New Variable Speed Constant Frequency Stand-alone Power Generating System

Abstract

Variable speed and constant frequency power generating systems using rotor excitation of the wound-rotor induction machines have been used for such applications as variable speed pump generators and flywheel energy storage systems. However, the stand-alone generating system of this type, has only been reported and has not yet been practically used.On the other hand, the stand-alone generating systems using diesel engines have been widely used for emergency supply of plants or isolated islands and so on. However, in these cases, the synchronous generators are usually used. If the output frequency is to be kept constant, there is the need to control the speed of the engine using a high performance governor. Even then, the output frequency changes in case of a sudden load change.This paper proposes a new stand-alone power generating system. In this system, the constant frequency output voltage can be obtained even though rotor speed changes by several percent.