DC/DC and DC/AC PWM Converters result problem

Hello sir.

I simulated demo model of simpowersystem.

Title is DC/DC and DC/AC PWM Converters

But It's something strange.

In first model Buck-boost converter. The duty is 0.8 in Pulse block properties

But Pulse block output is 0.9 duty ratio. It control half bridge.

Why is it different, If duty is 0.8, Output is 320V

Please check it.

Answer 1

[Purushottama Rao]

If duty is 0.8, the output was 359V.

If duty is 0.9, the output was 379V. pls see the attached results

[Purushottama Rao]

That demo modelis giving the expected results.

[Hyounglok Oh]

Thank you for your analysis.

DId you see PWM wave? Please check duty of PWM wave again. ( Like Below figure )

I checked the model, It set 80% ( Modulation index).

But PWM duty is 90% Final and current average is 160A

then duty modify to 80% the current average is 120A

Answer 2

[Purushottama Rao]

Yeah i do agree with your analysis. There is a mis understanding of the PWM pulse generation. In the model the carrier wave is generated between -1 to 1. By comparing with a constant value of 0.8 or 0.9, the expected output will not be 80% or 90%.

However if you want the duty ratio output as you expect, change the carrier wave to triangular wave between 0 and 1. Pls see the attached.

[Purushottama Rao]

Pls note that in this case, the given expression for Vout is not valiD if you change the carrier wave.

Now it will be m*Vin