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601.
阐述了死区效应的产生机理及其在开环控制下对逆变器输出基波电压的影响和死区谐波频谱分布情况。在此基础上,通过闭环传递函数带宽分析,定量地分析了闭环系统对死区效应的抑制作用以及控制带宽大小对抑制死区效应效果的关系。以单电流闭环控制的LCL滤波并网逆变器系统为例,进行闭环控制带宽对死区效应抑制的仿真验证。最后,在一台250kW三相并网逆变器上进行实验验证。仿真和实验结果证明了理论分析的正确性。 相似文献
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给出了FL-8风洞进行旋转天平试验支架干扰研究的情况,对试验方法、设备和试验结果进行了介绍。为了实现圆弧形滑轨与模型支杆的支撑和变角功能,特别设计了新型的变角支杆。试验结果表明:支架干扰对纵横向气动力的影响规律是不同的,对纵向结果的影响是与旋转方向无关的,而对横向结果的影响在正反旋转时是相反的。尾撑和背撑试验结果经过支架干扰修正后向相同的值靠近,说明支架干扰修正的结果是合理的,提高了试验结果的准度。 相似文献
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Φ5m立式风洞旋转天平试验装置是为开展飞机尾旋特性研究而研制的重要基础设备,主要用于测定模型在绕风轴以不同速率作等速旋转状态下的气动特性,为飞机尾旋特性的分析和预测提供必要的气动参数。该装置采用双立柱弧形轨结构形式,采用网络一体化试验管理和控制模式,不但能够开展旋转天平试验,而且还具备动导数试验、大迎角试验、旋转/振荡耦合试验等功能。主要介绍旋转天平试验装置系统组成和设计,分析了引导性试验结果,最后给出了结论。 相似文献
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Mohammad Ali Sharifi Abdolreza Safari Salim Masoumi Ali Sam Khaniani 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
In order to investigate the regular variations of the ionosphere, the least-squares harmonic estimation is applied to the time series of ionospheric electron densities derived from about five years of Global Positioning System radio occultation observations by FORMOSAT-3/COSMIC satellites. The analysis is done for different latitudes and altitudes in the region of Iran. The least-squares harmonic estimation is found to be a powerful tool for the frequency analysis of the completely unevenly spaced time series of radio occultation measurements. Although the obtained results are slightly different from the exact expected cycles (i.e. annual and diurnal components with their Fourier decompositions, and the 27-day period) due to the low horizontal resolution of radio occultation measurements, high vertical resolution of the observations enables us to detect not only the total electron content variations but also periodic patterns of electron densities at different altitudes of the ionosphere. The dominant diurnal and annual signals together with their Fourier series decompositions are obtained, which are consistent with the previous analyses on the total electron content. In the equatorial anomaly band, the annual component is weaker than its Fourier decomposition periods. In particular, the semiannual period dominates the annual component, indicating the relationship between the semiannual variation of the electron densities and the ionospheric equatorial anomaly. From detection of the phases of the components, it is revealed that the annual signal generally has its maximum value in summers at high altitudes, and in the winters at low altitudes. This is probably due to the higher [O/N2] ratios in winter than in the summer in the lower ionosphere. Furthermore, the semiannual component mostly peaks around solstices or about a month before/after them. 相似文献
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Manoranjan Sinha N.S. Gopinath N.K. Malik 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
This paper summarizes and provides a critical analysis of the historical developments of lunar gravitational models from the earliest use of ground based tracking systems of the Lunar Orbiter to the Lunar Prospector mission. This encompasses a comprehensive and critical analysis of the various methods used in the estimation of the gravity coefficients and the processing of large batches of diverse measurements and data types. It has been shown that weakness exists in the current models of the lunar gravity field, which is primarily due to the lack of far side lunar tracking data information, which makes the lunar potential modeling difficult but expected to be overcome as data from SELENE satellite-to-satellite tracking becomes available. Comparisons of various lunar models reveal an agreement in the low order coefficients of the spherical harmonics. However, substantial differences in the models exist in the higher-order harmonics. A numerical comparison has been presented showing the performance of all the contemporary lunar gravitational models used within the astrodynamics community and available in public domain. Improvements to the current models are part of a continuing process and the recent model improvements and future possibilities in lunar gravity modeling are discussed. A brief review of the recent missions has been presented. It is hoped that this critical review will benefit the researchers by presenting the historical as well as state of the art in this field. 相似文献