Solar Lattice

Function

Frequency-shift power control

ID
func:frequency-shift-power-control
IRI
https://solarlattice.org/kb/func/frequency-shift-power-control
Status
active
Also known as
FSPC, frequency shift power control, power adjustment via frequency, P(f), power control via frequency
Category
Control
Function kind
control

Frequency-shift power control lets a battery inverter curtail AC-coupled PV inverters by raising the frequency of the stand-alone grid, so the battery does not overcharge when PV output exceeds the loads. On the Sunny Island 4548-US / 6048-US, the Sunny Boy starts limiting power once the frequency rises above f0 by fAC Start delta, and its output falls to 0 W at fAC Limit delta. If the frequency drops below fAC Delta- or rises above fAC Delta+, the Sunny Boy inverters disconnect from the stand-alone grid. When a diesel generator is running, the generator sets the frequency, so in most cases the Sunny Boys keep feeding their full power. On newer SMA PV inverters, set the country standard to Island Mode 60 or Offgrid. By default, curtailment then starts at 61Hz and falls linearly to zero active power at 62Hz. On firmware below 4.0, the start and end points are under Device Parameters, AC Side, Island Mode. On firmware above 4.0, and on SBSE or STPX, search for P(f) in the inverter or ennexOS. Once a Sunny Boy has stand-alone grid parameters, it no longer complies with IEEE 1547. Only use these settings on inverters that are disconnected from the utility grid, and check with the power company.

<!-- review notes

Claims

subclass_of

c1 drafted · lead Frequency-Watt

PV inverter output is curtailed as the AC frequency set by the battery inverter rises

requires

c2 drafted · lead Sunny Island 4548-US / 6048-US

Scope: applications off-grid

The Sunny Island shifts the stand-alone grid frequency to signal Sunny Boy inverters to limit power

c3 drafted · lead Grid Guard code holder

A Grid Guard code may be needed to set the country standard to Island Mode 60 or Offgrid

review note: support check: partial - The article says to set the country standard with your Grid Guard Code 'if needed', which supports the note. It does not clearly state that FSPC requires a Grid Guard code holder.; review: partial - The SMA article says to set the Country Standard with your Grid Guard Code 'if needed', which supports the note, but it does not say frequency-shift power control always requires a Grid Guard code holder.

default_value

c4 drafted · lead nominal 61 HZ

Scope: applications off-grid, backup

Conditions: Start frequency of curtailment (buckling overfrequency) on SMA PV inverters with country standard set to Island Mode 60 / Offgrid

review note: possible conflict with c5 (same source; check the conditions)

c5 verified · fact nominal 62 HZ

Scope: applications off-grid, backup

Conditions: Frequency at which SMA PV inverter active power reaches 0% under the Island Mode default curve

verified by: review-workflowverified on: 2026-10-24review note: possible conflict with c4 (same source; check the conditions)

c6 verified · fact nominal 100 PERCENT

Scope: applications off-grid, backup

Conditions: Default active power change per Hz in case of overfrequency, Island Mode

verified by: review-workflowverified on: 2026-10-24

Data