PLC / Datalogger / Gateway as a slave
The EPSherpa EMS supports adding a PLC, Datalogger, Gateway or hub as a slave device through the EPSherpa EMS protocol. This function is provided for when there is a hub that has to receive control signals itself from the EPSherpa EMS.
When your device has implemented the protocol, you can add your device through the device wizard, choosing "Solar Inverter", "Generic", "Ethernet TCP" and "PLC (Generic protocol)".
Protocol implementation
You have two options when implementing the protocol on the hub:
- Or you only implement the data and control registers for the totals of all PV, storage etc. They are added in the EPSherpa EMS as one big aggregated device (or one EV charger, one energy meter, one hybrid inverter if applicable).
- Or you implement the data and control registers for each individual device. Each individual device is added in the EPSherpa EMS separately.
Warning
Adding devices that are controlled by the PLC directly to the EMS Do NOT add a device that is controlled by the PLC directly to the EMS. This could lead to conflicting control signals and doubly counted power values.
Warning
Aggregate device & groups In case your hub only implements the totals, the EPSherpa EMS will treat this as one big controllable aggregated device. You can still put the aggregated device in any group, just like any other device. However, there are a few things to keep in mind if the individual devices that form up the aggregated device are in reality spread among different groups:
- The EPSherpa EMS will not be able to guard properly against overload on those groups.
- The EPSherpa EMS will for those groups not be able to determine the complete path of all power. This may lead to the EPSherpa EMS seeing production by an "unknown source" or consumption by an "unknown load" if there are energy meters on those groups. Some power might be reported double.
If the devices behind the hub are spread out over different groups, you must implement the data and control registers for each individual device.
Examples
A PLC that controls PV production and wants to accept a control signal from the EPSherpa EMS
The premise of the EPSherpa EMS protocol in this case is that the EPSherpa EMS sees the PLC itself as a controllable PV inverter.
The minimum required if you want to control PV inverters through a PLC with a signal from the EPSherpa EMS, is that the PLC:
- tells the EPSherpa EMS that there is only PV;
- returns how much PV power is produced in total by the inverters;
- accepts the setpoints of the EPSherpa EMS;
For point 1:
- Input register 0, (32 bit unsigned int), must contain the fixed value "0x454E4952" (protocol identification)
- Input register 100, (16 bit unsigned int), must contain the value "0", so the EPSherpa EMS knows that the PLC doesn't supply grid energy measurements.
- Input register 300, (16 bit unsigned int), must contain the value "1", so the EPSherpa EMS knows that there is PV.
- Input register 400, (16 bit unsigned int), must contain the value "0", so the EPSherpa EMS knows that there is no storage.
For point 2:
- Input register 202, (32 bit signed int), contains the AC power of the inverters. Negative is towards the grid, positive is from the grid.
- Input register 303, (32 bit unsigned int), contains the total PV production power in W. (Always a positive number)
For point 3:
- Holding register 1001, (16 bit unsigned int), will be set to "1" by the EPSherpa EMS if it wants to apply a control setpoint, or "0" when the PLC should fall back to its own control
- Holding register 1002, (32 bit unsigned int), will be set by the EPSherpa EMS and contains the maximum allowed PV production power in W. (Always a positive number)
Warning
Non-implemented registers IMPORTANT: ALL NON-IMPLEMENTED REGISTERS MUST CONTAIN THE NON-IMPLEMENTED VALUE OF THEIR TYPE, AS DESCRIBED IN THE PROTOCOL.
The registers above are the absolute minimum required. The EPSherpa EMS will assume that all the PV that is connected to the PLC behaves as if it were a single PV inverter, with power factor 1 and symmetric three phase behaviour.
If enhanced control is necessary, e.g. to keep an eye on phase currents etc., it is best to implement the recommended registers as well.