V.F. da Costa’s research while affiliated with State University of Campinas (UNICAMP) and other places

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.

The connection of generators on distribution feeders may cause significant impact on the steady-state performance of the network. Quantification of the impacts on power losses, in a systematic way, is a difficult task due to the complexity of network operation since generators can operate with different lead and lag power factors and, occasionally, can inject variable active power on the network. This paper evaluates the impact of distributed generators on the active and reactive power losses of the system by using a sensitivity-based method. From one base case power flow solution it is possible to estimate the active and reactive power losses for a new generator installed at any bus of the system, for any combination of active power injection, and also for any operating power factor. The effects of varying the location, generation level and operating mode of the generators can be easily assessed by using the analytical method. Moreover, a numerical index to quantify the impact of multi-distributed generators on power losses is also proposed. The method is applied to a 70-bus distribution network. The simulations results are compared with those obtained by the repetitive power flow solutions in order to validate the results obtained by the sensitivity-based method.

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.

Continuous advances in terms of the capability of modern computers allow the development of power systems analysis tools that takes into consideration aspects that are usually neglected for power flow calculation. Examples are detailed models for generators, turbines, speed and voltage controllers that are usually over-simplified, flexible AC transmission systems devices, induction generators, dynamic loads, etc. This paper presents a generalized power flow method able to include the steady state characteristics of any dynamic device by using the same models considered for time domain simulation. The method solves simultaneously the power system set of algebraic and differential equations at the steady-state equilibrium, allowing monitoring the dynamic devices performance when certain parameter is changed, such as the load level or the voltage setpoint of a given controller, or after the occurrence of contingencies. Simulations in a 16-machines/69-buses test system show that the proposed method provides the system post-disturbance equilibrium point with the high degree of accuracy of time domain simulation and the low computational requirements of conventional power flow.

Continuous advances in the field of power electronics have resulted in new technologies connected to power systems. Examples are the different types of FACTS devices connected to the network to perform a number of control functions or to reinforce congested areas. However, conventional power flow methods are not capable of representing these new components with accuracy. This paper presents a generalized power flow method able to include the steady state characteristics of any dynamic device by using the same models considered for time domain simulation. The proposed method allows the monitoring of the performance of the dynamic devices when certain parameter is changed, such as the load level or the voltage setpoint of a given controller.

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 smallsignal and transient stability.

In order to accomplish specific compensation objectives a static synchronous series compensator (SSSC) may be controlled by several ways. The most common control modes of the SSSC are: (1) constant voltage mode, (2) constant impedance emulation mode, and (3) constant power control mode. Moreover, to improve the dynamic performance of the system, a SSSC may be equipped with supplementary controllers, such as damping controls. Therefore, this paper investigates the impacts of different SSSC control modes on small-signal and transient stability of a power system. The performance of different input signals to the power oscillation damping (POD) controller is also assessed. The stability analysis and the design of the SSSC controllers are based on modal analysis, non-linear simulations, pole placement technique, and time and frequency response techniques. The results obtained allow to conclude that the usage of the SSSC in the constant impedance emulation mode is the most beneficial strategy to improve both the small-signal and transient stability.

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.

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 H2 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.

This paper presents a detailed comparative analysis between synchronous and induction machines for distributed generation applications. The impacts of these generators on the performance of distribution networks are determined and compared by using different computational simulation tools and models.The technical factors analyzed are steady state voltage profile, electrical losses, voltage stability, transient stability, voltage sags due to unbalanced faults and short-circuit currents. The results show that the most suitable choice depends on the network technical characteristics, i.e. what are the main operating restrictions related to distributed generation.