目前,实际电力系统中广泛使用电力系统稳定器（power system stabilizer,PSS）进行低频振荡阻尼控制。但是,PSS在低频振荡控制中有一定的局限性,可能使其增益整定值难以同时满足系统阻尼水平以及《电力系统稳定器整定试验导则》规定的...目前,实际电力系统中广泛使用电力系统稳定器（power system stabilizer,PSS）进行低频振荡阻尼控制。但是,PSS在低频振荡控制中有一定的局限性,可能使其增益整定值难以同时满足系统阻尼水平以及《电力系统稳定器整定试验导则》规定的增益必须小于临界增益1/3的投运要求。该文通过分析,发现自并励条件下,PSS临界增益主要受励磁模式限制,而励磁模式是由励磁–PSS回路在3~8 Hz频段的固有特性形成。在上述分析的基础上,提出在励磁–PSS回路外环引入一个功率增量软反馈,形成一种带有并联环节的改进型PSS模型,改善了回路相位特性,提高了PSS临界增益,解决了上述问题。最后,以锡盟火电集中外送仿真系统为例,验证了所提方案的有效性。展开更多
利用矩形薄板面内2个不同模态作为工作模态的直线型超声电机,其频率一致性和压电单元的布置方式以及激励方式对电机的性能和效率有重要的影响。该文根据电机定子的位移振型和应变振型详细分析了压电陶瓷的布置方式和激励方式,并利用参...利用矩形薄板面内2个不同模态作为工作模态的直线型超声电机,其频率一致性和压电单元的布置方式以及激励方式对电机的性能和效率有重要的影响。该文根据电机定子的位移振型和应变振型详细分析了压电陶瓷的布置方式和激励方式,并利用参数化有限元方法(finite element method,FEM)对定子结构进行优化设计。设计制作的样机,两相工作模态频率差为270Hz,在电压峰峰值为350V、驱动频率为44.16kHz、预压力为50N的情况下,电机最大空载速度为100mm/s,最大输出力为3N。展开更多
在10 k V配电网中,电磁式电压互感器(TV)在一定条件下易产生铁磁谐振过电压,这严重影响了系统的安全运行。笔者通过JDZX9-10型与JSZW-10型电压互感器励磁特性的对比实验,获得了数字仿真所需的电压互感器励磁特性数据,并利用MATLAB建立了...在10 k V配电网中,电磁式电压互感器(TV)在一定条件下易产生铁磁谐振过电压,这严重影响了系统的安全运行。笔者通过JDZX9-10型与JSZW-10型电压互感器励磁特性的对比实验,获得了数字仿真所需的电压互感器励磁特性数据,并利用MATLAB建立了10 k V配电网由单相接地故障而引发铁磁谐振的模型。通过理论分析、对比实验和数字仿真可得,对于10 k V中性点经消弧线圈接地模型,TV开口三角绕组接阻尼电阻对铁磁谐振的抑制具有最明显的作用;而10 k V中性点经小电阻接地模型能够很好地对铁磁谐振进行消除;对于10 k V系统中性点不接地模型,TV高压侧中性点串非线性电阻则是预防或消除铁磁谐振的一种十分有效的方法。展开更多
We develop a method for creating two- and one-dimensional （2D and 1D） self-trapped modes in bi- nary spin-orbit-coupled Bose-Einstein condensates with the contact repulsive interaction, whose local strength grows su...We develop a method for creating two- and one-dimensional （2D and 1D） self-trapped modes in bi- nary spin-orbit-coupled Bose-Einstein condensates with the contact repulsive interaction, whose local strength grows sufficiently rapidly from the center to the periphery. In particular, an exact semi-vortex （SV） solution is found for the anti-Gaussian radial modulation profile. The exact modes are included in the numerically produced family of SV solitons. Other families, in the form of mixed modes （MMs）, as well as excited states of SVs and MMs, are also produced. Although the excited states are unstable in all previously studied models, they are partially stable in the present one. In the 1D version of the system, exact solutions for the counterpart of SVs, namely, semi-dipole solitons, are also found. Families of semi-dipoles, as well as the 1D version of MMs, are produced numerically.展开更多
Exploration of multicolor mechanochromic bulk polymers based on a single mechanophore is a big challenge to date.Herein,we report a versatile benzimidazole-substituted spirolactam mechanophore where excited state intr...Exploration of multicolor mechanochromic bulk polymers based on a single mechanophore is a big challenge to date.Herein,we report a versatile benzimidazole-substituted spirolactam mechanophore where excited state intramolecular proton transfer(ESIPT)coupled with rhodamine.The mechanophore was facilely synthesized and then covalently linked to polyurethane(PU)chains.The PU film containing the mechanophore(1@PU)showed cooperative photochromism upon irradiation involving simultaneous enhancement of normalized enol and rhodol emissions based on a cooperative ESIPT process and the ring-opening reaction of spirolactam.Moreover,the film exhibited dual-mode multicolor mechanochromism upon stretching and compression.The normalized intensity of enol emission increased and the fluorescence turned from light green to cyan after stretching,then red coloration appeared from colorless after compressing.Control experiments and density functional theory calculations confirmed that the stretch-induced increase of enol emission was attributed to torsion of the dihedral angle between xanthene and benzimidazole in the mechanophore via force-induced disaggregation and direct force action on the isolated mechanophore.Torsion of the dihedral angle and the ring-opening reaction of spirolactam in a single mechanophore occurred sequentially during compression,resulting in an observed red coloration.This study might provide a glimpse into the design of novel multicolor mechanochromic mechanophores.展开更多
