In the diagrams that I have seen showing the PWM plots vs the sign wave of the high and low side fets for each phase of BLDC sine commutation, they are shown as being the inverse of each other:
Please could someone explain why it is preferable to drive the gates on inverse signals? (ignoring deadtime for the purposes of this question)
IE Why is it better to pull a phase to high during the off cycle of the low side, rather than leave it floating when you actually want current flowing out of the low side of that phase? e.g. at 240 degrees on phase A
Obviously while the sine is positive for a phase, the high side would be needed, and in order keep the bootstrap capacity charged it will also need switching to low side during the off part for the high side - so that side of it I can see an explanation for - though I may be missing the whole picture and I am unsure why the entire inverse is the best setting, when only a fraction of that should be needed to keep the boot capacitor charged.
However when the sine value is negative for the phase, I do not see the reason for the high side gate being active at all (eg for phase A from 180 degrees to 360 degrees)?
Is this related to an inductive property of the windings that I am missing?
Note I am specifically looking for what the benefits might be in terms of optimal operation of a BLDC motor, such as avoiding torque ripple or other losses of those are factors.