This paper investigates the stability of LCL-filtered grid-connected inverters with capacitor current feedback(CCF) active damping. The impact of time delays in the digital controller on active damping and its equival...This paper investigates the stability of LCL-filtered grid-connected inverters with capacitor current feedback(CCF) active damping. The impact of time delays in the digital controller on active damping and its equivalent virtual impedance is analyzed. The inherent relationship between these time delays and stability is illustrated.Specially, a critical value of the CCF active damping coefficient kdamp_cis proposed to define three distinct regions of stability evaluation. If kdamp_c[ 0, a sufficient but smaller damping coefficient(kdamp\ kdamp_c) is recommended as optimum damping solution;if kdamp_c= 0,system will be unstable irrespective of active damping;and if kdamp_c\ 0, active damping is not necessary to design a stable system. Necessary conditions to ensure stability are identified;guidelines for controller design are then presented to optimize the performance of active damping and dynamic response. Simulation and experimental results confirm the presented analysis.展开更多
通过对0.23/0.4 k V电源系统的调谐电容器补偿电路的分析计算,导出变压器回路、电容器回路的谐波电流比值AT、AC的计算式;以已知频谱谐波源的数据,用电脑进行各种组态的计算;以计算结果为基础分析调谐电容器的作用,电抗率、电容器Y或△...通过对0.23/0.4 k V电源系统的调谐电容器补偿电路的分析计算,导出变压器回路、电容器回路的谐波电流比值AT、AC的计算式;以已知频谱谐波源的数据,用电脑进行各种组态的计算;以计算结果为基础分析调谐电容器的作用,电抗率、电容器Y或△接法对滤波和谐振频率的影响。为电抗率、电容器Y或△接线选择提供参考依据。展开更多
2D MXene nanosheets with metallic conductivity and high pseudo-capacitance are promising electrode materials for supercapacitors.Especially,MXene films can be directly used as electrodes for flexible supercapacitors.H...2D MXene nanosheets with metallic conductivity and high pseudo-capacitance are promising electrode materials for supercapacitors.Especially,MXene films can be directly used as electrodes for flexible supercapacitors.However,they suffer from sluggish ion transport due to self-restacking,causing limited electrochemical performance.Herein,a flexible 3D porous MXene film is fabricated by incorporating graphene oxide(GO) into MXene film followed by self-propagating reduction.The self-propagating process is facile and effective,which can be accomplished in 1.25 s and result in 3D porous framework by releasing substantial gas instantaneously.As the 3D porous structure provides massive ion-accessible active sites and promotes fast ion transport,the MXene-rGO films exhibit superior capacitance and rate performance.With the rGO content of 20%,the MXene-rGO-20 film delivers a high capacitance of 329.9 F g^(-1) at 5 mV s^(-1) in 3 M H2 SO4 electrolyte and remains 260.1 F g^(-1) at 1,000 mV s^(-1) as well as good flexibility.Furthermore,the initial capacitance is retained above 90% after 40,000 cycles at 100 A g^(-1),revealing good cycle stability.This work not only provides a high-performance flexible electrode for supercapacitors,but also proposes an efficient and time-saving strategy for constructing 3D structure from 2D materials.展开更多
As one of the essential components for flexible electronics,flexible electrochemical energy storage(EES)has garnered extensive interests at all levels of materials,devices,and systems.The successful implementation of ...As one of the essential components for flexible electronics,flexible electrochemical energy storage(EES)has garnered extensive interests at all levels of materials,devices,and systems.The successful implementation of high-performance flexible EES devices relies on exploring of suitable electrode/electrolyte materials that have both superior electrochemical and mechanical properties.For this function,one-dimensional electrospun nanofibers have emerged as a class of promising building blocks for the key components of flexible EES devices.In this overview,the fundamental principles and technical advances of electrospinning are examined,for both their successes and challenges in controllable fabrication of nanofibers with the desirable chemical compositions,micro/meso-/nanostructures,and therefore resultant properties.The advances in applications of electrospun nanofibers for various key flexible EES devices are critically looked into,including those in supercapacitors,metal-ion batteries,and metal-air batteries.The existing challenges and prospects of these electrospun nanofiber-based flexible EES are discussed,aiming to inspire continued efforts in developing the optimal high-performance and low cost flexible EES devices for long-awaited practical applications.展开更多
基金supported by National Key Research and Development Program of China(No.2016YFB0100700)
文摘This paper investigates the stability of LCL-filtered grid-connected inverters with capacitor current feedback(CCF) active damping. The impact of time delays in the digital controller on active damping and its equivalent virtual impedance is analyzed. The inherent relationship between these time delays and stability is illustrated.Specially, a critical value of the CCF active damping coefficient kdamp_cis proposed to define three distinct regions of stability evaluation. If kdamp_c[ 0, a sufficient but smaller damping coefficient(kdamp\ kdamp_c) is recommended as optimum damping solution;if kdamp_c= 0,system will be unstable irrespective of active damping;and if kdamp_c\ 0, active damping is not necessary to design a stable system. Necessary conditions to ensure stability are identified;guidelines for controller design are then presented to optimize the performance of active damping and dynamic response. Simulation and experimental results confirm the presented analysis.
