Solar Lattice

Frequency-Watt

ID: func:frequency-watt
IRI: https://solarlattice.org/kb/func/frequency-watt
Status: active
Also known as: frequency droop, frequency-power, P(f), Freq-Watt, over-frequency power reduction, DHFW, DLFW, Frequency-droop mode, Set F Derating, Frequency-Watt Control
Category: Grid support
Function kind: grid-support

Frequency-Watt changes the inverter's active power output when grid frequency moves away from nominal, which supports grid frequency. When frequency rises, output power goes down. IEEE 1547-2018 sets frequency droop parameters, including an overfrequency droop value kOF. A default settings document for IEEE 1547-2018 lists frequency-droop mode (Freq-Watt) as ON by default. Tesla controllers set up frequency droop with an enable flag, upper and lower deadbands around the reference frequency, upper and lower proportional gains, and a low-pass filter time response. A read-only register reports the resulting power command. On CSI inverters the Freq-Watt menu uses a start frequency, a power reduction gradient, a stop frequency and a hysteresis option. It applies only when a Rule 21 standard is selected, and it is meant for maintenance personnel only. Change these parameters only when the grid operator asks for it.

<!-- review notes

sentence 2: support check: partial - Table 38 title and overfrequency droop kOF are given and the default ON is listed, but the passages don't say IEEE 1547-2018 sets these or that the document is a default settings document, though it is implied. -->

Claims

`requires`

c1 drafted · lead Grid Guard code holder

Scope: products Sunny Island 4.4M / 6.0H / 8.0H

Sunny Island: the P(f) overfrequency active power reduction mode is an expert parameter protected by SMA Grid Guard.

SI30M-44M-60H-80H-BE-en-33W tbl=148.r13 h=a5e54afa1678

`default_value`

c2 drafted · lead nominal 0.036 HZ

Scope: products CPS SCA25KTL-DO/US-208

Conditions: Overfrequency droop deadband (FreqDroop_DbOf) in the grid setting table

CPS SCA25KTL-DO-US-208 User Manual Rev 1.2 tbl=35.r12 h=4fc0ff18e54b

c3 drafted · lead nominal 0.036 HZ

Scope: products CPS SCA25KTL-DO/US-208

Conditions: Underfrequency droop deadband (FreqDroop_DbUf) in the grid setting table

CPS SCA25KTL-DO-US-208 User Manual Rev 1.2 tbl=35.r13 h=68ec7831bf0b

`setting_range`

c4 drafted · lead 0–1800 SEC

Scope: products Solectria SGI 500/750XTM

Conditions: Freq Watt Time Window Modbus register 40381; default 0

Modbus Level 9 SGI XTM DOCR-071003-A tbl=31 h=ff0870582f8e

c5 verified · fact 0–64800 SEC

Scope: products Solectria SGI 500/750XTM

Conditions: Freq Watt Timeout Window Modbus register 40382; default 0

Modbus Level 9 SGI XTM DOCR-071003-A tbl=31 h=ff0870582f8e

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

c6 drafted · lead 0–600 SEC

Scope: products Solectria SGI 500/750XTM

Conditions: Freq Watt Ramp Time Modbus register 40383; default 0

Modbus Level 9 SGI XTM DOCR-071003-A tbl=31 h=ff0870582f8e

c7 verified · fact 2–10 NUM

Scope: products Solectria SGI 500/750XTM

Conditions: Number of points on the frequency-watt curve, Modbus register 40384

Modbus Level 9 SGI XTM DOCR-071003-A tbl=31 h=ff0870582f8e

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

c8 drafted · lead 2–10 NUM

Scope: products Solectria XGI 1500

Conditions: Active points on the Freq-Watt curve; at least 2 required

XGI 1500 Modbus Map DOCR-071063 rev H sec=h23 h=007e0baa414d

Referenced by

Active power related_to c4
Grid code setting related_to c12
Grid-forming inverter related_to c6
Frequency-shift power control subclass_of c1
CPS SCA25KTL-DO/US-208 implements c18

Data