MUSIC(Multiple Signal Classification)算法是波达角(the Direction of Arrival,DOA)估计的经典算法之一,但其在二维DOA估计中因需进行二维谱峰搜索而计算量十分巨大.为降低MUSIC算法的计算量,本文在引入变换域DOA概念的基础上提出了...MUSIC(Multiple Signal Classification)算法是波达角(the Direction of Arrival,DOA)估计的经典算法之一,但其在二维DOA估计中因需进行二维谱峰搜索而计算量十分巨大.为降低MUSIC算法的计算量,本文在引入变换域DOA概念的基础上提出了一种能够适用于任意阵列结构的二维DOA快速估计算法,即变换域MUSIC(transformed do-main-MUSIC,TD-MUSIC)算法.理论分析和仿真实验表明:该算法不但将空间谱峰搜索的范围减小一半而且具有更低维度的噪声子空间,因而其计算量远小于MUSIC算法.同时,新算法具有比MUSIC更高的空间分辨率.展开更多
As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, th...As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, the virtual synchronous generator(VSG), in which the power electronic inverter is controlled to mimic the characteristics of traditional synchronous generators, is a promising strategy. In this paper, the representation of the synchronous generator in power systems is firstly presented as the basis for the VSG. Then the modelling methods of VSG are comprehensively reviewed and compared.Applications of the VSG in power systems are summarized as well. Finally, the challenges and future trends of the VSG implementation are discussed.展开更多
The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid,which leads to the decline of grid stability.Therefore,a control strategy of ...The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid,which leads to the decline of grid stability.Therefore,a control strategy of brushless doubly-fed reluctance generator(BDFRG) based on virtual synchronous generator(VSG) control is proposed to solve the problem in this paper.The output characteristics of BDFRG based on VSG are similar to a synchronous generator(SG),which can support the grid frequency and increase the system ‘inertia’.According to the mathematical model of BDFRG,the inner loop voltage source control of BDFRG is derived.In addition,the specific structure and parameter selection principle of outer loop VSG control are expounded.The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy.Finally,the effectiveness and feasibility of the proposed strategy are verified in the simulation.展开更多
A novel numerical method for eliminating the singular integral and boundary effect is processed. In the proposed method, the virtual boundaries corresponding to the numbers of the true boundary arguments are chosen to...A novel numerical method for eliminating the singular integral and boundary effect is processed. In the proposed method, the virtual boundaries corresponding to the numbers of the true boundary arguments are chosen to be as simple as possible. An indirect radial basis function network （IRBFN） constructed by functions resulting from the indeterminate integral is used to construct the approaching virtual source functions distributed along the virtual boundaries. By using the linear superposition method, the governing equations presented in the boundaries integral equations （BIE） can be established while the fundamental solutions to the problems are introduced. The singular value decomposition （SVD） method is used to solve the governing equations since an optimal solution in the least squares sense to the system equations is available. In addition, no elements are required, and the boundary conditions can be imposed easily because of the Kronecker delta function properties of the approaching functions. Three classical 2D elasticity problems have been examined to verify the performance of the method proposed. The results show that this method has faster convergence and higher accuracy than the conventional boundary type numerical methods.展开更多
声源定位因素包括双耳时间差、双耳声级差、谱因素等,文章在介绍声源定位因素的基础上,引出了人体头部相关传输函数HRTF定义及其特性。基于美国MIT Media Lab发布的HRTF数据库,利用计算机合成两声道虚拟三维音频,并对虚拟声源进行了定...声源定位因素包括双耳时间差、双耳声级差、谱因素等,文章在介绍声源定位因素的基础上,引出了人体头部相关传输函数HRTF定义及其特性。基于美国MIT Media Lab发布的HRTF数据库,利用计算机合成两声道虚拟三维音频,并对虚拟声源进行了定位测试实验,12名听觉正常者参与了主观听音实验,选取10个具有方位信息的音频信号作为刺激信号,听音者将听到的方位记录下来,与预设方位进行对比。最后对实验结果进行了总结分析。展开更多
为了提高超声虚源次序波束形成的成像分辨率,提出一种基于虚源的延时乘累加波束形成算法,即VS-DMAS(delay multiply and sum beamforming based on virtual source)算法.该算法将DMAS的思想引入虚源次序波束形成的第二阶段,利用DMAS算...为了提高超声虚源次序波束形成的成像分辨率,提出一种基于虚源的延时乘累加波束形成算法,即VS-DMAS(delay multiply and sum beamforming based on virtual source)算法.该算法将DMAS的思想引入虚源次序波束形成的第二阶段,利用DMAS算法中相乘耦合运算的特点,充分考虑信号之间的相干性,以抑制低回声区域伪影的产生,提高超声成像的分辨率和对比度.对该算法进行了点目标仿体仿真以及实体数据成像实验.结果表明,相较于常规的聚焦方式,VS-DMAS算法具有更低的旁瓣和更窄的主瓣,能够更好地将点目标从背景噪声中分离出来,随着深度的增加,依然有着较高的成像分辨率.且随着算法中p值适当增大,成像分辨率和对比度均有一定的提升.展开更多
