low frequency oscillations
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2022 ◽  
Vol 12 (2) ◽  
pp. 589
Author(s):  
Abdul Waheed Khawaja ◽  
Nor Azwan Mohamed Kamari ◽  
Muhammad Ammirrul Atiqi Mohd Zainuri

Low frequency oscillations in large power systems may result in system instability under large disturbances. Power system stabilisers (PSS) play an effective role in damping these low frequency oscillations by injecting a modulating signal in the excitation loop of a synchronous machine. A new metaheuristic optimisation algorithm termed the sine cosine algorithm (SCA) was proposed for optimising PSS controller parameters to obtain an optimal solution with the damping ratio as an objective function. The SCA technique was examined on a single machine infinite bus (SMIB) system under distinct loading situations and matched with a moth flame optimisation technique and evolutionary programming to design a robust controller of PSS. The simulation was accomplished using a linearised mathematical model of the SMIB. The performance of a designed lead lag-controller of PSS was demonstrated using eigenvalue analysis with simulations, showing promising results. The dynamic performance was validated with respect to the damping ratio, the eigenvalue’s location in the s-plane and rotor angle deviation response to demonstrate system stability.


10.5219/1711 ◽  
2022 ◽  
Vol 16 ◽  
pp. 15-26
Author(s):  
Igor Palamarchuk ◽  
Oksana Zozulyak ◽  
Mikhailo Mushtruk ◽  
Ievgenii Petrychenko ◽  
Nataliia Slobodyanyuk ◽  
...  

The process of intensifying dehydration of pectin-containing raw materials by using centrifugation with simultaneous application of low-frequency oscillations to the working container creates an electroosmotic effect in unilateral diffusion to improve the filtration process. It is established that to reduce the technological resistance in the presented methods; it is necessary to create a fluidized bed of products due to the oscillating motion of the working capacity. An experimental vibration unit has been developed to determine the rational parameters of the vibrocentric moisture removal process using the electroosmotic effect. It is proved that the complex of the designed equipment provides consecutive carrying out of three-stage vibration filtration-convective drying of high-moisture production by an alternation of action of a stream of the heat carrier, an electromagnetic field, low-frequency fluctuations. According to the research results, the dependences of the kinetics of the moisture diffusion process on the electric field strength are obtained; frequency of electric current and duty cycle of pulses, which allowed to optimize the process parameters according to the criteria of minimizing energy consumption. It was found that the processing time to achieve the desired humidity with the application of vibration, filtration, and electroosmotic effect was twice less than for filtration drying in a fixed bed. In combination with the noted physical and mechanical factors, the proposed technology improves the technical and economic parameters of the studied process.


MAUSAM ◽  
2022 ◽  
Vol 45 (3) ◽  
pp. 261-266
Author(s):  
U. S. DE ◽  
J. C. NATU

TIle'low frequency Iluctu atio ns in the troposphe ric wind field over India has been studied by spec tnuu~ na l l"i, tech nique. duri ng con trasting mon soons. namely, d rought and good monsoons ba sed on rainfall3cti\il)·. Si~ lliflc ant spectral peaks d urin g these years ha ve bee n iden tified.Zon al wind shea r in the lower tropospher ehan' also bern examin ed and the periodici ty in th e near 4()..day mode have bee n documented . Th e interannual, 'n.riill1i1ily of the mode and its potential as medium range predicti on tool has been examined in therrnpn perspect ive.


2021 ◽  
Vol 12 (1) ◽  
pp. 42
Author(s):  
Giulio Bicciato ◽  
Emanuela Keller ◽  
Martin Wolf ◽  
Giovanna Brandi ◽  
Sven Schulthess ◽  
...  

