scholarly journals A Hilbert–Huang Transform-Based Adaptive Fault Detection and Classification Method for Microgrids

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5040
Author(s):  
Yijin Li ◽  
Jianhua Lin ◽  
Geng Niu ◽  
Ming Wu ◽  
Xuteng Wei
Keyword(s):  
Fault Detection ◽  
Phase Difference ◽  
High Frequency ◽  
Frequency Component ◽  
High Frequency Component ◽  
Hilbert Huang Transform ◽  
Instantaneous Phase ◽  
Fault Type ◽  
Fault Detection And Classification ◽  
Fault Characteristic

Fault detection in microgrids is of great significance for power systems’ safety and stability. Due to the high penetration of distributed generations, fault characteristics become different from those of traditional fault detection. Thus, we propose a new fault detection and classification method for microgrids. Only current information is needed for the method. Hilbert–Huang Transform and sliding window strategy are used in fault characteristic extraction. The instantaneous phase difference of current high-frequency component is obtained as the fault characteristic. A self-adaptive threshold is set to increase the detection sensitivity. A fault can be detected by comparing the fault characteristic and the threshold. Furthermore, the fault type is identified by the utilization of zero-sequence current. Simulations for both section and system have been completed. The instantaneous phase difference of the current high-frequency component is an effective fault characteristic for detecting ten kinds of faults. Using the proposed method, the maximum fault detection time is 13.8 ms and the maximum fault type identification time is 14.8 ms. No misjudgement happens under non-fault disturbance conditions. The simulations indicate that the proposed method can achieve fault detection and classification rapidly, accurately, and reliably.

Laser-Generated Ultrasonic Technique for Inspecting Delamination in CFRP

2006 ◽  
Vol 321-323 ◽  
pp. 968-971
Author(s):  
Won Su Park ◽  
Sang Woo Choi ◽  
Joon Hyun Lee ◽  
Kyeong Cheol Seo ◽  
Joon Hyung Byun
Keyword(s):  
High Frequency ◽  
Ultrasonic Method ◽  
Piezoelectric Sensor ◽  
Frequency Component ◽  
Guided Wave ◽  
Center Frequency ◽  
High Frequency Component ◽  
Ultrasonic Technique ◽  
Non Destructive Evaluation ◽  
Non Destructive

For improving quality of a carbon fiber reinforced composite material (CFRP) by preventing defects such as delamination and void, it should be inspected in fabrication process. Novel non-contacting evaluation technique is required because the transducer should be contacted on the CFRP in conventional ultrasonic technique during the non-destructive evaluation and these conventional contact techniques can not be applied in a novel fiber placement system. For the non-destructive evaluation of delamination in CFRP, various methods for the generation and reception of laser-generated ultrasound are applied using piezoelectric transducer, air-coupled transducer, wavelet transform technique etc. The high frequency component of laser-generated guided wave received with piezoelectric sensor disappeared after propagating through delamination region. Air-coupled transducer was tried to be adopted in reception of laser-generated guided wave generated by using linear slit array in order to generate high frequency guided wave with a frequency of 1.1 MHz. Nevertheless, it was failed to receive high frequency guided wave in using air-coupled transducer and linear slit array. Transmitted laser-generated ultrasonic wave was received on back-wall and its frequency was analyzed to establish inspecting technique to detect delamination by non-contact ultrasonic method. In a frequency spectrum analysis, intensity ratio of low frequency and center frequency was approvable parameter to detect delamination.

Hierarchal Predefined Codebook for High-Frequency Component Augmentation Image Enlargement

2010 ◽  
Author(s):  
Hakaru Tamukoh ◽  
Hideaki Kawano ◽  
Noriaki Suetake ◽  
Masatoshi Sekine ◽  
Byungki Cha ◽  
...  
Keyword(s):  
High Frequency ◽  
Frequency Component ◽  
High Frequency Component ◽  
Image Enlargement

Force fluctuations are modulated by alternate muscle activity of knee extensor synergists during low-level sustained contraction

2004 ◽  
Vol 97 (6) ◽  
pp. 2121-2131 ◽  
Author(s):  
Motoki Kouzaki ◽  
Minoru Shinohara ◽  
Kei Masani ◽  
Tetsuo Fukunaga
Keyword(s):  
Correlation Coefficient ◽  
Muscle Activity ◽  
High Frequency ◽  
Vastus Lateralis ◽  
Frequency Component ◽  
Knee Extension ◽  
Voluntary Contraction ◽  
High Frequency Component ◽  
Knee Extensors ◽  
Force Fluctuations

