Pulse Width Modulation or PWM has been widely used in traction motor control for electric propulsion systems. The associated switching noise has become one of the major NVH concerns of electric vehicles (EVs). This paper presents a multi-disciplinary study to analyze and validate current ripple induced switching noise for EV applications. First, the root cause of the switching noise is identified as high frequency ripple components superimposed on the sinusoidal three-phase current waveforms, due to PWM switching. Measured phase currents correlate well with predictions based on an analytical method. Next, the realistic ripple currents are utilized to predict the electro-magnetic dynamic forces at both the motor pole pass orders and the switching frequency plus its harmonics. Special care is taken to ensure sufficient time step resolution to capture the ripple forces at varying motor speeds. Furthermore, the dynamic ripple forces are applied to excite the structure paths including a stator model, a motor fixture model and a detailed electric drive unit model. Both radiated sound power and vibration data are predicted at the switching orders and its super- and sub-harmonics, as a function of the motor torque, speed and the PWM mode selection. Good correlations are achieved between analyses and tests for both the motor fixture and drive unit models. The validated analysis method not only provides insights into the switching noise source, but also enables trade study to optimize switching frequency and mode selection to balance the torque, efficiency and NVH performance for the traction motor control, with successful implementation for General Motors’ Ultium electric drive units.
