Journal articles on the topic 'Low-frequency oscillations (LFO)'
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1
Wang, Xiaoli, and Qi Zhou. "Application of Hilbert Spectrum based on SWT to Low-Frequency Oscillation Analysis." Journal of Physics: Conference Series 2378, no. 1 (December 1, 2022): 012032. http://dx.doi.org/10.1088/1742-6596/2378/1/012032.
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Abstract Low-frequency oscillation (LFO) appears in power systems with fast excitation of a unit or large-scale connections. An LFO signal exhibits typical nonstationary and time-varying characteristics. The paper proposed an LFO analyzing technique through the Hilbert spectrum of stationary wavelet transform (SWT). The SWT-based Hilbert spectrum contains time-varying and frequency information of LFO. The analytic framework is introduced, SWT is formulated to decompose an LFO signal into the sum of several coefficient components, the instantaneous parameters of each coefficient are then individually calculated, the complete time-frequency distribution is combined, and finally, the time-varying oscillations characteristics parameters are extracted. The simulation shows that the proposed method effectively reveals time-frequency features of the LFO signal.
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Feng, Chen, and Tang. "Identification of Low Frequency Oscillations Based on Multidimensional Features and ReliefF-mRMR." Energies 12, no. 14 (July 18, 2019): 2762. http://dx.doi.org/10.3390/en12142762.
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Low frequency oscillations (LFOs) in power systems usually fall into two types, i.e., forced oscillations and natural oscillations. Waveforms of the two are similar, but the suppression methods are different. Therefore, it is important to accurately identify LFO type. In this paper, a method for discriminating LFO type based on multi-dimensional features and a feature selection algorithm combining ReliefF and minimum redundancy maximum relevance algorithm (mRMR) is proposed. Firstly, 53 features are constructed from six aspects—time domain, frequency domain, energy, correlation, complexity, and modal analysis—which comprehensively characterize the multidimensional features of LFO. Then, the optimal feature subset with greater relevance and less redundancy is extracted by ReliefF-mRMR. In order to improve the classification performance, a modified Support Vector Machine (SVM) with Genetic Algorithm (GA) optimizing the key parameters is adopted, which is conducted in MATLAB. Finally, in 179-bus system, the samples of LFOs are generated by the Power System Analysis Toolbox (PSAT) and the accuracy of the LFO type identification model is verified. In ISO New England and East China power grid, it is proven that the proposed method can accurately identify LFO type considering the influences of noise, oscillation mode, and data incompletion. Hence, it has good robustness, noise immunity, and practicability.
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Zahalan, Arizadayana, Noor Fazliana Fadzail, and Muhammad Irwanto Misrun. "Comparing the Performance of UPFC Damping Controller on Damping Low Frequency Oscillations." Applied Mechanics and Materials 793 (September 2015): 242–46. http://dx.doi.org/10.4028/www.scientific.net/amm.793.242.
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This paper compares the performance of UPFC damping controller (, and ) to damp Low Frequency Oscillations (LFO) in power system equipped with UPFC based on Fuzzy Logic Power System Stabilizer (UPFC based FLPSS). The power system model was developed using linearized model of Phillips-Heffron Single Machine Infinite Bus (SMIB) and simulated in Matlab Simulink. The ability of each controller to damp LFO present in the rotor speed was monitored when the system being perturbed by small disturbances. The results obtained shown that UPFC controller had better performance to damp LFO compared to the other UPFC damping controllers as it had the lowest overshoot and less settling time.
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Song, Hua, and Yongjun Chen. "Study of WAMS Big Data Elastic Store Model in Low-Frequency Oscillation Analysis." Mathematical Problems in Engineering 2020 (September 22, 2020): 1–8. http://dx.doi.org/10.1155/2020/3541973.
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Low-frequency oscillation (LFO) is among the key factors that threaten interconnected power grids’ security and stability and restrict transfer capability. In particular, power systems incur now and then weak damping and forced oscillations. To monitor and control LFO, the principles of online calculation and analysis of two types of LFO are studied in this paper. The big data of wide area measurements is an important information source of LFO analysis. Hence, we should make sure it has access to online system continuously, accurately, and reliably. Nevertheless, the conventional linear data store model has difficulty to meet the processing requirements of high rate, multiple concurrency, and high reliability. To deal with it, a new model of double-set elastic store is proposed in this paper. It transforms the storage space linear model to plane model, realizes the management of power system substation group sets in vertical direction and the management of multiple Phase Measurement Units (PMU) uploading data sets in horizontal direction, and hence solves the problems in continuous and reliable access of the wide area measurements data, which is dense and of large scale and has quick update rate, providing technical support of accuracy and robustness of LFO analysis. The performance test and practical application of the proposed new model of double-set elastic store validate its accuracy.
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Lu, Chia Liang, and Pei Hwa Huang. "Power System Stability Study with Empirical Mode Decomposition." Advanced Materials Research 732-733 (August 2013): 905–8. http://dx.doi.org/10.4028/www.scientific.net/amr.732-733.905.
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Low frequency oscillations (LFO) reflect the damping and the stability of a power system and is essentially non-stationary. The LFO is a composite response of various oscillation modes and of which the frequency may be changing with time; thus, direct analysis of such time-domain responses is difficult. The main purpose of this paper is to apply the method of empirical mode decomposition (EMD) to the study of power system stability. First the method of EMD is to expand the time-domain responses under study into multiple intrinsic mode functions (IMFs). Then the 2D time-frequency information inherent in the response under study is obtained using the wavelet transform. The 2D time-frequency graph is further expanded into a 3D time-frequency-energy graph. Information from the 3D time-frequency graph is analyzed to determine those generators that have higher extent of oscillation involvement during the occurrence of LFO in the power system. The results from comparative analysis show that, at specific frequencies from LFOs, higher extent of oscillation involvement will reveal a greater factor of involvement in the frequency domain behavior.
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Bicciato, Giulio, Emanuela Keller, Martin Wolf, Giovanna Brandi, Sven Schulthess, Susanne Gabriele Friedl, Jan Folkard Willms, and Gagan Narula. "Increase in Low-Frequency Oscillations in fNIRS as Cerebral Response to Auditory Stimulation with Familiar Music." Brain Sciences 12, no. 1 (December 29, 2021): 42. http://dx.doi.org/10.3390/brainsci12010042.
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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 after first 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.
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Gonzalez-Jimenez, David, Jon Del-Olmo, Javier Poza, Fernando Garramiola, and Patxi Madina. "Data-Driven Low-Frequency Oscillation Event Detection Strategy for Railway Electrification Networks." Sensors 23, no. 1 (December 26, 2022): 254. http://dx.doi.org/10.3390/s23010254.
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Low-frequency oscillations (LFO) occur in railway electrification systems due to the incorporation of new trains with switching converters. As a result, the increased harmonic content can cause catenary stability problems under certain conditions. Most of the research published on this topic to date is focused on modelling the event and analysing it using frequency spectrums. However, in recent years, due to the new technologies linked to Big Data (BD) and data mining (DM), a new opportunity to study and detect LFO events by means of machine-learning (ML) methods has emerged. Trains continuously collect data from the most important catenary variables, which offers new resources for analysing this type of event. Therefore, this article presents the design and implementation of a data-driven LFO event detection strategy for AC railway network scenarios. Compared to previous investigations, a new approach to analyse and detect LFO events, based on field data and ML, is presented. To obtain the most appropriate detection approach for the context of this application, on the one hand, this investigation includes a comparison of machine-learning algorithms (support vector machine, logistic regression, random forest, k-nearest neighbours, naïve Bayes) which have been trained with real field data. On the other hand, an analysis of key parameters and features to optimize event detection is also included. Thus, the most significant result of this work is the high metric values of the solution, reaching values above 97% in accuracy and 93% in F-1 score with the random forest algorithm. In addition, the applicability and training of data-driven methods with real field data are demonstrated. This automatic detection strategy can help with speeding up and improving LFO detection tasks that used to be performed manually. Finally, it is worth mentioning that this research has been structured based on the CRISP-DM methodology, established as the de facto approach for industrial DM projects.
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Neda, Omar Muhammed. "Optimal coordinated design of PSS and UPFC-POD using DEO algorithm to enhance damping performance." International Journal of Electrical and Computer Engineering (IJECE) 10, no. 6 (December 1, 2020): 6111. http://dx.doi.org/10.11591/ijece.v10i6.pp6111-6121.
