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AC output wave distorted

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Hello. I am working on a 3 phase inverter. I have generated 6 SPWM. But output waves don't always seem like sinewave. I have connected three transformers ( delta ) to three IGBT modules. Output is taken with neutral common ( star connection ) and filtered using 10 MFD ( big! ) caps.
 
With capacitors attached and without load-
 

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I don't have simulator but this rough diagram could help. Boxes near the IGBTs represent isolated gate drivers. The numbers near them represent their switching sequence. SPWM signals are taken from a microcontroller. And the transformer windings are connected to IGBTs ( delta connection). The output is taken as a star connection with common neutral. And the caps connected between each phase and neutral. Tell me if I'm missing something else!
 
..... and we're still waiting for further details. Block diagrams aren't enough for dignosing your 'problem'. A full schematic (even hand sketched) clearly showing component values would be helpful.
 
There's nearly nothing between the IGBTs and the PIC microcontroller except the ISOLATED GATE DRIVERS- which are completely fine. If they would have problems why I would get sinewaves as shown in the pics above?
 
Perhaps the windings of your transformers (properties unknown) are saturating at parts of the sine cycle when you draw significant load current.
 
The transformers and IGBTs are taken from a 6 KVA old inverter. I also want to load it with 6 KVA. For now the load given is 200 W X 3 bulbs.
 
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