Limit maximum active power

ID: func:limit-active-power
IRI: https://solarlattice.org/kb/func/limit-active-power
Status: active
Also known as: active power limitation, power limiting, curtailment setpoint, WMaxLimPct, DWMX, Set active power limit, Active Power Limit, Maximum Active Power Limit, Active power limit ratio
Category: Control
Function kind: control

This function puts a cap on the active power a DER sends out. When it is enabled, the unit's output stays at or below a set maximum. Vendors configure it differently. Sungrow string inverters use an enable switch plus a limit ratio as a percentage of rated power. Huawei SUN2000 inverters take a maximum active power value in kW. SMA inverters use the parameter Set active power limit. On Tesla battery systems, the limit applies in the discharge direction. It is a per-unit fraction of nameplate real power, and both the limit and its enable flag can be read and written over Modbus. The SMA Cluster Controller receives active power limitation setpoints from the grid operator or a direct marketer as digital or analog signals or over Modbus, passes them to the inverters, and reports them back. When the setpoints conflict, it applies the one that limits power most. With self-consumption, the Cluster Controller uses closed-loop control based on the measured feed-in at the grid connection point. The inverters must be set to Act. power lim. via PV system ctrl, which requires installer login with an SMA Grid Guard code.

Claims

`requires`

c1 drafted · lead IEEE 1547-2018 4.6.2 Capability to limit active power proposed

Maximum Active Power setting range is referred to clause 4.6.2.

IEEE 1547 - 2018 [code/standard] sec=10.6.12 h=b92b721087a4
IEEE 1547 - 2018 [code/standard] tbl=47.r2 h=27491401308b

c2 drafted · lead SunSpec model 123 Immediate Controls

Scope: products KACO blueplanet 87.0-165 TL3

External power limitation on the KACO blueplanet is set through WMaxLimPct and WMaxLim_Ena in SunSpec model 123.

KACO blueplanet 87.0-165 TL3 Operating Manual EN 2020-10 (Siemens-hosted copy) tbl=56 h=252010cdf85b

c3 drafted · lead Grid Guard code holder

Scope: products SMA Cluster Controller

Setting inverters to accept Cluster Controller active power limitation setpoints requires installer login and an SMA Grid Guard code.

240154 sec=h205 h=c8f35fb9a618

review note: support check: partial - Procedure requires Installer login and Grid Guard code to enable inverters to accept Cluster Controller limits; the passage doesn't say the role 'holder' explicitly but it's essentially implied.

c4 drafted · lead Modbus

Scope: products Tesla Megapack platform (generation not stated) proposed

Tesla exposes the enable flag and the per-unit limit as read/write Modbus registers 22501 and 22502.