Grid-Forming Control has been developed for several years and becomes more important for the energy transition to a decentralized energy supply. The grid-forming functionalities are implemented to more converters and needed to be unified. For that reason, the FNN released a guideline “Technical requirements for grid-forming capabilities including provision of inertia”. In this work we develop test automation for grid-forming units, if it passes the defined FNN tests. For that, voltage curves have been defined for all mentioned FNN measurement-based verifications. All tests can be run automatically one after another. Furthermore, the GFI current is measured and directly determines if the unit passes the test. Using the developed tool, a grid-forming unit can thus be easily and automatically tested to determine whether it passes all defined FNN tests.

For each test, an enumeration is defined that includes the test name and is supplemented with a number if multiple tests are performed with only minor changes (for example, RoCof_1 and RoCof_2). In addition, a test definition script is created for each enumeration, which defines the time series of the grid test voltage by adding offsets to the voltage amplitude, rated frequency, or phase angle. Using offsets ensures that the rated voltage is present before the test begins, allowing the inverter to operate in steady-state mode. An XLSX file containing all tests is generated, with each test defined on its own sheet. The data is imported into a Simulink model and given into a ‘For Each’-subsystem with one instance for each test. A stateflow chart is used as the operations management which selects and enables individual tests or can run all defined tests in sequence.

During each test, an additional Stateflow diagram evaluates the measured signals and determines whether the tests have passed or failed. The goal of this work is to implement all defined FNN tests, including automated test evaluation. For demonstration purposes, we are performing this test automation in our laboratory, using an Egston CSU200GAMP6 as a power amplifier controlled by a OPAL real-time simulator and in connection with our in-house developed grid-forming inverter (GFI). The GFI, along with its control system and the test results, will be presented in a separate article.

To expand the operability and scalability of the automation, the open-source tool openSVP is used to orchestrate the devices involved in the testing procedures.

A dedicated driver interfaces with OPAL-RT to control and send commands to the operations management level. Additional drivers are implemented for the Devices Under Test (DuT), including a GFI and a DC source.

High-level user operations such as starting/stopping the model, initializing, and monitoring sequences and processes are implemented in openSVP.

The voltage curves are fed into a real-time Simulink model running on an OPAL-RT OP5707XG, which controls an Egston GAMP6 power amplifier (PA). The DuT is directly connected to the PA. After the simulation stops, measurement dumps are collected and analyzed in openSVP, producing a pass/fail result and a short report.