文摘通过对0.23/0.4 k V电源系统的调谐电容器补偿电路的分析计算,导出变压器回路、电容器回路的谐波电流比值AT、AC的计算式;以已知频谱谐波源的数据,用电脑进行各种组态的计算;以计算结果为基础分析调谐电容器的作用,电抗率、电容器Y或△接法对滤波和谐振频率的影响。为电抗率、电容器Y或△接线选择提供参考依据。
基金financially supported by the National Natural Science Foundation of China (NSFC, 51572011 and 51802012)the National Key Research and Development Program of China (2017YFB0102204)the Fundamental Research Funds for the Central Universities (buctrc201813 and buctrc201819)。
文摘2D MXene nanosheets with metallic conductivity and high pseudo-capacitance are promising electrode materials for supercapacitors.Especially,MXene films can be directly used as electrodes for flexible supercapacitors.However,they suffer from sluggish ion transport due to self-restacking,causing limited electrochemical performance.Herein,a flexible 3D porous MXene film is fabricated by incorporating graphene oxide(GO) into MXene film followed by self-propagating reduction.The self-propagating process is facile and effective,which can be accomplished in 1.25 s and result in 3D porous framework by releasing substantial gas instantaneously.As the 3D porous structure provides massive ion-accessible active sites and promotes fast ion transport,the MXene-rGO films exhibit superior capacitance and rate performance.With the rGO content of 20%,the MXene-rGO-20 film delivers a high capacitance of 329.9 F g^(-1) at 5 mV s^(-1) in 3 M H2 SO4 electrolyte and remains 260.1 F g^(-1) at 1,000 mV s^(-1) as well as good flexibility.Furthermore,the initial capacitance is retained above 90% after 40,000 cycles at 100 A g^(-1),revealing good cycle stability.This work not only provides a high-performance flexible electrode for supercapacitors,but also proposes an efficient and time-saving strategy for constructing 3D structure from 2D materials.
基金the financial supports by National Natural Science Foundation of China(Grant No.51902265)Fundamental Research Funds for the Central Universities,Key Research and Development Program of Shaanxi(No.2020KWZ-001)Project for graduate Innovation team of Northwestern Polytechnical University
文摘As one of the essential components for flexible electronics,flexible electrochemical energy storage(EES)has garnered extensive interests at all levels of materials,devices,and systems.The successful implementation of high-performance flexible EES devices relies on exploring of suitable electrode/electrolyte materials that have both superior electrochemical and mechanical properties.For this function,one-dimensional electrospun nanofibers have emerged as a class of promising building blocks for the key components of flexible EES devices.In this overview,the fundamental principles and technical advances of electrospinning are examined,for both their successes and challenges in controllable fabrication of nanofibers with the desirable chemical compositions,micro/meso-/nanostructures,and therefore resultant properties.The advances in applications of electrospun nanofibers for various key flexible EES devices are critically looked into,including those in supercapacitors,metal-ion batteries,and metal-air batteries.The existing challenges and prospects of these electrospun nanofiber-based flexible EES are discussed,aiming to inspire continued efforts in developing the optimal high-performance and low cost flexible EES devices for long-awaited practical applications.
