Performance evaluation of WPT based islanding detection for grid-connected PV systems

Recent developments in power electronics technology have emerged towards the generation of electrical power from the renewable energy sources. Among renewable energy sources, solar energy has garnered more importance because of less maintenance and environmental friendly. In grid connected mode, distributed power generation system (DPGS) requires reliable islanding detection technique to find the electrical grid status and operate the grid connected inverter effectively. This paper investigates a comparative performance analysis of wavelet transform (WT) and wavelet packet transform (WPT) based detection in a three-phase grid connected PV inverter system under various power quality disturbances and islanding situation. The WT and WPT coefficients are determined by applying db4 wavelet basis functions, which are obtained optimally for analyzing perturbations that occur in grid connected PV system. The wavelet transform produces large errors due to spectral leakages in frequency bands. On the other hand, WPT provides uniform frequency subband with better time frequency resolution over WT. Finally, the feasibility of proposed WPT based islanding detection method is verified by simulating the system in MATLAB/SIMULINK environment. The simulated results demonstrate the better performance of WPT over WT technique and proved as an accurate, fast and reliable detection technique.     

一种级数混合运算产生SPWM波新方法

提出了一种产生正弦脉宽调制波的新方法。介绍了采用级数混合运算产生数字化正弦波数据的基本原理,不需要专门的ROM存储器,利用传统查表法就能够得到所需要的SPWM信号。基于所提出的方法设计了一种通用型SPWM波形发生器,利用FPGA内部的RAM资源例化成所需要的虚拟ROM存储器,用来存储由级数混合运算得到的1/4周期数字化正弦波数据,然后利用中心对称和轴对称运算得到整周期的正弦波,与三角形载波进行比较后输出SPWM信号。实验结果表明,该SPWM发生器具有可靠性高,电路结构简单,使用灵活等特点。采用所提出的方法设计的SPWM光伏逆变器已投入应用,性能良好,工作稳定。     

汽轮发电机组轴系扭应力分析及保护装置的应用

论述了汽轮发电机组在电网各类扰动下对轴系形成的疲劳损耗,介绍了扭应力分析及保护装置的应用。     

等效多相整流系统直流侧环流的计算

分析了多台整流机组并联工作的大型整流装置中的环流电势及环流电流,并用等效正弦电势法和谐波分析法推导了其计算公式,给出了计算实例及实测结果．     

一种非线性控制的正弦波逆变器的研究

提出了一种基于ｏｎｅ－ｃｙｃｌｅ非线性控制的ＤＣ４８Ｖ／ＡＣ２２０Ｖ正弦波逆变器,详细阐明了控制原理,进行了谐波分析,仿真结果证明主出版社为器具有优良的抗线扰动性和限随性能。     

集值映射扰动多目标规划的稳定性

目的研究扰动集值映射多目标规划问题解集在上（下）半连续意义下的稳定性．方法依据拓扑、凸分析和泛函分析理论,对扰动集值映射多目标规划问题中特定的集值映射进行分析和研究．结果分别给出了锥有效解集和锥弱有效解集的上半连续和下半连续的充分性条件．结论进一步完善了多目标规划理论     

中弧线变形方式对扑翼能量吸收效率的影响

选用NACA0015翼型,在Re=1×10~4的条件下,采取正弦和分段函数两种不同的中弧线变形规律,通过对最大变形位置、变形幅值等参数的分析,揭示两种变形方式对于扑翼能量吸收效率的影响。研究表明:两种变形方式均能带来扑翼能量吸收效率的提升,且最大变形位置越靠后,扑翼能在更大的变形幅值范围内获得能量吸收效率的提升;随着最大变形位置的后移,正弦形式取代分段函数形式成为一种较优的变形方式;正弦的中弧线变形方式降低了输出功率系数曲线的第二个峰值,但其大幅提升第一、二峰值之间区域的数值,故正弦的中弧线变形方式仍是一种较优的变形方式。     

Rejection of narrow‐band disturbances subject to uncertain time delays

In this work, the problem of designing feedback contollers for the rejection of narrow‐band disturbances is considered. The design technique proposed herein is based on the overparametrization of a nominal minimum‐variance controller, which is designed by means of an ARMA model of a sinusoid in noise. The extra degrees of freedom so introduced are used to improve the robustness of the nominal controller, when the time delay of the plant is subject to uncertainties, by minimizing a minimum‐variance performance index along a one‐dimensional line. Copyright © 2000 John Wiley & Sons, Ltd.     

Some considerations on torque ripple suppression in reluctance motors

Although the reluctance motors are attractive from the standpoints of simple construction and drive electronics, the relatively high torque ripple and acoustic noise are major drawbacks. These drawbacks limit motor applications. In this paper, the torque ripple suppression of the reluctance motor under the sinusoidal current drive is examined. The analysis shows that the torque ripple is caused by the spatial harmonics of inductance. One approach is based on the compensation current generated with the spatial harmonics of inductance. Another is based on the modification of rotor tooth configuration to eliminate the spatial harmonics. According to the proposed strategies, torque ripple suppression characteristics can be evaluated at the design stage of the motor. Both approaches have been verified by experiments. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 118–128, 2000     

正弦力法动态力传感器灵敏度不确定度评定

随着汽车技术的日益发展,动态力传感器在汽车NVH、模态试验中用到的越来越多,一般采用动态法校准.本文依据振动与冲击传感器校准方法,以标准振动传感器为标准器,采用正弦力法校准动态力传感器灵敏度,并计算动态力传感器灵敏度测量值的不确定度,确保量准的准确一致和正确传递.