传统正交频分复用(orthogonal frequency division multiplexing,OFDM)帧同步方法,如基于前导序列、基于导频、基于深度学习的帧同步算法在面对Starlink高速率、高动态通信环境时局限于单路计算思路,且具有较多的资源消耗和较高的时钟...传统正交频分复用(orthogonal frequency division multiplexing,OFDM)帧同步方法,如基于前导序列、基于导频、基于深度学习的帧同步算法在面对Starlink高速率、高动态通信环境时局限于单路计算思路,且具有较多的资源消耗和较高的时钟需求。而基于差分相移键控(symmetric differential phase shift keying,SDPSK)调制的多路并行帧同步算法虽然引入频偏矫正和本地前导序列相关使得性能上有所提升并降低了时钟需求,但加大了计算量和硬件资源占用。针对以上情况,基于Starlink公开前导结构,提出了四路并行的基于频偏矫正辅助的Starlink下行信号帧同步轻量化电路设计。首先,设计基于延时相关复用的轻量化粗帧同步和频偏估计结构使电路在频偏估计时不需要再次计算延时相关值。然后,提出基于四路并行直接数字式频率合成器(direct digital synthesizer,DDS)的轻量化频偏矫正模块避免单路信号在多路结构下变频时需要缓存。最后,设计基于符号相关和查找表复数乘法器的轻量化精帧同步结构减少了本地序列和信号相关的资源耗用,在保证性能的前提下使得查找表(look-up table,LUT)、查找表随机存取存储器(look-up table random access memory,LUTRAM)、触发器(flip-flop,FF)、块随机存取存储器(block random access memory,BRAM)资源分别节省了7%、2%、5%和8%。对电路编写verilog代码进行现场可编程门阵列(field programmable gate array,FPGA)实现,并通过Xilinx生产的xczu47dr芯片上板验证了其资源占用及性能表现。展开更多
Polyether ether ketone(PEEK)-based continuous glass fiber reinforced thermoplastic composite offers advantages such as high strength,electrical insulation,and heat insulation.Parts manufactured using this composite an...Polyether ether ketone(PEEK)-based continuous glass fiber reinforced thermoplastic composite offers advantages such as high strength,electrical insulation,and heat insulation.Parts manufactured using this composite and 3D printing have promising applications in aerospace,automobile,rail transit,etc.In this paper,a high-temperature melt impregnation method was used to successfully prepare the 3D printing prepreg filaments of the aforementioned composite.In the FDM 3D printing equipment,a nozzle of high thermal conductivity and wear-resistant copper alloy and a PEEK-based carbon fiber thermoplastic composite build plate with uniform temperature control were innovatively introduced to effectively improve the quality of 3D printing.The porosity of the 3D printed samples produced from the composite prepreg filament was analyzed under different printing parameters,and the mechanical properties and fracture mechanism of the printed parts were studied.The results show that the printing layer thickness,printing speed,printing temperature and build plate temperature have varying effects on the porosity of printed parts,which in turn affects tensile strength and the interlaminar shear strength(ILSS).When the printing layer thickness is 0.4 mm,printing speed is 2 mm/s,nozzle temperature is 430℃ and build plate temperature is 150℃,the tensile strength and ILSS of the composite printed parts reach their maximum values of 463.76 and 24.95 MPa,respectively.Microscopic analysis of the fracture morphology of the tensile specimens reveals that the 3D printed CGF/PEEK composite sample has three types of fracture mode,which are single filament bundle fracture,fracture mode of delamination,and fracture failure of the sample at the cross-section.The essence of the above three kinds of fracture mode is the difference of the interface bonding force of 3D printed CGF/PEEK composites.The fracture failure at the cross-section is that the continuous glass fibers in the composite are pulled out until they break,which is the main form of the failure of the composite under tensile load.The interfacial region of the composite is prone to microscopic defects such as voids and delamination during 3D printing,which become the most vulnerable link of the composite.Understanding the relationship between voids and fracture behavior lays a foundation for defect suppression and performance improvement of subsequent printed parts.展开更多
当背景谐波电压与负载侧谐波电流在中高压配电网公共耦合点(Point of common coupling,PCC)处共存时,易导致PCC谐波电流超出限值,提出采用基于前馈-反馈复合控制的电力感应调控滤波(Controllably inductive power filtering,CIPF)系统...当背景谐波电压与负载侧谐波电流在中高压配电网公共耦合点(Point of common coupling,PCC)处共存时,易导致PCC谐波电流超出限值,提出采用基于前馈-反馈复合控制的电力感应调控滤波(Controllably inductive power filtering,CIPF)系统治理中高压配电网PCC处谐波,将网侧(PCC)谐波电流反馈控制和负载侧谐波电流前馈控制结合后,可以在提高系统稳定性的同时,提供谐振阻尼、实现对网侧/负载侧谐波的双向主动抑制。首先介绍CIPF系统的拓扑结构及特点;建立前馈-反馈复合控制下系统的谐波域数学模型和单相等效电路,在此基础上,分别研究网侧谐波电流相对于负载侧谐波电流和网侧背景谐波电压的传递特性;设计基于谐波分频检测方法的控制方案并推导出系统传递函数,基于此,进一步探讨控制系数取值与系统滤波性能、稳定性之间的关系;最后,通过仿真模型,验证了所提控制方法下CIPF系统滤波性能的优越性。展开更多
基金supported by the National Key Research and Development Program Project of China(Grant No.2018YFB1106700).
