Figure 14. Response on DFIG WECS starting on a DFIG based
system.
From the results obtained, starting of SCIG based WECS first requires
energization of a capacitor bank (at the 60th second) to supply its
reactive power requirements. Without the capacitor bank energization,
the SC as shown by the field current would be driven into overexcitation
prompting action of the OEL. For the case of the starting of the DFIG
based WECS, there is a sluggish response, but the SC is not driven into
overexcitation and in contrast it behaves as a capacitive element
reducing the operating level of SC field current.
3.3. Transformer Energization
Figs. 15 to 18 show the system response on transformer energization at
different excitation levels for both the SCIG and DFIG based hybrid
systems. Change of excitation level for the SCIG system is achieved by
energizing a 0.5MVAr capacitor bank while for the DFIG based system it
is achieved by setting the Q reference to 0.1pu on each WECS.