Good work Pete! sounds like your just about complete with repair. One thing that helped me out in past was to shut off the lights during testing to see if any tiny lights are flashing as carbon arcs around fets sometimes its hard to see all the carbon from the burned fets. Thanks for the photos on connections Doc! looks like i didnt need the middle one so only the switch and feedback are absolutely necessary. I really like this thing so far. Maybe its less prone to failure than pj!
I did a bit of reading up on bipolar vs unipolar sine wave synthesis. Its more complicated than it first seemed. Turns out bipolar switching scheme uses rail to rail power supply voltage in both polarities to drive the transformer primary. (Max vout=.78 x vbat) which is 34.32vac when batt is 44vdc. And uses high frequency switching on all 4 fet gate drives.
This method is simpler and produces maximum voltage possible at the transformer primary but has drawbacks.
Switching losses are higher.
Significantly more distortion.
Harder on fets.
Needs larger inductor to smooth to good sine wave.
Two types of unipolar switching schemes exist, one uses high frequency switching on all 4 fet drives, the other uses low frequency for two and high frequency for the other two (8010 unipolar does this)
This type is significantly more efficient.
More accurate sine wave output.
Smaller inductor filter is needed.
Maximum output voltage is less than power supply.
I couldnt find proof of lower output in writing but it seems obvious, as the wave simulation uses a different volt averaging scheme to minimize stress on the switches and load. (the reason the transformer is quieter with 8010 unipolar)
The 8010 has capability to do bipolar so i may switch it as an experiment when i have a backup ready to use
switching 8010 to bipolar will involve altering the feedback loop to include freqsel pin on 8010 and making sure the other two drivers are capable of the high frequency gate switching. I'm pretty sure the egs002 is not capable of the 8010 bipolar mode simply by shorting the jumper.
In conclusion unipolar has some serious advantages. I do think the highest reliability inverter is to add (or subtract) the necessary turns to transformer and go with unipolar. *note, if reducing primary turns, you are increasing flux density and you dont want saturation, safer to add secondary turns) Factory wound units generally have primary low volt side on inside layer so theres no risk of me going there HA!