The development of a microprocessor based excitation control system for brushless generators

Automatic voltage regulators (AVRs) have been used to control the excitation of generators for many years, the early electro-mechanical types being replaced by solid-state regulators utilising power transistors and thyristors controlled by various forms of analogue circuitry. Due to the availability of smaller and more reliable components, together with increased experience, AVRs are now readily available and include many additional features as standard which would previously not have been practical. Economic factors associated with the size of the machine and its application have to be considered but in general the larger the machine, the more sophisticated the specification for the excitation equipment. The current designs of AVR based mainly on analogue circuit techniques have proved very successful and reliable but their relative lack of flexibility has prompted the development of a microprocessor based AVR to overcome this limitation and provide additional facilities. The paper outlines briefly the basic requirements of a microprocessor based AVR targeted for machines ranging from 10 to 200 MW, and describes how the development progressed