Improving Drive Cycle Efficiency and NVH Performance in Traction Motor Drives through High-Fidelity Models

With the continuous rise in demand for more hybrid and battery electric vehicles on the road, the performance requirements are becoming more demanding and the time to market is significantly shorter. The stringent cost, efficiency, and power density targets and along with the reduced design/development time, necessitate rapid and high-fidelity models for achieving optimized designs that satisfy the demands. Pulse-width modulation (PWM) methods such as space vector and overmodulation are used widely in traction applications. The resultant harmonics generated from the inverter lead to increased electromagnetic noise, vibration and harshness (e-NVH) factors such as torque ripple and radial force harmonics, as well as harmonic losses in the stator and rotor. These unintended side effects of PWM are significant and need to be included in the design optimization and analysis stage to find the best combination of design variations and input conditions. This paper presents a high-fidelity model using a hybrid analytical and numerical approach to consider the motor-inverter interactions that can be used towards the optimization of the motor design and inverter control parameters. The current ripple from the inverter is calculated using an equivalent motor model based on flux linkages considering the non-linear effects such as space harmonics including slotting and winding effects, saturation, cross-saturation and temperature for various PWM schemes. The resultant losses and e-NVH factors are calculated and validated for select modulation strategies and skewing methods and corroborated with multi-physics co-simulation model of a permanent magnet synchronous motor. Furthermore, experimental investigations on a sample traction motor at various torque-speed operating points and over the WLTC drive cycle are used to validate the developed model.