3 phase power distribution?

Hi I have a question about the power distribution in a 3 phase drive bridge as seen below: http://www.dhcservice.com/EV/3phase.png

Lets say the 3 phase motor is running at 3kw is it then safe to amuse that each of the 3 (low and high) mosfet pairs is each proving 1kw? And is not does anyone know the right value?

I'm sure it won't be 1kw each all the time exactly but at any given moment in the 3 phase time period 2 other phases are active to some extend.

What I am getting at is, in a 3kw 3phase setup does each mosfet (high and low) pair need to be rated 3kw or 1kw? (Safety overhead margin not counted for in this example)