Just looking into how to control a multi - Multiplus set up whilst charging Lithium batteries. This question applies both to multiplus in parallel, and multiplus in a three phase group.
If you are charging from grid connect solar in either of the above situations, you need to control the PV output when the battery approaches full charge. Traditionally this is done by a grid frequency shift - either directly to 52Hz or on a linear ramp from 51 to 52Hz whereby the PV inverter detects the frequency and regulates it's output accordingly.
If all cells are in balance, this can be done with the virtual switch setting - shifting on battery voltage. If, however, there is one weak cell, and the cell voltage approaches maximum, the battery total voltage will be well under the limit set in the virtual switch.
The only way this can be controlled is from the BMS which knows the state of each cell.
So, the BMS needs an interface either directly to the PV inverter (if it has one) or to the Multiplus - which would be the preferred solution. This would have to use the Mk3 interface. Looking at the technical information for the Mk3 protocol V3.14; I see there is now a new command (not available to the Mk2) in section 6.4 Battery Operational Limits (BOL)
Can some one please tell me if this works whilst the Multi's are charging from the AC-out i.e. charging from grid connect solar, and how this actually regulates the charging? - or does this only work whilst the Multi's are charging from AC in - i.e. from generator.
If this does not work to regulate solar charging, is it possible to update the inverter period by setting RAM variable (7)? can this be done without resetting the inverter system? Logic is confused here, because the virtual switch can do this, and apparently there is also an assistant that can be loaded to do this (this has some reported issues and is not easily configurable) BUT would one need to update all inverter period variables simultaneously? Is it possible to do this ? or would one just update the master, and let this control the Slaves?