Introduction

Purposes

Given a model and the parameters of the generator and its exciter, there is little published in the literature describing the various methods for the tuning of automatic voltage regulators (AVRs) to achieve certain performance specifications for the generator off- and on-line.

An aim of this chapter is to introduce and provide an analytical basis for various tuning methodologies, which provide a set of parameters for the particular AVR model. Further analysis may depend on the type and form of the AVR supplied by a manufacturer. However, even for complex AVR structures, the proposed methodologies may provide an initial set of parameters based on a simplified model of the AVR. Subsequent fine-tuning, based on the complex structure, can then yield an appropriate final set of parameters.

It should be emphasized that the tuning methodologies considered here are based on the concept of transient gain reduction, though various other design approaches are employed [1]. Depending on the type of AVR, rate-feedback may also be used to essentially effect a similar behaviour as transient gain reduction. Furthermore, more modern systems which employ proportional-integral-derivative (PID) controls can be tuned to give a response akin to transient gain reduction. It is recognized that manufacturers of the equipment have their own, effective procedures for tuning. However, when tuning, it is important in a number of scenarios to account for the power system characteristics over an encompassing range of normal and outage conditions. The latter considerations are often of concern to the transmission service provider (TSP) who may be responsible for system security. It is therefore desirable that staff in such TSPs understand the relevant methodologies and can undertake or validate, if necessary, the tuning of AVRs.

A further objective in the description of the methodologies is to provide for young engineers an introductory and a reference text which not only covers the relevant control systems background but also highlights the power system requirements and performance.

Coverage of the topic

Because powerful methods of analysis are available in linear control systems theory, the tuning of AVRs is based on small-signal analysis and the linearized models of the power system and associated devices. The performance of the resulting tuned AVR, and the other elements of the power system, should then be subject to simulation studies for an appropriate set of large-signal disturbances over the range of operating conditions.