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Low-frequency oscillations (LFO) are an inevitable problem of power systems and they have a great effect on the capability of transfer and power system stability. The power system stabilizers (PSSs) as well as flexible AC transmission system (FACTS) devices can help to damp LFO. The target of this study is to tackle the problem of a dual-coordinated design between PSS and unified power flow controller (UPFC) implementing the task of power oscillation damping (POD) controller in a single machine infinite bus (SMIB) system. So, dolphin echolocation optimization (DEO) technique is utilized as an optimization tool to search for optimal parameter tunings based on objective function for enhancing the dynamic stability performance for a SMIB. DEO an algorithm has a few parameters, simple rules, provides the optimum result and is applicable to a wide range of problems like other meta-heuristic algorithms. Use DEO gave the best results in damping LFO compared to particle swarm optimization (PSO) algorithm. From the comparison results between PSO and DEO, it was shown that DEO provides faster settling time, less overshoot, higher damping oscillations and greatly improves system stability. Also, the comparison results prove that the multiple stabilizers show supremacy over independent controllers in mitigationg LFO of a SMIB.
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Anarkooli, M. Yousefi, and H. Afrakhteh. "Improvement Model Damping Low Frequency Oscillations Presence UPFC by Cuckoo Optimization Algorithm." Indonesian Journal of Electrical Engineering and Computer Science 3, no. 1 (July 1, 2016): 67. http://dx.doi.org/10.11591/ijeecs.v3.i1.pp67-79.
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<p>Low frequency oscillation (LFO) is a negative phenomenon repeated for the power system increases the risk of instability. In recent years, power systems stabilizer (PSS) for damping low frequency oscillations is used. With FACTS devices such as integrated power flow controller (UPFC) can control power flow and transient stability increase. So, UPFC low frequency oscillation damping can be used instead of PSS. UPFC through direct control voltage and low frequency oscillation damping can be improved. In this study, a single linear model of synchronous machine connected to an infinite bus Heffron-Philips in the presence of UPFC to improve low frequency oscillation damping is used. The selection of the output feedback parameters for the UPFC controllers is converted to an optimization problem which is solved by cuckoo optimization algorithm (COA). COA, as a new evolutionary optimization algorithm, is used in multiple applications. This optimization algorithm has a strong ability to find the most optimistic results for dynamic stability improvement. The controller UPFC and damping in MATLAB software environment is designed and simulated. The simulation was performed for a variety of loads and for various loads and more effective UPFC controller electromechanical oscillation damping compared to other algorithm types is shown.</p>
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Yin, Liyong, Fan Tian, Rui Hu, Zhaohui Li, and Fuzai Yin. "Estimating Phase Amplitude Coupling between Neural Oscillations Based on Permutation and Entropy." Entropy 23, no. 8 (August 18, 2021): 1070. http://dx.doi.org/10.3390/e23081070.
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Cross-frequency phase–amplitude coupling (PAC) plays an important role in neuronal oscillations network, reflecting the interaction between the phase of low-frequency oscillation (LFO) and amplitude of the high-frequency oscillations (HFO). Thus, we applied four methods based on permutation analysis to measure PAC, including multiscale permutation mutual information (MPMI), permutation conditional mutual information (PCMI), symbolic joint entropy (SJE), and weighted-permutation mutual information (WPMI). To verify the ability of these four algorithms, a performance test including the effects of coupling strength, signal-to-noise ratios (SNRs), and data length was evaluated by using simulation data. It was shown that the performance of SJE was similar to that of other approaches when measuring PAC strength, but the computational efficiency of SJE was the highest among all these four methods. Moreover, SJE can also accurately identify the PAC frequency range under the interference of spike noise. All in all, the results demonstrate that SJE is better for evaluating PAC between neural oscillations.
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Gholizadeh-Roshanagh, Reza, Behrouz Mohammadzadeh, and Sajad Najafi-Ravadanegh. "Optimal Siting of UPFC on a Transmission Line with the Aim of Better Damping of Low Frequency Oscillations." ECTI Transactions on Electrical Engineering, Electronics, and Communications 14, no. 1 (June 27, 2015): 56–64. http://dx.doi.org/10.37936/ecti-eec.2016141.171096.
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Low frequency oscillations may cause blackouts. Power system operators are increasingly facing instability problems due to the fact that the current system is much more loaded than before. Tuning the lead-lag controllers, as power system stabilizers (PSS) or FACTS-based supplementary stabilizers, is a well-established method to enhance the damping capability of power systems. In this paper we propose a technique to optimally locate the place of unified power flow controller (UPFC) on a transmission line considering low frequency oscillation (LFO) damping. The proposed method is applied to a single machine infinite bus system equipped with UPFC and the results obtained show its superiority.
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Tong, Yunjie, Kimberly P. Lindsey, and Blaise deB Frederick. "Partitioning of Physiological Noise Signals in the Brain with Concurrent Near-Infrared Spectroscopy and fMRI." Journal of Cerebral Blood Flow & Metabolism 31, no. 12 (August 3, 2011): 2352–62. http://dx.doi.org/10.1038/jcbfm.2011.100.
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The blood–oxygen level dependent (BOLD) signals measured by functional magnetic resonance imaging (fMRI) are contaminated with noise from various physiological processes, such as spontaneous low-frequency oscillations (LFOs), respiration, and cardiac pulsation. These processes are coupled to the BOLD signal by different mechanisms, and represent variations with very different frequency content; however, because of the low sampling rate of fMRI, these signals are generally not separable by frequency, as the cardiac and respiratory waveforms alias into the LFO band. In this study, we investigated the spatial and temporal characteristics of the individual noise processes by conducting concurrent near-infrared spectroscopy (NIRS) and fMRI studies on six subjects during a resting state acquisition. Three time series corresponding to LFO, respiration, and cardiac pulsation were extracted by frequency from the NIRS signal (which has sufficient temporal resolution to critically sample the cardiac waveform) and used as regressors in a BOLD fMRI analysis. Our results suggest that LFO and cardiac signals modulate the BOLD signal independently through the circulatory system. The spatiotemporal evolution of the LFO signal in the BOLD data correlates with the global cerebral blood flow. Near-infrared spectroscopy can be used to partition these contributing factors and independently determine their contribution to the BOLD signal.
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Islam, Naz Niamul, M. A. Hannan, Hussein Shareef, and Azah Mohamad. "Bijective Differential Search Algorithm for Robust Design of Damping Controller in Multimachine Power System." Applied Mechanics and Materials 785 (August 2015): 424–28. http://dx.doi.org/10.4028/www.scientific.net/amm.785.424.
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Low frequency oscillation (LFO) is a serious threat to the interconnection of power system and its safe operation. In this paper, optimum damping performances over LFO is achieved by implementing Bijective Differential Search Algorithm (B-DSA) to large interconnected power system. Conventional two stages lead-lag compensator is optimized as the Power System Stabilizer (PSS) and Linear Time Invariant (LTI) State Space system models are used to conduct stability analysis of power system. The tuning problem of PSS in multimachine system was formulated as a multi-objectives function. The simulations are conducted in 5-AREA 16 Machine test power system for severe system fault in order to verify the robust design of damping controller. The obtained results are compared with standard DSA optimization technique. The findings show the improved damping achieved by B-DSA than DSA algorithm. The settling times achieved using B-DSA based designed PSSs are 3.74sec and 4.57sec for local mode and inter-area mode of oscillations respectively. The successful damping over oscillation modes of LFO justifies the proposed technique is efficient for the improvement of power system security in adverse condition.
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Tumanov, Issakul, Seitzhan Orynbayev, Birzhan Baibutanov, Alexey Kruglikov, and Piotr Kacejko. "Modeling of Physical Subsystem Using an Example of Electromagnetic Exciter of Low-Frequency Oscillations." Applied Mechanics and Materials 736 (March 2015): 97–102. http://dx.doi.org/10.4028/www.scientific.net/amm.736.97.
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This work is devoted to modeling of physical subsystem, considering an electromagnetic exciter of low-frequency oscillations (EME LFO) as it, which is a classic example of an electromechanical system. For the simulation of electromagnetic exciter of low frequencies Simscape was chosen. Based on the principle of operation (reciprocating motion due to the configuration of the resonance circuit), and the structure of the apparatus, there is detected the operation character with several types of energy conversion: electrical to magnetic and magnetic to mechanical. And the main requirement to the developed model is the conservation of energy and power under the corresponding transformations.
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ALMa’aitah, Mohammad A., Tha’er O. Sweidan, Mohammed I. Abuashour, and Mohammed Al-Hattab. "Analysis of Inter Area Power System Oscillation using Eigenvalue Method." International Journal of Contemporary Research and Review 9, no. 06 (June 1, 2018): 20417–37. http://dx.doi.org/10.15520/ijcrr/2018/9/06/514.
