Analysis Of Low-frequency Oscillations Research Articles

Analysis of low frequency oscillations in power system using EMO ESPRIT

Identification of poorly damped low frequency oscillations present in the densely interconnected power system is of paramount importance to maintain its stable operation. Estimation of signal parameters via rotational invariance technique (ESPRIT) is a parametric method used for analysing such signals even under noisy conditions. However, this method requires precise information about the number of modes present in the signal. Hence, this work uses a combination of Exact Model Order (EMO) algorithm and ESPRIT for analysing these low frequency oscillations. The performance of the proposed method is tested using various synthetic signals with different levels of noise and PMU reporting rates. Further, the robustness of the proposed method towards noise resistance is compared with modified Prony, TLS-ESPRIT and ARMA methods. Finally, the proposed method is tested using real time probing test data obtained from Western Electricity Coordinating Council (WECC) network. Results reveal that the proposed method is accurate, precise and outperforms the other methods.

An Improved IRA Algorithm and Its Application in Critical Eigenvalues Searching for Low Frequency Oscillation Analysis

On the basis of implicitly restarted Arnoldi (IRA) method, an improved algorithm is proposed, in which the dimension of Krylov subspace is dynamically increased to compute eigenvalues in specified circle. First, the radius of searching circles is dynamically expanded through automatically increasing the number of eigenvalues and the dimension of Krylov subspace, based on the locking mechanism. Second, the region where the low frequency oscillation modes located is divided into small independent computing units, which are covered by specified searching circles. Third, the independent computing units can be calculated simultaneously with no effects on each other. The proposed method can avoid eigenvalues missing caused by inappropriate resetting of search number in equidistant-searching IRA method. Furthermore, no manual intervention is needed in the proposed method. Two systems with 570 and 5272 state variables are tested in this paper, and the results indicate that the proposed method is efficient, reliable, and practical.

Analysis of low frequency oscillation in multi-area power system based on incomplete elliptic integral

The stability of power system is an important index for safe operation of the system. With the expansion of interconnection scale of power system and the increasing transmission line power, the low frequency oscillation has gradually become a significant cause of the system instability. In this paper, based on incomplete elliptic integral, a new nonlinear method for low frequency oscillation frequency computation and analysis is presented, which can be useful for prediction and evaluation of the anti-disturbance ability in multi-area power system. By the equivalent simplification and construction of Hamilton energy function, an exact expression of the low frequency oscillation frequency is obtained. Simulation studies of the proposed method are conducted in the New England 10-generator 39-bus system and the influence of different disturbances is discussed to verify the correctness and effectiveness of the method. Comparative analysis with traditional linearization method demonstrates that the performance of the new approach is inspiring, and it is of higher processing efficiency as well as reliability.

Extracting inter-area oscillation modes using local measurements and data-driven stochastic subspace technique

In this paper, a data-driven stochastic subspace identification (SSI-DATA) technique is proposed as an advanced stochastic system identification (SSI) to extract the inter-area oscillation modes of a power system from wide-area measurements. For accurate and robust extraction of the modes’ parameters (frequency, damping and mode shape), SSI has already been verified as an effective identification algorithm for output-only modal analysis. The new feature of the proposed SSI-DATA applied to inter-area oscillation modal identification lies in its ability to select the eigenvalue automatically. The effectiveness of the proposed scheme has been fully studied and verified, first using transient stability data generated from the IEEE 16-generator 5-area test system, and then using recorded data from an actual event using a Chinese wide-area measurement system (WAMS) in 2004. The results from the simulated and recorded measurements have validated the reliability and applicability of the SSI-DATA technique in power system low frequency oscillation analysis.

Measurement-based solution for low frequency oscillation analysis

This paper presents a measurement-based solution for low frequency oscillation (LFO) analysis in both real time monitoring and off-line case study. An online LFO property discrimination method is developed first, which alternately uses empirical mode decomposition (EMD)/Hilbert transform (HT) and square calculation to process the measurement data. The method magnifies the variation trend of oscillating variables to accurately discriminate the property of the oscillation. Subsequently, an oscillation source locating method for the forced oscillation (FO) and a strongly correlated generator identification method for the weak damping oscillation (WDO) are proposed. Finally, numerical study results on a test system of the isolated Changdu grid in Tibet validate the proposed methods.

Probabilistic stability analysis of low frequency oscillation of large-scale interconnected power grid based on the theory of point estimation method and risk assessment

Probabilistic stability analysis of low frequency oscillation of large-scale interconnected power grid based on the theory of point estimation method and risk assessment

Analysis of Low Frequency Oscillation in Interconnected Power System under Hedge Operation Mode

A phenomenon that the damping ratio will decrease when the power flows from both sides to the primary power grid is summarized and analyzed in the paper. Based on analysis of the damping ratio change of West Inner Mongolia-Shandong oscillation under the sequential operation mode and the hedge operation mode, a three-machine equivalent system is established to study edge to edge (ETE) oscillation mode under hedge operating mode of the power system. The influence of magnitudes and trends of power flow on damping ratio is analyzed, and the reason that why damping ratios decreases when both sides send power to the mid-side power grid is explained.

