Voltage sags was a common power system disturbance, usually associated with power system faults. Nowadays, there were more and more methods to detect voltage sag, involving with RMS, peak voltage detect, FFT. Owing to their defections, they were too slow when they came to being applied to detect voltages sags. This paper presents a method based on wavelet energy entropy detection voltage sags, this method can detect the drop time quickly and sensitively. In order to verify the feasibility of the proposed method, a numerical example simulation has been done based on matlab / simulink , results show that there is a significant effect.
In this paper, a two-sided tag antenna’s equivalent circuit model and related formulas based on the complex impedance are derived to guide the design and adjustment of a tag antenna’s structure. An ENG-inspired NFRP element is introduced in the design of the tag antenna. A two-sided UHF RFID tag antenna, only 19.2×32×0.7mm3(0.059×0.098×0.002 λ03) in size, is proposed. Its central frequency is 915MHz which can be easily adjusted according to different requirements. The bandwidth of in S11 in -3dB is 10MHz.
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