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One of the power system crucial problems for stability is the oscillation at low frequencies. The low frequency oscillation (LFO) is a small signal stability of the power system and has a passive impact on the maximum power transfer (load flow) in power systems. The inter area oscillation using eigenvalue method is presented and analyzed by modeling and linearizing the system around the operating point. This paper introduces the inter area oscillation using Eigen value method by presenting and discussing a proposed power system of two-area, 4-machine into two different cases: The first case is the system running without power system stabilizer, and the second case is to deploy the power system stabilizer firstly in area 1 afterwards area 2 and finally in the two areas at the same time. The advantage of the damping of oscillations is found clearly in the system ability to increase the tie-line power flowing in the proposed system. All simulations results are carried out using MATLAB software.
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Pagard, Elahe, Shahrokh Shojaeian, and Mohammad Mahdi Rezaei. "Damping of Low-Frequency Oscillations in a Power System, Based on Multiple-Model Optimal Control Strategy." International Transactions on Electrical Energy Systems 2023 (January 9, 2023): 1–10. http://dx.doi.org/10.1155/2023/3992158.
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This paper proposes a new control strategy based on multimodel linear optimization control (MMLOC) to damp power system low-frequency oscillations (LFO) faster. The multimodel control strategy is used to anticipate synchronous generator dynamic behavior and linear optimization control for generating a control signal uncomplicatedly. The third-order model of synchronous machine is considered for each of the models. The probability of each model’s validity is evaluated from the difference between model outputs and the same actual power system outputs via the Bayesian approach. To improve the postfault dynamics of the case study power system, which contains a static VAR compensator, a linear optimal controller (LOC) is designed. The 8th order model of the machines is used in simulations to represent the plant as accurately as possible.
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Olivieri, Carlo, Francesco de Paulis, Antonio Orlandi, Cosimo Pisani, Giorgio Giannuzzi, Roberto Salvati, and Roberto Zaottini. "Estimation of Modal Parameters for Inter-Area Oscillations Analysis by a Machine Learning Approach with Offline Training." Energies 13, no. 23 (December 4, 2020): 6410. http://dx.doi.org/10.3390/en13236410.
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An accurate monitoring of power system behavior is a hot-topic for modern grid operation. Low-frequency oscillations (LFO), such as inter-area electromechanical oscillations, are detrimental phenomena impairing the development of the grid itself and also the integration of renewable sources. An interesting countermeasure to prevent the occurrence of such oscillations is to continuously identify their characteristic electromechanical mode parameters, possibly realizing an online monitoring system. In this paper an attempt to develop an online modal parameters identification system is done using machine learning techniques. An approach based on the development of a proper artificial neural network exploiting the frequency measurements coming from actual PMU devices is presented. The specifically developed offline training stage is fully detailed. The output results from the dynamic mode decomposition method are considered as reference in order to validate the machine learning approach. Some results are presented in order to validate the effectiveness of the proposed approach on data coming from recordings of real grid events. The main key points affecting the performance of the proposed technique are discussed by means of proper validation scenarios. This contribution is the first step of a more extended project whose final aim is the development of an artificial neural networks (ANN) architecture able to predict the system behavior (in a given time span) in terms of LFO modal parameters, and to classify the contingencies/disturbances based on an online training that has memory of the passed training samples.
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Yang, Yanan, Yujun Li, Xiaotian Yuan, Jiapeng Li, and Zhengchun Du. "Damping Torque Analysis of the PMSG-Based WT with Supplementary Damping Control for Mitigating Interarea Oscillations." International Transactions on Electrical Energy Systems 2022 (November 30, 2022): 1–15. http://dx.doi.org/10.1155/2022/2391770.
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This study presents a comprehensive analysis of the impact that a supplementary damping controller of the permanent magnet synchronous generator (PMSG)-based wind turbine (WT) has on low-frequency oscillation (LFO) damping. A reduced mathematical model of an interarea system is first established. Then, an auxiliary damping controller is designed using the PMSG active power control loop, enabling the WT to actively support the interarea LFO mitigation. Based on this, the damping torque analysis (DTA) method is applied to explore the contribution of the PMSG-based WT with an auxiliary damping controller to LFO damping enhancement, whose analytical expressions of the damping torque coefficients reveal the impacts of the control parameters and the operation conditions on the system damping characteristics. It is evident that the installation location of the wind power plant (WPP) plays a leading role in determining whether the damping provided by the PMSG controller is positive or negative. Also, the contribution of damping from the PMSG can be improved by tuning the droop coefficient of the PMSG controller properly. The results indicate that the proposed damping control is always helpful in improving the system damping when the wind power penetration increases. Accordingly, analytical conclusions can serve as guidelines for the control design. Case studies of a two-area test system integrated with a PMSG-based wind farm have been conducted to verify the theoretical analysis.
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Pathan, Md Ilius Hasan, Md Juel Rana, Mohammad Shoaib Shahriar, Md Shafiullah, Md Hasan Zahir, and Amjad Ali. "Real-Time LFO Damping Enhancement in Electric Networks Employing PSO Optimized ANFIS." Inventions 5, no. 4 (December 14, 2020): 61. http://dx.doi.org/10.3390/inventions5040061.
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In recent years, machine learning (ML) tools have gained tremendous momentum and received wide-spread attention in different segments of modern-day life. As part of digital transformation, the power system industry is one of the pioneers in adopting such attractive and efficient tools for various applications. Apparently, a nonthreatening, but slow-burning issue of the electric power systems is the low-frequency oscillations (LFO), which, if not dealt with appropriately and on time, could result in complete network failure. This paper addresses the role of a prominent ML family member, particle swarm optimization (PSO) tuned adaptive neuro-fuzzy inference system (ANFIS) for real-time enhancement of LFO damping in electric power system networks. It adopts and models two power system networks where in the first network, the synchronous machine is equipped with only a power system stabilizer (PSS), and in the other, the PSS of the synchronous machine is coordinated with the unified power flow controller (UPFC), a second-generation flexible alternating current transmission system (FACTS) device. Then, it develops the proposed ML approach to enhance LFO damping for both adopted networks based on the customary practices of statistical judgment. The performance measuring metrics of power system stability, including the minimum damping ratio (MDR), eigenvalue, and time-domain simulation, were used to analyze the developed approach. Moreover, the paper presents a comparative analysis and discussion with the referenced works’ achieved results to conclude the proposed PSO-ANFIS technique’s ability to enhance power system stability in real-time by damping out the unwanted LFO.
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Tong, Yunjie, Jinxia (Fiona) Yao, J. Jean Chen, and Blaise deB Frederick. "The resting-state fMRI arterial signal predicts differential blood transit time through the brain." Journal of Cerebral Blood Flow & Metabolism 39, no. 6 (January 15, 2018): 1148–60. http://dx.doi.org/10.1177/0271678x17753329.
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Previous studies have found that aperiodic, systemic low-frequency oscillations (sLFOs) are present in blood-oxygen-level-dependent (BOLD) data. These signals are in the same low frequency band as the “resting state” signal; however, they are distinct signals which represent non-neuronal, physiological oscillations. The same sLFOs are found in the periphery (i.e. finger tips) as changes in oxy/deoxy-hemoglobin concentration using concurrent near-infrared spectroscopy. Together, this evidence points toward an extra-cerebral origin of these sLFOs. If this is the case, it is expected that these sLFO signals would be found in the carotid arteries with time delays that precede the signals found in the brain. To test this hypothesis, we employed the publicly available MyConnectome dataset (a two-year longitudinal study of a single subject) to extract the sLFOs in the internal carotid arteries (ICAs) with the help of the T1/T2-weighted images. Significant, but negative, correlations were found between the LFO BOLD signals from the ICAs and (1) the global signal (GS), (2) the superior sagittal sinus, and (3) the jugulars. We found the consistent time delays between the sLFO signals from ICAs, GS and veins which coincide with the blood transit time through the cerebral vascular tree.
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Polyakov, I. V., G. V. Alekseev, L. A. Timokhov, U. S. Bhatt, R. L. Colony, H. L. Simmons, D. Walsh, J. E. Walsh, and V. F. Zakharov. "Variability of the Intermediate Atlantic Water of the Arctic Ocean over the Last 100 Years." Journal of Climate 17, no. 23 (December 1, 2004): 4485–97. http://dx.doi.org/10.1175/jcli-3224.1.
