The dual-mode stabilization scheme has been demonstrated as an efficient way to stabilize laser frequency.In this study,we propose a novel dual-mode stabilization scheme that employs a sizable Fabry-Pérot cavity ...The dual-mode stabilization scheme has been demonstrated as an efficient way to stabilize laser frequency.In this study,we propose a novel dual-mode stabilization scheme that employs a sizable Fabry-Pérot cavity instead of the microcavity used in previous studies and has enabled higher bandwidth for locking.The results demonstrate a 30-fold reduction in laser frequency drift,with frequency instability below 169 kHz for integration time exceeding 1 h and a minimum value of 33.8 kHz at 54 min.Further improvement could be achieved by optimizing the phase locking.This scheme has potential for use in precision spectroscopic measurement.展开更多
This paper presents a novel dual-mode step-up （boost） DC/DC converter. Pulse-frequency modulation （PFM） is used to improve the efficiency at light load. This converter can operate between pulse-width modulation （...This paper presents a novel dual-mode step-up （boost） DC/DC converter. Pulse-frequency modulation （PFM） is used to improve the efficiency at light load. This converter can operate between pulse-width modulation （PWM） and pulse-frequency modulation. The converter will operate in PFM mode at light load and in PWM mode at heavy load. The maximum conversion efficiency of this converter is 96%. The conversion efficiency is greatly improved when load current is below 100 mA. Additionally, a soft-start circuit and a variable-sawtooth frequency circuit are proposed in this paper. The former is used to avoid the large switching current at the start up of the converter and the latter is utilized to reduce the EMI of the converter.展开更多
二极管中点钳位NPC(neutral point clamped)三电平逆变器具备较低的开关应力、谐波分量和较好的抗干扰能力,促使其成为光伏、储能等新能源领域DC-AC变换器的主要拓扑之一。针对大功率应用场景中普遍采用的NPC三电平IGBT功率半导体模块...二极管中点钳位NPC(neutral point clamped)三电平逆变器具备较低的开关应力、谐波分量和较好的抗干扰能力,促使其成为光伏、储能等新能源领域DC-AC变换器的主要拓扑之一。针对大功率应用场景中普遍采用的NPC三电平IGBT功率半导体模块开展研究,分析NPC三电平功率模块的换流回路,并据此给出对应换流回路的寄生参数精准仿真评估方法。依据换流回路寄生参数最小原则,设计适用于NPC三电平功率半导体模块的动态特性测试电路。根据换流回路以及电路工作原理,设计NPC三电平功率模块的驱动电路,并给出增强驱动电流、防直通及死区时间可调的驱动方案。最后,通过对NPC三电平IGBT模块的动态测试,详细评估了不同工况下功率器件的动态损耗。展开更多
From 2002 through 2008 the secular rate of de-creasing sea ice area in the northern hemisphere accelerated by a factor of 18, whereas the secular rate of increasing sea ice area in the southern hemisphere accelerated ...From 2002 through 2008 the secular rate of de-creasing sea ice area in the northern hemisphere accelerated by a factor of 18, whereas the secular rate of increasing sea ice area in the southern hemisphere accelerated by a factor of 16, relative to the rates from 1978 through 2007. These were derived from the daily sea ice area retrieved from the Scanning Multi-channel Microwave Radiometer – Special Sensor Microwave/Imager and the Advanced Microwave Scan- ning Radiometer for the Earth Observation Sys- tem. The “annual” cycle of northern and southern sea ice areas, the number of days between maxima and minima is 372.4, on average, a frequency modulation, with a recurrence interval of 61.7 years. Significant spectral power occurs at the quasi-4-day through 120-day frequencies. The frequency content and modulation of the daily time series’ are consistent inter-monthly to inter-seasonal frequencies of solar irradiance, atmospheric-oceanic Rossby waves, length-of- day, and polar motion. This suggests conserva-tion of angular momentum of the atmosphere – sea-ice – ocean system. The near 60-year modu- lation and analysis of the detrended daily time series of the Arctic and Antarctic sea ice areas suggest the accelerations shown by the secular trends are relatively short-lived and reversible within an interval of one-quarter (15-years) to one-half (30-years) of the modulation period.展开更多
基金supported by the National Key R&D Program of China(No.2022YFC3700329)the National Natural Science Foundation of China(Nos.61905134,61905136,and62175139)+1 种基金the Shanxi Province Science and Technology Activities for Returned Overseas Researcher(No.20220001)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(No.2019L0062)。
文摘The dual-mode stabilization scheme has been demonstrated as an efficient way to stabilize laser frequency.In this study,we propose a novel dual-mode stabilization scheme that employs a sizable Fabry-Pérot cavity instead of the microcavity used in previous studies and has enabled higher bandwidth for locking.The results demonstrate a 30-fold reduction in laser frequency drift,with frequency instability below 169 kHz for integration time exceeding 1 h and a minimum value of 33.8 kHz at 54 min.Further improvement could be achieved by optimizing the phase locking.This scheme has potential for use in precision spectroscopic measurement.
