The Pulse Width Modulation (PWM) drives can create motor overvoltage failures due to differential mode transient voltages. This is a well-known problem since AC VSDs were introduced. Specify motors insulated for Adjustable Speed Drive application.
These overvoltage conditions are discussed in an article in IEEE Industry Applications Magazine July-August 2012, titled “System Design of Adjustable Speed Drives Part 1” by Skibinski, G.L.Tallam, R.M.; Pande, M.; Kerkman, R.J.; Schlegel, D.W.
One source of overvoltage is caused by the fast rate of rising of voltage (dv/dt) each time the voltage is switched. This can result in transient voltages double the dc bus voltage. Most drives limit the switching speed to 200 nsec.
A reactive filter in the drive (source) can control dv/dt.
Pulsing patterns can also be changed to reduce double pulsing. The PWM carrier frequency can be reduced to reduce the number of voltage transitions.
If required by the cable length, a filter (terminator) may be added at the motor terminations. This is a resistor-capacitor filter and results in additional power dissipation.
Finally, a normal two-level switching drive can be replaced with a three-level switching drive, which reduces the voltage transients in half.
The solutions cost money for the installation of the required components as well as increased power losses for the life of the equipment.