PLVBF1 Playback Scaling Inconsistency

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Hi there,

I'm currently working in PSS/E 36.4 and modeling an IBR interconnection to an infinite bus to test plant controller parameters. On the infinite bus, I have a slack generator with pgen=0, qmax=qmin=0, Scheduled=Vinitial, and the MBase=9999.99 MW. The interconnection tie between the IBR facility and the infinite bus is also along a zero-resistance line.

In dynamic modeling, I have the IBR utilizing the REGFMA1 and REPCA1 generator and plant models, and then slack generator utilizes the PLVBF1 model. I'm noticing while my .plb file might have set points to decrease system frequency down to 59.5 Hz, in simulation, the nadir of this frequency disturbance is still much higher than 59.5 Hz. The documentation for the model library describes that fscale=60 if the playback file is in nominal Hz, or fscale=1 if in per unit.

Here is my modeling for PLVBF1:

3 'PLBVF1'    1    0    1     'case02'
1.0000    60.0000    0.0000    0.00000    /

Here is my case02.plb file:

0.00, 1.00, 60.000
1.00, 1.00, 60.000
1.01, 1.00, 59.500

With this configuration, the frequency nadir is shown as 59.992 Hz instead of 59.5 Hz, even if in REPCA1 Fflag=0 and should not contribute an active power response. Is there something else I may not be considering which makes models this playback on a smaller scale? or any other suggestions on how to approach it? My end goal here is to measure how the IBR responds to a frequency event.

Thanks in advance!