基金the National Science Council of Taiwan, China, under Grant No. NSC 95-2221-E-305010.
文摘This paper presents a novel dual-mode step-up （boost） DC/DC converter. Pulse-frequency modulation （PFM） is used to improve the efficiency at light load. This converter can operate between pulse-width modulation （PWM） and pulse-frequency modulation. The converter will operate in PFM mode at light load and in PWM mode at heavy load. The maximum conversion efficiency of this converter is 96%. The conversion efficiency is greatly improved when load current is below 100 mA. Additionally, a soft-start circuit and a variable-sawtooth frequency circuit are proposed in this paper. The former is used to avoid the large switching current at the start up of the converter and the latter is utilized to reduce the EMI of the converter.
文摘二极管中点钳位NPC(neutral point clamped)三电平逆变器具备较低的开关应力、谐波分量和较好的抗干扰能力,促使其成为光伏、储能等新能源领域DC-AC变换器的主要拓扑之一。针对大功率应用场景中普遍采用的NPC三电平IGBT功率半导体模块开展研究,分析NPC三电平功率模块的换流回路,并据此给出对应换流回路的寄生参数精准仿真评估方法。依据换流回路寄生参数最小原则,设计适用于NPC三电平功率半导体模块的动态特性测试电路。根据换流回路以及电路工作原理,设计NPC三电平功率模块的驱动电路,并给出增强驱动电流、防直通及死区时间可调的驱动方案。最后,通过对NPC三电平IGBT模块的动态测试,详细评估了不同工况下功率器件的动态损耗。
文摘From 2002 through 2008 the secular rate of de-creasing sea ice area in the northern hemisphere accelerated by a factor of 18, whereas the secular rate of increasing sea ice area in the southern hemisphere accelerated by a factor of 16, relative to the rates from 1978 through 2007. These were derived from the daily sea ice area retrieved from the Scanning Multi-channel Microwave Radiometer – Special Sensor Microwave/Imager and the Advanced Microwave Scan- ning Radiometer for the Earth Observation Sys- tem. The “annual” cycle of northern and southern sea ice areas, the number of days between maxima and minima is 372.4, on average, a frequency modulation, with a recurrence interval of 61.7 years. Significant spectral power occurs at the quasi-4-day through 120-day frequencies. The frequency content and modulation of the daily time series’ are consistent inter-monthly to inter-seasonal frequencies of solar irradiance, atmospheric-oceanic Rossby waves, length-of- day, and polar motion. This suggests conserva-tion of angular momentum of the atmosphere – sea-ice – ocean system. The near 60-year modu- lation and analysis of the detrended daily time series of the Arctic and Antarctic sea ice areas suggest the accelerations shown by the secular trends are relatively short-lived and reversible within an interval of one-quarter (15-years) to one-half (30-years) of the modulation period.
