Grid Integration and Power Quality - Wind Energy Systems for Electric Power Generation - page 148

Fig. 7.6 Quadrant definition in consumer system
7.3.2 Active Power and Frequency
Utility guidelines require the WES to contribute to frequency control. Systems
must be capable of supplying established minimum power, delivering their share
to the power at underfrequency and overfrequency. In [Tra07] the limits are de-
fined in a curve (see Fig. 7.7a), under which the system is not allowed to cut off.
The Figure shows an example assuming a statics characteristic line of 5%. The
power limits are applicable in a voltage interval of the high-voltage grid accord-
ing to Fig. 7.7b where minimum time intervals before cutting is permissible are
described.
Other grid codes define different variants of requirements regarding minimum
sustained power delivery in dependence of frequency.