Characteristics extraction and controllability evaluation based on dynamic response of electro-mechanical oscillation

The system identification theory based on SSI(Stochastic Subspace Identification) algorithm is researched,a method of electro-mechanical oscillation characteristics identification based on SSI is designed for power system and a method of participation factor calculation based on response is proposed, by which the quantitative evaluation of system controllability is realized. The proposed method is applied to calculate the dynamic angular frequency response of each generator in a system and the system electro-mechanical oscillation characteristics can be globally analyzed to effectively avoid the defect of traditional low-frequency oscillation analysis with insufficient information based on single signal. Simulative results of IEEE 39-bus system show its high identification accuracy and calculation efficiency.

Análisis de Estabilidad de Pequeña Señal Utilizando Mediciones Sincrofasoriales PMU

Con el acelerado crecimiento de la demanda en los últimos años, las transferencias de potencia a largas distancias entre diferentes empresas de energía han ido aumentando constantemente, razón por la cual la seguridad y confiabilidad de los Sistemas Eléctricos de Potencia -SEP- pueden verse seriamente comprometidas, especialmente por el alto riesgo de violación de los límites de seguridad del sistema eléctrico.
 Uno de los desarrollos más importantes e innovadores en el área de monitoreo y control de los SEP está orientado a las Unidades de Medición Fasorial (PMU). Esta tecnología permite realizar el monitoreo de oscilaciones de baja frecuencia del Sistema Nacional Interconectado -S.N.I.- en tiempo real.
 En el presente trabajo se utiliza la información de las PMU’s, las cuales se encuentran estratégicamente ubicadas en el SNI, para realizar el análisis oscilatorio de baja frecuencia, mediante la aplicación de una de las técnicas de estimación modal conocida como Análisis Prony.

Application of Coherency Property of Generator to Analysis of Low-Frequency Oscillation in Power System

Coherency is used to characterize the degree of confusion between generators which oscillate against each other, so it can judge the process which generators oscillate from local mode to inter-area mode. The coherency is the value of the direction cosine by using angle of the generators. when the direction cosines of two generator is 1 that indicates the oscillation direction between the two generators is inter-area oscillation mode; when the direction cosines of two generator is-1 that indicates the oscillation direction between the two generators is local oscillation mode. Coherency is affected by speed governing system and excitation system of generator.Using two area systems verifies the theoretical analysis is correct.

Analysis of Low Frequency Oscillation in Power System

Around the type of power system of the low frequency oscillation, the mechanism of production, the analysis methods, the analysis tools and suppression method, etc, it summarized the research status of low frequency oscillation of power system. Therefore, based on this research status, the future analysis methods and developmental trend of the low frequency oscillation of power system were discussed.In the power system, the angle of attack among generators, the voltage on the nodal points and the tidal current of junctor and so on had the constant-amplitude or the increased range vibrates, and the oscillation frequency (generally is 0.2~2.5 Hz) is lower than the system frequency. This oscillation form is called the low frequency oscillation[1]. Then the frequency of the low frequency oscillation is low, cycle to be longer,and affected area to be wide, it is also big harm to the power system. Therefore, at present, studying low frequency vibration has the even more important meaning[2].

New Theories and Methods of Low Frequency Oscillation Analysis under Smart Grid Framework in Electrical Engineering

The low-frequency oscillation is one of the most important reasons that affects the stability of the power system. Under the background of building a unified and strong smart grid, the scale of the power system will continue to expand, the interconnection of systems will be more closely, the structure will be more complex, these factors will further increase the difficulty on the low-frequency oscillation control. This paper summarizes the methods to analysis low frequency oscillation signal, the way that suppresses the low frequency oscillation in electrical engineering. Further, based on smart grid framework, a on-line visualization technology and a self-recovery regulation strategy are proposed to damp low-frequency oscillation.

Survey of Ambient Excitation Based Power Oscillation Analysis Methods

In large-scale power system, low frequency power oscillation is becoming a serious threat to the power system operation. Analysis of low frequency oscillation includes model-based method and ambient-excitation-based method. Based on the investigation of the related recently-published papers, this paper presents a survey of ambient-excitation-based method. Firstly, the fundamental principle and underlying theory of ambient-excitation-based method are summarized. Furthermore, several ambient-excitation-based methods are categorized and their characteristics are introduced.

