Currently many literature's are seen on digital excitation control system , brushless synchronous generators are controlled by this system consisting AVR which gives PWM signal to control the voltage of the field winding of the generator.

The Following References may help you in your Work.

1. http://www.hitachipowersystems.us/supportingdocs/forbus/hpsa/technical_papers/r2000_02_104.pdf

Recent Developments on Generator Excitation Control System

— Introduction of Digital AVR and Power System Stabilization

Technology —

Yoshihiro Kitauchi, Takashi Shirasaki, Kunitaka Hayashi, Minoru Banjo,

Satoshi Kitamura

2. http://waset.org/publications/13694/design-and-construction-of-automatic-voltage-regulator-for-diesel-engine-type-stand-alone-synchronous-generator

Design and Construction of Automatic Voltage

Regulator for Diesel Engine Type Stand-alone

Synchronous Generator

Myinzu Htay and Kyaw San Win

3. http://www.roadranger.com/ecm/groups/public/@pub/@electrical/documents/content/ct_129972.pdf

DIGITAL EXCITATION SYSTEM PROVIDES ENHANCED PERFORMANCE AND IMPROVED DIAGNOSTICS

C. Allan Morse, C. Richard Mummert

Members, IEEE

Eaton / Cutler – Hammer

221 Heywood Road

Arden, NC 28704

4. http://www.allbookez.com/recent-trends-in-ac-voltage-regulator/

Gives a Couple of PDF Papers on AVR.

P.S.