Control and Design of Microgrid Components - Power Systems ...

characteristic will coincide with the slanted slope inside the limits and will become vertical as
the limits are reached, as per Figure 3.27.
Figure 3.31 shows the steady state characteristics that enforce output power limits for a mixed
system consisting of one unit controlling output power, P, and other unit controlling feeder flow,
F.
ω
ω
o
F
01
P
02
ω
1
F, P
P2=0
P2=Pmax
F1=F1min
P1=Pmax
F1=F1max
P1=0
Figure 3.31 Steady State Characteristics Including Limits on the Regulated Power vs. Frequency
Plane, with a Mixed System.
Figure 3.31 shows that the unit regulating output power has a rigid steady state characteristic,
while the unit regulating feeder flow has a sliding steady state characteristic, here shown in a
generic position. Figure 3.31 shows also that all the characteristic have the same slope. Units
controlling F and P have the sign reversed in the slope, but the magnitude of their slopes are
identical. If this magnitude is chosen as of Eq. 3.3, equal to the minimum slope, then it was seen
that as long as the power is within limits, then also the frequency is guaranteed to stay within
limits. Then it follows that the steady state characteristics shown in Figure 3.31 enforce both
limits on power and frequency when fixed minimum slope is used in all units of the mixed
system.
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