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Abstract Recent observations show dramatic changes of the Arctic atmosphere–ice–ocean system, including a rapid warming in the intermediate Atlantic water of the Arctic Ocean. Here it is demonstrated through the analysis of a vast collection of previously unsynthesized observational data, that over the twentieth century Atlantic water variability was dominated by low-frequency oscillations (LFO) on time scales of 50–80 yr. Associated with this variability, the Atlantic water temperature record shows two warm periods in the 1930s–40s and in recent decades and two cold periods earlier in the century and in the 1960s–70s. Over recent decades, the data show a warming and salinification of the Atlantic layer accompanied by its shoaling and, probably, thinning. The estimate of the Atlantic water temperature variability shows a general warming trend; however, over the 100-yr record there are periods (including the recent decades) with short-term trends strongly amplified by multidecadal variations. Observational data provide evidence that Atlantic water temperature, Arctic surface air temperature, and ice extent and fast ice thickness in the Siberian marginal seas display coherent LFO. The hydrographic data used support a negative feedback mechanism through which changes of density act to moderate the inflow of Atlantic water to the Arctic Ocean, consistent with the decrease of positive Atlantic water temperature anomalies in the late 1990s. The sustained Atlantic water temperature and salinity anomalies in the Arctic Ocean are associated with hydrographic anomalies of the same sign in the Greenland–Norwegian Seas and of the opposite sign in the Labrador Sea. Finally, it is found that the Arctic air–sea–ice system and the North Atlantic sea surface temperature display coherent low-frequency fluctuations. Elucidating the mechanisms behind this relationship will be critical to an understanding of the complex nature of low-frequency variability found in the Arctic and in lower-latitude regions.
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Fernandez Rojas, Raul, Mingyu Liao, Julio Romero, Xu Huang, and Keng-Liang Ou. "Cortical Network Response to Acupuncture and the Effect of the Hegu Point: An fNIRS Study." Sensors 19, no. 2 (January 18, 2019): 394. http://dx.doi.org/10.3390/s19020394.
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Acupuncture is a practice of treatment based on influencing specific points on the body by inserting needles. According to traditional Chinese medicine, the aim of acupuncture treatment for pain management is to use specific acupoints to relieve excess, activate qi (or vital energy), and improve blood circulation. In this context, the Hegu point is one of the most widely-used acupoints for this purpose, and it has been linked to having an analgesic effect. However, there exists considerable debate as to its scientific validity. In this pilot study, we aim to identify the functional connectivity related to the three main types of acupuncture manipulations and also identify an analgesic effect based on the hemodynamic response as measured by functional near-infrared spectroscopy (fNIRS). The cortical response of eleven healthy subjects was obtained using fNIRS during an acupuncture procedure. A multiscale analysis based on wavelet transform coherence was employed to assess the functional connectivity of corresponding channel pairs within the left and right somatosensory region. The wavelet analysis was focused on the very-low frequency oscillations (VLFO, 0.01–0.08 Hz) and the low frequency oscillations (LFO, 0.08–0.15 Hz). A mixed model analysis of variance was used to appraise statistical differences in the wavelet domain for the different acupuncture stimuli. The hemodynamic response after the acupuncture manipulations exhibited strong activations and distinctive cortical networks in each stimulus. The results of the statistical analysis showed significant differences ( p < 0.05 ) between the tasks in both frequency bands. These results suggest the existence of different stimuli-specific cortical networks in both frequency bands and the anaesthetic effect of the Hegu point as measured by fNIRS.
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Mijbas, Ayad Fadhil, Bahaa Aldin Abas Hasan, and Hussein Ali Salah. "Optimal Stabilizer PID Parameters Tuned by Chaotic Particle Swarm Optimization for Damping Low Frequency Oscillations (LFO) for Single Machine Infinite Bus system (SMIB)." Journal of Electrical Engineering & Technology 15, no. 4 (May 11, 2020): 1577–84. http://dx.doi.org/10.1007/s42835-020-00442-5.
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Aribowo, Widi, Bambang Suprianto, Unit Three Kartini, and Aditya Prapanca. "Dingo optimization algorithm for designing power system stabilizer." Indonesian Journal of Electrical Engineering and Computer Science 29, no. 1 (January 1, 2022): 1. http://dx.doi.org/10.11591/ijeecs.v29.i1.pp1-7.
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The dingo optimization algorithm (DOA) adopts the social life of dingo dogs. The dingo is a breed of ancient dog originating from Australia. Dingo hunting strategies such as assault with persecution, flocking, and scavenging behavior became the inspiration for DOA. In this paper, DOA is applied to a power system stabilizer (PSS) to dampen low-frequency oscillations (LFO) in a single-machine infinite bus (SMIB). DOA is used to obtain optimal parameters for PSS. The damping controller is designed for optimal lead-lag control. To obtain the performance of the DOA method, the results were compared with the uncontrolled method, conventional PSS, Whale optimization algorithm (WOA), and grasshopper optimization algorithm (GOA). Simulation using MATLAB with three different operating conditions, namely light load (20%), medium load (50%) and high load (100%). From the simulation using MATLAB with SMIB modeling, it was found that the application of the DOA method on PSS has the ability to reduce the average undershoot value by 28.16% and reduce the average undershoot value to 65.57% compared to the conventional PSS method.
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Frizzell, Tory O., Elisha Phull, Mishaa Khan, Xiaowei Song, Lukas A. Grajauskas, Jodie Gawryluk, and Ryan C. N. D’Arcy. "Imaging functional neuroplasticity in human white matter tracts." Brain Structure and Function 227, no. 1 (November 23, 2021): 381–92. http://dx.doi.org/10.1007/s00429-021-02407-4.
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AbstractMagnetic resonance imaging (MRI) studies are sensitive to biological mechanisms of neuroplasticity in white matter (WM). In particular, diffusion tensor imaging (DTI) has been used to investigate structural changes. Historically, functional MRI (fMRI) neuroplasticity studies have been restricted to gray matter, as fMRI studies have only recently expanded to WM. The current study evaluated WM neuroplasticity pre–post motor training in healthy adults, focusing on motor learning in the non-dominant hand. Neuroplasticity changes were evaluated in two established WM regions-of-interest: the internal capsule and the corpus callosum. Behavioral improvements following training were greater for the non-dominant hand, which corresponded with MRI-based neuroplasticity changes in the internal capsule for DTI fractional anisotropy, fMRI hemodynamic response functions, and low-frequency oscillations (LFOs). In the corpus callosum, MRI-based neuroplasticity changes were detected in LFOs, DTI, and functional correlation tensors (FCT). Taken together, the LFO results converged as significant amplitude reductions, implicating a common underlying mechanism of optimized transmission through altered myelination. The structural and functional neuroplasticity findings open new avenues for direct WM investigations into mapping connectomes and advancing MRI clinical applications.
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Alias, Feba, and Manohar Singh. "Coordinated control among PSS, WTG and BESS for improving Small-Signal Stability." International Journal of Emerging Electric Power Systems 22, no. 4 (June 2, 2021): 505–23. http://dx.doi.org/10.1515/ijeeps-2021-0102.
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Abstract The goal towards attaining a sustainable future has led to the rapid increase in the integration of converter control based generators (CCBGs). The low inertia response characteristics of CCBGs and the weak tie lines in interconnected systems pose a huge threat to Small-Signal Stability (SSS). Adequate damping of low-frequency oscillations (LFO) is pivotal in ensuring the maximum power transfer through the critical transmission corridors. These operational issues become more serious with the significant reduction in system inertia as a result of the high penetration of CCBGs. Therefore, appropriate control techniques are an absolute requirement for preventing LFOs from limiting the penetration of CCBGs in interconnected networks. This may also eventually lead to revisions in grid codes mandating CCBGs to provide auxiliary damping control. But, the progressive addition of multiple damping controllers for specific target modes can lead to the drifting of eigenvalues (EVs) associated with other electromechanical modes (EMs) in the system. This is due to the adverse interactions between multiple damping controllers in the uncoordinated control approach and may result in deteriorating SSS. Therefore, this paper proposes a simultaneous coordinated control among Battery Energy Storage System (BESS), Wind Turbine Generators (WTG) and Power System Stabilizer (PSS) for enhancing SSS in networks with high wind penetration by considering both inter-area (IA) and local modes. The performance of the proposed coordinated control is corroborated using IEEE 68 bus system for multiple operating scenarios for which the critical modes in the system have the lowest damping index (DI). The effectiveness of modulating the active power, reactive power and simultaneous modulation of both active and reactive power injected by BESS along with a dual-channel Optimized WTG Damping Controller (DOWDC) and PSS is evaluated. The impact of the different coordinated control strategies on voltage dynamics is also investigated. The simulation results validate the better performance of the proposed coordinated control over uncoordinated control approaches.
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Liu, Haoming, Suxiang Yang, and Xiaoling Yuan. "Inertia Control Strategy of DFIG-Based Wind Turbines Considering Low-Frequency Oscillation Suppression." Energies 15, no. 1 (December 21, 2021): 29. http://dx.doi.org/10.3390/en15010029.
