Figure 7. Response of both SCIG and DFIG based WECSs on the
described scenario.
It is seen that there is significant improvement in the voltage and
frequency response thus coordination is required between the dump load
and the WECSs. The DFIG based system performed better in its frequency
response due to presence of MPPT that prevents short term variability
affecting its operation. The response from the SCIG based system is slow
and the additional pitch regulation is not enough during the described
scenario thus depending on the overfrequency protection settings, the
hybrid windfarm operation would collapse. The dump load power is kept
within its limits as compared to the previous scenario. The pitch angle
increased as compared to the previous scenario to de-load the WECS in
trying to keep the frequency within acceptable limits.
3.1.2. Reactive Power
A similar exercise as above was conducted to assess the response of the
network on pick up of theoretically near-pure inductive load (for
example unloaded transformer and motor). In the case of SCIG based
system, the reactive power source in the system is the SC and available
reactive compensation in the form of capacitor banks while for the DFIG
based system, the reactive power source is still the SC and DFIG itself
which has an reactive power operational range of ±30% of its rated
capacity. The system capability to pick up reactive load, considering
both SCIG and DFIG based systems, is dependent on the network’s level of
excitation at the time of load pickup. Fig. 8 shows the response on the
SCIG based system on pickup of different sizes of inductive load at
different levels of excitation.