The study examined the hypothesis that altered synergistic activation of the knee extensors leads to cyclic modulation of the force fluctuations. To test this hypothesis, the force fluctuations were investigated during sustained knee extension at 2.5% of maximal voluntary contraction force for 60 min in 11 men. Surface electromyograms (EMG) were recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles. The SD of force and average EMG (AEMG) of each muscle were calculated for 30-s periods during alternate muscle activity. Power spectrum of force was calculated for the low- (≤3 Hz), middle- (4–6 Hz), and high-frequency (8–12 Hz) components. Alternate muscle activity was observed between RF and the set of VL and VM muscles. The SD of force was not constant but variable due to the alternate muscle activity. The SD was significantly greater during high RF activity compared with high VL and VM activity ( P < 0.05), and the correlation coefficient between the SD and AEMG was significantly greater in RF [0.736 (SD 0.095), P < 0.05] compared with VL and VM. Large changes were found in the high-frequency component. During high RF activity, the correlation coefficient between the SD and high-frequency component [0.832 (SD 0.087)] was significantly ( P < 0.05) greater compared with other frequency components. It is suggested that modulations in knee extension force fluctuations are caused by the unique muscle activity in RF during the alternate muscle activity, which augments the high-frequency component of the fluctuations.

scholarly journals High Frequency Resonance Damping Method for Voltage Source Converter Based on Voltage Feedforward Control

Energies ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1591
Author(s):  
Bo Pang ◽  
Feng Li ◽  
Hui Dai ◽  
Heng Nian
Keyword(s):  
High Frequency ◽  
Feedforward Control ◽  
Frequency Component ◽  
Voltage Source ◽  
High Frequency Component ◽  
Voltage Source Converter ◽  
Frequency Resonance ◽  
Significant High Frequency ◽  
Resonance Damping ◽  
High Frequency Resonance

High frequency resonance (HFR) is a subsistent problem which affects the operation of the voltage source converter (VSC) connected to the parallel compensated grid. The appearance of HFR introduces a significant high frequency component in the grid voltage, thereby the operation of VSC system will be seriously affected. For enhancing the operation capability of VSC system, an HFR damping method based on the voltage feedforward control is proposed in this paper, which can reshape the VSC system impedance effectively in a wideband range. Besides, different with the existing HFR damping methods, the proposed method introduces a correction factor instead of the series virtual impedance with fixed value, so that the effect of impedance reshaping is irrelevant to the parameters of controlled object. In addition, this paper analyzes the fundamental control performance of VSC system after equipping the proposed method, for verifying that the proposed method will not worsen the fundamental control. Experimental results are given to validate the effectiveness of the proposed damping method.

scholarly journals Extreme prolongation of expiration breathing: Effects on electroencephalogram and autonomic nervous function

2018 ◽  
Vol 10 (2) ◽  
pp. 62-65
Author(s):  
Teruhisa Komori
Keyword(s):  
High Frequency ◽  
Frequency Ratio ◽  
Low Frequency ◽  
Frequency Component ◽  
Small Sample ◽  
High Frequency Component ◽  
Deep Breathing ◽  
Continuous Eeg ◽  
Nervous Function ◽  
Electrocardiogram Ecg

To clarify the physiological and psychological effects of deep breathing, the effects of extreme prolongation of expiration breathing (Okinaga) were investigated using electroencephalogram (EEG) and electrocardiogram (ECG). Participants were five male Okinaga practitioners in their 50s and 60s. Participants performed Okinaga for 31 minutes while continuous EEG and ECG measurements were taken. After 16 minutes of Okinaga, and until the end of the session, the percentages of theta and alpha 2 waves were significantly higher than at baseline. After 20 minutes, and until the end of the session, the percentage of beta waves was significantly lower than at baseline. The high frequency component of heart rate variability was significantly lower after 12 minutes of Okinaga and lasted until 23 minutes. The low frequency/high frequency ratio was significantly lower after 18 minutes of Okinaga and until the end of the session. Okinaga produced relaxation, suggesting that deep breathing may relieve anxiety. However, study limitations include potential ambiguity in the interpretation of the low frequency/high frequency ratio, the small sample, and the fact that EEG was measured only on the forehead.

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