V.F. da Costa

Comparative analysis between synchronous and induction machines for distributed generation applications

This paper presents a detailed comparative analysis between synchronous and induction machines for distributed generation applications. The impacts of these generators on the distribution network performance are determined and compared by using computational simulations. The technical factors analyzed are steady-state voltage profile, electrical power losses, voltage stability, transient stability, voltage sags during unbalanced faults, and short-circuit currents. The results showed that the best technical choice depends on the network characteristics, i.e., the main factors that may limit the penetration level of distributed generation.

Continuation fast decoupled power flow with secant predictor

The conventional Newton and fast decoupled power flow methods are considered inadequate for obtaining the maximum loading point of power systems due to ill-conditioning problems at and near this critical point. At this point, the Jacobian matrix of the Newton method becomes singular. In addition, it is widely accepted that the P-V and Q-/spl theta/ decoupling assumptions made for the fast decoupled power flow formulation no longer hold. However, in this paper, a new fast decoupled power flow is presented that becomes adequate for the computation of the maximum loading point by simply using the reactive power injection of a selected PV bus as a continuation parameter. Besides, fast decoupled methods using V and /spl theta/ as parameters and a secant predictor are also presented. These new versions are compared to each other with the purpose of pointing out their features, as well as the influence of reactive power and transformer tap limits. The results obtained for the IEEE systems (14 and 118 buses) show that the characteristics of the conventional method are enhanced and the region of convergence around the singular solution is enlarged.

Dynamic VAr sources scheduling for improving voltage stability margin

This paper presents a methodology to be added at the power system dispatch problem in order to evaluate and improve voltage stability margin by optimizing generators and synchronous condensers reactive power injection. The main objective is to reschedule the reactive injection of the machines, from a perspective of improving voltage stability margin, without impact on the active economical dispatch.

A power sensitivity model for electromechanical oscillation studies

This paper describes the derivation of a power sensitivity model for dynamic studies of power systems, subjected to normal operation disturbances. The need of an infinite bus representation is avoided with the linearized nodal power balance approach. This permits the model to be easily extended to any number of network buses. In the linearized form, the resulting power sensitivity model (PSM), presents some interesting features, such as decoupled modelling and time scale decomposition properties. For presentation reasons, the PSM is first derived for a single generator connected to an infinite bus. Its performance is then compared with the classical Heffron-Phillips Model, as described by de Mello and Concordia (1969). Finally, it is extended for multinodal networks. >

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.

MVAr management on the pre-dispatch problem for improving voltage stability margin

This paper presents a methodology that includes at the power system pre-dispatch problem the evaluation and improvement of voltage stability margin by optimizing generators and synchronous condensers reactive power injections. From modal participation. factors it is defined penalty indices for all generators, which are added to the optimal power flow objective function. The purpose is to obtain the most adequate reactive power injection for each generator or synchronous condenser, from a perspective of maximizing voltage stability margins. Preliminary results presented in this paper, obtained for the New England test system of 39 buses and 10 generators, show that the proposed methodology leads to significant voltage stability margin improvement for all the critical time intervals of the day. A clear advantage of the proposed methodology is that the optimal solution for generators active injection is kept unchanged. It means no impact on generators energetic targets, and no impact on the total generation cost. Hence, voltage stability margin is improved by just managing the reactive power dispatch.

Parameterized fast decoupled load flow for tracing power systems bifurcation diagrams

The conventional Newton and fast decoupled load flow methods are considered to be inadequate to obtain the maximum loading point due to ill-conditioning problems at and near this critical point. At this point the Jacobian matrix of the Newton-Raphson method becomes singular, and the assumptions made for the fast decoupled formulation no longer hold. However, as shown in this paper, with small modifications these methods become adequate for the computation of the complete bifurcation diagrams. They are also adequate for obtaining a single solution near the nose point or at the lower part of PV curve with flat start initialization. These new methods are compared to each other with the purpose of pointing out their features, as well as the influence of reactive power and transformer tap limits. The results obtained for the IEEE systems (14, 30, 57 and 118 buses) show that the characteristics of the conventional methods are preserved.

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.

Transmission systems congestion management by using modal participation factors

Power system congestion management is a hard task, and the electricity industry restructuring process tends to difficult it even more. The competitive electric power market arises new congestion management perspectives and difficulties. This work demonstrates that modal analysis technique can be a powerful tool for defining corrective actions to overcome congestion problems. Extensive voltage stability margin assessment, for a test system, shows that modal participation factors allow the identification of congested areas, and also the most adequate active and reactive power based control actions to relieve congestion.

Preliminary results on improving the modal analysis technique for voltage stability assessment

This paper investigates the theoretical foundations and practical applications of the modal analysis technique applied to power system voltage stability assessment. Improvements are made to the existing technique. The results show that two reduced Jacobian matrices, one related to reactive power and the other related to active power, are needed for extracting complete modal information. There is no need to use a full Jacobian matrix for modal analysis. As a preliminary result, a technically sound generator participation factor index is proposed based on the findings.