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It has become a basic requirement for wind turbines (WTs) to provide frequency regulation and inertia support. The influence of WTs on the low-frequency oscillation (LFO) of the system will change after adopting inertia control methods. This paper intends to investigate and compare in detail the IC effects on LFO characteristics in two systems with different structures. First, the mechanism of inertia control of doubly fed induction generator (DFIG)-based WTs is analyzed. Then, the small-signal analysis method and modal analysis method are used to study the influence of the inertia control on the LFO characteristics based on the two-machine infinite-bus system and the four-machine two-area system, respectively. The difference in impact rules of IC on LFO is compared in detail. Finally, considering that the inertia control might worsen the LFO in some systems, an improved inertia control strategy of DFIG-based WTs is proposed to suppress the LFO. The simulation results demonstrate that, in systems with different structures, the impact rules of the inertia control parameters on LFO are different. With the improved inertia control strategy, DFIG-based WTs can suppress the LFO of the system and provide inertia support for the system.
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Qu, Bo, Jun Yong Wu, Hong Ke Ai, and Yan Heng Zhou. "Online Identification and Suppression of Low Frequency Oscillation in Power System Based on WAMS." Applied Mechanics and Materials 513-517 (February 2014): 2855–61. http://dx.doi.org/10.4028/www.scientific.net/amm.513-517.2855.
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With the assistance of Wide Area Measurement System (WAMS), this paper proposes a method based on Prony algorithm to identify Low Frequency Oscillation (LFO) online and apply Power System Stabilizer (PSS) for rapid suppression. WAMS monitors the power system in real time with high precision. When LFO occurs in the system, applying Prony algorithm to analyze the power angle, it can identify all kinds of LFO modes online. For each mode, PSS would be rapidly configured and applied into the system. When some LFO modes are successfully suppressed, the corresponding PSSs exit. Taking the 10-generator-39-bus system of New England for example, it verifies the correctness and effectiveness of the proposed approach.
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Hyun, Wonjeong, Jina Kim, Heesang Chae, and Changjin Lee. "Passive Control of Low-Frequency Instability in Hybrid Rocket Combustion." Aerospace 8, no. 8 (July 28, 2021): 204. http://dx.doi.org/10.3390/aerospace8080204.
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The occurrence of low-frequency instability (LFI) appears to be related to multiple interactions among many complex physical processes, such as vortex shedding, boundary-layer oscillation, and additional combustion in the post-combustion chamber. In this study, two combustion tests were conducted to suppress LFI and to examine which physical processes its occurrence was most sensitive. In the first test, two fuel inserts were used to modify the formation of a boundary layer, vortex shedding at the end of the fuel, and vortex impingement. In the second test, the fuel insert located at the front end was replaced with swirl injection. The first test was aimed at controlling and suppressing the initiation of LFI using fuel inserts, through which a small step appeared gradually due to differences in the regression rates of the two materials, i.e., polymethyl methacrylate and high-density polyethylene. The test results confirmed that (i) there are physical connections among several processes, such as the thermoacoustic coupling between p′and q′ and the oscillations of the upstream boundary flow, and (ii) LFI suppression is possible by disrupting or eliminating the connections among these physical processes. The second test was also aimed to control LFI while minimizing the deviation in combustion performance using proper swirl injection along with a fuel insert. Even when replaced by swirl injection, LFI suppression was still possible and showed reasonable combustion performance without causing too much deviation from the baseline in terms of the oxygen-to-fuel ratio and the fuel regression rate.
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Frutos, Paul, Philippe Ladoux, Nicolas Roux, Igor Larrazabal, Juan M. Guerrero, and Fernando Briz. "Low Frequency Stability of AC Railway Traction Power Systems: Analysis of the Influence of Traction Unit Parameters." Electronics 11, no. 10 (May 17, 2022): 1593. http://dx.doi.org/10.3390/electronics11101593.
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Dynamic interactions between AC railway electrification systems and traction unit power converters can result in low frequency oscillation (LFO) of the contact-line voltage amplitude, which can lead to a power outage of the traction substation and the shutdown of train traffic. Several system parameters can influence the low frequency stability of the railway traction power system, including contact-line length and traction unit parameters such as transformer leakage inductance, DC-link capacitance, control bandwidths and synchronization systems. This paper focuses on the influence of these parameters on the LFO. The methodology is based on a frequency-domain analysis. Nyquist and Bode diagrams are used to determine the stability limit. The validation of the method is performed through the use of time-domain simulations.
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Nicolau, Javier H., Gyungjin Choi, Jingyuan Fu, Pengfei Liu, Xishuo Wei, and Zhihong Lin. "Global gyrokinetic simulation with kinetic electron for collisionless damping of zonal flow in stellarators." Nuclear Fusion 61, no. 12 (November 12, 2021): 126041. http://dx.doi.org/10.1088/1741-4326/ac31da.
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Abstract Global gyrokinetic simulations with kinetic electrons for collisionless damping of zonal flows in LHD and W7-X stellarators show that the helical components of the equilibrium magnetic field responsible for helically trapped particles have significant impacts on zonal flow. Kinetic electrons reduce zonal flow residue and increase the frequency of low frequency oscillation (LFO). The LFO is induced by dominant helical harmonics of magnetic field strength. Furthermore, linear toroidal coupling of multiple toroidal n-harmonics barely affects the zonal flows, but can generate long wavelength toroidal harmonics with the same toroidal number as the helical magnetic field.
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Zhao, Jingbo, Ke Xu, Zheng Li, Shengjun Wu, and Dajiang Wang. "The Total Low Frequency Oscillation Damping Method Based on Interline Power Flow Controller through Robust Control." Processes 10, no. 10 (October 12, 2022): 2064. http://dx.doi.org/10.3390/pr10102064.
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The interline power flow controller (IPFC) can control the active power and reactive power of different lines in power system. To utilize the flexible control ability of IPFC and increase the damping characteristic of its controller AC system, this paper proposes a low-frequency oscillation (LFO) suppress method through IPFC. The LFO suppress method is designed by adding supplementary signals to the outer current control loop of IPFC. In addition to adding supplementary active power signals, the reactive supplementary signals are also added to related control loop, which is the total control scheme. To obtain the power system’s small signal model, the identification technology based on the PRONY algorithm is used. In addition, the robust control theory is also applied to make the controllers more adaptive. To verify the effectiveness of the proposed method, two controllers including both the active and reactive controllers are designed for in PSCAD software. Furthermore, the simulation results prove the proposed method can reach a better control effect and is also of robustness.
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Wang, Yaqi, and Zhigang Liu. "Suppression Research Regarding Low-Frequency Oscillation in the Vehicle-Grid Coupling System Using Model-Based Predictive Current Control." Energies 11, no. 7 (July 10, 2018): 1803. http://dx.doi.org/10.3390/en11071803.
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Recently, low-frequency oscillation (LFO) has occurred many times in high-speed railways and has led to traction blockades. Some of the literature has found that the stability of the vehicle-grid coupling system could be improved by optimizing the control strategy of the traction line-side converter (LSC) to some extent. In this paper, a model-based predictive current control (MBPCC) approach based on continuous control set in the dq reference frame for the traction LSC for electric multiple units (EMUs) is proposed. First, the mathematical predictive model of one traction LSC is deduced by discretizing the state equation on the alternating current (AC) side. Then, the optimal control variables are calculated by solving the performance function, which involves the difference between the predicted and reference value of the current, as well as the variations of the control voltage. Finally, combined with bipolar sinusoidal pulse width modulation (SPWM), the whole control algorithm based on MBPCC is formed. The simulation models of EMUs’ dual traction LSCs are built in MATLAB/SIMULINK to verify the superior dynamic and static performance, by comparing them with traditional transient direct current control (TDCC). A whole dSPACE semi-physical platform is established to demonstrate the feasibility and effectiveness of MBPCC in real applications. In addition, the simulations of multi-EMUs accessed in the vehicle-grid coupling system are carried out to verify the suppressing effect on LFO. Finally, to find the impact of external parameters (the equivalent leakage inductance of vehicle transformer, the distance to the power supply, and load resistance) on MBPCC’s performance, the sensitivity analysis of these parameters is performed. Results indicate that these three parameters have a tiny impact on the proposed method but a significant influence on the performance of TDCC. Both oscillation pattern and oscillation peak under TDCC can be easily influenced when these parameters change.
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Abumeteir, Hasan Ali, and Ahmet Mete Vural. "Design and Optimization of Fractional Order PID Controller to Enhance Energy Storage System Contribution for Damping Low-Frequency Oscillation in Power Systems Integrated with High Penetration of Renewable Sources." Sustainability 14, no. 9 (April 23, 2022): 5095. http://dx.doi.org/10.3390/su14095095.
