F. A. Uribe

Vulnerability Analysis of Power Grids Using Modified Centrality Measures

The aim of this paper is to propose modified centrality measures as a tool to identify critical nodes before a vulnerability analysis is performed in an electrical power grid. Pair dependency centrality is weighted using the grid active power flow, and this becomes the basis to define closeness and betweenness of its nodes, and hence to identify the most critical ones. To support the idea of using modified centralities, four power grids are tested to be either exponential or scale-free. To evaluate the proposal, information obtained via modified centrality measures is used to calculate global efficiency of the power grids.

Accurate Computation of Transient Profiles Along Multiconductor Transmission Systems by Means of the Numerical Laplace Transform

In this paper, transient internal profiles along multiconductor transmission lines are obtained from a model described in the q- s domain (spatial frequency-temporal frequency). In such domain, the telegrapher equations of the line are defined in a direct algebraic form. Applying boundary conditions, these equations can be easily solved for V (q,s) and I (q,s). Then, the inverse numerical Laplace transform is applied successively (twice) to obtain v (z,t) and i (z,t), that is, the voltage and current profiles along the line. Besides, since the lines electrical parameters are defined in the frequency domain, the frequency dependence of such parameters is included in a straightforward manner. Test cases corresponding to an overhead line, a transformer winding, an underground power cable, and a transmission network are evaluated in order to demonstrate the accuracy and versatility of the proposed method. The results are compared with those obtained with Alternative Transients Program/Electromagnetic Transients Program and PSCAD/EMTDC at specific points along the transmission systems under analysis, given that the space discretization is cumbersome and prone to error accumulation in these time-domain simulation programs.

Alternative Series-Based Solution to Approximate Pollaczek's Integral

In this letter, the Wedepohl-Wilcox series is combined with the trapezoidal rule of integration for calculating ground return impedances of buried cables. In this hybrid method, the former are used for low frequencies and the latter are for high frequencies. Based on a numerical analysis, a criterion for switching between series and numerical integration is proposed here and compared with the one proposed by Wedepohl-Wilcox. Validation of the improved criterion is made via an electromagnetic transient.

Ground-Impedance Graphic Analysis Through Relative Error Images

This paper proposes a contour image-based graphic method useful to estimate the relative error between approximate ground-impedance models and the algorithmic solution of the Carsons integral over a wide ranges of frequencies and soil conductivities for any overhead transmission-line configuration.

Synchronous Generator Emulator Prototype as a Testbed for Electric Equipment

The aim of this study is to describe a synchronous generator emulator prototype based on a three-phase power electronics converter. The physical structure of the emulator and its relation with the generator mathematical model is described. A voltage-behind-reactance model is used to reproduce the behavior of the generator. Comparison of experimental results against simulations confirms the validity of the proposal.

Efficient Truncation Criterion for the Parameter Estimation of a Stratified Ground Block

A truncation criterion to solve the vector potential integrals proposed by Takahashi and Kawase is described in this letter. The main aim of those integrals is to estimate the depth and resistivity parameters of a stratified ground block. The derivation of the proposed criterion considers the error introduced by the infinite limit truncation of the integrals. In addition, an efficient solution can be obtained by the use of the trapezoidal rule of integration.

Improvement of damping impedance method for Power Hardware in the Loop simulations

The aim of this study is to present an improvement of the Damping Impedance Method (DIM) Interface Algorithm for Power Hardware in the Loop (PHIL) simulations. The improvement is based on the calculation of the Hardware Under Test (HUT) impedance, in order to include it as part of the Damping Impedance Method to enhance its accuracy and stability. To verify the results, the improved DIM interface is simulated using MATLAB/Simulink, furthermore, a laboratory implementation of a PHIL simulation is carried out using a variable load. The stability of the interface algorithm is graphically observed using the Nyquist and Bode stability criteria, whereas the precision is validated through simulations that compare the Mean Square Error (MSE), as well as laboratory experiments.

Droop controller comparison for AC microgrids

The aim of this study is to analyze and compare three droop controller schemes to regulate the operation of a microgrid. Three droop control schemes are selected because of their capability to regulate voltage, frequency and power sharing without using communication links and complex measurement systems. Specifically, the conventional droop controller and two of its variants are compared, the angular and robust controllers. An analysis regarding their differences is given in terms of voltage, frequency, and power sharing performance.

Phase compensation scheme to improve the accuracy of a power hardware-in-the-loop experiment based on a synchronous generator

The aim of this study is to present a phase compensation scheme that improves the accuracy of a power hardware-in-the-loop simulation. The ideal transformer model interface method along with feedback current filtering is used to connect a synchronous generator simulation to a test system. The generator is modeled using a voltage-behind-reactance representation. Comparison of experimental results against simulations confirms the validity of the proposal.

Enhanced hybrid technique for calculating ground impedances of underground power cables

A recently investigation of the series solution presented by Wedepohl et al., in 1973, yields a new hybrid technique for calculating ZG of buried cables. An enhanced hybrid technique partly analytic-numeric is used in this paper to assess the behavior of other important techniques for calculating ground-return impedances of underground power cables. The accuracy of the here proposed technique is comparable to the Wedepohl series solution, hypergeometric confluent functions, numerical integration modified method and an image based closed-form approximation.