during the discharge,resulting in modulation of the species composition on the substrate compared with continuous excitation.Meanwhile,more negative ions,like Si H_3^-and Si H_2^-,may escape to the electrodes owing to the collapse of ambipolar electric fields,which is beneficial to films deposition.Pulse modulation is thus expected to provide additional methods to customize the plasma densities and components.

Removal of phenol by activated alumina bed in pulsed high-voltage electric field

A new process for removing the pollutants in aqueous solution-activated alumina bed in pulsed high-voltage electric field was investigated for the removal of phenol under different conditions. The experimental results indicated the increase in removal rate with increasing applied voltage, increasing pH value of the solution, aeration, and adding Fe^2＋. The removal rate of phenol could reach 72.1% when air aeration flow rate was 1200 ml/min, and 88.2% when 0.05 mmol/L Fe^2＋ was added into the solution under the conditions of applied voltage 25 kV, initial phenol concentration of 5 mg/L, and initial pH value 5.5. The addition of sodium carbonate reduced the phenol removal rate. In the pulsed high-voltage electric field, local discharge occurred at the surface of activated alumina, which promoted phenol degradation in the thin water film. At the same time, the space-time distribution of gas-liquid phases was more uniform and the contact areas of the activated species generated from the discharge and the pollutant molecules were much wider due to the effect of the activated alumina bed. The synthetical effects of the pulsed high-voltage electric field and the activated alumina particles accelerated phenol degradation.

Microstructure and mechanical properties of the joint of 6061 aluminum alloy by plasma-MIG hybrid welding

Plasma-MIG {metal inert gas arc welding） hybrid welding of aluminum alloy with 6 mm thickness using ER5356 welding wire was carried out. The microstructures and mechanical properties of the welded joint were investigated by optical microscopy, X-ray diffraction （XRD） , energy dispersive spectroscopy （EDS） , tensile test, hardness test and scanning electron microscope （ SEM） were used to judge the type of tensile fracture. The results showed that the tensile strength of welded joint was 142 MPa which was 53. 6% o f the strength o f the base metal. The welding seam zone was characterized by dendritic structure. In the fusion zone, the columnar grains existed at one side of the welding seam. The fibrous organization was found in the base metal, and also in the heat affected zone （HAZ） where the recrystallization occurred. The HAZ was the weakest position of the welded joint due to the coarsening of Mg2Si phase. The type of tensile fracture was ductile fracture.

Effects of Tailed Pulse-Bias on Ion Energy Distributions and Charging Effects on Insulating Substrates

Abstract A hybrid sheath model, including a fluid model and a Monte Carlo （MC） method, is proposed to study ion energy distributions （IEDs） driven by a radiofrequency （RF） with a tailed pulse-bias on an insulating substrate, where a charging effect is obviously caused by the ions accumulated. This surface charging effect will significantly affect the IEDs on the insulating substrate. In this paper, a voltage compensation method is employed to eliminate the charging effect by making the pulse-bias waveform have a certain gradient. Furthermore, we investigate the IEDs under the condition of different pulse-bias duty ratios, waveforms, amplitudes, and cycle proportions. It is found that the parameters of the pulsed source can effectively modulate the IEDs on the insulating substrate and the charging effect, and more desired IEDs are obtained by using the voltage compensation method with modulations of pulse parameters.

Polyaniline/AgCl Hybrid Materials for Selective Determination of Dopamine by Electrochemical Methods

A promising electrochemical sensor based on PANI/AgCl hybrid material has been developed. The organic/inorganic hybrid material has exhibited good electrocatalytic properties by cyclic voltammetry measurement and differential pulse voltammetry. The oxidation overpotential of dopamine decreased dramatically, and the oxidation peak current increased significantly at PANI/AgCl/GCE compared to those obtained at PANI/GCE, AgCl/GCE and bare GCE, corresponding to the synergistic effect between PANI and inorganic particle AgCl. Under the optimized conditions, the linear response in the concentration range of 0.7 to 6.0 μM for the selective determination dopamine on the PANI/AgCl/GCE is obtained with a detection limit of 5.4 × 10–8 M (S/N = 3) using differential pulse voltammetry. The results indicated that the modified electrode can be used to determine dopamine without the interference from ascorbic acid and ensure high sensitivity and good selectivity.

Quantum state transfer via a hybrid solid–optomechanical interface

We propose a scheme to implement quantum state transfer between two distant quantum nodes via a hybrid solid–optomechanical interface. The quantum state is encoded on the native superconducting qubit, and transferred to the microwave photon, then the optical photon successively, which afterwards is transmitted to the remote node by cavity leaking,and finally the quantum state is transferred to the remote superconducting qubit. The high efficiency of the state transfer is achieved by controllable Gaussian pulses sequence and numerically demonstrated with theoretically feasible parameters.Our scheme has the potential to implement unified quantum computing–communication–computing, and high fidelity of the microwave–optics–microwave transfer process of the quantum state.

