Theoretical Investigations of Spin Splittings and Optimization of the Rashba Coefficient in Asymmetric AlSb/InAs/GaSb Heterostructures

We use the Effective Bond Orbital Model (EBOM) method to examine the spin splitting due to the Rashba effect in AlSb/InAs/GaSb asymmetric heterostructures. We have explored different thicknesses of the constituent materials and we have found for the resulting two-dimensional electron gas (2DEG) in the optimized structure a theoretical value of the Rashba constant _R = 51 × 10^–10 eV·cm. This is, to our knowledge, the largest predicted value for this parameter. We provide an intuitive explanation for the behavior of the spins in the 2DEG. Finally, we study the effect of wide layers on the Rashba coefficient.     

Smooth Quantum Hydrodynamic Model vs. NEMO Simulation of Resonant Tunneling Diodes

The smooth quantum hydrodynamic model is an extension of the classical hydrodynamic model for semiconductor devices which can handle in a mathematically rigorous way the discontinuities in the classical potential energy which occur at heterojunction barriers in quantum semiconductor devices. Smooth QHD model simulations of the current-voltage curves of resonant tunneling diodes are presented which exhibit negative differential resistance—the experimental signal for quantum resonance effects—and are compared with the experimentally verified current-voltage curves predicted by the simulator NEMO, which uses a non-equilibrium Green function method.The NEMO work described in this article was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration. This material is also based upon work supported by the National Science Foundation under Grant No. EEC-0228390.     

Modeling the Inelastic Scattering Effect on the Resonant Tunneling Current

Resonant tunneling current with the inelastic scattering effect is modeled basing on the sequential tunneling approach. Simulations are performed for the case of a silicon double gate (n⁺)polySi/SiO₂/(i)Si/SiO₂/(n⁺)polySi structure     

Modeling of peak voltage and current of nanowire resonant tunneling devices: case study on InAs/InP double‐barrier heterostructures

In this paper, we develop an analytical model for the prediction of the peak voltage and the current in the current–voltage characteristics of nanowire resonant tunneling heterostructures. The model is applied in the case study of double‐barrier InAs/InP devices, and the results are obtained from numerical carrier transport calculations, in terms of structural parameters such as the nanowire radius as well as the width of the barriers and quantum well. Copyright © 2013 John Wiley & Sons, Ltd.     

谐振阻抗混合型有源电力滤波器的建模与补偿特性分析

针对谐振阻抗混合型有源电力滤波器的结构特点,建立了谐振阻抗混合型有源电力滤波器的数学模型。在该数学模型基础上,分析了基于检测电网侧谐波电流和负载侧谐波电流的复合控制策略下电流放大倍数变化、电网阻抗变化、无源滤波器失谐和基波串联谐振电路失谐对有源电力滤波器滤波特性的影响。仿真结果表明,该混合型有源电力滤波器具有良好的滤波特性,所得结果可为实际应用提供有效的参考。     

串并联谐振倍压变换器原理分析、建模及仿真

针对串联谐振和并联谐振直流环节存在的谐振峰值电压过高和谐振峰值电流过大的缺点,以及对高电压小电流的要求,提出了串并联谐振倍压变换器拓扑的概念。文中分析了该变换器的工作原理,建立了系统数学模型,给出了该变换器的输出特性。仿真和实验结果证明了新型变换器原理和理论分析的正确性。     

谐振式无线电能传输系统损耗模型

针对无线电能传输系统损耗的量化计算问题,本文以电流型谐振式无线电能传输系统为例,对其损耗进行了完整的分析与计算。考虑了电流型全桥谐振变换器开关管的旁路二极管和谐振回路带来的环流影响,使得建立的逆变器的损耗模型更为精确。该模型还充分考虑了高频效应带来的影响,给出了耦合机构的高频内阻计算公式。实验结果验证了模型的正确性和有效性。通过该模型可得到系统损耗的主要组成部分及主要决定因素,对无线电能传输系统的设计与改进具有重要的参考意义。     

基于形态滤波的谐振接地系统故障选线新方法

分析了基于小波理论暂态选线方法的现状后,提出一种基于形态滤波和相关分析的暂态选线新方法。与故障线不同,故障时在中性点零序电压作用下,非故障线暂态零序电流的暂态特性主要由自身对地电容充放电特性决定。将所有馈线零序电流对中性点电压的导数进行归一化处理,再利用相关分析得出每条馈线的综合相关系数,选出符合故障判据的故障线。其中,为有效地抑制各种干扰对算法的影响,对归一化后的零序电流利用改进的多结构元素复合形态学滤波器进行滤波处理。高压物理模拟实验及现场试验结果验证了本算法的可靠性和实用性。     

铁磁/重金属双层膜结构中电流驱动的铁磁共振

在理论上研究了具有垂直磁各向异性铁磁/重金属双层膜结构中电流驱动的铁磁共振。通过线性展开包含自旋霍尔效应自旋矩项的Landau-Lifshitz-Gilbert方程,获得了交流电流频率和直流电流密度调节的铁磁共振谱。发现平衡位置、共振位置和共振线宽都可以通过改变直流电流密度和外磁场的大小进行调节。联合自旋霍尔效应感应的交流和直流自旋矩,可以减小电流感应磁矩反转的临界电流密度。     

四桥臂有源滤波器在静止坐标系下的改进PR控制

有源电力滤波器(active power filter,APF)电流环控制要求补偿电流无误差地跟踪给定信号,传统的dq坐标系下P I控制很难消除稳态误差。采用并联的比例谐振(proportional resonant,PR)控制器,对不同频率的正弦分量进行跟踪控制,实现零稳态误差跟踪。针对电网频率波动和三相不平衡问题,在坐标系下采用改进PR控制器实现电流跟踪控制。在详细分析PR控制器各参数对性能指标影响的基础上,总结参数的调试方法,并给出控制器离散化方法。通过仿真与实验对所提控制策略进行验证,APF投入后,电网电流畸变率下降,中线电流有效值减小,负载和频率波动时仍有较好的补偿效果。该结果表明,所提的改进PR控制策略可以有效地抑制谐波,较好地解决三相不平衡问题,对负载突变和频率波动均有良好的适应性。     

Power Quality Improvement in a Four-Phase Switched Reluctance Motor Drive using Twelve-Pulse AC/DC Converter

This article deals with a 12-pulse AC/DC converter for improving power quality in a midpoint converter based switched reluctance motor drive at AC mains. The conventional six-pulse AC/DC converter fed midpoint converter based switched reluctance motor drive injects high content of current harmonics into AC mains. The proposed 12-pulse AC/DC converter with a small rating passive filter is capable of eliminating harmonic currents from light load to full load with a high power factor. The proposed switched reluctance motor drive system is designed, modeled and simulated in Matlab/Simulink environment and its performance is compared with a conventional six-pulse AC/DC converter fed switched reluctance motor to demonstrate the power quality at AC mains. The simulated performance of the proposed 12-pulse AC/DC converter fed switched reluctance motor drive is experimentally validated for power quality improvement.