Aiming at the fault line selection problem in the single-phase grounding system of the distribution network, a new fault line selection method based on VMD and permutation entropy feature extraction combined with K-means clustering algorithm is proposed. This method is a hybrid algorithm that can effectively identify fault line selection. Firstly, a simulation model is built and its zero sequence current is collected. The variational modal decomposition method is used to decompose the collected zero-sequence current into multiple intrinsic modal functions, which can not only effectively reduce the influence of harmonic components and noise in the characteristic signal but also facilitate the calculation. The extracted intrinsic mode function is calculated by permutation entropy (PE), and the calculated entropy value is constructed into a matrix to highlight the fault characteristics of the line; then, the matrix is subjected to K-means cluster analysis through the preprocessing algorithm and the faulty line is correctly distinguished. Then, regression verification is performed. Finally, it is verified by the recorded wave data of the real test site and then analyzed and compared with other algorithms. The proposed method shows that when a single-phase ground fault occurs, the ground fault line selection can be effectively identified under different transition resistances, grounding resistances, and fault distances. Therefore, this method can accurately identify the fault line selection, and the accuracy rate is 100%, which has a certain use value.
Recognizing vehicle license plate image captured in low illumination place is a difficult problem. To solve the problem, this paper proposes a new license plate image enhancement method using bidimensional empirical mode decomposition (BEMD) technique. BEMD is a 2D data-driven adaptive nonlinear signal decomposition approach derived from the 1D empirical mode decomposition (EMD). In the proposed algorithm, the main procedures are designed as the following: first, the license plate image is denoised by the use of alpha-trimmed mean filter and transformed from RGB color space into HSV color space, then, extract the V component to form intensity image for enhancement; second, with BEMD method, the intensity image is decomposed into a number of intrinsic mode functions (IMF) as well as a residual image; last, the brightness of residual image is adjusted using Retinex theory, and fused with the IMF images to achieve enhancement of license plate image. Experimental results show the proposed method provides superior performance over traditional schemes for license plate image enhancement in low illumination
Zr1-xAlxV2-xMoxO7 (0 x 0.9) is developed by the solid state method, and the near-zero thermal expansion is realized by adjusting the quantity of substitution of Al3+/Mo6+ for Zr4+/V5+ in ZrV2O7. For smaller x values (x 0.3), the samples remain the same cubic structure as that of ZrV2O7. The Coulomb interaction between (Al/Zr)- and (Mo/V)+ increases gradually with increasing the quantity of dual-ion substitution of Al3+/Mo6+ for Zr4+/V5+ in ZrV2O7, which reduces the fraction of the distortionless cubic structure in the sample. For x 0.7, the cubic structures could not be found. For Zr0.5Al0.5V1.5Mo0.5O7, near-zero thermal expansion is obtained in a temperature range from 425 to 750 K (-0.3910-6 K-1). The mechanism of low thermal expansion of Zr0.5Al0.5V1.5Mo0.5O7 could relate to the distortion of crystal structure due to partial substitution of Al3+/Mo6+ for Zr4+/V5+ in ZrV2O7 and the effect of the substitution on the unsubstituted lattice.
After a fault occurs in a high-voltage direct current transmission (HVDC) line, the natural frequency of the fault wave contains a wealth of transient information. The mathematical relationship between the main component of the natural frequency and the fault point can be determined and used for rapid and high-precision fault locations. To accurately extract the natural frequency of a fault and improve the positioning accuracy, a single-ended ranging scheme for extracting the natural frequency of an HVDC transient traveling wave based on the rotation-invariant technology signal parameter estimation algorithm (TLS-ESPRIT) and the total least square method is proposed for the first time. The simulation platform is used to build a dual-ended unipolar and bipolar DC transmission system model, and the scheme is simulated and verified for metallic grounding at different locations and with different transition resistances at the same location. The verification experiment was carried out on the recorded wave data of the “3.21” grounding fault of the Tianguang (Tianshengqiao-Guangdong) DC line. The results showed that the algorithm can rapidly locate the ground fault in the HVDC line and provide high ranging accuracy and good practicality.
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