Marine ecological disasters occurred frequently in recent years and raised widespread concerns about the ecological health of the ocean.We analyzed the spatiotemporal distributions of Ulva prolifera and Sargassum from...Marine ecological disasters occurred frequently in recent years and raised widespread concerns about the ecological health of the ocean.We analyzed the spatiotemporal distributions of Ulva prolifera and Sargassum from April to July each year between 2016 and 2020 in the South Yellow Sea using multisource(GF-1 and HJ-1A/1B)remote sensing images,combined with the MODIS sea surface temperature(SST)data,photosynthetically active radiation(PAR)data,and Quick SCAT sea surface wind(SSW)data,to explore the potential influencing factors.The results show that(1)U.prolifera and Sargassum appeared mainly from May to July and April to June,respectively;(2)U.prolifera showed an impact in larger spatial scope than that of Sargassum.U.prolifera originated in the shoal area of northern Jiangsu and finally disappeared in the sea near Haiyang-Rongcheng area.The spatial scope of the impact of Sargassum tended to expand.Sargassum was first detected in the ocean northeast of the Changjiang(Yangtze)River estuary and disappeared near 35°N;and(3)correlation analysis showed that the SST influenced the growth rate of U.prolifera and Sargassum.PAR had varied eff ects on U.prolifera and Sargassum at different times.A moderate light conditions could accelerate the growth and reproduction of U.prolifera and Sargassum.High irradiance levels of ultraviolet radiation may cause photoinhibition and damage on U.prolifera and Sargassum.The southeast monsoon and surface currents promoted the drift of U.prolifera and Sargassum from the southeast to the northwest and north.Therefore,the spatial and temporal similarities and differences between U.prolifera and Sargassum were influenced by a combination of factors during their growth processes.展开更多
当常规地震勘探数据处理方法不能对地下存在的陡倾角地质构造获得满意的成像效果时,应用虚拟震源方法将垂直地震剖面(VSP,vertical seismic profile)数据重构成单井剖面(SWP,single well profile)数据,可以使得观测系统重构到更接近于...当常规地震勘探数据处理方法不能对地下存在的陡倾角地质构造获得满意的成像效果时,应用虚拟震源方法将垂直地震剖面(VSP,vertical seismic profile)数据重构成单井剖面(SWP,single well profile)数据,可以使得观测系统重构到更接近于井附近目标体的位置,震源和检波器都位于复杂的覆盖之下并避免井和地表之间未知速度信息的影响,从而获得对地下地质构造更好的成像分辨率。尤其是当地下存在诸如断层这样的陡倾角地质构造时,虚拟震源方法可以对目标体产生很好的成像效果。本文进行了声波数据和弹性波数据的模拟实验,将模型中的陡构造设置为断层,测试虚拟震源方法用于探测地下陡倾角地质构造的能力,对声波和弹性波介质都获得了满意的成像结果;在应用稀疏观测系统进行测量时,仍然可以得到较好的成像效果。展开更多
文摘MUSIC(Multiple Signal Classification)算法是波达角(the Direction of Arrival,DOA)估计的经典算法之一,但其在二维DOA估计中因需进行二维谱峰搜索而计算量十分巨大.为降低MUSIC算法的计算量,本文在引入变换域DOA概念的基础上提出了一种能够适用于任意阵列结构的二维DOA快速估计算法,即变换域MUSIC(transformed do-main-MUSIC,TD-MUSIC)算法.理论分析和仿真实验表明:该算法不但将空间谱峰搜索的范围减小一半而且具有更低维度的噪声子空间,因而其计算量远小于MUSIC算法.同时,新算法具有比MUSIC更高的空间分辨率.
文摘As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, the virtual synchronous generator(VSG), in which the power electronic inverter is controlled to mimic the characteristics of traditional synchronous generators, is a promising strategy. In this paper, the representation of the synchronous generator in power systems is firstly presented as the basis for the VSG. Then the modelling methods of VSG are comprehensively reviewed and compared.Applications of the VSG in power systems are summarized as well. Finally, the challenges and future trends of the VSG implementation are discussed.
基金supported in part by the National Natural Science Foundation of China under Grant 51537007。
文摘The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid,which leads to the decline of grid stability.Therefore,a control strategy of brushless doubly-fed reluctance generator(BDFRG) based on virtual synchronous generator(VSG) control is proposed to solve the problem in this paper.The output characteristics of BDFRG based on VSG are similar to a synchronous generator(SG),which can support the grid frequency and increase the system ‘inertia’.According to the mathematical model of BDFRG,the inner loop voltage source control of BDFRG is derived.In addition,the specific structure and parameter selection principle of outer loop VSG control are expounded.The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy.Finally,the effectiveness and feasibility of the proposed strategy are verified in the simulation.
