Considering the advantages and limitations of traditional identification method,combined with the strategy of active detection,the principle of DC grid pilot protection based on active detection is proposed to improve...Considering the advantages and limitations of traditional identification method,combined with the strategy of active detection,the principle of DC grid pilot protection based on active detection is proposed to improve the sensitivity and reliability of hybrid MMC DC grid protection,and to ensure the accurate identification of fault areas in DC grid.By using the DC fault ride-through control strategy of the hybrid sub-module MMC,the fault current at the converter station DC terminal is limited.Based on the high controllability of hybrid MMC,sinusoidal fault detection signals with the same frequency are injected into the line at each converter station.Based on model recognition,the capacitance model condition is satisfied by the detected signals at both ends during external faults whereas not satisfied during internal faults.The Spearman correlation coefficients is then introduced,and the correlation discriminant of capacitance model is constructed to realize fault area discrimination of DC grid.The simulation results show that the active detection protection scheme proposed in this paper can accurately identify the fault area of DC grid,and is not affected by fault impedance and has low sampling rate requirement.展开更多
Polarized-light photodetectors are the indispensable elements for practical optical and optoelectronic device applications.Two-dimensional(2D)hybrid perovskite ferroelectrics,in which the coupling of spontaneous polar...Polarized-light photodetectors are the indispensable elements for practical optical and optoelectronic device applications.Two-dimensional(2D)hybrid perovskite ferroelectrics,in which the coupling of spontaneous polarization(P_(s))and light favors the dissociation of photo-induced carriers,have taken a booming position within this portfolio.However,polarized-light photodetectors with a low detectionlimit remain unexplored in this 2D ferroelectric family.In this work,the high-quality individual crystals of a 2D perovskite ferroelectric,BA_(2)CsPb_(2)Br_(7)(1,where BA^(+)is n-butylammonium),were used to fabricate ultrasensitive polarized-light detectors.Its unique bilayered structural motif results in quite strong electric and optical anisotropy with a large absorption ratio of a_(c)/α_(a)≈3.2(λ=405 nm).Besides,the presence of ferroelectric Psalso endows high built-in electric field along the polar c-axis that favors photoelectric activities.Under an extremely low detectable limit of 40 n W/cm^(2),the detector of 1 exhibits a notable dichroism ratio(I_(ph)^(c)/I_(ph)^(a)≈1.5),a large responsivity of~39.5 m A/W and a specific detectivity of~1.2×10^(12)Jones.Moreover,crystal-based devices of 1 also exhibit a fast response speed(~300μs)and excellent anti-fatigue merits.This work highlights great potentials of hybrid perovskite ferroelectrics toward polarized-light photodetection.展开更多
Navigation and positioning in harsh environments is still a great challenge for many applications. Collective Detection (CD) is a powerful approach for acquiring highly attenuated satellite signals in challenging envi...Navigation and positioning in harsh environments is still a great challenge for many applications. Collective Detection (CD) is a powerful approach for acquiring highly attenuated satellite signals in challenging environments, because of its capacity to process all visible satellites collectively taking advantage of the spatial correlation between GNSS signals as a vector acquisition scheme. CD combines the correlator outputs of satellite channels and projects them onto the position/clock bias domain in order to enhance the overall GNSS signal detection probability. In CD, the code phase search for all satellites in view is mapped into a receiver position/clock bias grid and the satellite signals are not acquired individually but collectively. In this concept, a priori knowledge of satellite ephemeris and reference location are provided to the user. Furthermore, CD addresses some of the inherent drawbacks of the conventional acquisition at the expenses of an increased computational cost. CD techniques are computationally intensive because of the significant number of candidate points in the position-time domain. The aim of this paper is to describe the operation of the CD approach incorporating new methods and architectures to address both the complexity and sensitivity problems. The first method consists of hybridizing the collective detection approach with some correlation techniques and coupling it with a better technique for Doppler frequency estimate. For that, a new scheme with less calculation load is proposed in order to accelerate the detection and location process. Then, high sensitivity acquisition techniques using long coherent integration and non-coherent integration are used in order to improve the performance of the CD algorithm.展开更多
基金supported by The National Natural Science Foundation key project(U1766209).
