grid tied inverter... mosfet damage problem

[atiarali]

hello everyone,
i am new member in this forum. i have design a grid tied inverter. this inverter works nicely but the problem is MOSFET (one side) burn frequently. this inverter have more than 80% efficiency.
i connect a diode in source-drain pin. but no good things come out.
any body please help me...
i use 100k variable resistor, irf640 mosfet.

 

[andre_luis]

I could not see any snubber circuit at the schematic.
This could give some protection for transistors.

Anyway, there is no consistency in burning just on side, unless potentiometers were not well balanced.



+++

 

[BradtheRad]

The two sides appear balanced. There appears to be no reason for one side particularly to go bad.

Questions:

* Is your load balanced? Or does one half of the cycle draw more current?

* Your mosfet gates receive a peak of +17V and then -17V. Is this within allowable specs?

* Your mosfets must carry many times the amperes going to your load. Example, if your load draws 1/2 A peak, the mosfets must carry 24 A (according to my simulation). Is this within allowable specs?

* Do you habitually connect or disconnect one side before the other? This might conceivably create high V spikes on the side which is connected.

* Have you tried switching a few components right-for-left, to see if you can track down a faulty component?

 

[atiarali]

i have found the problem of burning mosfet.
the problem was ... i did not insert any resistor in the MOSFET gate pin.
i insert a 100k resistor at the gate pin.
now my device runs good.

thanks every body to reply me...