When a high impedance fault(HIF)occurs in a distribution network,the detection efficiency of traditional protection devices is strongly limited by the weak fault information.In this study,a method based on S-transform...When a high impedance fault(HIF)occurs in a distribution network,the detection efficiency of traditional protection devices is strongly limited by the weak fault information.In this study,a method based on S-transform(ST)and average singular entropy(ASE)is proposed to identify HIFs.First,a wavelet packet transform(WPT)was applied to extract the feature frequency band.Thereafter,the ST was investigated in each half cycle.Afterwards,the obtained time-frequency matrix was denoised by singular value decomposition(SVD),followed by the calculation of the ASE index.Finally,an appropriate threshold was selected to detect the HIFs.The advantages of this method are the ability of fine band division,adaptive time-frequency transformation,and quantitative expression of signal complexity.The performance of the proposed method was verified by simulated and field data,and further analysis revealed that it could still achieve good results under different conditions.展开更多
显示器电磁木马是通过控制计算机屏幕电磁辐射达到窃取信息目的的一种新型木马。当前的主流防护思想是用软件防护代替较为成熟但造价昂贵的硬件防护机制,然而目前软防护思想大多侧重于理论方法的探索,在实现机制上相对比较复杂。针对显...显示器电磁木马是通过控制计算机屏幕电磁辐射达到窃取信息目的的一种新型木马。当前的主流防护思想是用软件防护代替较为成熟但造价昂贵的硬件防护机制,然而目前软防护思想大多侧重于理论方法的探索,在实现机制上相对比较复杂。针对显示器电磁木马的工作特点提出了Soft-TEMPEST防护机制,设计了显示器电磁木马的ADFA(API Detection and Frequency Analysis)检测方法。该方法通过API函数序列的周期性挖掘分析,结合对屏幕像素信息的傅里叶变换及频谱分析,达到检测出木马进程的目的。测试结果表明,该方法能够成功检测出多种显示器电磁木马,而且原理简单,方便投入使用。展开更多
The presence of renewable energy resources in LV distribution networks may lead to a distribution transformer,also known as a Smart Transformer(ST),experiencing the bidirectional power flow.Therefore,the ST must have ...The presence of renewable energy resources in LV distribution networks may lead to a distribution transformer,also known as a Smart Transformer(ST),experiencing the bidirectional power flow.Therefore,the ST must have the capability to operate in both directions.However,the reverse power is less as compared to the forward power,thus the design of ST with the same capacity in both directions increases the hardware cost and decreases the system efficiency.This paper proposes a Hybrid-modular-ST(H-ST),composed of a mixed use of single active bridge-based series resonant converter and dual active bridge instead of complete use of uni-or bi-directional converter adopted in the conventional solid-state-transformer.Based on the proposed H-ST,the impacts of power imbalance among cascaded modules in reverse operation mode are analyzed and then an effective solution based on reactive power compensation combined with the characteristics of the proposed architecture is adopted.The simulation and experimental results clearly validate the effectiveness and feasibility of the theoretical analyses.展开更多
基金financial supported by the Natural Science Foundation of Fujian,China(2021J01633).
文摘When a high impedance fault(HIF)occurs in a distribution network,the detection efficiency of traditional protection devices is strongly limited by the weak fault information.In this study,a method based on S-transform(ST)and average singular entropy(ASE)is proposed to identify HIFs.First,a wavelet packet transform(WPT)was applied to extract the feature frequency band.Thereafter,the ST was investigated in each half cycle.Afterwards,the obtained time-frequency matrix was denoised by singular value decomposition(SVD),followed by the calculation of the ASE index.Finally,an appropriate threshold was selected to detect the HIFs.The advantages of this method are the ability of fine band division,adaptive time-frequency transformation,and quantitative expression of signal complexity.The performance of the proposed method was verified by simulated and field data,and further analysis revealed that it could still achieve good results under different conditions.
文摘随着分布式光伏等新能源接入电网的规模快速增长,给新能源电力汇聚、疏散、消纳和电网潮流优化控制带来严峻挑战。基于电力电子技术的柔性交流输电系统装置可有效提升输电网络的传输容量,由大容量Sen变压器(sen transformer,ST)和小容量统一潮流控制器(unified power flow controller,UPFC)组成的混合式潮流控制器(hybrid unified power flow controller,HPFC)在实现潮流连续调节的基础上,能够有效提升装置的经济性,具有很好的应用前景。为了确保HPFC调节潮流的准确性和可靠性,给出了HPFC容量分配的一般性方法及其主电路参数确定方法;为解决ST机械有载分接开关和UPFC电力电子开关二者响应速度的协调问题,提出了一种基于预测电流控制的潮流控制策略,并在Simulink中搭建220 kV双回线路及三机九节点系统进行仿真。仿真结果验证了HPFC容量分配方法正确有效,且预测电流控制策略能够合理计算抽头位置,减缓过渡电流对HPFC控制系统的冲击,使系统功率快速调节至目标值。
文摘显示器电磁木马是通过控制计算机屏幕电磁辐射达到窃取信息目的的一种新型木马。当前的主流防护思想是用软件防护代替较为成熟但造价昂贵的硬件防护机制,然而目前软防护思想大多侧重于理论方法的探索,在实现机制上相对比较复杂。针对显示器电磁木马的工作特点提出了Soft-TEMPEST防护机制,设计了显示器电磁木马的ADFA(API Detection and Frequency Analysis)检测方法。该方法通过API函数序列的周期性挖掘分析,结合对屏幕像素信息的傅里叶变换及频谱分析,达到检测出木马进程的目的。测试结果表明,该方法能够成功检测出多种显示器电磁木马,而且原理简单,方便投入使用。
基金supported in part by National Key Research&Development Project of China(2017YFE0134300)in part by Shanghai 2022 Science and Technology Innovation Action Plan-Star Cultivation(Sailing Program)(22YF1415700)in part by the National Natural Science Foundation of China under Grant 52307215.
文摘The presence of renewable energy resources in LV distribution networks may lead to a distribution transformer,also known as a Smart Transformer(ST),experiencing the bidirectional power flow.Therefore,the ST must have the capability to operate in both directions.However,the reverse power is less as compared to the forward power,thus the design of ST with the same capacity in both directions increases the hardware cost and decreases the system efficiency.This paper proposes a Hybrid-modular-ST(H-ST),composed of a mixed use of single active bridge-based series resonant converter and dual active bridge instead of complete use of uni-or bi-directional converter adopted in the conventional solid-state-transformer.Based on the proposed H-ST,the impacts of power imbalance among cascaded modules in reverse operation mode are analyzed and then an effective solution based on reactive power compensation combined with the characteristics of the proposed architecture is adopted.The simulation and experimental results clearly validate the effectiveness and feasibility of the theoretical analyses.
