u/CMTEQ

I’m working on a G99 compliance study in DigSILENT PowerFactory for a grid-forming inverter, specifically testing LFSM (over- and under-frequency response).

What I’m trying to do is:

• Apply frequency deviations to the grid
• Measure the inverter’s active power response at the PCC
• Validate droop / LFSM behaviour

But I’m stuck on the setup side:

How do you actually control or vary the frequency of the external grid in a dynamic simulation?

A few specific things I’m unsure about:

• Is the correct approach to manipulate the external grid (slack) frequency directly, or do I need a controller/DSL model?
• How do you implement frequency steps vs ramps in PowerFactory?
• Is there a standard way people simulate grid frequency events for compliance testing?
• Any tips to make sure the inverter actually responds (and isn’t just following the slack)?

If anyone has done LFSM or G99-type studies in PowerFactory, I’d really appreciate some guidance or example approaches.

Thanks!