The performance of DFIG-based wind generation systems that interconnected to solid networks is well understood and prevalent in Europe and North America. However, the application of these renewable generating stations...The performance of DFIG-based wind generation systems that interconnected to solid networks is well understood and prevalent in Europe and North America. However, the application of these renewable generating stations to weak network has been examined in very limited occasions. Weak networks have a range of limitations from system capacities to CFCT restrictions which would need to be well understood prior to wind energy integration. Of particular interest would be how much wind generation could be integrated into a weak network prior to increasing voltage and frequency stability issues brought about by penetration issues. This paper introduces a simple and practical approach based on the equal area criteria to investigate the stability of weak networks. Simulation results that are presented to show the proposed approach is a viable preliminary assessment tool to determine system stability on weak networks with wind power penetration.展开更多
In this study,we investigate the tunneling of fermions with arbitrary spin near the event horizon of a nonstationary Vaidya-Bonner-de Sitter(VBdS)black hole under Lorentz invariance violation(LIV).The modified Hawking...In this study,we investigate the tunneling of fermions with arbitrary spin near the event horizon of a nonstationary Vaidya-Bonner-de Sitter(VBdS)black hole under Lorentz invariance violation(LIV).The modified Hawking temperature of VBdS black holes is calculated by using tortoise coordinate transformation,Feynman prescription,and Wentzel-Kramers-Brillouin approximation.By considering the cosmological constant as a thermodynamic pressure in the extended phase space,we construct a Maxwell's equal area law under LIV and study the phase transitions of VBdS black hole in P-v,P-V,and T-S planes.The LIV increases the length of the liquid-gas coexistence region.The thermodynamic quantities such as the entropy,heat capacity,Helmholtz free energy,internal energy,enthalpy,and Gibbs free energy of the VBdS black hole are discussed.These quantities tend to increase under LIV.The stability of the black hole is also discussed in the presence of LIV.展开更多
The iteration-free physical description of pyramidal indentations with closed mathematical equations is comprehensively described and extended for creating new insights in this important field of research and app...The iteration-free physical description of pyramidal indentations with closed mathematical equations is comprehensively described and extended for creating new insights in this important field of research and applications. All calculations are easily repeatable and should be programmed by instrument builders for even easier general use. Formulas for the volumes and side-areas of Berkovich and cubecorner as a function of depth are deduced and provided, as are the resulting forces and force directions. All of these allow for the detailed comparison of the different indenters on the mathematical reality. The pyramidal values differ remarkably from the ones of so-called “equivalent cones”. The worldwide use of such pseudo-cones is in severe error. The earlier claimed and used 3 times higher displaced volume with cube corner than with Berkovich is disproved. Both displace the same amount at the same applied force. The unprecedented mathematical results are experimentally confirmed for the physical indentation hardness and for the sharp-onset phase-transi</span></span><span style="white-space:normal;"><span style="font-family:"">- </span></span><span style="white-space:normal;"><span style="font-family:"">tions with calculated transition energy. The comparison of both indenters pro</span></span><span style="white-space:normal;"><span style="font-family:"">vides novel basic insights. Isotropic materials exhibit the same phase transition onset force, but the transition energy is larger with the cube corner, due to higher force and flatter force direction. This qualifies the cube</span></span><span style="white-space:normal;"><span style="font-family:""> </span></span><span style="white-space:normal;"><span style="font-family:"">corner for fracture toughness studies. Pile-up is not from the claimed “friction with the indenter”. Anisotropic materials with cleavage planes and channels undergo sliding along these</span></span><span