Analysis of Low Frequency Oscillations in Magnetron Injection Guns

In our gyro-TWT experiments, low-frequency oscillations (LFOs) had been observed. LFOs is a physical phenomenon usually caused by the electrons trapped between the magnetron injection guns (MIGs) and the interaction region. In this paper, the formation procedure and physical mechanism of LFOs are reported. Available methods including optimizing the magnetic field distribution in the beam compression region and loading bevel cuts on the second anode are involved to capture the trapped electrons, suppress the LFOs and improve the helical electron beam quality. Simulations and experimental results are in good agreement with each other and also reveal the reasonableness of this means. Finally, the influence of current capture ratio on LFOs and the beam quality are studied. With the current capture ratio increasing, the amplitude of LFOs decreases, the pitch factor maintains a constant about 1.2 and we also demonstrate a low transverse velocity spread about 3%.

Nonlinear Analysis of Low-Frequency Oscillations in Gyrotrons

Low-frequency oscillations (LFOs) had been observed in many gyrotron experiments. These oscillations are believed to be caused by electrons trapped in the region between the electron gun and the cavity. A 1-D numerical simulation method is developed to analyze the self-consistent accumulation and bunching caused by the space-charge field of these trapped electrons. Velocity spread and loss mechanisms for the trapped electrons are taken into account. The threshold conditions for excitation, the spatial character, and the nonlinear evolution of the LFOs are analyzed and interpreted. The numerical simulation results agree with some experimental data.

Prony analysis of low frequency oscillations based on empirical mode decomposition filtering

Since traditional Prony analysis of low frequency oscillations has strict requirements to the input signal and is sensitive to the noise of data, this paper proposes a empirical mode decomposition filtering and Prony analysis combined method for low frequency analysis. In this method, empirical mode decomposition is used to adaptively filter the noise of the input signals before improved Prony analysis is carried out. The order of improved Prony analysis is determined by the normalized singular value method. This method is applied to analyze the test signal and the IEEE 4-machine system oscillation signals, and compared with the Prony analysis based on low pass filter. The simulation shows the effectiveness of this method which indicates that the result of the analysis is good even in highly noisy environment.

On asymptotics of low-frequency oscillations of the liquid core: 1. Basic relations

Asymptotic analysis of low-frequency oscillations of a rotating liquid bounded by a solid surface is performed under the condition that the oscillation frequency is much smaller than the angular rate of rotation. Simple analytical relations describing comprehensively asymptotic modes of these oscillations are obtained.

Distinguishing low frequency oscillations within the 1/f spectral behaviour of electromagnetic brain signals

BackgroundIt has been acknowledged that the frequency spectrum of measured electromagnetic (EM) brain signals shows a decrease in power with increasing frequency. This spectral behaviour may lead to difficulty in distinguishing event-related peaks from ongoing brain activity in the electro- and magnetoencephalographic (EEG and MEG) signal spectra. This can become an issue especially in the analysis of low frequency oscillations (LFOs) – below 0.5 Hz – which are currently being observed in signal recordings linked with specific pathologies such as epileptic seizures or attention deficit hyperactivity disorder (ADHD), in sleep studies, etc.MethodsIn this work we propose a simple method that can be used to compensate for this 1/f trend hence achieving spectral normalisation. This method involves filtering the raw measured EM signal through a differentiator prior to further data analysis.ResultsApplying the proposed method to various exemplary datasets including very low frequency EEG recordings, epileptic seizure recordings, MEG data and Evoked Response data showed that this compensating procedure provides a flat spectral base onto which event related peaks can be clearly observed.ConclusionFindings suggest that the proposed filter is a useful tool for the analysis of physiological data especially in revealing very low frequency peaks which may otherwise be obscured by the 1/f spectral activity inherent in EEG/MEG recordings.

An evaluation of satellite and in situ based sea surface temperature datasets in the North Indian Ocean region

Satellite based daily fields of Pathfinder SST (PFSST) and blended-analysed fields like National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and Reynolds weekly SST data were compared with the in situ measurements obtained from several drifting buoys and a moored buoy in the north Indian Ocean. The mean differences (bias) and scatter (root mean square deviation (RMSD)) were higher than the ideally expected values of <0.01° C and 0.5° C for all three datasets. There was very little difference in the error statistics from one region to another. The error statistics differed significantly from year to year. The PFSST fields reported cooler SSTs ∼0.5° C, during August 1991 to April 1992, due to the increased input of aerosols in the atmosphere caused by the eruption of Mount Pinatubo. Being a high resolution dataset, the PFSST is best able to mimic the sudden changes in the in situ SSTs that happen over a couple of days to a couple of weeks. Neither NCEP/NCAR data nor the Reynolds data were able to mimic the changes in SST that occur over a period of a few days. All three datasets are useful for the analysis of low frequency oscillations like annual and semi-annual cycles. PFSST and NCEP/NCAR SSTs are also useful for the analysis of higher frequency oscillations in the SST fields such as the 26-day period oscillations in the equatorial Indian Ocean.

Non-adiabatic analysis of low-frequency oscillations of uniformly rotating stars

En resolvant les equations differentielles lineaires d'oscillations non radiales et non adiabatiques, on examine la stabilite des oscillations de basse frequence pour des etoiles massives de la sequence principale en rotation uniforme