Forced Oscillation Source Location via Multivariate Time Series Classification

Precisely locating low-frequency oscillation sources is the prerequisite of suppressing sustained oscillation, which is an essential guarantee for the secure and stable operation of power grids. Using synchrophasor measurements, a machine learning method is proposed to locate the source of forced oscillation in power systems. Rotor angle and active power of each power plant are utilized to construct multivariate time series (MTS). Applying Mahalanobis distance metric and dynamic time warping, the distance between MTS with different phases or lengths can be appropriately measured. The obtained distance metric, representing characteristics during the transient phase of forced oscillation under different disturbance sources, is used for offline classifier training and online matching to locate the disturbance source. Simulation results using the four-machine two-area system and IEEE 39-bus system indicate that the proposed location method can identify the power system forced oscillation source online with high accuracy.Comment: 5 pages, 3 figures. Accepted by 2018 IEEE/PES Transmission and Distribution Conferenc

Eigenvalue Analysis and Applications of the Legendre Dual-Petrov-Galerkin Methods for Initial Value Problems

In this paper, we show that the eigenvalues and eigenvectors of the spectral discretisation matrices resulted from the Legendre dual-Petrov-Galerkin (LDPG) method for the $m$th-order initial value problem (IVP): $u^{(m)}(t)=\sigma u(t),\, t\in (-1,1)$ with constant $\sigma\not=0$ and usual initial conditions at $t=-1,$ are associated with the generalised Bessel polynomials (GBPs). The essential idea of the analysis is to properly construct the basis functions for the solution and its dual spaces so that the matrix of the $m$th derivative is an identity matrix, and the mass matrix is then identical or approximately equals to the Jacobi matrix of the three-term recurrence of GBPs with specific integer parameters. This allows us to characterise the eigenvalue distributions and identify the eigenvectors. As a by-product, we are able to answer some open questions related to the very limited known results on the collocation method at Legendre points (studied in 1980s) for the first-order IVP, by reformulating it into a Petrov-Galerkin formulation. Moreover, we present two stable algorithms for computing zeros of the GBPs, and develop a general space-time spectral method for evolutionary PDEs using either the matrix diagonalisation, which is restricted to a small number of unknowns in time due to the ill-conditioning but is fully parallel, or the QZ decomposition which is numerically stable for a large number of unknowns in time but involves sequential computations. We provide ample numerical results to demonstrate the high accuracy and robustness of the space-time spectral methods for some interesting examples of linear and nonlinear wave problems.Comment: 25 pages, 31 figure

Longitudinally uniform transmission lines with frequency-enabled mode conversion

ABSTRACT: A class of longitudinally uniform transmission lines with low loss, low dispersion, and high-field confinement, called mode-selective transmission lines (MSTLs), has been proposed for ultra-broadband and ultra-fast electromagnetic signal guidance and processing. Their operation is mainly based on the concept of frequency-enabled mode selectivity. This paper presents our latest research results on this emerging MSTL, including its operating mechanism, propagation characteristics, higher-order modes, and transition design. Throughout the detailed discussion, two MSTL structures operating in distinct frequency ranges (DC to 60 GHz and DC to 500 GHz as showcased here) are considered. First of all, a comparative study among MSTLs and several conventional transmission lines is made, illustrating significant differences in structural features, wave guidance, field distributions, and frequency characteristics. Second, the phenomenon of mode selectivity occurred in MSTLs is examined by means of identified physical evidence (i.e., field distributions in connection with modal behavior) and theoretical foundation. It is verified that, with increasing frequency, the dominant modes of MSTLs are converted from a quasi-TEM microstrip mode to a quasi-TE 10 waveguide mode over a certain frequency range. Following this thread, a more rigorous analysis is carried out by defining and formulating three characteristic frequencies based on the observed inherent physical dispersions, and the operating frequency ranges of MSTLs are thus divided into several distinct frequency regions associated with the frequency-related variable dominant mode. In addition, a general analysis of the attenuation characteristics of MSTLs and higher order modes in MSTLs is conducted. To facilitate practical measurements and to expedite the integrated applications of MSTLs, we propose a low-loss and ultra-broadband transition between MSTL and microstrip line, through which undesired higher order modes are effectively suppressed. The numerical and theoretical analyses of MSTLs are carried out with experimental verifications. At the end of this paper, different fabrication and measurement techniques for the two MSTLs of interest are briefly described

Antibacterial performance of a porous Cu-bearing titanium alloy by laser additive manufacturing

Porphyromonas gingivalis (P. gingivalis) is the most common species that causes peri-implantitis. It forms an irreversible dense biofilm and causes inflammation. A novel 3D-printed porous TC4-6Cu alloy was fabricated using selective laser melting (SLM) technology for the dental implant, which is anticipated to inhibit biofilm formation. We attempted to investigate the antibacterial ability and antibacterial mechanism of the 3D-printed porous TC4-6Cu alloy against P. gingivalis. This work used scanning electron microscopy (SEM) and laser confocal microscopy (CLSM) to detect the antimicrobial ability of the alloy against sessile P. gingivalis. The results indicated that the 3D-printed porous TC4-6Cu alloy could cause bacterial fragmentation and deformation. Plate antimicrobial counting experiments showed that the antibacterial rates of the alloy against adherent bacteria and planktonic bacteria after 24 h were 98.05% and 73.92%, respectively. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Cu2+ were tested to appraise the antibacterial property of the alloy against planktonic P. gingivalis. The relationship between the antibacterial mechanism of the alloy with oxidative stress was evaluated through ROS fluorescence intensity and protein leakage concentration. The results revealed that the alloy significantly eliminated adherent bacteria and inhibited biofilm formation. Moreover, 3D-printed porous TC4-6Cu alloy demonstrated significant bactericidal ability by inducing the production of reactive oxygen species (ROS), which could result in protein leakage from the bacterial cell membrane. This research may open a new perspective on the development and biomedical applications for dental implantation