文摘目前,实际电力系统中广泛使用电力系统稳定器（power system stabilizer,PSS）进行低频振荡阻尼控制。但是,PSS在低频振荡控制中有一定的局限性,可能使其增益整定值难以同时满足系统阻尼水平以及《电力系统稳定器整定试验导则》规定的增益必须小于临界增益1/3的投运要求。该文通过分析,发现自并励条件下,PSS临界增益主要受励磁模式限制,而励磁模式是由励磁–PSS回路在3~8 Hz频段的固有特性形成。在上述分析的基础上,提出在励磁–PSS回路外环引入一个功率增量软反馈,形成一种带有并联环节的改进型PSS模型,改善了回路相位特性,提高了PSS临界增益,解决了上述问题。最后,以锡盟火电集中外送仿真系统为例,验证了所提方案的有效性。
文摘利用矩形薄板面内2个不同模态作为工作模态的直线型超声电机,其频率一致性和压电单元的布置方式以及激励方式对电机的性能和效率有重要的影响。该文根据电机定子的位移振型和应变振型详细分析了压电陶瓷的布置方式和激励方式,并利用参数化有限元方法(finite element method,FEM)对定子结构进行优化设计。设计制作的样机,两相工作模态频率差为270Hz,在电压峰峰值为350V、驱动频率为44.16kHz、预压力为50N的情况下,电机最大空载速度为100mm/s,最大输出力为3N。
文摘在10 k V配电网中,电磁式电压互感器(TV)在一定条件下易产生铁磁谐振过电压,这严重影响了系统的安全运行。笔者通过JDZX9-10型与JSZW-10型电压互感器励磁特性的对比实验,获得了数字仿真所需的电压互感器励磁特性数据,并利用MATLAB建立了10 k V配电网由单相接地故障而引发铁磁谐振的模型。通过理论分析、对比实验和数字仿真可得,对于10 k V中性点经消弧线圈接地模型,TV开口三角绕组接阻尼电阻对铁磁谐振的抑制具有最明显的作用;而10 k V中性点经小电阻接地模型能够很好地对铁磁谐振进行消除;对于10 k V系统中性点不接地模型,TV高压侧中性点串非线性电阻则是预防或消除铁磁谐振的一种十分有效的方法。
基金This work was supported in part by the National Natural Science Foundation of China through Grant Nos. 11575063, 61471123, and 61575041, the Joint Program in Physics of the NSF and the Binational （US-Israel） Science Foun- dation through Project No. 2015616, the Israel Science Founda- tion （project No. 1287/17）, and the Natural Science Foundation of Guangdong Province through Grant No. 2015A030313639. B.A.M. is grateful for a foreign-expert grant from Guangdong province （China） and a Ding-Ying professorship provided by the SouthChina Agricultural University （Guangzhou） at its College of Elec- tronic Engineering.
文摘We develop a method for creating two- and one-dimensional （2D and 1D） self-trapped modes in bi- nary spin-orbit-coupled Bose-Einstein condensates with the contact repulsive interaction, whose local strength grows sufficiently rapidly from the center to the periphery. In particular, an exact semi-vortex （SV） solution is found for the anti-Gaussian radial modulation profile. The exact modes are included in the numerically produced family of SV solitons. Other families, in the form of mixed modes （MMs）, as well as excited states of SVs and MMs, are also produced. Although the excited states are unstable in all previously studied models, they are partially stable in the present one. In the 1D version of the system, exact solutions for the counterpart of SVs, namely, semi-dipole solitons, are also found. Families of semi-dipoles, as well as the 1D version of MMs, are produced numerically.
基金financially supported by the National Natural Science Foundation of China (grant nos.22375013,22175015,and 21704002)the Beijing Natural Science Foundation (grant no.2182054)+1 种基金the Big Science Project from BUCT (grant no.XK180301)the Fundamental Research Funds for the Central Universities to Z.Y.Ma.
文摘Exploration of multicolor mechanochromic bulk polymers based on a single mechanophore is a big challenge to date.Herein,we report a versatile benzimidazole-substituted spirolactam mechanophore where excited state intramolecular proton transfer(ESIPT)coupled with rhodamine.The mechanophore was facilely synthesized and then covalently linked to polyurethane(PU)chains.The PU film containing the mechanophore(1@PU)showed cooperative photochromism upon irradiation involving simultaneous enhancement of normalized enol and rhodol emissions based on a cooperative ESIPT process and the ring-opening reaction of spirolactam.Moreover,the film exhibited dual-mode multicolor mechanochromism upon stretching and compression.The normalized intensity of enol emission increased and the fluorescence turned from light green to cyan after stretching,then red coloration appeared from colorless after compressing.Control experiments and density functional theory calculations confirmed that the stretch-induced increase of enol emission was attributed to torsion of the dihedral angle between xanthene and benzimidazole in the mechanophore via force-induced disaggregation and direct force action on the isolated mechanophore.Torsion of the dihedral angle and the ring-opening reaction of spirolactam in a single mechanophore occurred sequentially during compression,resulting in an observed red coloration.This study might provide a glimpse into the design of novel multicolor mechanochromic mechanophores.
