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.