Hello,

Please find the uploaded two schematics in ‘PureSineInv.zip’:

[1] Sinewave inverter using a bridge to drive a two-winding linear transformer with no load and whose model include somehow its parasite LPF elements.

[2] Sinewave inverter using a push-pull drive for three-winding linear transformer (loaded) whose model doesn’t include its parasite LPF elements.

In vain, I tried tweaking the three-winding linear transformer to let it act as a LPF as done on the schematic [1].

I hope that someone can do it for me in any possible way or notify me that it cannot be done, at least for LTspice.

Your help will be much appreciated.

(In these days, I cannot afford building a push-pull inverter and its 3-winding transformer, even for 500W only, to find out that the PWM high frequency, about 16 KHz (Tpwm=64us), cannot be filtered out as it was done in the case of the full-bridge.)??

?

Best Regards,

Kerim

Missing:

? ? 74hc86.asy
? ? 74hc.lib

Andy

开云体育

Present: far too much stuff not relevant to the question of the transformer acting as a low-pass filter.

Kerim, if you accept that a two-winding transformer acts as a low-pass filter, you should be able to see that the presence of a third winding doesn't change that.? The leakage inductance and the load resistance are still there, as for the two-winding transformer.

开云体育

More: You don't see any LPF effect because you set K to 1, so there is no leakage inductance. If you set K to say 0.98 you will see a filtering effect.

Kerim,

But your 3-winding transformer:

1. is really just a 2-winding transformer but with a center-tapped primary (does that matter?);
2. is "perfect", with no leakage inductance.

If the leakage inductance is responsible for the transformer's low-pass filtering, the 3-winding transformer lacks any.? What did you do to it when tweaking it to act as an LPF?? You did not leave your tweaks on the schematic, right?

Andy

开云体育

The 74HC model is missing.

On Sat, Jul 8, 2023 at 11:30 PM, Andy I wrote:

Kerim,

But your 3-winding transformer:

1. is really just a 2-winding transformer but with a center-tapped primary (does that matter?);
2. is "perfect", with no leakage inductance.

If the leakage inductance is responsible for the transformer's low-pass filtering, the 3-winding transformer lacks any.? What did you do to it when tweaking it to act as an LPF?? You did not leave your tweaks on the schematic, right?

Andy

Andy,

You are right in all you said.
I was somehow shy to upload what I tried doing because their responses were rather ridiculous :(
So, I uploaded the schematic with a conventional 3-winding transformer so that it could be replaced with a practical model and tested.

Kerim

On Sun, Jul 9, 2023 at 12:05 AM, Jerry Lee Marcel wrote:

The 74HC model is missing.

Sorry, I uploaded it too.

On Sat, Jul 8, 2023 at 11:22 PM, John Woodgate wrote:

Present: far too much stuff not relevant to the question of the transformer acting as a low-pass filter.

Kerim, if you accept that a two-winding transformer acts as a low-pass filter, you should be able to see that the presence of a third winding doesn't change that.? The leakage inductance and the load resistance are still there, as for the two-winding transformer.

Although I added a load, the new 3-winding model needs to act as LPF even without it, as in the case of the 2-winding one. I am afraid that with an open output, any leakage inductance cannot filter out the high frequency.
Did you see my humble solution on the subcircuit schematic of my 2-winding transformer, 'SineXF_lk__01_HY_'?

OT:

Obviously, implementing the push-pull topology is much easier than the bridge one. But this has a price:

[1] The amplitude of the driving PWM voltage is doubled. It is from Vbat to –Vbat instead of Vbat to 0 or -Vbat to 0 in case of the bridge.

[2] The PWM resolution is halved. Its duty cycle is 50% for the zero voltage output, while it is 0% in case of the bridge.

[3] The resistance of the low-voltage side (primary?) is doubled (by splitting the primary 1-winding to 2 windings that take the same space).

Kerim, can you simplify your 2-winding transformer model a little?? Having an ideal transformer at its core, I think you can "push" the other elements through it to the other side and combine them.? Then can't you apply it to your 3-winding transformer too?

Andy