Vivaldo Fernando da Costa

Evaluation of the impact of distributed generation on power losses by using a sensitivity-based method

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.

Alternative parameters for the continuation power flow method

Abstract The conventional Newtons method has been considered inadequate to obtain the maximum loading point (MLP) of power systems. It is due to the Jacobian matrix singularity at this point. However, the MLP can be efficiently computed through parameterization techniques of continuation methods. This paper presents and tests new parameterization schemes, namely the total power losses (real and reactive), the power at the slack bus (real or reactive), the reactive power at generation buses, the reactive power at shunts (capacitor or reactor), the transmission lines power losses (real and reactive), and transmission lines power (real and reactive). Besides their clear physical meaning, which makes easier the development and application of continuation methods for power systems analysis, the main advantage of some of the proposed parameters is that its not necessary to change the parameter in the vicinity of the MLP. Studies on the new parameterization schemes performed on the IEEE 118 buses system show that the ill-conditioning problems at and near the MLP are eliminated. So, the characteristics of the conventional Newtons method are not only preserved but also improved.

Impacts of dynamic reactive power compensation devices on the performance of wind power generators

This paper investigates the main impacts of dynamic reactive power compensation devices on the performance of induction machine-based wind power generators. The dynamic reactive power compensation devices analysed are the SVC (Static Var Compensator) and the DSTATCOM (Distributed Static Synchronous Compensator). The usage of these devices as a power factor regulator or a voltage regulator is investigated. The technical factors analysed are small-signal voltage stability, transient stability and interactions with the anti-islanding protection system. The analyses are carried out by using a wind farm composed of 30 units of 1 MW induction generators. Such wind farm is connected to a 60 Hz, 33 kV distribution system. The results are a useful guideline to evaluate which control strategy and device are suitable for a determined application as well as to understand the dynamic interactions that can occur.

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.

Análise comparativa entre geradores síncronos e geradores de indução com rotor tipo gaiola de esquilo para aplicação em geração distribuída

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.

Power System Voltage Stability Assessment Using Enhanced Power Flow Models

This paper presents an enhanced method for power system voltage stability assessment. Key features of this method are the inclusion of the characteristics of key dynamic devices and an efficient method to solve the associated algebraic and differential equation sets in steady-state conditions. It offers an accurate representation of equipment operating characteristics for voltage stability margin calculation. The importance of the proposed modeling approach is demonstrated with simulation results.This paper presents an enhanced method for power system voltage stability assessment. Key features of this method are the inclusion of the characteristics of key dynamic devices and an efficient method to solve the associated algebraic and differential equation sets in steady-state conditions. It offers an accurate representation of equipment operating characteristics for voltage stability margin calculation. The importance of the proposed modeling approach is demonstrated with simulation results.

Comparative Studies on Methods of Modeling Generator Var Limit for Power-Flow Calculations

In power flow calculations, usually a generator is represented as a P V bus, and a simplified method is used to model its reactive power limit. The P Q modeling approach, which converts the generator from P V bus to P Q bus when the reactive power limit is reached, is widely accepted and used by professional load flow programs; however, in reality, a generator on the limit behaves as a constant field voltage instead of a constant reactive output. This fact has raised frequent discussions on the literature about the accuracy or errors introduced by the conventional P Q model on power flow computations. Unfortunately, the real differences between the two modeling approaches for power flow studies have not been researched by these previous efforts. The purpose of this paper is to carry out comprehensive investigation on the impact of the two modeling methods for power flow studies. They are compared from three different perspectives: impact on load flow results, impact on voltage stability margin, and convergence behavior. Based on the results, advantages and dis advantages of the two modeling approaches are discussed, and conclusions are made on the appropriate approach for representing generator var limit for load flow studies.In power flow calculations, usually a generator is represented as a P V bus, and a simplified method is used to model its reactive power limit. The P Q modeling approach, which converts the generator from P V bus to P Q bus when the reactive power limit is reached, is widely accepted and used by professional load flow programs; however, in reality, a generator on the limit behaves as a constant field voltage instead of a constant reactive output. This fact has raised frequent discussions on the literature about the accuracy or errors introduced by the conventional P Q model on power flow computations. Unfortunately, the real differences between the two modeling approaches for power flow studies have not been researched by these previous efforts. The purpose of this paper is to carry out comprehensive investigation on the impact of the two modeling methods for power flow studies. They are compared from three different perspectives: impact on load flow results, impact on voltage stability margin, and conver...

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.

A PROCEDURE FOR TUNING STATCOM PARAMETERS FOR DAMPING POWER SYSTEM OSCILLATIONS

Abstract This work investigates the effects of the STATCOM (Static Synchronous Compensator), a FACTS (Flexible AC Transmission Systems) device, on small-signal power system angle stability. This investigation is carried out for a single machine connected to an infinite bus via a loss-less transmission line. The study is based on investigation of the eigenvalues of the linearized power system model 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 simulations results enable an analysis of the effects of this controller for damping power systems low frequency electromechanical oscillations.