According to the schematic below, I made a 12 to 220 volt inverter
Normally everything works fine
The problem started when the DC bus voltage exceeded 310 volts
A strange shape is seen in the one of the high side H-Bridge MOSFET gate voltage
just in one side of high side MOSFET
And I do not know why this wave is created and how to solve it?
I have used FDPF18N50 in H-Bridge
if DC BUS under ~ 310V Gate Wave is ok
if DC BUS voltage Over ~ 310 volt we have this shape
I'd start with the gate drive, which could be marginal
or mis-built and allow high dV/dt switching to induce
on-state oscillation in the power FET. At least follow
the bad side back toward the control IC, until it starts
looking the same as the "good" side. Then you'll have
bounded the problem area, at least.
We cannot see the layout - but the clever money is on RFI getting into your control from the hard switching on the pri side coupled with the hard reverse recovery of the diodes on the sec -
remedies: - slow the fet turn on
- put snubbers on the fets & diodes
--- Updated ---
the current spikes into C13 will be significant too