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This paper proposes adding a controller to the energy storage system (ESS) to enhance their contribution for damping low-frequency oscillation (LFO) in power systems integrated with high penetration of different types of renewable energy sources (RES). For instance, wind turbines and photovoltaic (PV) solar systems. This work proposes superconducting magnetic energy storage (SMES) as an ESS. The proportional–integral–derivative (PID) and fractional-order PID (FOPID) are suggested as supporter controllers with SMES. The PID and FOPID controller’s optimal values will be obtained using particle swarm optimization (PSO) is used as the optimization method. Both local area and inter-area oscillation is considered in this work as a LFO. To investigate the impact of adding the SMES with the proposed controller, a multimachine power system with different integration scenarios and cases is carried out with a PV system and wind turbine. The system responses are presented and discussed to show the superiority of the proposed controller both in the time domain and by eigenvalues analysis.
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Gemignani, Matteo, and Salvo Marcuccio. "Dynamic Characterization of a High-Altitude Balloon during a Flight Campaign for the Detection of ISM Radio Background in the Stratosphere." Aerospace 8, no. 1 (January 17, 2021): 21. http://dx.doi.org/10.3390/aerospace8010021.
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Sounding balloons, available at very low cost from commercial vendors and operable with minimal training, have an excellent potential as testing platforms in the near-space environment. The work reported here was motivated by the need to perform an experimental assessment of the radio frequency (RF) background present in the ISM (Industrial, Scientific and Medical) bands, namely 868 MHz (Ultra High Frequency—UHF) and 2.4 GHz (S-Band), simulating the operational environment of a Low Earth Orbit (LEO) constellation forInternet of Things (IoT) telecommunications. To this end, five balloons were flown with a dedicated RF payload. Along with the radio measurements, the flights provided a convenient opportunity to collect data on the dynamic behavior of the payload gondola. We report on the system design and the operational phase of the mission, and discuss the data collected throughout the successful flight campaign. As a result, a preliminary understanding of the gondola dynamics has been gained, including both linear accelerations and attitude oscillations. It is also concluded that the two ISM bands considered are actually suitable for IoT ground-to-LEO links.
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Konstantopoulos, Christos, and Thomas Ussmueller. "A Nano-Power 0.5 V Event-Driven Digital-LDO with Fast Start-Up Burst Oscillator for SoC-IoT." Journal of Low Power Electronics and Applications 10, no. 4 (December 1, 2020): 41. http://dx.doi.org/10.3390/jlpea10040041.
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Towards the integration of Digital-LDO regulators in the ultra-low-power System-On-Chip Internet-of-Things architecture, the D-LDO architecture should constitute the main regulator for powering digital and mixed-signal loads including the SoC system clock. Such an implementation requires an in-regulator clock generation unit that provides an autonomous D-LDO design. In contrast to contemporary D-LDO designs that employ ring-oscillator architecture which start-up time is dependent on the oscillating frequency, this work presents a design with nano-power consumption, fabricated with an active area of 0.035 mm2 at a 55-nm Global Foundries CMOS process that introduces a fast start-up burst oscillator based on a high-gain stage with wake-up time independent of D-LDO frequency. In combination with linear search coarse regulation and asynchronous fine regulation, it succeeds 558 nA minimum quiescent current with CL 75 pF, maximum current efficiency of 99.2% and 1.16x power efficiency improvement compared to analog counterpart oriented to SoC-IoT loads.
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Zaid, Sherif A., Abualkasim Bakeer, Gaber Magdy, Hani Albalawi, Ahmed M. Kassem, Mohmed E. El-Shimy, Hossam AbdelMeguid, and Bassel Manqarah. "A New Intelligent Fractional-Order Load Frequency Control for Interconnected Modern Power Systems with Virtual Inertia Control." Fractal and Fractional 7, no. 1 (January 5, 2023): 62. http://dx.doi.org/10.3390/fractalfract7010062.
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Since modern power systems are susceptible to undesirable frequency oscillations caused by uncertainties in renewable energy sources (RESs) and loads, load frequency control (LFC) has a crucial role to get these systems’ frequency stability back. However, existing LFC techniques may not be sufficient to confront the key challenge arising from the low-inertia issue, which is due to the integration of high-penetration RESs. Therefore, to address this issue, this study proposes an optimized intelligent fractional-order integral (iFOI) controller for the LFC of a two-area interconnected modern power system with the implementation of virtual inertia control (VIC). Here, the proposed iFOI controller is optimally designed using an efficient metaheuristic optimization technique, called the gray wolf optimization (GWO) algorithm, which provides minimum values for system frequency deviations and tie-line power deviation. Moreover, the effectiveness of the proposed optimal iFOI controller is confirmed by contrasting its performance with other control techniques utilized in the literature, such as the integral controller and FOI controller, which are also designed in this study, under load/RES fluctuations. Compared to these control techniques from the literature for several scenarios, the simulation results produced by the MATLAB software have demonstrated the efficacy and resilience of the proposed optimal iFOI controller based on the GWO. Additionally, the effectiveness of the proposed controller design in regulating the frequency of interconnected modern power systems with the application of VIC is confirmed.
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He, Ping, Mingming Zheng, Haoran Jin, Zhijie Gong, and Jie Dong. "Introducing MRAC-PSS-VI to Increase Small-Signal Stability of the Power System after Wind Power Integration." International Transactions on Electrical Energy Systems 2022 (January 31, 2022): 1–20. http://dx.doi.org/10.1155/2022/3525601.
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With the gradual increase of wind power penetration in the power system, the impact of wind farm on system stability is becoming more significant. This study designs the power system stabilizer (PSS) based on the model reference adaptive control (MRAC) method and virtual impedance (VI) control strategy. Then, the active power difference of the doubly fed induction generator (DFIG) is selected as input signal of MRAC-PSS-VI. The small-signal stability of the power system with the DFIG is enhanced by installing MRAC-PSS-VI on the rotor side control (RSC) control link. The controller model is built in DigSILENT/PowerFactory. The improvement effect of the controller on the low-frequency oscillation (LFO) characteristics of the power system is verified by using eigenvalue analysis and the time domain simulation method under different transmission powers of the tie line and different installed positions of the DFIG.
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Saadatmand, Mahdi, Gevork B. Gharehpetian, Innocent Kamwa, Pierluigi Siano, Josep M. Guerrero, and Hassan Haes Alhelou. "A Survey on FOPID Controllers for LFO Damping in Power Systems Using Synchronous Generators, FACTS Devices and Inverter-Based Power Plants." Energies 14, no. 18 (September 21, 2021): 5983. http://dx.doi.org/10.3390/en14185983.
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In recent decades, various types of control techniques have been proposed for use in power systems. Among them, the use of a proportional–integral–derivative (PID) controller is widely recognized as an effective technique. The generalized type of this controller is the fractional-order PID (FOPID) controller. This type of controller provides a wider range of stability area due to the fractional orders of integrals and derivatives. These types of controllers have been significantly considered as a new approach in power engineering that can enhance the operation and stability of power systems. This paper represents a comprehensive overview of the FOPID controller and its applications in modern power systems for enhancing low-frequency oscillation (LFO) damping. In addition, the performance of this type of controller has been evaluated in a benchmark test system. It can be a driver for the development of FOPID controller applications in modern power systems. Investigation of different pieces of research shows that FOPID controllers, as robust controllers, can play an efficient role in modern power systems.
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Cho, Y. S., S. B. Kim, E. J. Powers, R. W. Miksad, and F. J. Fischer. "Stabilization of Moored Vessels Using a Second-Order Volterra Filter and Feedforward Compensator." Journal of Offshore Mechanics and Arctic Engineering 113, no. 2 (May 1, 1991): 137–41. http://dx.doi.org/10.1115/1.2919909.
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Modeling and forecasting of the sway of a moored vessel subjected to random waves were studied recently using quadratic digital filtering techniques. Moreover, it was observed that the future response of the vessel can be predicted with relatively high accuracy. This paper describes a control scheme, which utilizes a quadratic digital filter, to stabilize the low-frequency drift oscillation (LFDO) of moored vessels by a process, whose transfer function may be unknown or time-varying, and an appropriately chosen feedforward compensator. The feedforward compensator generates a control signal that counteracts the LFDO. The predictive filter coefficients are determined from experimental time series data of random sea excitation and the associated sway response of a scaled (1:48) moored barge. The parameters of the process are estimated using a recursive least squares (RLS) method. Simulation results show that the sway of the controlled vessel is reduced considerably, compared with that of a uncontrolled vessel.
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Ndiitwani, D. C., and P. R. Sutcliffe. "A study of L-dependent Pc3 pulsations observed by low Earth orbiting CHAMP satellite." Annales Geophysicae 28, no. 2 (February 3, 2010): 407–14. http://dx.doi.org/10.5194/angeo-28-407-2010.