Recognition of typical patterns of brain response to external stimuli using near-infrared spectroscopy (fNIRS) may become a gateway to detecting covert consciousness in clinically unresponsive patients. This is the first fNIRS study on the cortical hemodynamic response to favorite music using a frequency domain approach. The aim of this study was to identify a possible marker of cognitive response in healthy subjects by investigating variations in the oscillatory signal of fNIRS in the spectral regions of low-frequency (LFO) and very-low-frequency oscillations (VLFO). The experiment consisted of two periods of exposure to preferred music, preceded and followed by a resting phase. Spectral power in the LFO region increased in all the subjects after the first exposure to music and decreased again in the subsequent resting phase. After the second music exposure, the increase in LFO spectral power was less distinct. Changes in LFO spectral power were more proGfirst music exposure and the repetition-related habituation effect strongly suggest a cerebral origin of the fNIRS signal. Recognition of typical patterns of brain response to specific environmental stimulation is a required step for the concrete validation of a fNIRS-based diagnostic tool.


2021 ◽  
Author(s):  
Joaquin Gonzalez ◽  
Diego M. Mateos ◽  
Matias Cavelli ◽  
Alejandra Mondino ◽  
Claudia Pascovich ◽  
...  

Recently, the sleep-wake states have been analysed using novel complexity measures, complementing the classical analysis of EEGs by frequency bands. This new approach consistently shows a decrease in EEG's complexity during slow-wave sleep, yet it is unclear how cortical oscillations shape these complexity variations. In this work, we analyse how the frequency content of brain signals affects the complexity estimates in freely moving rats. We find that the low-frequency spectrum - including the Delta, Theta, and Sigma frequency bands - drives the complexity changes during the sleep-wake states. This happens because low-frequency oscillations emerge from neuronal population patterns, as we show by recovering the complexity variations during the sleep-wake cycle from micro, meso, and macroscopic recordings. Moreover, we find that the lower frequencies reveal synchronisation patterns across the neocortex, such as a sensory-motor decoupling that happens during REM sleep. Overall, our works shows that EEG's low frequencies are critical in shaping the sleep-wake states' complexity across cortical scales.


2021 ◽  
Author(s):  
Mikhail Vladimirovich Vartanov ◽  
Zinina Inna Nikolaevna ◽  
Klimenko Irina Leontievna ◽  
Tran Dinh Van

Abstract Purpose – Providing the technological reliability of the robotic assembly of joints with RK-profile on the basis of adaptation devices and low-frequency oscillations. Design/methodology/approach – Ensuring the assembly conditions is achieved by the vibration device that provides oscillations relative to the two axes, perpendicular to the assembly direction and rotation about the assembly axis. Compensation of the linear error in the position of the parts is attained by an adaptive gripper with a flexible link. Findings – A mathematical model describing the assembly process of parts relative to the non-inertial coordinate system is developed. The technological modes of profile parts assembly are defined. Originality/value – The robotic assembly method of profile joints by the adaptation devices, namely a combination of elastic fixing of the installed profile part and the simultaneous rotation and vibration of the base part to improve the process reliability is developed. Experimental studies confirmed the adequacy of the created mathematical model. The patent for the assembly method of profile joints with a gap is received.


Author(s):  
Ahmed Hesham Abd El-Kareem ◽  
Mohamed Abd Elhameed ◽  
Mahmoud M. Elkholy

AbstractHigh penetration of renewable sources into conventional power systems results in reduction of system inertia and noticeable low-frequency oscillations (LFOs) in the rotor speed of synchronous generators. In this paper, we propose effective damping of LFOs by incorporating a supplementary damping controller with a photovoltaic (PV) generating station, where the parameters of this controller are coordinated optimally with those of a power system stabilizer (PSS). The proposed method is applied to damp local electromechanical modes by studying a system comprising a synchronous generator and a PV station connected to an infinite bus. The PV station is modeled following the instructions of the Western Electricity Coordinating Council. The problem is modeled as an optimization problem, where the damping ratio of the electromechanical modes is designed as the objective function. Constraints including upper and lower limits of decision parameters and damping ratio of other modes are considered by imposing penalties on the objective function. Different optimization algorithms are used to pursue the optimal design, such as political, improved gray wolves and equilibrium optimizers. The results validate the effectiveness of the proposed controller with PSS in damping local modes of oscillations.


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