Looking for some technical details on Volt / Var and Frequency / Watt modulation.

[scrambler]

Well in my probably too basic understanding of this issue, if I remove 30% of the DC input, I do not understand how any manipulation of the AC could make up for that....

[solardreamer]

Well in my probably too basic understanding of this issue, if I remove 30% of the DC input, I do not understand how any manipulation of the AC could make up for that....

Hmm ... you may have misunderstanding of Volt-VAR and/or how AC power works. Volt-VAR specifies adjustment (absorption or injection) up to 30% of *max available VAR* from a GTI system. Not 30% of DC input.

Assume you have GTI system that generates apparent power of 5KVA with minimum power factor of 0.8 and max of 1.0. So, the max VAR is 3KVAr and associated real power is 4KW. Volt-VAR control specifies 0.9 minimum power factor, so GTI would adjust the power factor and apparent power to 4.44KVA (likely result of DC input modulation) with VAR of 2.29KVAr (76% of max VAR) at same real power of 4KW. Depending on grid conditions, Volt-VAR control may specifically call for VAR absorption of 30% so that would be 1KVAr so GTI would adjust apparent power to 4.12KVA and maintain same real power of 4KW with power factor of 0.97.

[scrambler]

We were just miscommunicating, but thanks for the additional details.
After doing more digging, I got a lot more on the subject and am starting to get a clearer picture.
There is actually a Volt / Watt mode that can be triggered as a backup to Volt / Var if it is not adequate to mitigate the excessive Voltage excursion.

The PG&E Doc below has great info
Smart Inverter Implementation Workshop:
Smart Inverter Implementation Workshop (pge.com)
And the side Side reference doc below have more specific data :
ELEC_5129-E.pdf (pge.com)
Distribution Interconnection Handbook (pge.com)


Phase One tools (starts at page 17):

• Voltage ride through for extreme Voltage events
• Frequency ride through for extreme Frequency Events
• Dynamic Volt / VAR control for mitigating Voltage rise during PV back feed by absorbing reactive power at high voltage.
  Page 16 of distribution interconnection handbook above has the Volt / Var profile
  On the voltage rise side we have:
  120V – 123.96 (103.3% of Vref) no action
  123.96V – 128.4 (103.3% - 107% of Vref) linear ramp up to -30% of usable VAR
• Fixed power Factor control, similar to Volt / VAR but using PF)
• Ramp Rate / Soft reconnect (avoid fast voltage fluctuations during cloud effect)
• Volt / Watt is backup to Volt / Var if not adequate to mitigate excessive Voltage excursion
  Page 6 of the ELEC 5129 above has the response curve
  On a voltage rise, the Volt / Watt would kick in at 106% of Vref (254.4 / 127.2) and could reduce production all the way down to zero by 108% of Vref (259.2 / 129.6)
  So there should be no impact on DC production below 106% of Vref
• Frequency / Watt to reduce generation in over frequency events,

Also below is and Interesting link on active power modulation:
EnglishPaperLACGT (osti.gov)