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Hello David, What version of LTspice are you using? This sounds like a problem that was fixed LTspice 17.1+ Could you please download the latest version and let us know if that solves the problem?

Hi, my attention got caught by https://www.youtube.com/watch?v=Gs9cbeGl7Rw https://www.youtube.com/watch?v=JBOHCfrccCE https://www.youtube.com/watch?v=BRezuwQCaKI Amazing, isn't?

Not so much. Actually leakage inductance does not vary too much, but since the effective inductance of the winding decreases, the leakage factor increases. Leakage exists even when there is a single

Yes, this is a practical solution in many applications. In fact, my first thought was to look if there is a hidden third resonant winding. But I found out that the inverter transformer is indeed a

So, you mean that the impedance Z of the leakage inductance, is somehow proportional to F^2 (since Z=wL is proportional to F already). For instance, to allow some flux leakage to exist, the

Just like the nominal inductance largely varies between 50Hz and 16kHz, so does the leakage. The magnetic permeability decreases significantly at HF, so te fraction that goes through the air becomes

You may insist, but the? OP gives contrary evidence: "pure sinewave *inverters* which use conventional two-winding iron core transformers. Their transformer is *driven by a MOSFET bridge* "... "

It seems all here agreed that the other element in LPF is Rpar(hi) which represent the various core losses at the PWM high frequency. Now I have to find out a rather simple practical test to measure,

Rpar = R(af+bf^2) near enough, for suitable values or R, a and b. You need data on the core material to determine them. af is eddy-current loss and bf^2 is hysteresis loss.

I understand that, but the resonant winding is not visible to users. Ferroresonant xformers appear to be two-winding devices for all practical purposes. Donald.

Are you adding a shunt resistance (Rpar) to simulate core loss? -- Regards, Tony

Losses as a resistor in parallels with the winding and less significantly paraitic capacitance. Remember that losses increase largely with frequency, so harmonics and switching residuals are

Now the question is how we can translate this to an equivalent circuit. None of the actual various equivalent circuits of a transformer seems being able to simulate its function as a stand-alone LPF!

Don't forget that the iron core will have losses at the switching frequency, along with the inductance of the windings which will have a significant impedance to the high frequency switching. These

So, in your opinion, what could be the other element in the transformer to complete its LPF response since there is no load at its HV output?

That's because the leakage inductance is rather high.

Your answer is logical. But I was surprised when I tested a ready-made inverter, its HV output (of a conventional iron core transformer) was sinewave even without a capacitor as a load!

OP specified "pure sinewave inverters which use conventional *two-winding* iron core transformers."

Sounds like a ferroresonant power conditioner. Does that ring a bell? I don't think they are very efficient, but they are quite effective at producing sine waves from all kinds of nasty inputs.

The leakage inductance, in conjunction with the resistive part of the load, constitutes a 1st-order LPF. The stray capacitances are in most cases negligible in this respect.