I burnt almost dozen mosfet while trying to test the switching of secondary mosfet of my flyback inverter. It was in fact something trivial because i thought to switch one mosfet at a time to get a half wave waveform at a time. I discussed it with my supervisor and he pointed me towards the solution. "Operate both the secondary mosfet instead of one at a time" he said. "Because when you operate only one switch there comes a problem, that is during its turn off time there is no alternate path for the energy stored. Therefore, high voltage spikes emerge that are resulting in the failure of mosfet" he added.

Flyback inverter (Click to zoom)

I operated both the switches simultaneously, such that for positive half cycle S_ac1 i turned on and for negative half cycle S_ac2 is turned on. The experiment of getting one half cycle only by trying to switch the S_ac1 alone should be avoided.