Inverter Output Transformer Saturation

[franticEP]

Hi,
i'm testing an inverter with these features:
Fswitching=220KHz
Fout=3KHz-10Khz
Vout=150Vac
Pout=150W
Current feedback.
Sinusoidal output is obtained with transformer leakage inductor+output capacitor.
In the figure below there is the schematic.



The problem is that a little DC component (about 100mA) put transformer into saturation and the output waveform has a distorsion as in figure



I don't understand from where it can come this DC component. Could you help me?

A capacitor could solve my problem? what features should have this capacitor? Ceramic or film cap? I had thought of 47uF@25volt as the voltage across it should never be too high.

Let me know.

 

[duke37]

What has temperature (K) to do with it?
The H bridge needs two n channel fets and two p channel fets and a level shifter to drive the p channel fets.
The four transistors will need to be matched to get an average zero transformer current.
Passing high voltage, high current AC through a low voltage electrolytic capacitor is likely to lead to tears.

 

[(*steve*)]

I don't understand from where it can come this DC component. Could you help me?

If the total time your H bridge remains in one state does not equal the total time in the other state over some large number of cycles, then there will be a net DC voltage across the transformer and a net DC current.

Yes, a cap would improve things, but the voltage rating would be significantly larger than you imagine.

 

[(*steve*)]

What has temperature (K) to do with it?

Not the dreaded KelvinHertz!

 

[franticEP]

Yes, a cap would improve things, but the voltage rating would be significantly larger than you imagine.

Why? Could you explain me better?

 

[(*steve*)]

Why? Could you explain me better?

It's quite possible for it to have -70V on one side and +70 on the other.

 

[franticEP]

It's quite possible for it to have -70V on one side and +70 on the other.

In case of failure i'm thinkin of protecting device with transzorb across capacitor

 

[(*steve*)]

You should possibly study the voltages in series resonant circuits.

You may want to stay away from resonance, but even still, there will be effects.