求半正定Hermitian矩阵特征向量的改进乘幂法

经典乘幂法结合压缩法是计算半正定Hermitian矩阵最大前n个特征值对应特征向量的重要方法,但其固定的迭代次数使得待分解矩阵的随机变化和初始向量的不同选择导致计算精度波动较大,同时,较大特征值对应特征向量的计算误差也会影响较小特征值对应特征向量的计算。为克服这些缺点,提出了一种将前后两次迭代所求向量的距离作为迭代终止条件的改进乘幂法,并证明了它在有误差传播时的收敛性。理论计算结果表明,对4阶半正定Hermitian随机矩阵,在相同计算精度前提下,所提方法比经典方法可至少降低一半计算复杂度。     

一种基于ADS仿真的射频放大器设计方法

针对当前无线通信系统研发周期缩短、研发费用节省的需要,EDA设计工具越来越被电子技术研究的各领域所采用。以EDA中的ADS软件为设计工具,通过具体设计步骤的展示,描述了一种基于ADS仿真的射频放大器设计方法,具有积极的指导意义。在设计过程中,着重注意增益、三阶交调、稳定性等参数。最后列举了实例,说明了该设计方法的可行性。     

Control of three phase PWM rectifier using virtual flux‐based predictive direct power control and SVM under harmonic conditions

In this paper, a new predictive direct power control algorithm to control the PWM rectifier based on virtual flux (VF) is presented. In this algorithm, supply network and the line inductances are assumed as an induction machine and so virtual flux space vectors are assumed corresponding with the space vector of the network voltages. Instantaneous active and reactive powers and finally convertor average voltage in both stationary and rotating reference frames are calculated by the virtual flux space vector components. The main advantages of the proposed method are low total harmonic distortion of the input current and low ripple in the instantaneous active and reactive powers and direct current‐bus voltage under harmonic distorted condition of the supply voltage in comparison with voltage‐based predictive direct power control (V‐PDPC) method. Proposed VF‐PDPC method with space vector modulation switching strategy was tested in simulations and compared with the V‐PDPC method. Copyright © 2015 John Wiley & Sons, Ltd.     

Rigorous analyses of a power distribution system with distribution transformer banks serving unbalanced loads and wind turbine generator systems

Three‐phase power distribution transformer banks (DTrBs) are widely applied to serve single‐phase lighting loads and three‐phase power loads in a medium‐voltage three‐phase four‐wire (3Φ4W) power distribution systems simultaneously. Furthermore, the growing small‐scale wind turbine generator (WTG) systems are directly connected to the secondary side of DTrBs. It has been found that the system imbalance of a power distribution system might be significantly enlarged when WTGs are operated in parallel. Because of the determination the system imbalances of these systems are extremely complicated. In this paper, we introduce an effective method to develop the mathematical models of asymmetrical DTrBs, rigorously. These models can be easily applied in an unbalanced 3Φ4W power distribution system for more detailed analyses. In addition, such a kind of unbalanced system will be solved with an aid of the computer program, Matlab^®/Simulink^®, to analyze the effects of system imbalances when an asymmetrical DTrB serves the single‐ and three‐phase loads and the WTG system in parallel operation simultaneously. The simulation results and conclusion are of value to power distribution engineers for better planning, operating, and promoting their distribution system. Copyright © 2016 John Wiley & Sons, Ltd.     

3D FEM analysis,dynamic modeling,and performance assessment of transverse flux PMSG for small‐scale gearless wind energy conversion systems

The transverse flux permanent magnet synchronous generator has a great potential for use in direct‐drive wind energy conversion systems due to its large pole numbers, high torque, and power density. This research work develops dynamic model of a single‐side transverse flux permanent magnet synchronous generator for use in a small‐scale gearless wind energy conversion system. For acquiring the parameters of the considered generator, required for dynamic modeling, 3D finite element model of the machine is developed and analyzed in both magneto‐static and transient modes. Field‐oriented control approach is employed for tracking maximum power point from the variable wind speed. The simulation results illustrate an accurate response of the system to the wind speed variation and proper performance of the developed dynamic model and control approach of the system. Copyright © 2015 John Wiley & Sons, Ltd.     

半导体激光器在不同制冷条件下散热研究

对半导体激光器在不同制冷条件下的散热进行实验研究.通过设计温度测试系统,分别在被动制冷、单条水路主动制冷和U型回路主动制冷的条件下,测量了多个高功率LD在不同工作电流下的温度,研究了在不同制冷条件下LD温度随电流的变化,发现U型回路主动制冷条件下,LD的散热效果最好.     

基于智能手机的光功率检测模块

光通信维护人员使用光功率计对线路进行检测时,需将检测数据录入网管系统进行数据分析,但经常存在误录、少录或晚录等情况,给线路的维护带来不便.为了解决此问题,设计了基于智能手机的光功率检测模块,给出了该模块的硬件、软件组成和实测数据.     

内蒙古电力高清视频会议系统的建设

随着通信与信息技术的发展,视频会议系统广泛应用于各个领域.传统的标清视频会议系统逐渐不能满足当前的要求,高清视频会议系统已经成为主流.文章简述了内蒙古电力高清视频会议系统的建设方案和电力数据网结构.     

基于MoO3和Re-Bphen修饰有机太阳能电池性能的研究

有机太阳能电池(OSCs)的性能与材料及器件结构密切相关。以MoO3为阳极缓冲层,有机金属配合物Re-Bphen为阴极缓冲层,制备了结构为ITO/MoO3/CuPc/C60/Re-Bphen/Al的OSCs。在标准太阳光照条件下,当MoO3和Re-Bphen的厚分别为5nm和8nm时实现了器件的最佳性能,能量转换效率(PCE)和器件寿命均显著提高。结合器件结构,分析了工作机制。     

大功率LED散热回路热管的实验研究

大功率LED热问题是制约大功率 LED的稳定性、可靠性和寿命的技术瓶颈之一,有效的低热阻封装LED热设计是提高LE D性能的关键。本文提 出一种应用于大功率LED散热的铜-水回路热管(LHP),研究了加热方 式、充液率、风压和倾角 等对LHP均温性、起动性和热阻等的影响。研究结果表明:在输入功率为30W时,LHP的启动时间约为 6.5min;热阻范围为0.48～1.62K/W;在热 负荷为30W时,蒸发器的温度可以稳定控制在75℃以下;蒸发器表 面均温差被控制在1.6℃以下;LHP的最佳的充液率为60%;冷凝器侧 风压在一定范围内(小于130Pa)时,冷凝器侧风压力越大,LED产 品的散热性能越好。