Use Of Frequency Domain Methods Research Articles

Frequency Domain Methods for Accuracy Assessment of Wideband Models in Electromagnetic Transient Stability Studies

Modern power systems face several problems at frequencies above the range of traditional stability studies due to the increasing penetration of power electronic devices. This phenomenon has been recently referred to as electromagnetic transient stability and is a growing issue in systems with power electronic converters at any power and voltage level, such as FACTS, high-voltage DC, interfaces for grid connection of renewable energies, custom power devices for power quality enhancement, among others. The study of power systems stability is usually carried out by simulation tools that represent the power system through phasor models. However, due to the faster dynamics of modern systems, the harmonic interaction among the controllers, converters, and electric power components, recent research results suggest that some stability analyses should be conducted with models suitable for wider frequency ranges, e.g., electromagnetic transient models. This paper reviews the use of frequency domain methods to analyze the influence of the modeling approach of passive power components on the results of electromagnetic transient stability studies.

Real time high cycle fatigue estimation algorithm and load history monitoring for vehicles by the use of frequency domain methods

Abstract Real time high cycle fatigue estimation problem for vehicles is examined by the use of frequency domain methods. The purpose was twofold: monitoring of fatigue damage and tracking of load history in real time. Firstly, power spectral density functions (PSDs) of acceleration measurement at a selected location are calculated in a piecewise manner by dividing the acceleration-time history into pieces. Following, Frequency Response Functions (FRF’s), whose outputs are the absolute maximum principal stress values at selected components, are calculated by finite element methods to account for multi-axial stress state in fatigue life estimations. Then, fatigue damage intensity at selected output locations is estimated using the FRF results. To this end, the following frequency domain fatigue estimation methods (FDFEMs) proposed for Gaussian and stationary data sets are applied to the selected components of a heavy duty truck: narrow-band approximation, Tovo and Benasciutti, Zhao and Baker, Dirlik and Tovo’s α 0.75 methods. Gaussianity and stationarity of acceleration-time data set used to estimate fatigue life of a component is checked to ensure the validity of FDFEMs. Numerical results are compared with experimental fatigue lives and damage calculations in time domain made by the combination of rainflow counting and Miner-Palmgren rules. There are two difficulties in implementing this approach using on-board equipment in real time such as overcoming the limited memory to store data sets and completing the computations sufficiently fast. To overcome them, the proposed approach is implemented in a piecewise manner and associated normalized PSDs are updated accordingly. Then, spectral moments and damage intensities are calculated in frequency domain. Implementation of the proposed approach is described in detail and numerical results are presented. It is shown that the proposed approach is able to predict the fatigue damage accurately and can keep track of loading conditions in real time.

Aircraft and Rotorcraft System Identification: Engineering Methods with Flight Test Examples (M.B. Tischler et al.; 2006) [Bookshelf

The world of aircraft system identification is divided into two camps, namely, those who use time-domain methods and those who use frequency-domain methods. Tischler and Remple are firmly in the frequency-domain camp. and their entire book is dedicated to this approach to system identification. The book also features the software package Comprehensive Identification from Frequency Responses (CIFER), which was developed by Tischler's group and is widely used throughout the rotorcraft industry. Topics covered in the text include: an overview of the aircraft system identification process and a review of basic concepts; an overview of the frequency-domain method; an overview of the CIFER software; details of collecting and validating flight test data; the theory and implementation of frequency-domain identification methods incorporated in the CIFER software; state-space models; time-domain verification; and issues relating to the development of high-order dynamic models of rotorcraft, and, in particular, models that involve rotor-body coupling. The book presents numerous examples with real flight test data. It is an essential reference for those working in system identification of rotorcraft and anyone who is using CIFER. The book might also be useful to those engineers considering the use of frequency-domain methods for system identification. It could possibly serve as a textbook for a special topics course.

Discussion of "Modeling and analysis guidelines for slow transients. III. The study of ferroresonance"

The author comments on the paper by M.R. Iravasi et al. (see ibid., vol. 15, p.255-65, 2000). The aim of this discussion is twofold. First, it aims to complete the extensive reference list with a couple of papers describing some cases of ferroresonance experienced in Belgium. Second, some misunderstandings regarding the use of frequency domain methods with respect to nonlinear circuits are cleared out.