Improvement of output performance of solid oxide fuel cell by optimizing Ni/samaria-doped ceria anode functional layer

Anode functional layers (AFLs) were fabricated using slurry spin coating method on anode substrates to improve the performance of cells based on samaria-doped ceria (SDC) films. The effects of the chemical compositions of AFL and AFL thickness on the performance of solid oxide fuel cell anodes were investigated by studying their effect on the ohmic loss, electrode overpotential, and output performance of cells in different atmospheres. With humidified hydrogen used as fuel and oxygen as oxidant, the cell with an 8-μm-thick AFL (NiO:SDC = 6:4) exhibited excellent maximum power densities of 3.41, 2.89, 1.46 and 0.80 W cm⁻² at 650, 600, 550 and 500 °C, respectively.     

A three-phase current-fed dc/dc converter with a three-leg high frequency transformer for fuel cells

In this paper, a three-phase current-fed dc/dc converter with an active clamp is introduced, and a new three-phase three-leg high frequency transformer is proposed for the converter. The three-phase dc/dc converter transfers power through transformer leakage inductances in the discontinuous current mode; a single common active clamp branch is employed for zero-voltage switching (ZVS) in all active switches. Further, the converter's three-phase power configuration increases power transfer, and it reduces the rms current per phase, thus reduces conduction losses. Moreover, a delta–delta connection on the three-phase transformer provides parallel current paths and reduces conduction losses in the transformer windings. A three-phase transformer can be constructed by connecting three discrete single-phase transformers, but this process results in a higher volume and higher material costs. Therefore, a new three-phase three-leg high frequency transformer is designed with three discrete cores integrated into a single transformer core. The proposed transformer is analyzed according to the several operating modes of the converter, and its design rules are determined. Experimental results are obtained on a 500-W prototype unit; the design is fully verified and analyzed.     

Modeling of Three-Phase Flows and Slag Layer Behavior in an Argon Gas Stirred Ladle

建立了底吹钢包内气/钢液/渣三相流动数学模型, 利用多相流动体积法(VOF)模拟了渣层运 动行为. 模型结果再现了底吹钢包内气/钢液/渣三相流动现象. 当Ar气被吹进钢包时, 在 钢液内产生气泡, 上升的气泡间 歇地冲击并突破渣层, 产生渣眼; 同时, 渣层发生波动, 波动频率随着Ar气流量的增加而增加. 参数研究显示: 220 t钢包底吹流量由100增加到 300 L/min, 渣眼直径由0.43增加到 0.81 m. 计算的无量纲渣眼面积与文献中渣眼的实 验结果很接近. Ar气喷吹期间, 渣层发生重大的变形, 近渣眼处的渣层变薄, 近钢包壁 处的渣层变厚. 渣眼周围钢液流速很大, 并导致部分渣滴卷入钢液中.     

三相四线制并联型有源电力滤波器及其仿真

对于不对称三相四线制电网系统中谐波畸变,可以采用三相四线制有源电力滤波器动态地抑制谐波和进行无功补偿.本文从理论上分析了三相四线制并联型有源电力滤波器的工作原理、主电路结构、数学模型及补偿控制方法,并运用MATLAB仿真软件对其进行了仿真.     

An intelligent dc current minimization method for transformerless grid-connected photovoltaic inverters

Due to the scaling and zero-drift of current sensor errors, unbalanced grid voltages, tolerance of power switching devices, and asymmetry of PWM gate driving pulses, transformerless grid-connected inverters usually have certain amount of dc components injected to the ac grid. Therefore, power quality of the grid is degraded. Many efforts, such as using blocking capacitors, a dc current feedback control method, and a voltage dc component feedback control method, etc., have been introduced to minimize the dc injection. This paper proposes an intelligent control strategy of dc current injection suppression to the grid by utilizing adaptive-back-propagation (ABP) neural network PID controller. The performance of the proposed scheme is evaluated and compared with the traditional and existing method. Finally, the control scheme is verified on a 2-kW three-phase grid-connected inverter in the laboratory.     

高等级三相电能表测试的研究

本文指出影响高等级三相电能表准确度的主要因素是相间影响，并提出了“相间影响矩阵”或“三相误差矩阵”的新概念。介绍了００２级三相电能表的测试方法及相应的测试用标准系统，提出了验证这一标准系统的旁证实验，并给出了实验结果。     

MASS TRANSFER WITH A FIRST ORDER CATALYTIC REACTION IN A THREE-PHASE SYSTEM. TRICKLE FLOW ANALYSIS IN A PERIODICALLY CURVED CATALYTIC SOLID

The present work analyzes the process of mass transfer with chemical reaction in a system formed by a periodically curved catalytic wall, which is wetted by a descending film. Through the film a limiting gaseous reactant is transferred from the stagnant gas phase to the catalyst where the chemical reaction takes place.

The film hydrodynamics is first solved with the unknown free surface through a regular perturbation technique, by expanding the resulting equations in terms of a small parameter: the ratio between the film average thickness and the wave length of the curved solid wall. Assuming that the system is isothermal and at steady state, the mass transfer of the gas is afterwards incorporated. A first order kinetics whose limiting reactant is in the gas phase occurs in the solid phase.

Once the model is established and solved, the influence of the dimensionless parameters upon the effectiveness factor and the solid-liquid Biot number is then studied; important effects are found by changing the solid surface curvature at constant flow rate and catalyst volume. Besides, changes in the flow rate, the Peclet number and the ratio between the solid average width and the film average thickness, show significant effects on the net mass transfer process.     

中小型三相异步电动机节能研究的现状及其发展

近年来,电动机节能问题引起了广泛的重视。国内外科学工作者在节能方面进行大量的研究,取得了卓有成效的进展。本文将从电机设计等方面综述异步电动机的节能问题。     

三相整流变压器有载调压开关过渡电阻烧毁原因与解决方法

通过详细的分析计算，找出了三相整流变压器有载调压开关切换过波电阻烧毁的主要原因，并提出了相应的解决办法。     

Novel compound PWM strategy of a four-leg shunt active power filter

The currently used hysteresis method is of low control accuracy, and the PWM-based strategy fails to provide a high enough response speed; thus, there is always a trade-off between the performances of control accuracy and response speed for a four-leg shunt active power filter (APF) to cope with the large variation in the load harmonic profile. First, an improved SVPWM strategy is proposed in this paper; with the aim to increase the response speed of a four-leg APF by simplifying the implementation of current 3D-SVPWM methods, the principle and realisation of this strategy are explained in detail. Based on these works, a compound PWM algorithm that effectively integrates the improved SVPWM and a PI-based current hysteresis method is proposed to simultaneously guarantee a higher response speed and a higher control accuracy for a four-leg APF. The realisation and parameter tuning of the compound PWM are elaborated. The correctness and effectiveness of the improved SVPWM and the compound PWM strategy are verified by simulations using Matlab/Simulink software. Finally, experimental results on a four-leg APF implemented in a closed-loop real-time simulation platform are presented.