style="white-space:normal;"><span style="font-family:""> under pressure</span></span><span style="white-space:normal;"><span style="font-family:"">, both to the surface and internally. Their volumes add to the depression volume. These volumes are essential for the exemplified pile-up management. Phase-transitions produce polymorph interfaces that are nucleation sites for cracks. Technical materials must be developed with onset forces higher than the highest thinkable stresses (at airliners, bridges</span></span><span style="white-space:normal;"><span style="font-family:"">,</span></span><span style="white-space:normal;"><span style="font-family:""> etc</span></span><span style="white-space:normal;"><span style="font-family:"">.</span></span><span style="white-space:normal;"><span style="font-family:"">). This requires urgent revision of ISO 14577-ASTM stan</span></span><span style="white-space:normal;"><span style="font-family:"">dards.展开更多
全球离散格网系统(discrete global grid systems,DGGS)是一类新兴的数字地球参考框架,在大尺度多源地理空间数据集的组织、集成与分析方面具有天然优势。现有全球离散格网系统构建方法中,基于多面体投影方法生成的格网系统具有更加优...全球离散格网系统(discrete global grid systems,DGGS)是一类新兴的数字地球参考框架,在大尺度多源地理空间数据集的组织、集成与分析方面具有天然优势。现有全球离散格网系统构建方法中,基于多面体投影方法生成的格网系统具有更加优异的几何性质,因而被广泛研究。基础多面体及投影方法是格网系统设计选项中影响格网单元几何性质的主要因素。为构建更加均匀、高效的格网系统,选择菱形三十面体作为基础多面体,推导菱形三十面体与地球球体等积投影的正反算解析公式,并将其应用于3种不同单元形状等积全球离散格网的生成。对比实验结果表明,与二十面体Snyder等积投影相比,所提方法的角度变形减小约51%,且克服了Snyder逆投影迭代求解导致格网生成效率较低的不足,为全球离散格网系统的相关应用提供了优选解决方案。展开更多
由跟网型变换器(grid-following voltage source converter,GFL-VSC)及构网型变换器(grid-forming voltage source converter,GFM-VSC)构成的混联系统中,复杂的暂态交互作用使系统的安全稳定运行面临挑战,明确变换器间的动态耦合机理及...由跟网型变换器(grid-following voltage source converter,GFL-VSC)及构网型变换器(grid-forming voltage source converter,GFM-VSC)构成的混联系统中,复杂的暂态交互作用使系统的安全稳定运行面临挑战,明确变换器间的动态耦合机理及其对系统暂态稳定性的影响至关重要。GFM-VSC中设置的电流限幅环节会导致其暂态运行方式发生切换,进一步增加了GFM-VSC与GFL-VSC之间的耦合机理的复杂性。为揭示GFM-VSC发生暂态模式切换时与GFL-VSC之间的动态耦合机理及该耦合对GFM-VSC故障恢复过程的作用机制,首先,建立考虑GFM-VSC限幅环节的混联系统暂态耦合模型;基于此模型,分析故障期间及故障切除后,GFL-VSC的参数对GFM-VSC工作模式切换的影响机理;随后,针对不同程度的电网电压跌落故障,分析故障切除后GFM-VSC的工作模式切换过程,得到混联系统中GFM-VSC在故障切除后可切换回正常工作模式的临界条件;最后,构建混联系统的仿真模型,验证理论分析的正确性。展开更多
风电场站配置一定容量的无功补偿装置(如静止无功发生器(static var generator,SVG))可以提高风电外送能力。同时为了满足风电场站对于惯量和电压支撑的要求,SVG可以在直流侧集成功率型储能元件同时采用构网型控制。然而由于风电场出力...风电场站配置一定容量的无功补偿装置(如静止无功发生器(static var generator,SVG))可以提高风电外送能力。同时为了满足风电场站对于惯量和电压支撑的要求,SVG可以在直流侧集成功率型储能元件同时采用构网型控制。然而由于风电场出力的影响,构网型SVG存在着暂态同步失稳的风险。针对此问题,首先通过对构网型SVG接入风电场站的并网系统进行化简等效,得到构网型SVG的功角曲线。然后,利用等面积法则揭示风电场站中构网型SVG的失稳机理,并给出相应的稳定判据。进一步,提出一种基于惯量和阻尼系数协调自适应的暂态同步稳定性提升方法。在判断SVG发生暂态同步失稳时自适应改变惯量和阻尼系数,强迫SVG回到稳定平衡点。该方法可以提高构网型SVG的暂态同步稳定性,有利于风电外送能力的提升。最后在PSCAD/EMTDC中建立电磁暂态仿真模型,验证了构网型SVG失稳机理的正确性以及暂态同步稳定性提升方法的有效性。展开更多
文摘The performance of DFIG-based wind generation systems that interconnected to solid networks is well understood and prevalent in Europe and North America. However, the application of these renewable generating stations to weak network has been examined in very limited occasions. Weak networks have a range of limitations from system capacities to CFCT restrictions which would need to be well understood prior to wind energy integration. Of particular interest would be how much wind generation could be integrated into a weak network prior to increasing voltage and frequency stability issues brought about by penetration issues. This paper introduces a simple and practical approach based on the equal area criteria to investigate the stability of weak networks. Simulation results that are presented to show the proposed approach is a viable preliminary assessment tool to determine system stability on weak networks with wind power penetration.
文摘In this study,we investigate the tunneling of fermions with arbitrary spin near the event horizon of a nonstationary Vaidya-Bonner-de Sitter(VBdS)black hole under Lorentz invariance violation(LIV).The modified Hawking temperature of VBdS black holes is calculated by using tortoise coordinate transformation,Feynman prescription,and Wentzel-Kramers-Brillouin approximation.By considering the cosmological constant as a thermodynamic pressure in the extended phase space,we construct a Maxwell's equal area law under LIV and study the phase transitions of VBdS black hole in P-v,P-V,and T-S planes.The LIV increases the length of the liquid-gas coexistence region.The thermodynamic quantities such as the entropy,heat capacity,Helmholtz free energy,internal energy,enthalpy,and Gibbs free energy of the VBdS black hole are discussed.These quantities tend to increase under LIV.The stability of the black hole is also discussed in the presence of LIV.
