Influence of Inverter Modulation Strategy on Electric Drive Efficiency and Perceived Sound Quality

This paper presents an evaluation of different modulation techniques and different levels of switching frequency randomization for a rear axle electrical drive unit used in automotive applications. Inverter and machine losses, and perceived sound quality of high-frequency acoustic noise are investigated by finite element calculations, experimental testing, and subjective noise assessment. Additionally, stator current harmonics, airgap flux density harmonics, and force density harmonics are compared for space vector modulation (SVM) and discontinuous pulsewidth modulation through finite element modeling. The main conclusion is that, primarily in the field weakening region, significant energy savings can be achieved (up to 17% decrease in total inverter losses with a switching frequency of 10 kHz). This is obtained without deterioration of perceived sound quality by the use of discontinuous pulsewidth modulation with switching frequency randomization. Furthermore, randomization of the switching frequency does not improve the perceived sound quality of the acoustic noise when using SVM. However, for discontinuous pulsewidth modulation, improvements in perceived sound quality when randomizing the switching frequency are observed, primarily below base speed.