文摘Considering the advantages and limitations of traditional identification method,combined with the strategy of active detection,the principle of DC grid pilot protection based on active detection is proposed to improve the sensitivity and reliability of hybrid MMC DC grid protection,and to ensure the accurate identification of fault areas in DC grid.By using the DC fault ride-through control strategy of the hybrid sub-module MMC,the fault current at the converter station DC terminal is limited.Based on the high controllability of hybrid MMC,sinusoidal fault detection signals with the same frequency are injected into the line at each converter station.Based on model recognition,the capacitance model condition is satisfied by the detected signals at both ends during external faults whereas not satisfied during internal faults.The Spearman correlation coefficients is then introduced,and the correlation discriminant of capacitance model is constructed to realize fault area discrimination of DC grid.The simulation results show that the active detection protection scheme proposed in this paper can accurately identify the fault area of DC grid,and is not affected by fault impedance and has low sampling rate requirement.
基金supported by the National Natural Science Foundation of China(21622108,21875251,21525104,and 21833010)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB20010200)Youth Innovation Promotion of Chinese Academy of Sciences。
文摘Polarized-light photodetectors are the indispensable elements for practical optical and optoelectronic device applications.Two-dimensional(2D)hybrid perovskite ferroelectrics,in which the coupling of spontaneous polarization(P_(s))and light favors the dissociation of photo-induced carriers,have taken a booming position within this portfolio.However,polarized-light photodetectors with a low detectionlimit remain unexplored in this 2D ferroelectric family.In this work,the high-quality individual crystals of a 2D perovskite ferroelectric,BA_(2)CsPb_(2)Br_(7)(1,where BA^(+)is n-butylammonium),were used to fabricate ultrasensitive polarized-light detectors.Its unique bilayered structural motif results in quite strong electric and optical anisotropy with a large absorption ratio of a_(c)/α_(a)≈3.2(λ=405 nm).Besides,the presence of ferroelectric Psalso endows high built-in electric field along the polar c-axis that favors photoelectric activities.Under an extremely low detectable limit of 40 n W/cm^(2),the detector of 1 exhibits a notable dichroism ratio(I_(ph)^(c)/I_(ph)^(a)≈1.5),a large responsivity of~39.5 m A/W and a specific detectivity of~1.2×10^(12)Jones.Moreover,crystal-based devices of 1 also exhibit a fast response speed(~300μs)and excellent anti-fatigue merits.This work highlights great potentials of hybrid perovskite ferroelectrics toward polarized-light photodetection.
文摘Navigation and positioning in harsh environments is still a great challenge for many applications. Collective Detection (CD) is a powerful approach for acquiring highly attenuated satellite signals in challenging environments, because of its capacity to process all visible satellites collectively taking advantage of the spatial correlation between GNSS signals as a vector acquisition scheme. CD combines the correlator outputs of satellite channels and projects them onto the position/clock bias domain in order to enhance the overall GNSS signal detection probability. In CD, the code phase search for all satellites in view is mapped into a receiver position/clock bias grid and the satellite signals are not acquired individually but collectively. In this concept, a priori knowledge of satellite ephemeris and reference location are provided to the user. Furthermore, CD addresses some of the inherent drawbacks of the conventional acquisition at the expenses of an increased computational cost. CD techniques are computationally intensive because of the significant number of candidate points in the position-time domain. The aim of this paper is to describe the operation of the CD approach incorporating new methods and architectures to address both the complexity and sensitivity problems. The first method consists of hybridizing the collective detection approach with some correlation techniques and coupling it with a better technique for Doppler frequency estimate. For that, a new scheme with less calculation load is proposed in order to accelerate the detection and location process. Then, high sensitivity acquisition techniques using long coherent integration and non-coherent integration are used in order to improve the performance of the CD algorithm.
