Source Of Low-frequency Oscillations Research Articles

Sources of Low-Frequency Oscillations in Power Systems, Their Localization and Damping

Sources of Low-Frequency Oscillations in Power Systems, Their Localization and Damping

Insights Into Dissipating Energy-Based Source/Sink Characterization of TCSC and STATCOM for Low-Frequency Oscillations

Determination of the sources of oscillations in the power system helps operators take appropriate preventive actions. In recent years, the dissipating energy flow (DEF) method has emerged as a promising tool for the online localization of low-frequency oscillation sources. In literature, the mathematical foundation of the DEF method is well-studied for networks with synchronous generators. In this paper, we extend the analysis to flexible AC transmission systems (FACTS). We derive the DEF-expressions for a thyristor controlled series capacitor (TCSC) and a static synchronous compensator (STATCOM) operating with conventional control strategies. Specifically, TCSC with both fixed and variable compensation, and STATCOM in grid-following mode with dc-link voltage and ac voltage-reactive power droop control are considered. Analyzing their respective DEFs, we obtain the conditions for which these FACTS devices could appear as the sources of low-frequency oscillations. Our findings are structured into propositions and are supported through numerical case studies on IEEE test systems.

Sparse learning of network-reduced models for locating low frequency oscillations in power systems

With increasing penetration intermittent renewable energy and the interactions between different power sources in an interconnected system, low frequency oscillations may occur and potentially threaten the security of power systems if the grid cannot support adequate damping. Locating sources of low frequency oscillations is of great importance, which needs finding the mechanism of the damping of low frequency oscillations for interpretation. The difficulty of this problem lies in the fact that the parameters associated with the power system model can range from slightly uncertain to entirely unknown. Therefore, we firstly focus on identifying the network-reduced model to characterize low frequency oscillation, and then utilizing Hamilton analysis to reveal mechanism of oscillation. Accordingly, the problem of locating low frequency oscillation is equivalent to identify equivalent negative damping coefficient. In this paper, we propose a novel data-driven method that estimates equivalent damping coefficients and topological parameters of the network-reduced model simultaneously. More specifically, the proposed method utilizes the sparse representation to select the most dominant nonlinear terms from a set of dictionary functions, which finally balances the data fitness and achieves dynamics learning. We validate and evaluate the proposed method on IEEE 9-bus test system and IEEE 39-bus test system. The results demonstrate the effectiveness of the proposed method in achieving dynamics learning and locating sources of low frequency oscillations from measurement data.

Representation of Transient Processes on a Hyperplane Using Examples from Electrical Engineering

Vector representation of transient processes on a plane with two coordinate systems makes it possible to visualize all the parameters of transient oscillations, namely, amplitude, frequency, phase, and attenuation. On a complex plane with two coordinate systems, the origin of the vector is determined by the damping factor and the cyclic frequency and is set on the scale of axes of the complex frequency plane, while the length and the phase of the vector are set on the scale of complex amplitude. Such a representation significantly improves visualization of processes and, consequently, increases the informativeness of the research. The use of the hypervector representation of transients is illustrated by various examples. When analyzing the functioning of an automatic excitation controller (AEC) in certification tests, the vector representation of transient processes clearly demonstrates the effect of the AEC and allows one to quantitatively control the effect of channel stabilization on oscillation modes. The vector representation of the dominant oscillations in various implementations of the circuits reveals the most extreme situations for which it is necessary to test the AEC tuning for a specific station. Investigation of the vectors of the voltage-frequency oscillation measured at different points of the system makes it possible to localize the source of low-frequency oscillations.

Transient energy dissipation of resistances and its effect on power system damping

The transient energy flow method is a newly proposed method for locating the sources of low frequency oscillations and shows good performances in tests and actual applications. It is found in previous work that resistances in networks or loads may produce transient energy and exhibit as oscillation sources. In this paper, the transient energy dissipation of resistances and its effect on power system damping is studied. The transient energy flow into a resistance is generally non-conservative but whether it is dissipative is indefinite. A resistance may dissipate or produce transient energy. However, the relationship between system damping represented with the real-part of the eigenvalue and the total energy dissipation is definite, and an equation describing the relationship is obtained in simple power systems. Transient energy dissipation is an indicator of the damping of a component. When a resistance dissipates transient energy, it is beneficial to system damping, otherwise it is detrimental. The results are verified with simulations and explanations for constant impedance loads at different locations having different effects on damping are given.

Virtual anode as a source of low-frequency oscillations of a high-current electron beam

The research into the transportation of a relativistic electron beam with an above-critical current in the cylindrical drift chamber in the presence of an ion stream is described. The theoretical analysis of the electron-ion formation dynamics is based on a particle-in-cell (PIC) method. It shows that at a joint injection of a supercritical electron beam and a low-energy low-current ion beam in the drift chamber a virtual anode may appear along with an electron virtual cathode. This virtual anode pulsates periodically. Numerical results obtained for hydrogen and nitrogen ions show that the ratio of pulsation frequencies is in inverse proportion to the ion mass ratio. Oscillations of a virtual anode result in a time modulation of electron and ion currents at the same frequency at the drift chamber output.

Experience with the analysis of small signal stability in longitudinal systems: a case study with the Mexican interconnected system

In this paper a fundamental study of the small signal stability characteristics of a longitudinal system representing a major equivalent of the Mexican power system is presented. The special characteristics of the Mexican system are emphasized and a number of studies regarding the nature and sources of low frequency oscillations are discussed. These studies reveal the emergence of an undamped swing mode involving the interaction of several machines and their controllers spread out over a large geographical area. The influence of system structure and loading, load effect and the application of several controllers on system damping is discussed.

A general approach to low-frequency instability in the ring current plasma

A very general approach to hydromagnetic instability in a magnetospheric geometry is given. The specific effects of the presence of finite ..beta.. ring current particles and cold particles of ionospheric origin are included. The generality of approach allows the theory to interrelate various approaches to low-frequency stability. It is concluded that resonant particle instabilities are likely to be the source of low-frequency oscillations that have been observed. Instability conditions and growth rates are estimated. Alfven waves may be excited with ..beta..<1, while for ..beta..approximately-greater-than1, compressional disturbances are expected to be generated. (AIP)