On my 3 -phase charger the Amps are adjusted, using a raspberry, according to what is given as available on the energy meter of my solar plant.
On a sunny winter day I easily get the 11 KW my EV will take: 16 Amps.
But there are frequent cloudy days or low sun conditions with solar outputs around 3KW, when I cannot charge with 3-phase on 6 Amps without topping up with grid power, which I buy 3x my selling price.
It's very easy to add a relay, run by the raspberry, on the mains line, to on and off L2 and L3.
But how how will the EV take this?
Take the following with a rather large chunk of salt as I'm not an expert in the inner workings of the various EV charging standards or of the firmware that runs OpenEVSE. However I do have an OpenEVSE, have read the descriptions of the protocols provided by Chris, and have an EE degree.
My immediate thought would be to have the Raspberry Pi disconnect the pilot so that both the EV and OpenEVSE would gracefully disconnect and stop drawing power after a short time. Then after waiting a second or two, have the Pi perform the 1-to-3 or 3-to-1 phase conversion. This way neither device experiences a sudden change in the way power is delivered and the inherent protections / fault recovery mechanisms are left intact.
As long as you provide OpenEVSE power off leg-1, I don't believe it will "care" that you're disconnected leg-2 and leg-3 of mains power. Providing a pilot disconnect should be relatively easy as it's a low-voltage, low-current line, but I would suggest a small relay for this as well rather than trying to pass that signal through the RaspberryPi or a BJT/FET in some way. You don't want to really "mess with" the pilot signal, just pass it through or not.
could achieve the same effect as disconnecting the pilot signal by leveraging the RAPI / MQTT interface available, depending on your coding skills.
I definitely agree, as long as I do not know beforehand how the EV system reacts to a phase conversion without disconnects, sending FS and FE commands between the phase conversions is the right approach.