Automatic precharge voltage control

[mvgalen]

Context

The MEB platform and CCS charge ports both need an external voltage applied before closing contactors.
For possible hardware, see this wiki page.
To make this work, the battery needs to be able to measure the external voltage and report this to Battery-Emulator. An alternative is to add an external circuit, like a shunt to measure the voltage.

Goal of this issue is to have some discussion on how to implement this in the Battery-Emulator

I have made a quick and dirty proof of concept implementation in my repo in this commit.

So my ideas:

• Use the datalayer.shunt.measured_voltage_dV as source for the external voltage. The MEB platform could write its datalayer_extended.meb.BMS_voltage_intermediate_dV value into datalayer.shunt.measured_voltage_dV.
• Share the PRECHARGE_PIN (io25 )
• Add a define EXTERNAL_VOLTAGE_CONTROL to enable it
• Use statemachine comparable to the PRECHARGE CONTACTOR state machine
• Maybe add battery/inverter dependend maximum?
• Maybe add a define to setup a start voltage / start frequency?
• Do we foresee that this will be used with external contactor control?
• ?

If we have a good idea of what the implementation should look like, I will change the proof-of-concept to the chosen implementation.