Analysis and Validation of Torque Ripple Cancellation to Reduce Electric Motor Noise for Electric Vehicles

The electric motor represents a significant noise source for electric vehicles (EVs). Conventional hardware-based NVH optimization techniques may prove insufficient, often resulting in trade-offs between motor torque or efficiency performance. The implementation of the motor controlled based torque ripple cancellation (TRC) technology can effectively reduce the targeted order with a minimum impact on other motor performance. This paper presents an explanation of the mathematical theory that underlies the TRC method, with a particular focus on the various current injection methods, including those that enables up to 4DOFs (degrees-of-freedom). In the case study, the injection of controlled fifth or seventh order current harmonics into a three-phase AC motor has been demonstrated to be an effective method for cancelling the most dominant sixth order torque ripple. Furthermore, comprehensive finite-element models are developed for both the electric motor and the motor fixture system to characterize the noise transfer path. The electromagnetic forces are calculated with and without TRC injections and subsequently mapped on the stator teeth to predict the noise and vibration responses at the motor fixture system. A dedicated feedforward harmonic current generation module has been developed, which enables the application of harmonic current commands to a motor control system with adjustable magnitude and phase. The predicted TRC inputs for the Id and Iq injection currents are then compared with the optimal parameters obtained from motor dynamometer tests. Good correlation is achieved between the predicted and measured optimal inputs, resulting in a reduction of over 10 dB at the most dominant sixth electric order, or the 24th mechanical order. The validated TRC injection analysis method and control algorithm have been successfully implemented in General Motors' Ultium electric propulsion systems.