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Abstract. Field line resonances (FLR) driven by compressional waves are an important mechanism for the generation of ULF geomagnetic pulsations observed at all latitudes during local daytime. References to observations of toroidal standing Alfvén mode oscillations with clearly L-dependent frequencies from spacecraft in the outer magnetosphere for L>3 are limited in the literature. Such observations in the inner magnetosphere for L<3 have not yet been reported in the literature. This study offers two interesting case studies of observations of ULF waves by the low Earth orbiting CHAMP satellite. The magnetic field measurements from CHAMP, which are of unprecedented accuracy and resolution, are compared to Hermanus magnetometer data for times when CHAMP crosses the ground station L-shell, namely for 13 February 2002 and 18 February 2003. The data were analysed for Pc3 pulsation activity using the Maximum Entropy Spectral Analysis (MESA) method to visualise FLRs in the vector magnetometer data. For the first time observations of Pc3 toroidal oscillations with clearly L-dependent frequencies for lower L-shell values (L<3) observed by an LEO satellite are reported. These observations show FLR frequencies increasing as a function of decreasing latitude down to L=1.6 and then decreasing as a result of the larger plasma density of the upper ionosphere. The L-dependent frequency oscillations were observed in the presence of a broadband compressional wave spectrum. Our observations thus confirm the well-known magnetohydrodynamic (MHD) wave theoretical prediction of a compressional wave being the driver of the field line resonance.
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Bielajew, R., G. D. Conway, M. Griener, T. Happel, K. Höfler, N. T. Howard, A. E. Hubbard, et al. "Edge turbulence measurements in L-mode and I-mode at ASDEX Upgrade." Physics of Plasmas 29, no. 5 (May 2022): 052504. http://dx.doi.org/10.1063/5.0088062.
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The I-mode confinement regime is promising for future reactor operation due to high energy confinement without high particle confinement. However, the role of edge turbulence in creating I-mode's beneficial transport properties is still unknown. New measurements of edge turbulence ([Formula: see text]) in L-modes and I-modes at low and high densities at ASDEX Upgrade are presented in this paper. A high radial resolution correlation electron cyclotron emission radiometer measures the broadband turbulence throughout the L-mode and I-mode edge and pedestal. The weakly coherent mode (WCM) is measured in both L-mode and I-mode near the last closed flux surface with Te fluctuation levels of 2.3%–4.2%, with a frequency shift between the two phases related to a deeper Er well in I-mode. An [Formula: see text] phase diagnostic captures a change of the WCM [Formula: see text] phase between L-mode and I-mode from [Formula: see text] to [Formula: see text]. The thermal He beam diagnostic measures a WCM wavenumber range of −0.5 to −1.0 cm−1. A low-frequency edge oscillation (LFEO) appears in the I-mode phase of these discharges and displays coupling to the WCM, but the LFEO does not appear in the L-mode phase. Linear gyrokinetic simulations of the outer core and pedestal top turbulence indicate that while the dominant turbulent modes in the outer core are ion directed and electrostatic, the turbulence becomes increasingly electron directed and electromagnetic with increasing radius. Collisionality is not found to impact characteristics of the L-mode and I-mode edge turbulence with respect to the presence of the WCM; however, the quality of global confinement decreases with collisionality.
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Wu, Melinda, Kimberly Wisneski, Gerwin Schalk, Mohit Sharma, Jarod Roland, Jonathan Breshears, Charles Gaona, and Eric C. Leuthardt. "Electrocorticographic Frequency Alteration Mapping for Extraoperative Localization of Speech Cortex." Neurosurgery 66, no. 2 (February 1, 2010): E407—E409. http://dx.doi.org/10.1227/01.neu.0000345352.13696.6f.
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Abstract OBJECTIVE Electrocortical stimulation (ECS) has long been established for delineating eloquent cortex in extraoperative mapping. However, ECS is still coarse and inefficient in delineating regions of functional cortex and can be hampered by afterdischarges. Given these constraints, an adjunct approach to defining motor cortex is the use of electrocorticographic (ECoG) signal changes associated with active regions of cortex. The broad range of frequency oscillations are categorized into 2 main groups with respect to sensorimotor cortex: low-frequency bands (LFBs) and high-frequency bands (HFBs). The LFBs tend to show a power reduction, whereas the HFBs show power increases with cortical activation. These power changes associated with activated cortex could potentially provide a powerful tool in delineating areas of speech cortex. We explore ECoG signal alterations as they occur with activated region of speech cortex and its potential in clinical brain mapping applications. METHODS We evaluated 7 patients who underwent invasive monitoring for seizure localization. Each had extraoperative ECS mapping to identify speech cortex. Additionally, all subjects performed overt speech tasks with an auditory or a visual cue to identify associated frequency power changes in regard to location and degree of concordance with ECS results. RESULTS Electrocorticographic frequency alteration mapping (EFAM) had an 83.9% sensitivity and a 40.4% specificity in identifying any language site when considering both frequency bands and both stimulus cues. Electrocorticographic frequency alteration mapping was more sensitive in identifying the Wernicke area (100%) than the Broca area (72.2%). The HFB is uniquely suited to identifying the Wernicke area, whereas a combination of the HFB and LFB is important for Broca localization. CONCLUSION The concordance between stimulation and spectral power changes demonstrates the possible utility of EFAM as an adjunct method to improve the efficiency and resolution of identifying speech cortex.
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Celada, Pau, Laia Lladó-Pelfort, N. Santana, L. Kargieman, Eva Troyano-Rodriguez, M. S. Riga, and Francesc Artigas. "Disruption of thalamocortical activity in schizophrenia models: relevance to antipsychotic drug action." International Journal of Neuropsychopharmacology 16, no. 10 (November 1, 2013): 2145–63. http://dx.doi.org/10.1017/s1461145713000643.
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Abstract Non-competitive NMDA receptor antagonists are widely used as pharmacological models of schizophrenia due to their ability to evoke the symptoms of the illness. Likewise, serotonergic hallucinogens, acting on 5-HT2A receptors, induce perceptual and behavioural alterations possibly related to psychotic symptoms. The neurobiological basis of these alterations is not fully elucidated. Data obtained in recent years revealed that the NMDA receptor antagonist phencyclidine (PCP) and the serotonergic hallucinogen 1-(2,5-dimethoxy-4-iodophenyl-2-aminopropane; DOI) produce a series of common actions in rodent prefrontal cortex (PFC) that may underlie psychotomimetic effects. Hence, both agents markedly disrupt PFC function by altering pyramidal neuron discharge (with an overall increase) and reducing the power of low frequency cortical oscillations (LFCO; < 4 Hz). In parallel, PCP increased c-fos expression in excitatory neurons of various cortical areas, the thalamus and other subcortical structures, such as the amygdala. Electrophysiological studies revealed that PCP altered similarly the function of the centromedial and mediodorsal nuclei of the thalamus, reciprocally connected with PFC, suggesting that its psychotomimetic properties are mediated by an alteration of thalamocortical activity (the effect of DOI was not examined in the thalamus). Interestingly, the observed effects were prevented or reversed by the antipsychotic drugs clozapine and haloperidol, supporting that the disruption of PFC activity is intimately related to the psychotomimetic activity of these agents. Overall, the present experimental model can be successfully used to elucidate the neurobiological basis of schizophrenia symptoms and to examine the potential antipsychotic activity of new drugs in development.
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Ødegård, Siv Steinsmo, Hans Torp, Turid Follestad, Martin Leth-Olsen, Ragnhild Støen, and Siri Ann Nyrnes. "Low frequency cerebral arterial and venous flow oscillations in healthy neonates measured by NeoDoppler." Frontiers in Pediatrics 10 (November 28, 2022). http://dx.doi.org/10.3389/fped.2022.929117.
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BackgroundA cerebroprotective effect of low frequency oscillations (LFO) in cerebral blood flow (CBF) has been suggested in adults, but its significance in neonates is not known. This observational study evaluates normal arterial and venous cerebral blood flow in healthy neonates using NeoDoppler, a novel Doppler ultrasound system which can measure cerebral hemodynamics continuously.MethodUltrasound Doppler data was collected for 2 h on the first and second day of life in 36 healthy term born neonates. LFO (0.04–0.15 Hz) were extracted from the velocity curve by a bandpass filter. An angle independent LFO index was calculated as the coefficient of variation of the filtered curve. Separate analyses were done for arterial and venous signals, and results were related to postnatal age and behavioral state (asleep or awake).ResultsThe paper describes normal physiologic variations of arterial and venous cerebral hemodynamics. Mean (SD) arterial and venous LFO indices (%) were 6.52 (2.55) and 3.91 (2.54) on day one, and 5.60 (1.86) and 3.32 (2.03) on day two. After adjusting for possible confounding factors, the arterial LFO index was estimated to decrease by 0.92 percent points per postnatal day (p < 0.001). The venous LFO index did not change significantly with postnatal age (p = 0.539). Arterial and venous LFO were not notably influenced by behavioral state.ConclusionThe results indicate that arterial LFO decrease during the first 2 days of life in healthy neonates. This decrease most likely represents normal physiological changes related to the transitional period. A similar decrease for venous LFO was not found.
