Chris J. Dafis

Analysis of power system transient disturbances using an ESPRIT-based method

The area of electric power quality has witnessed increased attention, especially in the area of modeling and analysis of power quality measurements. This paper concentrates on the harmonic decomposition of capacitor-switching transient disturbances with a main objective on introducing a new technique in the area of power system analysis, an ESPRIT-based method. Initial sensitivity tests indicate promising results in providing a new and improved tool in the harmonic decomposition of capacitor-switching transients. The sensitivity tests focus on corrupting the data sequences with zero-mean white Gaussian noise at different voltage deviation levels, and analyzing the performance of the decomposition method. The transient disturbances used in the analysis are real data, created in the Center for Electric Power Engineering, Drexel University.

A nonlinear observability formulation for power systems incorporating generator dynamics

Traditionally, a nonlinear algebraic model of the power system is used to determine the system observability. In particular, the sensitivity of the system measurements (real and reactive power for example) to the change in the system states (bus voltages and angles) is used as a measure of observability, derived from the power system state-estimation problem. It ignores, however, the nonlinear dynamics of the system related to generator performance, nonlinear components, etc. The proposed observability formulation accounts for these nonlinearities and provides a more comprehensive observability determination. The formulation is derived from a DAE model of the power system, and incorporates the dynamics of the generators present in the system.

Characteristics of Degree of Observability Measure for Nonlinear Power Systems

The concept of developing a measure that evaluates the degree of system observability for nonlinear power systems modeled as DAEs has been introduced by the authors in the past with an emphasis on the dependence of this measure to the available measurement sets and changes in the inherent differentiation indices. This work extends this analysis by investigating the sensitivity of the observability measure to system initial conditions and dynamic parameter variations. In particular, the sensitivity of the measure to the generator parameters (inertia and damping) and variations in the system load trajectories (PV-curves) is investigated. The presented results indicate that the degree of observability is robust to small deviations of the system initial conditions, and dependent on the generator damping and inertia coefficients.

Examining characteristics of an observability formulation for nonlinear power systems

The concept of developing a technique to evaluate the observability of nonlinear systems in general, and its specific application to nonlinear power systems has been introduced in the past. This technique allows for the evaluation of system observability along the trajectories of the system dynamic states, providing the ability to trick the system through various perturbations. This paper focuses on qualifying the implications associated with the evaluation of the observability Jacobian due to the presence of dynamic loads (exponential recovery model) and varying the system/measurement differentiation indices for a given measurement set. These conditions are illustrated with a qualitative analysis of a 3-bus power system.

Multi-converter observability issues associated with shipboard MVDC power systems

In power electronics systems, such as the planned Naval Shipboard Medium Voltage Direct Current (MVDC) system, multiple converters are used in distribution and generation subsystems to provide different voltage levels and form. A measure of observability of such systems will allow one to quantify their operational performance. This paper attempts to account for observability of these multiconverter systems through the inclusion of other dynamics such as electromechnical behavior of generators and loads, providing a more comprehensive view of system performance. The example section will focus on a DAE model of a simplified MVDC system where the observability formulation is applied and results reflect the influence of these additional states on overall observability and system performance.

Nonlinear observability formulation for shipboard power systems incorporating converter dynamics

Performance of planned shipboard distribution/generation systems can be affected by power fluctuations and inappropriate control strategies. A measure of observability of such systems will allow one to quantify their operational performance. This paper attempts to account for observability of these systems through the incorporation of nonlinear dynamics of converters and electromechanical behavior of generators and loads. The example section will focus on a DAE model of a shipboard system where observability formulation is applied and results reflect the influence of these additional states on overall observability and system performance.

A measure of observability for multiconverter shipboard power systems

Perturbations in shipboard power systems can make controllers useless if improper control strategies are used. Incorporating the nonlinear dynamics of the shipboard power system in the control methodology is the solution to this problem. Before this solution is designed, the concept of nonlinear observability should be first investigated. A measure of observability of such systems will allow one to quantify their operational performance. This paper attempts to account for an observability measure of these multiconverter systems through the inclusion of other dynamics such as electromechnical behavior of generators and loads, providing a more comprehensive view of system performance. In the example section the observability condition number will lead to an indicator of how far the system is from being unobservable based on the system load profile.

A study on the prediction of capacitor-switching transient times

This paper presents a unique approach in the analysis of capacitor-switching transient disturbances, in an automated switching scenario. Unlike previous research attempts, which analyze the generated disturbance waveform, this study focuses on modeling the switching action of the network device responsible for the switching operation. Successful models were developed, allowing for the prediction of future switching operations. The determination of the minimum sample size needed for an accurate model, along with the associated prediction error criteria are presented. The results are based on an automated capacitor switching voltage support experiment, constructed at the Center for Electric Power Engineering, Drexel University, using the General Electric Type FKC-2 motorized oil switch. For the extracted transient time data sequences, the models can predict future switching operations within 2.1 msec.