Optimization of a simulation framework for assessing the NVH signature of an electric drive unit

E-motors are one of the most important components of today's industrial environment. Currently, the main focus for designing electric drives is energy efficiency, so several new engineering challenges emerge. New components are introduced and because of the intrinsic problem that range implicates in electric mobility, performance parameters such as energy consumption acquire an even more important value. Electric motor manufacturers are increasingly realizing that this must be complemented by including acoustic behavior. Indeed, incorporating sound quality markers into optimization objectives is useful in order to design more high-quality powertrains. Although the noise resulting from e-drives is generally less than the one produced by their Internal Combustion Engines (ICEs) counterparts, it can be characterized by a high tonal tone which compromises heavily sound quality. The effect can also be aggravated by structural resonances. This work focuses on the vibroacoustic response of a Permanent Magnet Synchronous Motor (PMSM), an electric motor designed by the Electrical Engineering Department at Universitat Politècnica de Catalunya (UPC), and kindly made available for this analysis. The e-motor is characterized by five pairs of magnetic poles, internal permanent magnets and its powered by three-phase currents. These currents are provided by an inverter and the modulation technique is the Pulse Width Modulation (PWM). This Noise Vibration and Harshness (NVH) problem is based on the presence of harmonics in the reluctance forces that are generated in the motor. These harmonics are linked to the topology of the machine and the presence of current ripples which respectively cause low and high frequency harmonics. The topology of the machine is responsible for the so-called “slotting effect” while the current ripples are a direct consequence of the PWM control of the currents, performed by the inverter. In particular, the effect of carrier frequency and the type of PWM is investigated. A digital framework that combines different simulation environments is modeled to recreate the vibroacoustic behavior of the PMSM. A high-frequency, linear, 1D model of the electric drive unit is modeled to estimate the phase currents and the angular position of the rotor in time domain. These results are employed in a 2D electromagnetic FE model in order to estimate the magnetic forces in the air gap. While the conventional workflow included a complete section of the electric motor as the 2D electromagnetic model, for this analysis these results are employed in a partial one, consisting of only an angular sector. The comparison between this reduced model and the complete one highlights a significant gain in computational time and results size. A complete structural FE model is then built to obtain the structural modes of the stator of the motor. Finally, the vibroacoustic simulation based on a 3D model of the stator matches the structural modes and the EM forces from the 2D simulation in order to obtain the sound pressure level at a microphone point outside the stator.