Query on Auxiliary Converter.

[RMADHUSUDHAN]

I was testing an Auxiliary Converter having 3 stages: 3 phase half wave rectifier (320VDC o/p), Buck (220VDC o/p) and a Half bridge inverter (+100 -100 square wave, 30 KHz). Used IRFP460 Mosfet as switch for Buck. I rigged up the ckt using a 3 phase, 50Hz dimmerstat and everything was fine till the o/p of rectifier reached 320V. Suddenly some sound came from inverter bulk capacitor and got damaged. **Gate signal was not given to the mosfet**. Mosfet was fine after this. My question is "How can inverter capacitor go bad when mosfet (switch of Buck converter) was off (no gate signal)?
Was this problem due to the absence of gate signal (+15V pulse at 60KHZ)?
Please help me..

 

[Tahmid]

What is the voltage rating of the capacitors? Overvoltage may have caused them to explode.

 

[RMADHUSUDHAN]

Its 2 capacitors of 200V each.

 

[FvM]

The circuit isn't clear. Anything connected to the capacitor centerpoint? Capacitors series connection without parallel resistors is said to work up to 160V each, but only if the capacitors are same value and type. Also with parallel resistors, same capacitor value is required.