柔性直流输电技术已经发展为超高压直流输电的一种主要方式。然而多个工业现场出现低频振荡现象,从而影响了供电的可靠性。现有理论从感应发电机效应和次同步控制相互作用角度解释了暂态短路等异常工况下低频振荡的原因,却无法分析正常...柔性直流输电技术已经发展为超高压直流输电的一种主要方式。然而多个工业现场出现低频振荡现象,从而影响了供电的可靠性。现有理论从感应发电机效应和次同步控制相互作用角度解释了暂态短路等异常工况下低频振荡的原因,却无法分析正常功率调动时低频振荡的机理。基于此,该文从多个角度,系统地研究了柔性直流输电系统的低频振荡问题:1)通过数学模型定量地分析了其作用机理,MMC阻抗特性、开关频率、低频运行特征和环流的低通特性共同引起了低频振荡;2)采用环流抑制、开关频率优化和有源阻尼等多种控制手段,改进了现有的低频振荡抑制算法;3)搭建了双端±420kV柔性直流输电系统的基于实时数字仿真系统(real time digital simulation system,RTDS)的硬件在环仿真,利用典型柔性直流输电工程的参数,对比所提算法和传统算法的实现结果,验证工业现场的适用性。该文所提低频振荡机理能够解释低频振荡发生的各种原因,所提控制策略可以抑制低频振荡发生,提高柔性直流输电系统的可靠性。展开更多
不间断电源(uninterrupted power supply,UPS)是电力系统电能质量问题的重要解决方案,环流抑制问题是目前多台UPS并联技术中的研究重点与难点.基于CAN总线的模块化UPS并联控制策略,应用虚拟多回路输出阻抗下垂控制,并采用CAN总线通信实...不间断电源(uninterrupted power supply,UPS)是电力系统电能质量问题的重要解决方案,环流抑制问题是目前多台UPS并联技术中的研究重点与难点.基于CAN总线的模块化UPS并联控制策略,应用虚拟多回路输出阻抗下垂控制,并采用CAN总线通信实现各并联UPS模块间的同步和均流控制.实验结果表明,提出的方法在抑制子模块环流的同时解决了分布式系统的信号稳定性问题,保证了模块化UPS并联系统数据传输的准确性和实时性.展开更多
To reveal the resonance suppression mechanism of the blood circulation in dragonfly wings,a numerical modeling method of dragonfly wings based on Voronoi diagrams is proposed,and the changes in mass,aerodynamic dampin...To reveal the resonance suppression mechanism of the blood circulation in dragonfly wings,a numerical modeling method of dragonfly wings based on Voronoi diagrams is proposed,and the changes in mass,aerodynamic damping,and natural frequencies caused by blood circulation in veins are investigated.The equivalent mass of blood,boundary conditions,and aerodynamic damping are calculated theoretically.Modal analysis and harmonic response analysis of wing models with different blood circulation paths are performed using the finite-element method(FEM).The vibration reduction ratioδis introduced to compare the damping efficiency of different mass regions.Finally,a natural frequency testing device is constructed to measure the natural frequencies of dragonfly wings.The results indicate that the shape,mass,and natural frequencies of the dragonfly wing model constructed by numerical method agree well with reality.The mass distribution on the wing can be altered by blood circulation,thereby adjusting the natural frequencies and achieving resonance suppression.The highestδof 1.013 is observed in the C region when blood circulates solely in secondary veins,but it is still lower than theδof 1.017 when blood circulates in complete veins.The aerodynamic damping ratio(1.19–1.79%)should not be neglected in the vibration analysis of the beating wing.展开更多
文摘柔性直流输电技术已经发展为超高压直流输电的一种主要方式。然而多个工业现场出现低频振荡现象,从而影响了供电的可靠性。现有理论从感应发电机效应和次同步控制相互作用角度解释了暂态短路等异常工况下低频振荡的原因,却无法分析正常功率调动时低频振荡的机理。基于此,该文从多个角度,系统地研究了柔性直流输电系统的低频振荡问题:1)通过数学模型定量地分析了其作用机理,MMC阻抗特性、开关频率、低频运行特征和环流的低通特性共同引起了低频振荡;2)采用环流抑制、开关频率优化和有源阻尼等多种控制手段,改进了现有的低频振荡抑制算法;3)搭建了双端±420kV柔性直流输电系统的基于实时数字仿真系统(real time digital simulation system,RTDS)的硬件在环仿真,利用典型柔性直流输电工程的参数,对比所提算法和传统算法的实现结果,验证工业现场的适用性。该文所提低频振荡机理能够解释低频振荡发生的各种原因,所提控制策略可以抑制低频振荡发生,提高柔性直流输电系统的可靠性。
文摘不间断电源(uninterrupted power supply,UPS)是电力系统电能质量问题的重要解决方案,环流抑制问题是目前多台UPS并联技术中的研究重点与难点.基于CAN总线的模块化UPS并联控制策略,应用虚拟多回路输出阻抗下垂控制,并采用CAN总线通信实现各并联UPS模块间的同步和均流控制.实验结果表明,提出的方法在抑制子模块环流的同时解决了分布式系统的信号稳定性问题,保证了模块化UPS并联系统数据传输的准确性和实时性.
基金sponsored by the Shandong Natural Science Foundation of the People's Republic of China(No.ZR2022ME213,ZR2023ME081).
文摘To reveal the resonance suppression mechanism of the blood circulation in dragonfly wings,a numerical modeling method of dragonfly wings based on Voronoi diagrams is proposed,and the changes in mass,aerodynamic damping,and natural frequencies caused by blood circulation in veins are investigated.The equivalent mass of blood,boundary conditions,and aerodynamic damping are calculated theoretically.Modal analysis and harmonic response analysis of wing models with different blood circulation paths are performed using the finite-element method(FEM).The vibration reduction ratioδis introduced to compare the damping efficiency of different mass regions.Finally,a natural frequency testing device is constructed to measure the natural frequencies of dragonfly wings.The results indicate that the shape,mass,and natural frequencies of the dragonfly wing model constructed by numerical method agree well with reality.The mass distribution on the wing can be altered by blood circulation,thereby adjusting the natural frequencies and achieving resonance suppression.The highestδof 1.013 is observed in the C region when blood circulates solely in secondary veins,but it is still lower than theδof 1.017 when blood circulates in complete veins.The aerodynamic damping ratio(1.19–1.79%)should not be neglected in the vibration analysis of the beating wing.
