New Integrated Electromagnetic and NVH Analyses for Induction Traction Motors for Hybrid and Electric Vehicle Applications

Electric motor whine is one of the main noise sources of hybrid and electric vehicles. Compared with permanent magnetic motors, characterization and prediction of traction induction motor is particularly challenging due to high computational costs to calculate the electro-magnetic (EM) forces as noise source, as well as motor slip and harmonic orders change at different torque/speed operating conditions. Historically, induction motor NVH is designed qualitatively by optimizing motor topology including rotor bar, pole number and slot counts etc. A new integrated electromagnetic and NVH analysis method is developed and successfully validated at all dominant motor orders for an automotive traction motor, which enables quantitative prediction of induction motor N&V performance in early design stage: First, a new equivalent rotor current method is used that significantly reduces the computational time required to calculate the EM force over transient responses. Dominant force orders are compared with conventional EM finite-element (FE) results and the new method shows good correlation. Next, a High-Fidelity (Hi-Fi) mechanical FE model is developed for the induction motor stator, with less than 2% error at all measured stator modes below 2 kHz. The EM forces are then mapped to the stator FE model to predict vibration and radiated Sound Power Level from a specially designed motor fixture assembly at dominant N&V orders. Lastly, analysis results are validated using test data over a wide range of motor torque and speed during sweep tests. Good correlation is observed across all critical N&V orders including the pole pass harmonics, winding harmonics, rotor bar order and stator slot order. Overall, the new integrated electromagnetic and NVH analysis method provides an efficient process that accurately predicts N&V responses of induction traction motors at all dominant orders, which is critical to optimize N&V performance of induction motors in early development phase for hybrid and electric vehicle applications.