文摘The iteration-free physical description of pyramidal indentations with closed mathematical equations is comprehensively described and extended for creating new insights in this important field of research and applications. All calculations are easily repeatable and should be programmed by instrument builders for even easier general use. Formulas for the volumes and side-areas of Berkovich and cubecorner as a function of depth are deduced and provided, as are the resulting forces and force directions. All of these allow for the detailed comparison of the different indenters on the mathematical reality. The pyramidal values differ remarkably from the ones of so-called “equivalent cones”. The worldwide use of such pseudo-cones is in severe error. The earlier claimed and used 3 times higher displaced volume with cube corner than with Berkovich is disproved. Both displace the same amount at the same applied force. The unprecedented mathematical results are experimentally confirmed for the physical indentation hardness and for the sharp-onset phase-transi</span></span><span style="white-space:normal;"><span style="font-family:"">- </span></span><span style="white-space:normal;"><span style="font-family:"">tions with calculated transition energy. The comparison of both indenters pro</span></span><span style="white-space:normal;"><span style="font-family:"">vides novel basic insights. Isotropic materials exhibit the same phase transition onset force, but the transition energy is larger with the cube corner, due to higher force and flatter force direction. This qualifies the cube</span></span><span style="white-space:normal;"><span style="font-family:""> </span></span><span style="white-space:normal;"><span style="font-family:"">corner for fracture toughness studies. Pile-up is not from the claimed “friction with the indenter”. Anisotropic materials with cleavage planes and channels undergo sliding along these</span></span><span style="white-space:normal;"><span style="font-family:""> under pressure</span></span><span style="white-space:normal;"><span style="font-family:"">, both to the surface and internally. Their volumes add to the depression volume. These volumes are essential for the exemplified pile-up management. Phase-transitions produce polymorph interfaces that are nucleation sites for cracks. Technical materials must be developed with onset forces higher than the highest thinkable stresses (at airliners, bridges</span></span><span style="white-space:normal;"><span style="font-family:"">,</span></span><span style="white-space:normal;"><span style="font-family:""> etc</span></span><span style="white-space:normal;"><span style="font-family:"">.</span></span><span style="white-space:normal;"><span style="font-family:"">). This requires urgent revision of ISO 14577-ASTM stan</span></span><span style="white-space:normal;"><span style="font-family:"">dards.
文摘全球离散格网系统(discrete global grid systems,DGGS)是一类新兴的数字地球参考框架,在大尺度多源地理空间数据集的组织、集成与分析方面具有天然优势。现有全球离散格网系统构建方法中,基于多面体投影方法生成的格网系统具有更加优异的几何性质,因而被广泛研究。基础多面体及投影方法是格网系统设计选项中影响格网单元几何性质的主要因素。为构建更加均匀、高效的格网系统,选择菱形三十面体作为基础多面体,推导菱形三十面体与地球球体等积投影的正反算解析公式,并将其应用于3种不同单元形状等积全球离散格网的生成。对比实验结果表明,与二十面体Snyder等积投影相比,所提方法的角度变形减小约51%,且克服了Snyder逆投影迭代求解导致格网生成效率较低的不足,为全球离散格网系统的相关应用提供了优选解决方案。
文摘由跟网型变换器(grid-following voltage source converter,GFL-VSC)及构网型变换器(grid-forming voltage source converter,GFM-VSC)构成的混联系统中,复杂的暂态交互作用使系统的安全稳定运行面临挑战,明确变换器间的动态耦合机理及其对系统暂态稳定性的影响至关重要。GFM-VSC中设置的电流限幅环节会导致其暂态运行方式发生切换,进一步增加了GFM-VSC与GFL-VSC之间的耦合机理的复杂性。为揭示GFM-VSC发生暂态模式切换时与GFL-VSC之间的动态耦合机理及该耦合对GFM-VSC故障恢复过程的作用机制,首先,建立考虑GFM-VSC限幅环节的混联系统暂态耦合模型;基于此模型,分析故障期间及故障切除后,GFL-VSC的参数对GFM-VSC工作模式切换的影响机理;随后,针对不同程度的电网电压跌落故障,分析故障切除后GFM-VSC的工作模式切换过程,得到混联系统中GFM-VSC在故障切除后可切换回正常工作模式的临界条件;最后,构建混联系统的仿真模型,验证理论分析的正确性。
文摘风电场站配置一定容量的无功补偿装置(如静止无功发生器(static var generator,SVG))可以提高风电外送能力。同时为了满足风电场站对于惯量和电压支撑的要求,SVG可以在直流侧集成功率型储能元件同时采用构网型控制。然而由于风电场出力的影响,构网型SVG存在着暂态同步失稳的风险。针对此问题,首先通过对构网型SVG接入风电场站的并网系统进行化简等效,得到构网型SVG的功角曲线。然后,利用等面积法则揭示风电场站中构网型SVG的失稳机理,并给出相应的稳定判据。进一步,提出一种基于惯量和阻尼系数协调自适应的暂态同步稳定性提升方法。在判断SVG发生暂态同步失稳时自适应改变惯量和阻尼系数,强迫SVG回到稳定平衡点。该方法可以提高构网型SVG的暂态同步稳定性,有利于风电外送能力的提升。最后在PSCAD/EMTDC中建立电磁暂态仿真模型,验证了构网型SVG失稳机理的正确性以及暂态同步稳定性提升方法的有效性。