文摘Polyether ether ketone(PEEK)-based continuous glass fiber reinforced thermoplastic composite offers advantages such as high strength,electrical insulation,and heat insulation.Parts manufactured using this composite and 3D printing have promising applications in aerospace,automobile,rail transit,etc.In this paper,a high-temperature melt impregnation method was used to successfully prepare the 3D printing prepreg filaments of the aforementioned composite.In the FDM 3D printing equipment,a nozzle of high thermal conductivity and wear-resistant copper alloy and a PEEK-based carbon fiber thermoplastic composite build plate with uniform temperature control were innovatively introduced to effectively improve the quality of 3D printing.The porosity of the 3D printed samples produced from the composite prepreg filament was analyzed under different printing parameters,and the mechanical properties and fracture mechanism of the printed parts were studied.The results show that the printing layer thickness,printing speed,printing temperature and build plate temperature have varying effects on the porosity of printed parts,which in turn affects tensile strength and the interlaminar shear strength(ILSS).When the printing layer thickness is 0.4 mm,printing speed is 2 mm/s,nozzle temperature is 430℃ and build plate temperature is 150℃,the tensile strength and ILSS of the composite printed parts reach their maximum values of 463.76 and 24.95 MPa,respectively.Microscopic analysis of the fracture morphology of the tensile specimens reveals that the 3D printed CGF/PEEK composite sample has three types of fracture mode,which are single filament bundle fracture,fracture mode of delamination,and fracture failure of the sample at the cross-section.The essence of the above three kinds of fracture mode is the difference of the interface bonding force of 3D printed CGF/PEEK composites.The fracture failure at the cross-section is that the continuous glass fibers in the composite are pulled out until they break,which is the main form of the failure of the composite under tensile load.The interfacial region of the composite is prone to microscopic defects such as voids and delamination during 3D printing,which become the most vulnerable link of the composite.Understanding the relationship between voids and fracture behavior lays a foundation for defect suppression and performance improvement of subsequent printed parts.
文摘当背景谐波电压与负载侧谐波电流在中高压配电网公共耦合点(Point of common coupling,PCC)处共存时,易导致PCC谐波电流超出限值,提出采用基于前馈-反馈复合控制的电力感应调控滤波(Controllably inductive power filtering,CIPF)系统治理中高压配电网PCC处谐波,将网侧(PCC)谐波电流反馈控制和负载侧谐波电流前馈控制结合后,可以在提高系统稳定性的同时,提供谐振阻尼、实现对网侧/负载侧谐波的双向主动抑制。首先介绍CIPF系统的拓扑结构及特点;建立前馈-反馈复合控制下系统的谐波域数学模型和单相等效电路,在此基础上,分别研究网侧谐波电流相对于负载侧谐波电流和网侧背景谐波电压的传递特性;设计基于谐波分频检测方法的控制方案并推导出系统传递函数,基于此,进一步探讨控制系数取值与系统滤波性能、稳定性之间的关系;最后,通过仿真模型,验证了所提控制方法下CIPF系统滤波性能的优越性。
