Inverters
You need to hook up a 'scope and look at some things.
First off, huge ground currents need to be kept to very
tight, short loops. If they can, they will corrupt your
analog and possibly digital sections. Among common
behaviors from this, is a reswitching or chatter on the
FET drive signals, which can suck a lot of current.
Second, if you are using an H-bridge driver IC to run
the power FETs, look for guidance on anti-shoot-through
timing and how to ensure no cross-conduction. That is
one way to get really, really bad ground currents.
You may as well post a schematic.