Hi everyone
now I'm doing a project,I think it called Low-Frequency AC Inverter,and I got several problems.

This is first question.
This is main circuit.and this is simulation results.
The purpose of this project is to control the amplitude of a sine wave using PWM, so that the output voltage reaches 110VRMS.
but now i don't know why output is limited about 10v.

Second question.
this is PWM control without h-bridge circuit.
simulation results of PWM control without h-bridge circuit.
but when I add in full circuit and check PWM,it looks really bad.
I want to make it look like the image above.

How can I solve these problems.
My English is really bad,sorry about this.
Thank you for your attention up to this point.

 

What is the mysterious device that looks like an op-amp that you are using as a gate driver?

 

What is the mysterious device that looks like an op-amp that you are using as a gate driver?

it is Comparator
Compare a sine wave with a triangular wave to produce a square wave.

 

it is Comparator View attachment 350543
Compare a sine wave with a triangular wave to produce a square wave.

You need to control the transistors correctly. This is especially true for the upper transistors. A voltage must be applied between the gate and the source. It's not done! That's why you got nonsense.

 

As Bordodynov noted, you don't have the correct gate signals for the MOSFETs.
It's the proper gate-source voltage that turns on a MOSFET, not just the gate voltage.

Obviously you need to study more about how MOSFETs work.

 

it is Comparator View attachment 350543
Compare a sine wave with a triangular wave to produce a square wave.

Most comparators will have insufficient output current to drive a power MOSFET.
You will need a gate driver. Look for half-bridge gate drivers.
If you use one like the UCC21331 you can have all the control circuitry isolated from the 400V supply.

 

You need to control the transistors correctly. This is especially true for the upper transistors. A voltage must be applied between the gate and the source. It's not done! That's why you got nonsense.

Holy, I swear I tried that before, but now it works. I think the last time I applied voltage to VGS, it didn't work because the other part of circuit was wrong. Thank you for saving my project

 

As Bordodynov noted, you don't have the correct gate signals for the MOSFETs.
It's the proper gate-source voltage that turns on a MOSFET, not just the gate voltage.

Obviously you need to study more about how MOSFETs work.

Yes, there's still so much knowledge waiting for me to learn. I'll do my best!

 

But the comparator's output still ugly.
The comparator output appears to be experiencing interference.

 

View attachment 350563
But the comparator's output still ugly.
The comparator output appears to be experiencing interference.

Because it doesn't have enough current to drive a MOSFET gate.

 

Because it doesn't have enough current to drive a MOSFET gate.

ok I'll try it later.THANKS

 

Another thing to learn about MOSFETs is they have a large gate-source capacitance that must be rapidly charged/discharged with a high current drive for fast switching.
Look at the MOSFET's data sheet for the gate-source capacitance or gate charge.
The gate charge value tells how much charge must be transferred to turn the MOSFET on or off.
This can require a high peak-current for rapid switching.

 

ok I'll try it later.THANKS

It won’t work better later.

 

It won’t work better later.

So how about you teach me how to do it better?

 

So how about you teach me how to do it better?

You have been told twice. Do you not read the replies?

 

You have been told twice. Do you not read the replies?

I missed the first replay.
But that's none of your business.