SMA SC 500CP XT - Manual (Page 95)

If the power frequency exceeds a threshold defined in the parameter P‑HzStr, shown here at point A, the inverter will
store the current feed-in power P
cur
. The reduced feed-in power is calculated based on this saved value. The reduction
of the feed-in power is defined via the parameter P-WGra. This parameter indicates the percentage of the saved
power P
cur
by which the power per Hz will be reduced if the power frequency continues to rise. If the power frequency
decreases again as shown in point B, the last feed-in power value reached will remain valid. Only when the power
frequency falls below the threshold defined in the parameter P-HzStop, as shown here at point C, can the feed-in
power be increased again. In this case, the saved value P
mom
forfeits its validity. In addition, a minimum threshold for
power frequency shortfall can be defined with the parameter P-HzStopMin, shown here at point D. If the power
frequency falls below the grid limit, the inverter will shut down and switch to the operating state "Grid monitoring". The
inverter will remain in the operating state "Grid monitoring" until all feed-in conditions are fulfilled again.
Calculation of the power limit:
P
max
= P
cur
‒ [(f
AC
‒ P-HzStr) · P-WGra · P
cur
]
P
max
Power limit P
cur
Current power
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 Function Description SMA Solar Technology AG
User Manual 95 SCCPXT-BA-E4-en-54