Marcelo Souza de Castro

A didactic procedure for designing power oscillation dampers of FACTS devices

Abstract An important issue related to power system stability is to properly damp low frequency oscillations. Traditionally, these oscillations have been damped by means of power system stabilizers. In recent years, FACTS devices equipped with a power oscillation damper have been also efficiently used for damping oscillations. This paper is a tutorial for designing such power oscillation damper. The paper presents design projects suitable for students in the power system control area at the M.Sc. and Ph.D. levels. For educational purposes, the procedure is based on Matlab and on two specific toolboxes, namely the Power System Analysis Toolbox and the Control System Toolbox. A single-machine infinite bus and a two-area test systems, with a thyristor controlled series compensator and an unified power flow controller, respectively, are used as examples for the POD design. Classroom experience has shown that the procedure helps in consolidating a better understanding of power system stability and control.

Impacts of FACTS controllers on damping power systems low frequency electromechanical oscillations

This paper presents a study comparing the effects of four flexible ac transmission systems (FACTS) controllers, the static var compensator (SVC), the static synchronous compensator (STATCOM), the thyristor controlled series compensator (TCSC) and the static synchronous series compensator (SSSC) on power systems small-signal angle stability. This investigation is carried out for a single generator connected to an infinite bus via a loss-less transmission line. The study is based on the investigation of the critical eigenvalues of the power system linearized model in the framework of the dynamic bifurcation theory. The presented simulation results allow a comparative analysis of the effects of these four controllers and reveal that the SSSC exhibits the best effectiveness on damping power systems low frequency electromechanical oscillations.

A Comparative Analysis of AC and DC Incremental Methods for Transmission Loss Allocation

This paper intends to analyze the accuracy of incremental DC methods for loss allocation in electricity markets. The model under implementation at the Brazilian electricity market is one of this kind and has motivated this investigation. The model to be used in Brazil is based on incremental methods and defines loss factors for generators and loads. This technique uses a DC load flow to calculate the loss factor, and so it does not consider the complete power flow equations. Consequently, this method may provide unfair loss allocation depending on the system operation condition. Hence a method is developed to calculate the loss factors, based on incremental methods but using an AC load flow that takes into account the system nonlinearity. Both methods are applied to a small system for conceptual discussions and to a version of the Brazilian North-Northwest system for the validation of the results by using a real system. The results demonstrate the limitations of the DC method for loss allocation, justifying the use of an AC load flow to calculate the total system losses and the loss factors. The loss factors calculated by both methods depend on the choice of the slack bus. In order to overcome this limitation, the concept of distributed slack bus is included into the AC power flow, and new slack-bus independent results are obtained.

H 2 Norm-Oriented STATCOM Tuning for Damping Power System Oscillations

This work is mainly concerned with the effects of the static synchronous compensator (STATCOM), a flexible AC transmission system (FACTS) controller, on small-signal power system angle stability. This investigation is carried out for both inter-area and local oscillations mode. The study is based on the investigation of the eigenvalues of the linearized power system models in the framework of dynamic bifurcation theory. The tuning method of the STATCOM gains aiming the H 2 norm minimization is briefly explained, and the presented simulation results are sufficient to provide a comprehensive analysis of the effects of this controller for damping power systems low frequency electromechanical oscillations.

A influência do modo de operação do SSSC na estabilidade de ângulo de sistemas elétricos de potência

In order to accomplish specific compensation objectives, a Static Synchronous Series Compensator (SSSC) can be controlled according different methods. In the literature, the most discussed control modes of the SSSC are 1) constant voltage mode, 2) constant impedance emulation mode, and 3) constant power control mode. The first two modes above cited are used when purely series reactive compensation is required, whereas the third one also enables to control the power flow in the transmission network. Since these modes can have different impacts on system angle stability, this paper aims to assess the influence of SSSC operation mode on both small-signal and transient stability of power systems. The study is based on modal analysis and time domain simulations which are carried out by using the Power System Analysis Toolbox (PSAT). The results obtained allow to conclude that, when performing purely series reactive compensation, the SSSC usage in the constant impedance emulation mode is the most beneficial strategy to improve both small-signal and transient stability.

Interfacial-tension-force model for the wavy stratified liquid-liquid flow pattern transition: The usage of two different approaches

The study of the hydrodynamic stability of flow patterns is important in the design of equipment and pipelines for multiphase flows. The maintenance of a particular flow pattern becomes important in many applications, e.g., stratified flow pattern in heavy oil production avoiding the formation of emulsions because of the separation of phases and annular flow pattern in heat exchangers which increases the heat transfer coefficient. Flow maps are drawn to orientate engineers which flow pattern is present in a pipeline, for example. The ways how these flow maps are drawn have changed from totally experimental work, to phenomenological models, and then to stability analysis theories. In this work an experimental liquid-liquid flow map, with water and viscous oil as work fluids, drawn via subjective approach with high speed camera was used to compare to approaches of the same theory: the interfacial-tension-force model. This theory was used to drawn the wavy stratified flow pattern transition boundary. This pa...