Chika O. Nwankpa

Local bifurcation in power systems: theory, computation, and application

This paper provides an of overview of local bifurcation theory and its application to power system voltage stability analysis. The qualitative behavior of power system dynamics as modeled by differential-algebraic equations is discussed, followed by a summary of the concepts and tools for the analysis of local bifurcation from equilibria. Computational methods for locating and classifying bifurcation points as they have been applied in power system analysis are reviewed. Several examples are given.

Induction motor tests using MATLAB/Simulink and their integration into undergraduate electric machinery courses

This work describes MATLAB/Simulink implementation of three induction motor tests, namely dc, no-load, and blocked-rotor tests performed to identify equivalent circuit parameters. These simulation models are developed to support and enhance electric machinery education at the undergraduate level. The proposed tests have been successfully integrated into electric machinery courses at Drexel University, Philadelphia, PA, and Nigde University, Nigde, Turkey.

Computation of singular and singularity induced bifurcation points of differential-algebraic power system model

In this paper, we present an efficient algorithm to compute singular points and singularity-induced bifurcation points of differential-algebraic equations for a multimachine power-system model. Power systems are often modeled as a set of differential-algebraic equations (DAE) whose algebraic part brings singularity issues into dynamic stability assessment of power systems. Roughly speaking, the singular points are points that satisfy the algebraic equations, but at which the vector field is not defined. In terms of power-system dynamics, around singular points, the generator angles (the natural states variables) are not defined as a graph of the load bus variables (the algebraic variables). Thus, the causal requirement of the DAE model breaks down and it cannot predict system behavior. Singular points constitute important organizing elements of power-system DAE models. This paper proposes an iterative method to compute singular points at any given parameter value. With a lemma presented in this paper, we are also able to locate singularity induced bifurcation points upon identifying the singular points. The proposed method is implemented into voltage stability toolbox and simulations results are presented for a 5-bus and IEEE 118-bus systems.

A stochastic approach to small disturbance stability analysis

A systematic approach to the construction of stochastic models of electric power systems for small disturbance stability analysis is presented. In this study, the cumulative effects of small-magnitude random fluctuations of electrical loads are considered as sources of eventual loss of stability, and a security measure is derived to determine the small-disturbance stability limits of the stochastic system. The electric power system models were tested on a 30-bus power system and compared according to the relative effects of load fluctuations on the proposed security measure. >

Identification of capacitor position in a radial system

As modern equipment is more sensitive to power quality phenomena, transients introduced by capacitor switching become an increasing concern. The paper addresses the identification of switched capacitor position such that on-line or post-fault measures can be taken. The position is given in terms of proportional line impedance seen from the load bus. Perturbation methods are used to find an asymptotic expression for capacitor position as a function of the transient frequency. This paper presents analytical and simulation results for a standard radial distribution system.

An Exact Method for Computing Delay Margin for Stability of Load Frequency Control Systems With Constant Communication Delays

The extensive usage of open communication networks in power system control causes inevitable time delays. This paper studies impacts of such delays on the stability of one-area and two-area load frequency control (LFC) systems and proposes an analytical method to determine delay margins, the upper bound on the delay for stability. The proposed method first eliminates transcendental terms in characteristic equation of LFC systems without making any approximation and transforms the transcendental characteristic equation into a regular polynomial. The key result of the elimination process is that real roots of the new polynomial correspond to imaginary roots of the transcendental characteristic equation. With the help of new polynomial, it is also possible to determine the delay-dependency of system stability and root tendency with respect to the time delay. An analytical formula is then developed to compute delay margins in terms of system parameters. For a large set of controller gains, delay margins of LFC systems are computed to investigate the qualitative effect of controller gains on the delay margin. Finally, simulations studies are carried out to verify the effectiveness of the proposed method.

Interconnected power systems laboratory: a computer automated instructional facility for power system experiments

This paper presents a unique facility capable of exhibiting the operation of modem-day power system energy management systems (EMS) for educational and possible research applications. We present the design and construction of the laboratory facility. Key elements include a real-life, flexible power system network, signal conditioning hardware, data acquisition equipment, and client/server industry-standard computer networking technology. The system allows students to get experience on the realistic operation and control of power systems and exposes them to modem data acquisition and supervisory control (SCADA) equipment and procedures used by the industry.

Transformer tests using MATLAB/Simulink and their integration into undergraduate electric machinery courses

This article describes MATLAB/Simulink realization of open‐circuit and short‐circuit tests of transformers that are performed to identify equivalent circuit parameters. These simulation models are developed to support and enhance electric machinery education at the undergraduate level. The proposed tests have been successfully integrated into electric machinery courses at Drexel University, Philadelphia, PA and Nigde University, Nigde, Turkey.

Voltage Stability Toolbox for Power System Education and Research

This paper presents a Matlab-based voltage stability toolbox (VST) designed to analyze bifurcation and voltage stability problems in electric power systems. VST combines proven computational and analytical capabilities of bifurcation theory, and symbolic implementation and graphical representation capabilities of Matlab and its toolboxes. The motivation for developing the package is to provide a flexible simulation environment for an ongoing research conducted at the Center for Electric Power Engineering (CEPE) of Drexel University, Philadelphia, PA, and to enhance undergraduate/graduate power engineering courses. VST is a very flexible tool for load flow, small-signal and transient stability, and bifurcation analysis. After a brief summary of power system model and local bifurcations, the paper illustrates the capabilities of VST using the IEEE 14-bus system as an example and describes its successful integration into power engineering courses at Nigde University, Nigde, Turkey

Dynamic reactive load model

A new dynamic reactive load model for power system dynamic voltage stability studies is introduced in this paper. The model is measurement-based and incorporates the effect of voltage regulating equipment, specifically, switched distribution capacitor banks and subtransmission substation on-load tap changer transformers. A set of parameters that reflect these delayed-action devices are involved in the proposed model. A parameter estimation scheme is introduced with the aim of minimizing errors between model and collected data at two Pennsylvania Power and Light Company 230/64 kV substations. System simulation is also carried out based on the estimated parameters.