UCC28950: control in the primary or secondary?

Hello
I am designing a 108Vdc input source (battery input) and a 400V output. the design is for an online ups, and this stage is responsible for providing power to the inverter circuit, when the 120v network is not present. The power of this converter is 3100W.
I am using the ic ucc28950, since I have some experience with this. but I have a question about where to locate the driver. where is it better to locate the controller in the primary section or in the secondary section?
I would prefer to place it in the secondary section because this way I avoid using an optocoupler for the feedback loop, besides that the control would be a little faster, but I do not know if the high voltage in the secondary (400v) can cause some problems.
Thank you