SMA SC 500HE-US - Manual (Page 36)

7 Active Power Limitation SMA America, LLC
36 SC500HEUS-eng-BE-BUS120320 Operating Manual
Calculating the active power limit
Formula: P
Grenz
= P
mom
– ( (f
Netz
– P-HzStr) * P-WGra * P
mom
)
7.2 Power Frequency-Independent Active Power Limitation
7.2.1 Selecting the Procedure using the Parameter "P-WMod"
Use the "P-WMod" parameter to set the procedure for the frequency-independent active power
limitation. Use the parameter to configure how the parameters of the grid operator should be received
and implemented. The default value for this parameter is "WCnst".
There are five different procedures for power frequency-independent active power limitation:
P
Grenz
Power limit
P
mom
Current power
f
Netz
Power frequency
P-HzStr Selected frequency limit at which the active power will be reduced
P-WGra Gradient of the active power limitation
Example: Calculating the active power limit
A Sunny Central with 500 kW feeds in 350 kW (P
mom
) into the power distribution 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
mom
(350 kW). This results in an active power limitation of 140 kW and a
maximum active power of 210 kW.
Calculation:
210 kW = 350 kW – ( (51.2 Hz – 50.2 Hz) * 40 %/Hz * 350 kW )
Procedure Description
Off The active power is limited to the nominal device power "Pmax".
WCtlCom The active power limitation is received by the Sunny WebBox via
the Power Reducer Box and then forwarded to the Sunny Central.
WCnst The active power limitation is entered as an absolute value via the
parameter "P-W".
WCnstNom The active power limitation is entered as a percentage value via
the parameter "P-WNom".
WCnstNomAnIn Active power limitation is set at the input terminals using an analog
signal for specifying the target value.