Interoperable SCADA protocols for PV inverters

Researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have evaluated a prototype code for standard SCADA software to enable the interoperability of PV inverters with other components in the system.

The new prototype, which the scientists described as deployable in simple embedded controllers, was developed with two different protocols: the Distributed Network Protocol 3, which is an open and optimized protocol developed for Supervisory Control and Data Acquisition (SCADA) systems used by energy utilities to request data from substations using pre-defined control function commands; and the International Electrotechnical Commission 61850, which is an international standard defining communication protocols for intelligent electronic devices at electrical substations.

As for the software code for the DNP3 protocol, the NREL researchers used a DNP3 source code library from the Triangle MicroWorks’s (TMW’s) software platform, which provides software libraries, conformance testing software, protocol gateways, and OPC drivers/translators for industry-standard communication protocols, and the Distribution test manager, which is a software simulator from TMW that can simulate the DNP3 client and server.

For the IEC 61850 protocol, the scientists utilized IEC 61850 protocol source-code libraries, two types of software from TMW – the SCL Navigator and the Test Suite Pro. The latter is a Windows application with a set of tools for IEC 61850 testing and the former is an application for creating IEC 61850 System Configuration Language (SCL) files.

The prototype was assessed through a simulation testbed. “The setup runs the code in real time and uses a laptop to mimic the inverter controller actions, whereas the hardware setup uses an sbRIO inverter controller that was developed in the Additively Manufactured
Photovoltaic Inverter (AMPVI),” the researchers explained.

The research team, with the support of experts from TMW, was able to identify a translator that is able to exchange data between the IEC server and the DNP3 client inside the embedded controller. “The protocol translation module contains the mapping points to exchange information from IEC 61850 to DNP3,” it said. “The advantage of the developed module is that it can accept different mapping files.”

The group also created two different sets of codes. “The first code can be used directly to enable the IEC 61850 server on a PV inverter,” it specified. “The second code converts the data from the IEC 61850 client, initiates communication with a DNP3 client, and exchanges information with a DNP3 server through the DNP3 client.” According to the scientists, these codes enable utilities to “seamlessly” communicate to IEC 61850 and DNP3 distributed energy resources.

This interoperable module is claimed to enable legacy inverters, which are PV inverters that are not capable of providing some or all of the grid support functions to participate in advanced distribution management. “In addition, the interoperability code developed in this research work reduces the cost of adding additional communication protocols by inverter manufactures, which can result in cost savings to the customers,” the researchers said.

The standard SCADA software code was presented in the paper Enabling Interoperable SCADA Communications for PV Inverters through Embedded Controllers.