How can we get dc voltage more than the input of dc bus

Good day Gents,

hope all do well

could i get any abstract how can we get dc voltage more than input of dc bus in case of deceleration motor ?

i do understand there are diodes across IGBT and this would return power and added more peaks in network than 3 phase inputs but how does  it happen while decelerating motor?

if somebody has in details , please share 

Hazem 

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Split from All possible reasons of DC link over voltage and DC link under voltage faults.