Figure 6 . Response of both SCIG and DFIG based WECSs on the
described scenario.
It can be seen that at excess generation conditions and maximum dump
load absorption capacity, the system would collapse on overfrequency for
the SCIG based system and overvoltage for the DFIG based system. The
DFIG based system tried to regulate its power output through the pitch
control system but it was not enough to avoid the overfrequency which
happened at a later stage as compared to the SCIG based system. The
simulation was discontinued at the 80th second due to the collapse thus
other events are not shown. An additional simple pitch regulation scheme
dependent on the dump load power is proposed. It is implemented using a
PI controller obtaining its input from dump load power and if it reaches
80% of its capacity, the pitch angle is increased to de-load the WECS.
Fig. 7 shows the improved network response.