Electromagnetic Vibration Analysis of Homopolar Inductor Machine Considering Field Current Ripple

For the homopolar inductor machine (HIM), armature reaction has a significant effect on electromagnetic performance and vibration. In the vibration analysis of traditional integer slot synchronous machines, it is generally believed that the armature reaction only increases the vibration amplitude without creating an additional frequency. However, the armature reaction flux path of HIM differs from the main flux path, which greatly interferes with the field current. The effect of the field current ripples on the air-gap magnetic field and vibration is compared and analyzed. The results show that the field current ripples greatly enhance the zeroth- and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i>th-order (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> is the number of pole pairs) mode vibration at the electrical frequencies and the vibration at the nonelectrical frequencies. Furthermore, the vibration caused by the armature reaction could be significantly reduced by suppressing the current ripples at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> times and 2<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> times the fundamental ripple frequency. Finally, a 54-slot/6-pole HIM is tested to validate the existence of the zeroth- and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i>th-mode vibration at the frequency generated by the field current ripples.