Frequency-dependent active power adjustment

The characteristic curve in the ActiveByFrequency parameter adjusts the active power of the power generating plant depending on the grid frequency as soon as a transition to a grid-critical operating state occurs. This function is part of the requirements of the VDE and EN standards. It covers both overfrequency (LFSM-O) and underfrequency (LFSM-U). Configuration is carried out via the ActiveByFrequency parameter group (see ActiveByFrequency).

In the EN standards, this operation mode is also referred to as Limited Frequency Sensitive Mode (LFSM).

A non-critical grid condition exists if the grid frequency is within the permissible limits. If a frequency limit is exceeded and the configured delay time (StpDelay) expires, the critical operating state is activated (LFSM-U or LFSM-O). This state is signaled in the Status via Critical.

For both under-frequency and over-frequency operation, the reference value for active power (P_Ref) can be individually set using the parameters ActiveByFrequencyOvPowerRef and ActiveByFrequencyUdPowerRef to either the current instantaneous value via Pmom or to the nominal value Pmax (in accordance with the EN standard or P_b,Inst according to the VDE standard).

• LFSM-U (underfrequency operation): The demand response ΔP is calculated using the reference value P_Ref and the UdDroop parameter.
• LFSM-O (overfrequency operation): The demand response ΔP is calculated using the reference value P_Ref and the OvDroop parameter.

The system returns to the non-critical state when the frequency is back within the permissible range and the release delay (StrDelay) has expired.

The reference value P_Ref must be set using the ActiveNominal parameter (see Parameters) to match the nominal power of the generation plant.

Frequency measurement, pre-filtering and control are optimized in terms of propagation delay. Delays can also be deliberately configured to avoid unwanted switching frequencies.

In the critical operating state, the rise limitation ActiveTargetSlopeCritical (see ActivePower) takes effect for the fActivePowerSet setpoint.