Designing sine wave inverter

Hi Engineeners...

Here I want to design a sine wave inverter. The technology I wanna use is modulating by high frequency. Say, every 50Hz carrying 10KHz inside, then the transformer size will reduce, and finally the output is filtered by LC filter. then it will be easy to get pure sine wave.

What do you think? Please suggest me on this topics.
Thanks
Mithun

Hello,

First go from low voltage to high voltage DC (isolated converter, think of 400V for a 230V mains supply). For this you need a transformer. Depending on the topology of the DC-DC converter, the transformer has to store energy also (that means air-gap).

Then use your full bridge PWM circuit with LC filter fed from about 400V DC bus. I would recommend to use a frequency above the audio frequency range (for example >20 kHz).

If the above is what you have in mind, it is OK.

You will not be able to pass 50 Hz AC through a small transformer, even when you modulate the 50 Hz with a higher frequency. You need the intermediate DC step.

so you thik that it will be easier to make 220V AC(sine wave) from 12VDC converting (Busting up) into 400V DC & then sepping it down into 220VAC?? but why are you suggenting this intermidiate stage? loss may occure here, isn't it? and what should be the configuration in the second step? please give some detail information.

Thanks

Added after 1 minutes:

any way, if I use Farrite core, then will it be possible to modulate?

Added after 11 minutes:

what about using H-Bridge ckt?

Hello,

It is not a question of "easier". Without the DC step in between, it doesn't work, even with the best ferrite transformer. Try a simple circuit in a spice program where you use some uH primary inductance (use coupled inductors to make a simple transformer).

Maybe there is scheme where you have a synchronous rectifier (change over switch synchronized with the primary switching frequency) at the secondary side. I never have seen this in practice, so it is very likely not competitive with the two step approach.

The two-step approach also allows reactive loads as the electrolytic capacitors at the about 400V DC bus can store the reactive energy from the load. In that case energy is temporary flowing from the load via the bridge to the storage capacitors.

Added after 7 minutes:

Hello,

correct the H- or full-bridge will do the conversion from about 400V bus to 230VAC without transformer, you only have LC filtering betwen the load and the output of the bridge. As there is no transformer here, you need an isolated DC to 400V converter to avoid safety issues.

"correct the H- or full-bridge will do the conversion from about 400V bus to 230VAC without transformer"


Have you any circuit diagram of this? If its possible without any transformer then its great. please help...

Hello,

You need at least a transformer in the DC to about 400V converter, in the H-bridge there is no transformer. When you leave out the transformer (so you make a non-isolated DC converter, you will have a significantly less safe inverter as you may get half the mains supply voltage on your low voltage DC).

I do not have a ready circuit. I am sure when you do some search you will find application notes and/or circuit diagrams to give you guidance so that you don't need too much iterative steps to get your inverter.

Keep in mind that you are working with potentially lethal voltage

in the output of the pwm inverters, there is a noise mixed. how can it be removed using filters? have you any idea about it?



I've got a sine wave oscillator ckt. I'm thinking that if a 50Hz sine wave is be the driving frequency and 100Khz square wave will be the carrier frequency. what may happen here? give your ideas.

see it: https://obrazki.elektroda.pl/23_1273245483.gif

would you like to use it as a power converter? I think it's not a good idea!