Solar Lattice

Function

Constant reactive power mode

ID
func:constant-reactive-power
IRI
https://solarlattice.org/kb/func/constant-reactive-power
Status
active
Also known as
constant var, fixed reactive power, Q setpoint, DVAR, Fixed VAR, Q Fixed, Q Set, Q constant, Fixed Reactive, Fixed Reactive Power mode, Q setting, Constant Q Mode
Category
Grid support
Function kind
grid-support

Constant reactive power mode holds the inverter's reactive power at a fixed target level, set as either injection or absorption. The default IEEE 1547-2018 settings list this mode as off by default. The Solis S6-EH2P hybrid uses Modbus registers 43451 for the enable and 43051 for the setpoint, with a range of -60 to 60 percent. The CPS single-phase hybrid takes separate L1 and L2 setpoints plus a reactive power response step. In SMA documentation, the Q setting mode works with active power draw, zero active power and active power output. Cos phi setpoint mode does not work at zero active power.

Claims

response_time

c1 drafted · lead ≤ 10 SEC

Scope: standard IEEE 1547-2018 proposed

Conditions: Maximum DER response time to maintain constant reactive power

The maximum DER response time to maintain constant reactive power shall be 10 s or less.
— IEEE 1547-2018 §5.3.5. Quoted with attribution; the text remains the publisher's copyright.

c9 drafted · lead nominal 1 SEC

Scope: products KACO blueplanet 87.0-165 TL3

Conditions: Transient time when the reactive power specification is changed; first-order (PT-1) filter

Filter time constant Tau is 200 ms.

setting_range

c2 verified · fact -60–60 PERCENT

Scope: products Solis S6-EH2P(9.6-16)K-SV-YD-L-US

Conditions: Reactive Power Setting Value (CONST_Q-AS, Modbus register 43051)

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

c4 drafted · lead -60–60 PERCENT

Conditions: CPS single-phase hybrid inverter, L1 and L2 reactive power settings (InvL1CSQPer, InvL2CSQPer); same for IEEE 1547-2018, Rule 21 and HECO profiles

c6 drafted · lead 0.1–100.1 PERCENT

Conditions: CPS single-phase hybrid inverter, reactive power response step (QActStep), IEEE 1547-2018 and HECO profiles

c7 drafted · lead 0.1–100 PERCENT

Conditions: CPS single-phase hybrid inverter, reactive power response step (QActStep), Rule 21 profile

default_value

c3 drafted · lead nominal 0 PERCENT

Scope: products Solis S6-EH2P(9.6-16)K-SV-YD-L-US

Conditions: Reactive Power Setting Value (CONST_Q-AS, Modbus register 43051); mode enable defaults to Disable

c5 drafted · lead nominal 0 PERCENT

Conditions: CPS single-phase hybrid inverter, L1 and L2 reactive power settings; IEEE 1547-2018, Rule 21 and HECO profiles

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

c8 drafted · lead nominal 100 PERCENT

Conditions: CPS single-phase hybrid inverter, reactive power response step (QActStep), all listed profiles

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

Referenced by

Data