Influence of load following units on the static and dynamic characteristics of power system

The objective of this thesis is to introduce the concept of multiple slack buses into the analysis of static and dynamic characteristics of power systems. The experiments conducted in this thesis will show that when system loads fluctuate, the commonly used approximation that only one generator or all generators in the system are slack buses almost always lead to wrong conclusions about static or dynamic characteristics of the power system. As a result of this, we conclude that the real position of the slack buses must be included in the mathematical model of the power system in order to get a more accurate estimate of the static and dynamic characteristic of the studied power system. In order to include the position of slack buses in the analysis, a novel method for load flow with multiple slack buses is used.; Once the connection between slack bus position and static and dynamic characteristic power system has been established, the question of optimal selection of the AGC/load-following units arises naturally. In this thesis we propose the Q-sensitivity strategy for slack bus selection, which minimizes voltage violations in the power systems. Experimental results will show that while having a minor effect on the economics, the Q-sensitivity strategy can significantly improve system loadability and stability.; Chapter 1 gives an overview of power system elements that will be used in the static analysis of power systems. Special emphasis is given to load flow analysis, and a novel method for load flow with multiple slack buses is introduced.; Chapter 2 introduces automatic generation and control (AGC) and economic dispatch concepts in power systems as a response to load variations.; Chapter 3 contains a detailed presentation of the Q-sensitivity strategy for the slack bus selection. In this chapter we establish a correlation between load following units and voltage sensitivities in the power systems.; Chapter 4 is used to introduce a technique for the simulation of multimachine power systems using a two-axis model with an IEEE-Type I exciter.; Chapter 5 is the final chapter of the thesis, and presents yet another effect of the slack bus selection on the power systems. This time we examine effects of the slack bus selection on the dynamic characteristics of the power system using bifurcation theory. Experiments on IEEE 39 and IEEE 118 bus systems show that the choice of slack buses has substantial effect on power system dynamics, and that the previously proposed Q-sensitivity strategy for slack bus selection can also reduce the sensitivity of bifurcations to load-related parameters. (Abstract shortened by UMI.)...