An Improved Hybrid Space Vector PWM Technique for IM Drives

In this paper, an improved hybrid space vector pulse width modulation (HSVPWM) technique is proposed for IM (induction motor) drives. The basic principle involved in the proposed random pulse width modulation (RPWM) cuddled SVPWM is amalgamating the pre-calculated switching timings for various sections of hexagonal space vector boundary and the random selection of carrier between two triangular signals, in order to disband acoustic switching noise spectrum with improved fundamental component. The arbitrary selection between triangular carriers, which is decided by digital signal states (Low or High) of the linear feedback shift register (LFSR) based pseudo random binary sequence (PRBS) generator. The SVPWM offers a control degree of freedom in terms of positioning of vectors inside every sampling interval and hence it has six possible variants of the voltage vectors arrangements in each sector. The developed HSVPWM is thoroughly analyzed in using the MATLAB? based simulation for all SVPWM variants. From the simulation and experimental results viz. harmonic spectrum, harmonic spread factor (HSF), total harmonic distortion (THD) etc., and the superiority of the proposed scheme such as better utilization of DC bus and the randomization of the harmonic power are evidenced. For the practical implementation, Xilinx XC3S500E FPGA device has been used.

Implementation of FPGA Based Hybrid Power Generator for PV and Wind Grid Applications

This paper deals with implementation of Sinusoidal Pulse-Width-Modulation (SPWM) for a single-phase hybrid power filter generator for Photovoltaic (PV) and wind grid applications. Using policy iteration algorithm, an improved variable step-size perturbation and observation algorithm is contrived and it is implemented proficiently using a hard-ware description language (VHDL) (Very High Speed Integrated Circuit Hardware Description Language). Subsequently, the new generated grid source supplements the existing grid power in rural houses during its cut off or restricted supply period. The software is used for generating SPWM modulation integrated with a solar-power & wind power grid system which is implemented on the Spartan 3 FPGA. The proposed algorithm performs as a conventional controller in terms of tracking speed and mitigating fluctuation output power in steady state operation which is shown in the experimental results with a commercial PV array and HPW (Height Weight Proportional) show. Simulation results demonstrate the validity with load of the proposed algorithm.

近远场地震下RC大跨轻柔拱桥减隔震支座方案优化

为探明不同地震动输入对某大跨轻柔拱桥减隔震的影响,通过非线性有限元模型分析近远场地震下桥梁结构的响应规律,得到大桥支座的优化布置方案.首先,基于模态分析,对比该桥与传统钢筋混凝土(RC)拱桥动力特性差异;其次,选取不同脉冲周期的近场地震动、近场无脉冲及远场长周期地震动记录;最后,研究近远场地震下拱桥的响应行为和损伤演化路径,得到优化桥梁的减隔震支座设计方案.研究结果表明:近场脉冲及远场长周期地震下的桥梁结构响应大于无脉冲地震响应;纵竖向地震下高墩柱剪力及弯矩包络曲线呈“S”形,墩身中部易形成塑性铰,高阶振型影响显著;桥梁纵桥向先于横向震损,损伤路径依次为矮柱、高墩柱及拱肋实心-空心截面段;摩擦摆支座减震效果最佳但位移较大,高阻尼支座方案在近场中长脉冲周期及远场长周期地震下仍会发生损伤,板式橡胶支座方案因无法保证支座同步滑移而不能形成准隔震体系;“高阻尼+摩擦摆”混合方案的支座位移小,拱肋及墩柱均处于弹性,是近断层大跨轻柔RC拱桥的优选减隔震方案.

从美国EMPIRE软件看大型高功率脉冲电磁等离子体程序研发趋势

EMPIRE软件是美国针对下一代高性能计算平台开发的电磁等离子体模拟软件,可用于高置信度地开展高功率脉冲产生、传输以及与物质互作用的全过程模拟。解读EMPIRE软件的研制进展对发展大型高功率脉冲电磁等离子体软件具有重要借鉴意义。首先分析了EMPIRE软件的架构及数学物理方案,然后着重讨论了其性能可移植性的软件特征和各子模块的算法特点,最后结合具体的应用案例展示了EMPIRE的强大计算能力。解读EMPIRE的启示包括如下几点:使用异构架构是实现未来E级(百亿亿次级)计算能力部署的关键点;研制灵活的功能模块,开展分层级的建模计算,最后拉通整个物理过程链条模拟,能够有效发挥装置指标的数值评估作用;多团队协作共同开发是丰富软件功能的基础;软件的置信度需要全方位的验证与确认。

