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.
The use of a permanent magnet AC generator (PMACG) with a salient-pole rotor design combined with an appropriate power converter has recently been shown to be an attractive practical approach for implementing small power systems. Although a classical approach to realizing voltage regulation may be developed on the basis of reactive power control in power systems, it presents special challenges for variable-frequency operation, made more difficult by the presence of lightly-damped machine dynamics. This paper presents a simple and effective means for regulating the terminal voltage of the generator by controlling the DC voltage of a stator-connected voltage-source inverter. The paper presents a dynamic model that illustrates the source of lightlydamped behavior, followed by the introduction of power derivative equivalent feedback into the control system to obtain excellent performance. Computer simulations and experimental results are presented to demonstrate the effectiveness of this control approach.
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