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Saito, Yasuyuki, Tohru Suga, Kazuhiko Inoue, Tatsuro Mitani, Yutaka Tomizawa, Johji Nishio, Kazutaka Terashima, et al. "Drain Current DLTS Spectra and GaAs Substrate Crystal Effect on Low-Frequency-Oscillations of Si-Implanted Mesfets." MRS Proceedings 262 (1992). http://dx.doi.org/10.1557/proc-262-791.
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ABSTRACTWe report drain-current (Id) deep level transient spectroscopy (DLTS) spectra and liquid-encapsulated-Czochralski-technique (LEC) GaAs crystal effect on low-frequency-oscillation (LFO) of wide gate (400-μm) Si-implanted GaAs metal- semiconductor field- effect- transistors (MESFETs). In the range of this experiment we could not find distinguishing DLTS peaks surely to be linked with Id-LFO of the MESFETs. Stoichiometric-melt growth LEC-boules showed relatively large Id-LFO phenomena. As-rich-melt growth LEC-boules showed tolerance to Id-LFO. We conclude that Id-LFO is not directly linked to deep centers themselves but interaction between deep centers and potential profiles and electrons. Stability of potential profile or band profile depends on “pinning’ center, which affects Fermi-level or quasi-Fermi-level stability. ‘Pinning’ center such as EL2s of ‘LEC GaAs crystals” is essential.
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Jamiolkowski, Ryan M., Wesley Baker, W. Andrew Kofke, and Ramani Balu. "Acute Brain Injury Is Associated With Prolonged Suppression of Cerebral Blood Flow Oscillations." Neurosurgery 66, Supplement_1 (August 20, 2019). http://dx.doi.org/10.1093/neuros/nyz310_680.
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Abstract INTRODUCTION Low-frequency oscillations (LFOs, < 0.1 Hz) in cerebral blood flow (CBF) reflect changes in the coordinated activity of neuronal assemblies. Synchronized LFOs across multiple brain regions can be identified using magnetic resonance imaging to reveal functionally connected networks; however, how LFOs are altered by brain injury is largely unknown. METHODS We quantified changes in LFO magnitude over time in brain-injured patients where CBF was recorded continuously using invasive thermal diffusion flowmetry. Intracranial pressure (ICP), brain tissue oxygen (PbO2), and arterial blood pressure (ABP) were recorded concurrently in all patients. For each epoch of uninterrupted CBF data, the power spectral density within the 0.05 to 0.1 Hz frequency band was calculated. Periods of LFO suppression were defined as occurring when equal to 10% of the total power across all frequencies occurred in the 0.05 to 1 Hz frequency band. Average values of CBF, ICP, PbO2, and ABP were compared between suppressed and nonsuppressed epochs across all patients. RESULTS Twenty-five patients were included in this retrospective observational study. LFO suppression was associated with a lower average CBF (11.3 mL/100 g/min suppressed vs 31.6 mL/100 g/min unsuppressed, P < .0001) and lower average PbO2 (21.6 mm Hg suppressed vs 31.0 mm Hg unsuppressed, P < .0001). In a subset of patients, LFO suppression was associated with intracranial hypertension (ICP 25-60 mm Hg). Patients that regained consciousness and were discharged to acute rehab had a lower median fraction of time spent in the suppressed state (0.03 rehab vs 0.67 death/nursing home, P = .053). CONCLUSION Brain injury is associated with the suppression of low-frequency CBF fluctuations. LFO suppression is associated with periods of physiological distress and may provide a sensitive marker of disrupted brain function. The degree of LFO suppression may have a prognostic significance, and the re-emergence of LFOs after a period of suppression may provide a marker of return of consciousness after coma.
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Becker, Sabeth, Franziska Klein, Katja König, Christian Mathys, Thomas Liman, and Karsten Witt. "Assessment of dynamic cerebral autoregulation in near-infrared spectroscopy using short channels: A feasibility study in acute ischemic stroke patients." Frontiers in Neurology 13 (November 21, 2022). http://dx.doi.org/10.3389/fneur.2022.1028864.
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IntroductionIn acute ischemic stroke, progressive impairment of cerebral autoregulation (CA) is frequent and associated with unfavorable outcomes. Easy assessment of cerebral blood flow and CA in stroke units bedside tools like near-infrared spectroscopy (NIRS) might improve early detection of CA deterioration. This study aimed to assess dynamic CA with multichannel CW-NIRS in acute ischemic stroke (AIS) patients compared to agematched healthy controls.MethodsCA reaction was amplified by changes in head of bed position. Long- and short channels were used to monitor systemic artery pressure- and intracranial oscillations simultaneously. Gain and phase shift in spontaneous low- and very low-frequency oscillations (LFO, VLFO) of blood pressure were assessed.ResultsA total of 54 participants, 27 with AIS and 27 age-matched controls were included. Gain was significantly lower in the AIS group in the LFO range (i) when the upper body was steadily elevated to 30. and (ii) after its abrupt elevation to 30°. No other differences were found between groups.DiscussionThis study demonstrates the feasibility of NIRS short channels to measure CA in AIS patients in one single instrument. A lower gain in AIS might indicate decreased CA activity in this pilot study, but further studies investigating the role of NIRS short channels in AIS are needed.
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Kim, Ye Eun, Min Kyung Kim, Sang-il Suh, and Ji Hyun Kim. "Altered trigeminothalamic spontaneous low-frequency oscillations in migraine without aura: a resting-state fMRI study." BMC Neurology 21, no. 1 (September 7, 2021). http://dx.doi.org/10.1186/s12883-021-02374-7.
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Abstract Background Recent resting-state fMRI studies demonstrated functional dysconnectivity within the central pain matrix in migraineurs. This study aimed to investigate the spatial distribution and amplitude of low-frequency oscillations (LFOs) using fractional amplitude of low-frequency fluctuation (fALFF) analysis in migraine patients without aura, and to examine relationships between regional LFOs and clinical variables. Methods Resting-state fMRI data were obtained and preprocessed in 44 migraine patients without aura and 31 matched controls. fALFF was computed according to the original method, z-transformed for standardization, and compared between migraineurs and controls. Correlation analysis between regional fALFF and clinical variables was performed in migraineurs as well. Results Compared with controls, migraineurs had significant fALFF increases in bilateral ventral posteromedial (VPM) thalamus and brainstem encompassing rostral ventromedial medulla (RVM) and trigeminocervical complex (TCC). Regional fALFF values of bilateral VPM thalamus and brainstem positively correlated with disease duration, but not with migraine attack frequency or Migraine Disability Assessment Scale score. Conclusions We have provided evidence for abnormal LFOs in the brainstem including RVM/TCC and thalamic VPM nucleus in migraine without aura, implicating trigeminothalamic network oscillations in migraine pathophysiology. Our results suggest that enhanced LFO activity may underpin the interictal trigeminothalamic dysrhythmia that could contribute to the impairments of pain transmission and modulation in migraine. Given our finding of increasing fALFF in relation to increasing disease duration, the observed trigeminothalamic dysrhythmia may indicate either an inherent pathology leading to migraine headaches or a consequence of repeated attacks on the brain.
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A.S.V, Vijaya Lakshmi, Ramalinga Raju Manyala, and Siva Kumar Mangipudi. "Design of a robust PID-PSS for an uncertain power system with simplified stability conditions." Protection and Control of Modern Power Systems 5, no. 1 (September 29, 2020). http://dx.doi.org/10.1186/s41601-020-00165-9.
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Abstract In a deregulated power system uncertainty exists and lack of sufficient damping can lead to Low Frequency Oscillations (LFO). The problem can be addressed using robust Power System Stabilizers (PSS). In this paper, an optimal procedure to design a robust PID-PSS using interval arithmetic for the Single Machine Infinite Bus (SMIB) power system is proposed. The interval modelling captures the wide variations of operating conditions in bounds of system coefficients. In the proposed design procedure, simple and new closed loop stability conditions for an SMIB interval system are developed and are used to design an optimum PID-PSS for improving the performance of an SMIB system. The optimum PID-PSS is attained by tuning the parameters using the FMINCON tool provided in MATLAB. The robustness of the proposed PID-PSS design is validated and compared to other notable methods in the literature when the system is subjected to different uncertainties. The simulation results and performance error values show the effectiveness of the proposed robust PID-PSS controller.