文摘A novel numerical method for eliminating the singular integral and boundary effect is processed. In the proposed method, the virtual boundaries corresponding to the numbers of the true boundary arguments are chosen to be as simple as possible. An indirect radial basis function network （IRBFN） constructed by functions resulting from the indeterminate integral is used to construct the approaching virtual source functions distributed along the virtual boundaries. By using the linear superposition method, the governing equations presented in the boundaries integral equations （BIE） can be established while the fundamental solutions to the problems are introduced. The singular value decomposition （SVD） method is used to solve the governing equations since an optimal solution in the least squares sense to the system equations is available. In addition, no elements are required, and the boundary conditions can be imposed easily because of the Kronecker delta function properties of the approaching functions. Three classical 2D elasticity problems have been examined to verify the performance of the method proposed. The results show that this method has faster convergence and higher accuracy than the conventional boundary type numerical methods.
文摘声源定位因素包括双耳时间差、双耳声级差、谱因素等,文章在介绍声源定位因素的基础上,引出了人体头部相关传输函数HRTF定义及其特性。基于美国MIT Media Lab发布的HRTF数据库,利用计算机合成两声道虚拟三维音频,并对虚拟声源进行了定位测试实验,12名听觉正常者参与了主观听音实验,选取10个具有方位信息的音频信号作为刺激信号,听音者将听到的方位记录下来,与预设方位进行对比。最后对实验结果进行了总结分析。
文摘为了提高超声虚源次序波束形成的成像分辨率,提出一种基于虚源的延时乘累加波束形成算法,即VS-DMAS(delay multiply and sum beamforming based on virtual source)算法.该算法将DMAS的思想引入虚源次序波束形成的第二阶段,利用DMAS算法中相乘耦合运算的特点,充分考虑信号之间的相干性,以抑制低回声区域伪影的产生,提高超声成像的分辨率和对比度.对该算法进行了点目标仿体仿真以及实体数据成像实验.结果表明,相较于常规的聚焦方式,VS-DMAS算法具有更低的旁瓣和更窄的主瓣,能够更好地将点目标从背景噪声中分离出来,随着深度的增加,依然有着较高的成像分辨率.且随着算法中p值适当增大,成像分辨率和对比度均有一定的提升.
基金Supported by the National Natural Science Foundation of China(No.42071385)the Natural Science Foundation of Shandong Province,China(No.ZR2019MD041)。
文摘Marine ecological disasters occurred frequently in recent years and raised widespread concerns about the ecological health of the ocean.We analyzed the spatiotemporal distributions of Ulva prolifera and Sargassum from April to July each year between 2016 and 2020 in the South Yellow Sea using multisource(GF-1 and HJ-1A/1B)remote sensing images,combined with the MODIS sea surface temperature(SST)data,photosynthetically active radiation(PAR)data,and Quick SCAT sea surface wind(SSW)data,to explore the potential influencing factors.The results show that(1)U.prolifera and Sargassum appeared mainly from May to July and April to June,respectively;(2)U.prolifera showed an impact in larger spatial scope than that of Sargassum.U.prolifera originated in the shoal area of northern Jiangsu and finally disappeared in the sea near Haiyang-Rongcheng area.The spatial scope of the impact of Sargassum tended to expand.Sargassum was first detected in the ocean northeast of the Changjiang(Yangtze)River estuary and disappeared near 35°N;and(3)correlation analysis showed that the SST influenced the growth rate of U.prolifera and Sargassum.PAR had varied eff ects on U.prolifera and Sargassum at different times.A moderate light conditions could accelerate the growth and reproduction of U.prolifera and Sargassum.High irradiance levels of ultraviolet radiation may cause photoinhibition and damage on U.prolifera and Sargassum.The southeast monsoon and surface currents promoted the drift of U.prolifera and Sargassum from the southeast to the northwest and north.Therefore,the spatial and temporal similarities and differences between U.prolifera and Sargassum were influenced by a combination of factors during their growth processes.
文摘当常规地震勘探数据处理方法不能对地下存在的陡倾角地质构造获得满意的成像效果时,应用虚拟震源方法将垂直地震剖面(VSP,vertical seismic profile)数据重构成单井剖面(SWP,single well profile)数据,可以使得观测系统重构到更接近于井附近目标体的位置,震源和检波器都位于复杂的覆盖之下并避免井和地表之间未知速度信息的影响,从而获得对地下地质构造更好的成像分辨率。尤其是当地下存在诸如断层这样的陡倾角地质构造时,虚拟震源方法可以对目标体产生很好的成像效果。本文进行了声波数据和弹性波数据的模拟实验,将模型中的陡构造设置为断层,测试虚拟震源方法用于探测地下陡倾角地质构造的能力,对声波和弹性波介质都获得了满意的成像结果;在应用稀疏观测系统进行测量时,仍然可以得到较好的成像效果。
