Decrease in Sub-harmonics Frequency Noise Induced by Rotor Eccentric Motion and its Induction Currents between Parallel Stator Circuits

Abstract

A hybrid electric vehicle (HEV) is one of the solutions to improve the efficiency of a drive and to reduce CO₂ emissions. It is desirable to decrease the motor size and to increase the maximum torque to minimize the size of the driving units. For these purposes, motors employing permanent magnet have been commonly used recently. Depending on the electrical output up-rating of an HEV motor, parallel circuit will be employed in the armature circuit. However, this could possibly cause noise and vibration in the motor because the motor driving systems of HEVs or electric vehicles (EVs) must operate over large variable speed ranges of up to 1: 5. The authors analyzed the features of the noise patterns and identified the main cause. Mock-up tests were conducted to confirm the main cause, and the countermeasures including a winding scheme change, were determined. This paper describes the mechanism of sub-harmonics frequency noise and vibrations arising from rotor eccentric motion and currents in parallel circuits and a method to decrease them.