一种混合滞环控制的LLC控制器应用研究

为优化LLC变换器的瞬态性能、间歇工作特性及轻载效率,提出了一种LLC的混合滞环控制方法及变换器实现方案。在深入分析混合滞环控制原理、对称半桥LLC变换器设计方法的基础上,给出基于混合滞环控制的模拟控制器应用方法及200 W对称半桥LLC变换器的关键参数设计,包括控制器外围电路设计,对称半桥电路设计,驱动电路设计,LLC谐振腔各项参数设计等,并通过实验样机进行详细验证。实验结果表明,所提出的混合滞环控制方法及控制器的应用设计科学可行。

基于混合谐波注入的潜水感应电机电磁噪声削弱

针对感应电机在变频供电时会在绕组中产生时间谐波而导致电机的电磁振动和噪声增大的问题,提出了一种采用混合谐波注入的改进型正弦脉宽调制控制策略。以一台1120 kW的潜水感应电机为研究对象,通过对电机进行3、9次混合谐波注入,削弱了电压的调制波和载波谐波及其边带谐波分量,从而降低了电机的振动和噪声。对3、9次混合谐波注入方法中的谐波占比系数进行优化,进一步强化了对边带谐波的削弱效果,整体降低了电机噪声。最后通过对采用混合谐波注入方法的电机与优化前的常规电机进行铁耗、铜耗等方面的性能对比,验证了所提策略在不影响电机的基本性能的前提下,有效削弱了电机的电磁噪声。

用于细胞活性研究的高重频脉冲磁场装置

一定时间的脉冲磁场序列可刺激某些类型的细胞和组织产生有益的生物效应。由于磁体本质上是一个大感性负载,难以同时实现磁体电流的高di/dt和高精度调节。为此,该文提出一种两级联合调控拓扑,前级电路为同步降压电路,用于实现di/dt随磁场期望值同步调节,后级电路是桥式电路,用于实现脉冲磁场波形周期、振幅、稳定度、刺激间隔等参数的控制,为了实现电流从快速上升到稳定值的平滑过渡,引入一种由滞环控制器和PI控制器组成的混合型控制器。在此基础上,研制了频率范围为1 Hz~5 kHz、脉冲边沿小于50μs、可调精度为0.1 mT、峰值强度高达10 mT的便携式高频脉冲磁场发生装置样机,并应用于脉冲磁场对高龄小鼠的体外成熟卵母细胞受精和胚胎发育能力影响的研究。在脉冲磁场作用下囊胚形成率从15.15%提高至52.94%,表明脉冲磁场显著促进了高龄小鼠体外成熟卵母细胞的发育能力。

基于卷积神经网络-长短期记忆神经网络模型利用光学体积描记术重建动脉血压波信号

目的直接动脉血压(arterial blood pressure,ABP)连续监测是侵入式的,传统袖带式的间接血压测量法无法实现连续监测。既往利用光学体积描记术(photoplethysmography,PPG)实现了连续无创血压监测,但其为收缩压和舒张压的离散值,而非ABP波的连续值,本研究期望基于卷积神经网络-长短期记忆神经网络(CNN-LSTM)利用PPG信号波重建ABP波信号,实现连续无创血压监测。方法构建CNN-LSTM混合神经网络模型,利用重症监护医学信息集(medical information mart for intensive care,MIMIC)中的PPG与ABP波同步记录信号数据,将PPG信号波经预处理降噪、归一化、滑窗分割后输入该模型,重建与之同步对应的ABP波信号。结果使用窗口长度312的CNN-LSTM神经网络时,重建ABP值与实际ABP值间误差最小,平均绝对误差(mean absolute error,MAE)和均方根误差(root mean square error,RMSE)分别为2.79 mmHg和4.24 mmHg,余弦相似度最大,重建ABP值与实际ABP值一致性和相关性情况良好,符合美国医疗器械促进协会(Association for the Advancement of Medical Instrumentation,AAMI)标准。结论CNN-LSTM混合神经网络可利用PPG信号波重建ABP波信号,实现连续无创血压监测。

Numerical simulation for pulsed laser-gas tungsten arc hybrid welding of magnesium alloy

Based on the extended application of COMSOL multiphysics, a novel dual heat source model for pulsed laser-gas tungsten arc （GTA） hybrid welding was established. This model successfully solved the problem of simulation inaccuracy caused by energy superposition effect between laser and arc due to their different physical characteristics. Numerical simulation for pulsed laser-GTA hybrid welding of magnesium alloy process was conducted, and the simulation indicated good agree- ments with the measured thermal cycle curve and the shape of weld beads. Effects of pulse laser parameters （laser-excited current, pulse duration, and pulse frequency） on the temperature field and weld pool morphology were investigated. The experimental and simulation results suggest that when the laser pulse energy keeps constant, welding efficiency of the hybrid heat source is increased by increasing laser current or decreasing pulse duration due to the increased ratio of the weld bead depth to width. With large laser currents, severe spatters tend to occur. For optimized welding process, the laser current should be controlled in the range of 150-175 A, the pulse duration should be longer than 1 ms, and the pulse frequency should be equal to or slightly greater than 20 Hz.