Torque Ripple Cancellation to Reduce Electric Motor Noise for Electric Vehicles

Electric motor whine is a major NVH source for electric vehicles. Traditional mitigation methods focus on e-motor hardware optimization, which requires long development cycles and may not be easily modified when the hardware is built. This paper presents a control- and software-based strategy to reduce the most dominant motor order of an IPM motor for General Motors’ Ultium electric propulsion system, using the patented active Torque Ripple Cancellation (TRC) technology with harmonic current injection. TRC improves motor NVH directly at the source level by targeting the torque ripple excitations, which are caused by the electromagnetic harmonic forces due to current ripples. Such field forces are actively compensated by superposition of a phase-shifted force of the same spatial order by using of appropriate current. A feedforward harmonic current generation module is developed, which allows the application of harmonic current commands to a motor control system with adjustable magnitude and phase. In the 3-phase, 8-pole AC machine with concentrated windings of this study, both 5^th and 7^th electric order harmonic currents are injected in the stationary reference frame to cancel the 6^th electric order torque ripple in the synchronous reference frame, which corresponds to the most dominant 24^th mechanical order. Test data confirm that TRC is highly effective in reducing the motor whine by 10+ dB over a wide range of motor torque. Loss study is also performed which shows TRC has a minimal impact on the motor efficiency. Overall, TRC offers a flexible NVH solution without hardware change and has minimum impact on motor performance or efficiency. The technology has been successfully implemented in GM’s Ultium electric propulsion systems.