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Can we give a PWM of amplitude more than the rated voltage to a motor but making sure that the averaged voltage is lower than that of the rated voltage of the motor.Is it safe for the motor?

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    \$\begingroup\$ To a point, yes. If the voltage is too high, the insulation of the winding could fail. Please update your question to include more detail, such as the actual motor (with link to datasheet if possible) and what voltage you intend to use for your DC bus (in other words, amplitude of PWM). \$\endgroup\$
    – mkeith
    Oct 11 '16 at 17:30
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Depends...

While the average is important the instantaneous is equally important. Higher voltage usually create higher dv/dt and all the associated considerations: stray capacitance (and associated current), transmission line effects and corona breakdown of cabling and winding.

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Generally when a motor is rated to certain voltage, that means that on rated velocity under rated current (in the working point of the rating conditions) the voltage is what they wrote. Usually it's fine to go beyond the working point, at least 20%-30% for speed, and sometimes even more. The motor may deliver less performance, but definitely working point is not it's limit.

So the answer is "it depends". If you just want to use 48V with a 24V motor- probably it will be fine. If you want to use 310V with a 6V motor- i would rather not. Both because it would be a nightmare to control it and who knows what can the isolation of the wires withstand.

Bottom line- i would say don't exceed the rated voltage by more than 100%-200% and it will be OK.

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