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 (StrDelay) expires, the critical operating state is activated (LFSM-U or LFSM-O). This state is signaled in the Status via Critical.

• LFSM-U (underfrequency operation): The power adjustment ΔP is calculated using the reference value P_Ref = ActiveNominal and the UdDroop parameter.
• LFSM-O (overfrequency operation): The reference value P_Ref depends on the plant type. For plants with PlantType = Converter, ActiveActual is used, otherwise ActiveNominal. The power is then reduced via P_Ref and OvDroop.

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

The reference value P_Ref must be set via the ActiveNominal parameter according to the nominal output of the generation system (see parameter).

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 slope limitation ActiveTargetSlopeCritical (see ActivePower) takes effect for the fActivePowerSet setpoint.