Structural dynamics of electric machines subjected to PWM excitations

Pulse Width Modulation (PWM) is commonly used for driving asynchronous machines. The mechanical torque is the result of the combination of several multiphysics conversions. The PWM is generally defined on the basis of the electromagnetic performances determined with simple mechanical behavior: typically, rigid bodies are considered to be representative of the mechanical load. However, since PWM generates numerous harmonics of current and voltage, it may have an impact on the structural dynamics of the system. In particular, the rotor is subjected to torque oscillations over a wide frequency range that may result in large vibration amplitudes when coincidences occur. These excitations can induce severe damages like fans ruptures. In this work, a finite element model and an analytical model are compared in terms of ability to describe the structural dynamics of the system when the electric machine is driven with PWM. The results are compared and discussed in terms of applicability for the design of electric machines.