ABB VSN300 Product Manual page 60

7 - Operation
Sunspec Alliance has standardised the Modbus register map in which
the inverter data is stored. This allows SCADA systems to use standard
Modbus read commands to gather information from legacy ABB inver-
ters, stored previously in these Modbus Sunspec registers. In the same
way, a SCADA system can send a supported Modbus write command to
a SunSpec inverter control register.
The VSN300 board will transcode the standard Modbus commands into
Aurora Protocol command sequences to be sent to the legacy ABB
inverter which will then execute the requested actions, such as grid di-
sconnection or output power reduction.
The Modbus commands sent by a Modbus TCP client cannot be passed
directly to legacy ABB inverters which communicates via the proprietary
Aurora Protocol. So the VSN300's Modbus TCP server/gateway pas-
ses an incoming Modbus command to the SunSpec Adapter first. When
a Modbus TCP client sends read commands to a legacy ABB inverter,
the VSN300's Modbus TCP server will respond based on data that has
been cached for that inverter by the SunSpec adapter; when a Modbus
TCP client sends a supported write command to a legacy ABB inverter
using the inverter's SunSpec Modbus data map, the SunSpec adapter
will convert this command to Aurora Protocol for communication to the
inverter. If there are any problems with the command, an exception re-
sponse will be sent back to the Modbus TCP client. There is no confirma-
tion that a command is successful and that the inverter has performed
the control action; For this reason, write commands should always be
followed up shortly after with read commands to confirm the change (s).
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