Integrated Damper Cage for THD Improvements of Variable Speed Salient-Pole Synchronous Generators for the More Electric Aircraft

Wound field synchronous generators have been implemented as aircraft main AC power generation for decades. The trend of moving towards more electric aircraft made DC and variable frequency AC buses favorable for the next generation power systems in aircraft, as opposed to constant frequency AC grid systems. The minimization of the generators’ output voltage total harmonic distortion is an ever-more critical objective, especially for variable frequency power systems where this target has to be met within the whole range of operating speeds. In conventional, constant speed, wound field synchronous generators, a number of consolidated techniques are implemented to meet this requirement. In variable speed synchronous generators intended for the more electric aircraft, these techniques are no longer fully effective and new methodologies are thus necessary. This paper replaces the conventional squirrel-type damper cage with a new integrated damper cage located at the inter-pole regions. The proposed integrated damper cage, while acting as a mechanical structure to retain the field windings at high operating speeds, also achieves very low voltage total harmonic distortion values at different speeds, thus complying with the power quality requirement. A 250 kVA prototype is designed, analyzed, built and tested to prove the proposed concepts and methodologies.