Design considerations for a stator side voltage regulated permanent magnet AC generator

The application of permanent magnet generators in variable-speed applications is made difficult by the lack of a direct field control and the variation of the stator voltage with shaft speed and also with load. This paper presents the use of reactive power injection into the stator as a means of regulating the stator voltage. Design-oriented analysis of the machine stator current and reactive power requirements for this mode of operation leads to the conclusion that high machine saliency enables excellent terminal voltage regulation over a specified speed and load range while minimizing stator current requirements. It is shown that the incorporation of saliency into the permanent magnet generator can significantly reduce the size of the reactive current source and the stator current that is required to regulate the stator voltage during operation over a broad range of speeds and loads. Experimental results are presented to confirm the basic principles of this approach.