Solar Lattice

Function

Low-frequency ride-through

ID
func:low-frequency-ride-through
IRI
https://solarlattice.org/kb/func/low-frequency-ride-through
Status
active
Also known as
LFRT, DLFT
Category
Grid support
Function kind
grid-support

Low-frequency ride-through keeps a DER online and synchronized with the grid during a temporary underfrequency event, rather than tripping straight away. During such an event the DER must not reduce active power below the value set for its performance category, though output may drop in proportion to grid voltage if the voltage is below the continuous operating level. The Eversource CT technical requirements apply no ride-through requirements below 57.0 Hz. PPL EU's required under-frequency settings, effective 11/30/2023, are a 58.5 Hz trip with a 301 s clearing time and a 56.5 Hz trip with a 0.2 s clearing time. On the Yaskawa SGI XTM, LFRT is set over Modbus with up to 10 [%Frequency, Time] points that define the must-ride-through curve. Enter the points in ascending time order, then enable and trigger the function using bit 1 of the control and trigger registers. When LFRT is enabled on the SGI XTM, it overrides the UL1741/IEEE1547 under-frequency protection setpoints. The over-frequency setpoints stay unchanged unless HFRT is also enabled.

<!-- review notes

Claims

part_of

c1 drafted · lead Frequency ride-through

Yaskawa describes frequency ride-through as covering low (LFRT) and high (HFRT) frequency conditions, and the two can be enabled separately.

trip_threshold

c2 drafted · lead nominal 58.5 HZ

Scope: valid from 2023-11-30

Conditions: PPL EU required under-frequency shall-trip setting UF1

review note: possible conflict with c4 (same source; check the conditions)

c4 drafted · lead nominal 56.5 HZ

Scope: valid from 2023-11-30

Conditions: PPL EU required under-frequency shall-trip setting UF2

review note: possible conflict with c2 (same source; check the conditions)

trip_time

c3 drafted · lead nominal 301 SEC

Scope: valid from 2023-11-30

Conditions: PPL EU UF1 clearing time at 58.5 Hz

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

c5 verified · fact nominal 0.2 SEC

Scope: valid from 2023-11-30

Conditions: PPL EU UF2 clearing time at 56.5 Hz

verified by: review-workflowverified on: 2026-10-24review note: possible conflict with c3 (same source; check the conditions)

c7 drafted · lead nominal 1 SEC

Scope: products Solectria SGI 500/750XTM

Conditions: Minimum time for the Yaskawa SGI XTM to trip on abnormal frequency, firmware D002

review note: possible conflict with c8 (same source; check the conditions)

c8 drafted · lead nominal 0.5 SEC

Scope: products Solectria SGI 500/750XTM

Conditions: Minimum time for the Yaskawa SGI XTM to trip on abnormal frequency, firmware D003

review note: possible conflict with c7 (same source; check the conditions)

setting_range

c6 drafted · lead ≤ 10 NUM

Scope: products Solectria SGI 500/750XTM

Conditions: Number of [%Frequency, Time] ordered pairs defining the LFRT must-ride-through curve on Yaskawa SGI XTM

response_time

c9 drafted · lead ≤ 500 MilliSEC

Scope: products Solectria SGI 500/750XTM

Conditions: Yaskawa SGI XTM recovery after an abnormal frequency event that did not require a trip

review note: support check: partial - Passage says it will recover within 500 ms if not required to trip; this matches 'up to 500 ms', though it is not specific to low frequency, which is minor.

c10 drafted · lead ≤ 2 SEC

Scope: products Solectria SGI 500/750XTM

Conditions: Yaskawa SGI XTM time to reach full output power after momentary cessation, firmware D003

Data