SMA SUNNY CENTRAL CP XT Series - Frequency-Independent Active Power Limitation; No Active Power Limitation: off Mode; Active Power Limitation with Setpoint Command Via Modbus Protocol: Wctlcom Mode; Active Power Limitation with Absolute Value: Wcnst Mode

10 Function Description
SMA Solar Technology AG
User ManualSCCPXT-E7-BA-en-5894
f
AC
Power frequency P-WGra Gradient for reducing active power
P-HzStr Selected frequency limit from which feed-
in power will be reduced
Example:
An inverter with 500kW is feeding 350kW (P
cur
) into the utility grid. The frequency will reach up to 51.2Hz. The
difference between the current power frequency and P-HzStr (51.2Hz ‒ 50.2Hz) multiplied by the gradient P-
WGra (40%/Hz) results in an active power reduction of 40% of the last available power P
cur
(350kW). This results
in a power limitation of 140kW and thus a maximum active power of 210kW.
Calculation:
210kW = 350kW ‒ [(51.2Hz ‒50.2Hz) · 40%/Hz · 350 kW]
10.3.2 Frequency-Independent Active Power Limitation
10.3.2.1 No Active Power Limitation: Off Mode
The feed-in power is limited to the parameter Pmax.
The parameter Pmax defines the inverter power at the feed-in point and is adjusted to the local conditions during
commissioning. The parameter Pmax can only be changed when the device is in the operating state "Stop" and the
installer password has been entered.
10.3.2.2 Active Power Limitation with Setpoint Command via Modbus Protocol:
WCtlCom Mode
The communication unit receives the setpoint for active power limitation and transmits it to the inverter. If the inverter
has received no signal for five minutes, an error message will be displayed in the instantaneous value P-
WModFailStt.
10.3.2.3 Active Power Limitation with Absolute Value: WCnst Mode
The active power limitation is entered as an absolute value via the parameter P-W. The parameter P‑W defines the
active power to be fed in. The parameter P-W can be changed in feed-in operation. The parameter P-W must not be
greater than the parameter Pmax.
10.3.2.4 Active Power Limitation as a Percentage of Nominal Power: WCnstNom Mode
The active power limitation is set as a percentage value via the parameter P‑WNom. The percentage value refers to
the parameter Pmax. The parameter P‑WNom indicates what percentage of the maximum possible power is to be
fed in. The parameter P-WNom can be changed during feed-in operation.
10.3.2.5 Active Power Limitation via Standard Signal: WCnstNomAnIn Mode
The active power limitation is set via an analog signal at the input terminals for the setpoint. This is usually implemented
by a ripple control signal. The electrical current strength of the connected signal determines the nominal active power.
The analog measured values must be between 4mAand19mA. If the analog signal is less than 2mA, an error
message will be displayed in the instantaneous value P-WModFailStt.
Signal Power limit Description
< 2 mA
Last valid value or Pmax after restart
Signal is in the invalid range.
2mA to 4mA 0 kW No power is fed into the grid.
4mA to 19mA
0 kW to Pmax
The energy fed into the grid is determined by a character-
istic curve.
> 19 mA
Pmax The energy fed into the grid equals Pmax.