This red inverter board was originally locked to 50hz, i swapped out the mystery controller (drive module) with a EG8010 board that happens to be pin compatible.
There are quite a few variants of this inverter board available on aliexpress and alibaba.
They are all designed around this EG8010 controller, the data sheet is here:
this effectively gives you the entire schematic for this inverter.
This red one is from here:
I got the EG8010 driver module here:
The blue one I got for testing/learning is here:
but it isn't as good as the red one which has better circuitry.