IEEE Electrification - March 2021 - 85

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Time (s)

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Active Power

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Time (s)
(a)
CCGT

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Frequency (Hz)

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Power (MW)

Power (MW)

Frequency (Hz)

last remaining combined-cycle gas turbine (CCGT) plant
provision of these services by PV generation results in a
dispatched at 230 MW is still online. Two cases, with and
much better frequency response than in previous cases.
without 300 Mvar of synchronous condensers, were simThis demonstrates a benefit of the IBRs' fast and precise
ulated [Figure  12(a) and (b)]. These cases represent a
response to frequency events. One particular scenario
roughly 92% instantaneous IBR penetration. The rotating
[Figure 14(a)] showed oscillatory behavior during the sysinertia of the synchronous condensers improves the fretem frequency recovery, due to dynamic interactions
quency nadir, as in Figure 12. A more extreme continbetween GFM inverters and synchronous condensers.
gency event is described in Figure  13. In this case, the
More detailed analysis would be needed in the future to
last remaining CCGT trips, so the frequency response of
thoroughly understand and address this type of instabilithe system without conventional generation can be
ty in the PREPA system during the design stages of the
observed. Figure 13(a) conveys the case when the system
future modernized grid; it could likely be mitigated by
still has some rotating inertia from the synchronous
using oscillation damping controls in IBRs and by retuncondensers. This rotating inertia helps improve the freing IBR controllers.
quency nadir compared to the
case without synchronous con369-MW CCGT
densers [Figure 13(b)].
Finally, Figure 14 documents
376-MW Peaking Plants
the system response after a
3.42-GW PV
240-MW CCGT trip when the PV
2.02-GW/6-h BESS
generation had a 5% power headroom to provide inertia and PFR for
the cases with and without 300Mvar synchronous condensers,
120-MW Wind
300-MVA SC
res--pectively. (Here, inertial response
means that the resource active
369-MW CCGT
power changes in proportion to
the frequency time derivative.
This is one possible form of FFR.) Figure 11. One future scenario for Puerto Rico's grid. CCGT: combined-cycle gas turbine; SC: synAs seen in Figure 14(a) and (b), chronous condenser. (Source: NREL; used with permission.)

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GFM BESS

PV

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Active Power

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Time (s)
(b)
SC

Figure 12. The simulated system frequency response after the loss of 250 MW of PV generation (only one 240-MW CCGT is online).
The scenario with (a) 300-MVA condensers online and (b) no condensers.

	

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IEEE Electrification - March 2021

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