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Abstract Reliable and fast identification of high‐voltage direct current (HVDC) transmission line faults is important to the safety of power system. In traditional DC transmission line protection, differential protection is invulnerable to high fault resistance, but it needs long time delay for the influence of distributed capacitance current. In order to solve this problem, a novel pilot protection is proposed. The characteristics of the voltage and current processed by low‐pass filter under different fault conditions are analysed, and based on it the protection criteria is proposed. When external fault occurs, it reflects the line capacitance where the first forward fault traveling wave passes, which is increasing until equal to the whole line capacitance, then remains constant. However, when internal fault occurs, its value is negative in the initial stage, and after that its value is very different from the whole line capacitance. The analysis proves that this pilot protection method has fast operation speed, and can be applied for a relatively long period of time. What is more, the applicable time of superposition principle is considered in the analysis, which is not considered in many literatures. An UHVDC system is modelled for simulation in PSCAD/EMTDC, and the correctness and effectiveness of the proposed scheme is verified.

Reliable and fast identification of high‐voltage direct current (HVDC) transmission line faults is important to the safety of power system. In traditional DC transmission line protection, differential protection is invulnerable to high fault resistance, but it needs long time delay for the influence of distributed capacitance current. In order to solve this problem, a novel pilot protection is proposed. The characteristics of the voltage and current processed by low‐pass filter under different fault conditions are analysed, and based on it the protection criteria is proposed. When external fault occurs, it reflects the line capacitance where the first forward fault traveling wave passes, which is increasing until equal to the whole line capacitance, then remains constant. However, when internal fault occurs, its value is negative in the initial stage, and after that its value is very different from the whole line capacitance. The analysis proves that this pilot protection method has fast operation speed, and can be applied for a relatively long period of time. What is more, the applicable time of superposition principle is considered in the analysis, which is not considered in many literatures. An UHVDC system is modelled for simulation in PSCAD/EMTDC, and the correctness and effectiveness of the proposed scheme is verified. [ABSTRACT FROM AUTHOR]

Due to the fast speed or long imaging distance, the road traffic monitoring image is blurred, and there are some problems such as incomplete, wrong extraction and low contrast when extracting the image. There- fore, a road traffic fuzzy image enhancement method based on multi-scale Retinex is proposed. The image is de- composed into low frequency component and high frequency component by Shearlet transform. Linear mapping is used to map the low-frequency coefficients to a specific interval for normalization, and multi-scale Retinex is used to enhance the low-frequency components. Robust median method and hard threshold shrinkage method are used to remove noise and illumination interference in each scale and direction of high frequency component. The fuzzy contrast and linear membership function are used to fuse the two parts of the image, and finally the enhanced clear image is obtained. The experimental results show that the proposed method can optimize the image visual effect, highlight the image detail features, and has good noise suppression performance. Compared with the genera- tive adversarial network method and the feature pyramid method, the peak signal-to-noise ratio, structural simi- larity, information entropy, average gradient and spatial frequency of the image are better. [ABSTRACT FROM AUTHOR]

In this paper, a modified multiple-parameter fractional Fourier transform (MMPFRFT) is proposed which is another form of fractional Fourier transform in term of its degree of freedom. The defect has been found in encryption technique, illustrated in (R. Tao, J. Lang, Y. Wang, Opt. Lett. 33 (06) (2008) 581–583), dissolved and verification has been done on MATLAB ® . A novel technique for single channel, four-image encryption is also proposed based on MMPFRFT and pixel scrambling technique. The low frequency components which are extracted from four primitive images and placed in the center position, have utilized pixel scrambling technique and then encrypted based on MMPFRFT. Scrambling technology is utilized to enhance the security of the system. Numerical simulations are presented and it is claimed that this technique is superior to the existing techniques (Z. Liu et al., Optik 122 (11) (2011) 1010–1013, J. Wu, X. Luo, N. Zhou, Opt. Laser Technol. 45 (2013) 571–577). [ABSTRACT FROM AUTHOR]

This work proposes evidence using zero frequency filtering (ZFF) that gives an approximate measure of vocal tract constriction in terms of the low frequency component present in the speech signal. The vocal tract is completely closed in the case of voice bars and nasals and is wide open for low vowels. Intermediate cases are for high vowels, semivowels, laterals, voiced fricatives and other sounds. Vocal tract constriction affects the spectrum by reducing the first formant and attenuating the amplitude of the spectrum. The attenuation is relatively high in higher frequencies resulting in an increase in the low frequency component. The proposed method exploits the sinusoid like nature of ZFF signal (ZFFS) to obtain the evidence. Epoch synchronous analysis is performed and the ZFFS between successive epochs is compared with the corresponding speech segment using a cosine kernel. The low frequency dominant voiced regions match closely with ZFFS as compared to other regions and hence give higher value. This evidence when used as a feature gives relatively higher performance for the constricted phones in an HMM-based phoneme recognizer. [ABSTRACT FROM AUTHOR]

Several spectrum correction approaches have been developed, but their improvements deteriorate significantly when they are applied to the correction of the low frequency component (LFC). It is due to that the parameter model underlying the conventional approaches neglects the influence of the negative frequency in the real signal. A new approach is proposed to obtain the LFC parameters from fast Fourier transform (FFT) spectrum lines, which can take into account the contribution from the negative frequency. This explicit approach works only for the rectangular window, and makes use of three spectrum lines around the spectrum main lobe. The proposed approach has been validated by 351 × 180 simulation signal samples. The parameters in these simulated samples distribute widespread. The oscillating cycles covered in record (CiR) range from 1 to 8 by 0. 02, and each CiR case included series samples with the initial phases increased from 0° to 179° by 1°. The maximum error by the proposed approach among 180 phase samples for each CiR is inspected. The simulation results show that so far as the aforementioned widespread parameters range is concerned, the frequency error of the proposed approach is no greater than 0. 000 6Δω, where Δω is the FFT resolution. The errors of the amplitude and phase are not greater than 0. 3% and 0. 3°, respectively. The general trend of error decreases as the CiR increases, but fluctuation indeed exists with the local minimum error aligning with the coherent sampling where the CiR is an integer. [ABSTRACT FROM AUTHOR]