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

ω
o
P
o
P
+
_
m
+
+
+
ω
1 δ
V
(t)
s
P
max
+
errP max
Ki
s
0
Δ ω max
P
+
P = 0 min
errP
min
0
Ki
s
Δ ω min
Figure 3.20 Control Diagram to Enforce Limits with Unit Power Control.
The equation that governs this control has been formally changed from Eq. 3.4 to an equation
that keeps into account of changes made in Eq. 3.5 and Eq. 3.6 when respectively dealing with
maximum and minimum power limits. The final equation is:
ω
( P − P ) + Δω
max+
Δ min
i
= ωo
−
o, i i
ω
m Eq. 3.7
The quantities Δωmax and Δωmin are added to the frequency as calculated in Eq. 3.4. Both
quantities are zero when the unit operates within power limits. When Pmax is exceeded, then
Δωmax becomes negative (never positive) to enforce the limit. Conversely, when Pmin = 0 is
exceeded, then Δωmin becomes positive (never negative) to enforce the limit.
This control has been implemented in simulation and hardware and the results obtained prove the
effectiveness of the control design. The control is tested with all known events that can cause
either limit to be exceeded: these hardware results are all included in Chapter 7.
3.2.2 Steady State Characteristics with Feeder Flow Control
Another possible option for controlling power is to regulate to a constant the flow of active
power in the feeder where the unit is installed. The main reason why there is an interest in
exploring the load tracking configuration is because when regulating power on the branches to a
constant value, then the power supplied from the grid will remain unchanged when a load
changes inside the microgrid. There are cases when the utility is interested in having large
customers to draw a constant amount of power from the grid, regardless of their changing local
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