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2001年西北太平洋热带气旋的统计特点 被引量:1
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作者 陈登俊 《中国航海》 CSCD 北大核心 2002年第4期39-43,共5页
对 2 0 0 1年西北太平洋热带风暴等级以上的热带气旋进行了比较详细的统计分析 ,将统计结果与多年历史资料进行了对比 ,得到一些值得注意的有价值的结论。
关键词 2001年 西北太平洋 统计特点 统计分析 热带气旋 海上风暴
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H.264快速运动估计算法的改进 被引量:12
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作者 李桂菊 刘刚 梁静秋 《光学精密工程》 EI CAS CSCD 北大核心 2010年第11期2489-2496,共8页
为了提高视频压缩效率,对H.264中采用的快速运动估计算法UMhexagonS进行了改进。首先,在起点预测后加入一个结束搜索条件,判断是否结束对当前宏块的运动估计。然后,对于需要进一步运动估计的宏块,从两个方面对原算法进行了改进。提出了... 为了提高视频压缩效率,对H.264中采用的快速运动估计算法UMhexagonS进行了改进。首先,在起点预测后加入一个结束搜索条件,判断是否结束对当前宏块的运动估计。然后,对于需要进一步运动估计的宏块,从两个方面对原算法进行了改进。提出了搜索模板分割方法,在进行十字形模板和大六边形模板搜索时,只需要根据该方法选择少量搜索点进行运动估计。根据运动矢量的统计特点,减少了正方形模板和扩展六边形模板的搜索点数。同时验证了所采用的搜索区域分割方法的合理性。实验结果显示,改进算法的运动估计时间比原算法平均减少了15.59%,而峰值信噪比和码率基本不变,并且能够适应各种运动类型的视频序列。得到的结果表明改进算法提高了总体编码性能。 展开更多
关键词 视频压缩 区域分割 UMHEXAGONS算法 运动估计 统计特点
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Coordinated and uncoordinated design of LFO damping controllers with IPFC and PSS using ICA and SFLA 被引量:1
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作者 Mahdi Toupchi Khosroshahi Farhad Mohajel Kazemi +1 位作者 Mohammad Reza Jannati Oskuee Sajad Najafi-Ravadanegh 《Journal of Central South University》 SCIE EI CAS CSCD 2015年第9期3418-3426,共9页
A single machine-infinite-bus(SMIB) system including the interline power flow controllers(IPFCs) and the power system stabilizer(PSS) controller is addressed. The linearized system model is considered for investigatin... A single machine-infinite-bus(SMIB) system including the interline power flow controllers(IPFCs) and the power system stabilizer(PSS) controller is addressed. The linearized system model is considered for investigating the interactions among IPFC and PSS controllers. To improve the stability of whole system again different disturbances, a lead-lag controller is considered to produce supplementary signal. The proposed supplementary controller is implemented to improve the damping of the power system low frequency oscillations(LFOs). Imperialist optimization algorithm(ICA) and shuffled frog leaping algorithm(SFLA) are implemented to search for optimal supplementary controllers and PSS parameters. Moreover, singular value decomposition(SVD) method is utilized to select the most effective damping control signal of IPFC lead-lag controllers. To evaluate the system performance, different operating conditions are considered. Reponses of system in five modes including uncoordinated and coordinated modes of IPFC and PSS using ICA and SFLA are studied and compared. Considering the results, response of system without controller shows the highest overshoot and the longest settling time for rotor angel at the different operating conditions. In this mode of system, rotor speed has the highest overshoot. Rotor angel in the system with only PSS includes lower overshoot and oscillation than system without controller. When PSS is only implemented, rotor speed deviation has the longest settling time. Rotor speed deviation in the uncoordinated mode of IPFC and PSS shows lower overshoot than system with only PSS and without controller. It is noticeable that in this mode, rotor angel has higher overshoot than system with only PSS. The superiority of the suggested ICA-based coordinated controllers is obvious compared with SFLA-based coordinated controllers and other system modes. Responses of coordinated PSS and IPFC SFLA-based supplementary controllers include higher peak amplitude and longer settling time compared with coordinated IPFC and PSS ICA-based controllers. This comparison shows that overshoots, undershoots and the settling times are reduced considerably in coordinated mode of IPFC based controller and PSS using ICA. Analysis of the system performance shows that the proposed method has excellent response to different faults in power system. 展开更多
关键词 interline power flow controller(IPFC) controller imperialist competitive optimization algorithm power system stabilizer(PSS)
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