AC output wave distorted

P

Pravin Gosavi

Member

• Aug 18, 2017

• #1

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.

 

P

Pravin Gosavi

Member

• Aug 18, 2017

• #2

With capacitors attached and without load-

 

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P

Pravin Gosavi

Member

• Aug 18, 2017

• #3

With capacitors attached and with 200W bulb load-

 

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P

Pravin Gosavi

Member

• Aug 18, 2017

• #4

With load and two of the capacitors removed-

 

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D

Diver300

Well-Known Member

Most Helpful Member

• Aug 18, 2017

• #5

Can you post a circuit?

If you are creating a sinewave with PWM, you need to have some sort of filter.

 

P

Pravin Gosavi

Member

• Aug 19, 2017

• #6

Capacitors are the only filter.

 

ronsimpson

Well-Known Member

Most Helpful Member

• Aug 19, 2017

• #7

Diver300 said:

Can you post a circuit?

Click to expand...

Pravin Gosavi said:

Capacitors are the only filter.

Click to expand...

"Something is wrong but I will not post my circuit, please tell me what is wrong"

My guess is that R5 is the wrong value. lol
If you want help you need to help us understand what you are doing.

 

P

Pravin Gosavi

Member

• Aug 19, 2017

• #8

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!

 

P

Pravin Gosavi

Member

• Aug 19, 2017

• #9

Diagram-

 

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Pravin Gosavi

Member

• Aug 22, 2017

• #10

Waiting!

 

alec_t

Well-Known Member

Most Helpful Member

• Aug 23, 2017

• #11

..... 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.

 

P

Pravin Gosavi

Member

• Aug 23, 2017

• #12

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?

 

alec_t

Well-Known Member

Most Helpful Member

• Aug 23, 2017

• #13

Perhaps the windings of your transformers (properties unknown) are saturating at parts of the sine cycle when you draw significant load current.

 

P

Pravin Gosavi

Member

• Aug 23, 2017

• #14

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.