Damping of Electromechanical Oscillations Using Power System Stabilizers

Abstract

This thesis deals with the damping of electromechanical oscillations using Power System

Stabilizers (PSS). The thesis focuses on three problems associated with the damping of

these oscillations, namely the determination of the optimal locations of the PSS, the

determination of the best control structure of the PSS and the design of robust PSS.

We develop two new methods for determining the optimal locations of the PSS. These two

methods are based on Total Modified Coupling Factors (TMC) and optimization by

Simulated Annealing (SA). The TMC is a measure of the damping influence of each

machine pair on several power system modes. The TMC incorporates the effect of the

performance and the type of excitation system of the generator. The method based on TMC

is tested on a nine-bus benchmark network. In the method based on SA, we formulate the

PSS placement problem as a discrete nonlinear optimization problem. The objective

function corresponds to the damping of the electromechanical modes of the system. In this

method, the placement is performed simultaneously for all PSS. Using SA, we obtain a

placement scheme which guarantees that the undesired poles can be controlled with finite

control energy. As a result of the optimization formulation, the method based on SA is

computationally more intensive than the method based on TMC. We demonstrate the

method based on SA on two networks namely, a seven-bus network and a 35-bus

equivalent of the Eskom network.

The problem of determining the control structure for damping of the electromechanical

oscillations is composed of three aspects namely, the type of feedback, the type of signal

and the type of control.

The type of feedback investigates the use of State Feedback and Output Feedback. We

present a new method of determining the parameters of a fixed structure PSS by

transforming the Dynamic Output Feedback problem into a Static Output Feedback

problem.