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pure Sinewave Inverter

aaronmawunze99

New Member
Hie, I want to build a pure sinewave inverter. Most pure sinewave inverters use small ferrite core transformers at high frequencies. Is it possible to build a pure sinewave inverter using a low frequency soft iron core transformer
 

Nigel Goodwin

Super Moderator
Most Helpful Member
What affects the efficiency, provided the square wave types employing the same types of transformer are quite efficient
High frequency is much more efficient, and uses high frequency PWM to create the low frequency sinewave - a crude squarewave inverter followed by a brute force low-pass filter is going to be a great deal less efficient.
 

audioguru

Well-Known Member
Most Helpful Member
You can use a linear audio amplifier with a sinewave oscillator at its input and a transformer at its output to make a sinewave like the electricity mains. But the linear amplifier wastes almost as much power producing heat as the load power.

A simple old fashioned squarewave inverter has a transistor on one side turned on with plenty of current but hardly any voltage across it so its heating is low. The other side has its transistor turned off with plenty of voltage across it but with no current so it does not produce any heating. Then the transistors switch sides back and forth.
But many products do not work properly when fed a squarewave.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
So what topology is used by those manufacturers who make pure sinewave inverters with heavy soft iron core transformers
Do any? - how would they possibly compete with switch-mode designs?.

If you want to, I refer you to post #4 - a brute force (large, expensive and inefficient) filter to filter the squarewave to a sinewave.

If you want an inverter, then buy one - you're not going to make one anywhere near as good, and it will cost you a great deal more to make.
 

crutschow

Well-Known Member
Most Helpful Member
You can use AG's approach but use a switching (Class-D) audio amp to drive the iron-core transformer.
That should give efficiency comparable to other switching inverter designs.
 

audioguru

Well-Known Member
Most Helpful Member
A class-D audio amplifier with a sinewave input that drives a transformer will probably not be able to use negative feedback from the output of the transformer. Then it will have poor voltage regulation unless the transformer has a power rating much higher than you need.
 

crutschow

Well-Known Member
Most Helpful Member
A class-D audio amplifier with a sinewave input that drives a transformer will probably not be able to use negative feedback from the output of the transformer.
I don't see why it would be significantly different compared to a linear amp.
In either case you would need to add feedback from the transformer output back to the amp analog input (with appropriate loop compensation, of course).
 

audioguru

Well-Known Member
Most Helpful Member
The class-D audio amplifier will already have its own negative feedback so it must be disconnected and replaced with negative feedback from the output of the transformer with compensation.
It is complicated resulting in many vacuum tube audio amplifiers not having any negative feedback from the output of their transformer.
 

crutschow

Well-Known Member
Most Helpful Member
The class-D audio amplifier will already have its own negative feedback so it must be disconnected and replaced with negative feedback from the output of the transformer with compensation.
How is that different from a linear audio amp?
It is complicated resulting in many vacuum tube audio amplifiers not having any negative feedback from the output of their transformer.
True, but that was mostly due to the difficulty of keeping the feedback negative over the full audio range.
Here the feedback can have a narrow bandwidth since the output is a single frequency.
 

shortbus=

Well-Known Member
https://www.lz2gl.com/data/power-inverter-3kw/eg8010_datasheet_en.pdf Read this lot, this is how some of the commercial pure sinewave inverters work. The driver board is avalable on Ebay quite cheap, then all you need is the switching Mosfets & transformer. I agree with Nigel its cheaper to buy a ready made one.
Just a quick look at that link, it seems like that chip could be used to make a single phase VFD. What would your thoughts be on doing that?
 

audioguru

Well-Known Member
Most Helpful Member
If you add negative feedback from the transformer output of a class-D amplifier then the phase shift caused by the switching-frequency-filter must be compensated for, because you do not want to feed the switching frequency into the negative analog feedback.
 

crutschow

Well-Known Member
Most Helpful Member
If you add negative feedback from the transformer output of a class-D amplifier then the phase shift caused by the switching-frequency-filter must be compensated for, because you do not want to feed the switching frequency into the negative analog feedback.
I doubt that phase-shift is significant at 50-60Hz, where you need the feedback correction.
Higher feedback frequencies can be rolled off.
 

debe

Active Member
Just a quick look at that link, it seems like that chip could be used to make a single phase VFD. What would your thoughts be on doing that?
Acording to the data sheet you can. I just used the board to make a replacement inverter for a generator. But it did not last very long before the switching MOSFETs were destroyed. Just gave up on that project.
 

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