Environmental Engineering Reference
In-Depth Information
S
=
P
+
jQ
i
Z
θ
o
°
I
0
~
E
δ
( i )
(
v )
Figure 21.2
Power delivery to a current source through an impedance by a voltage source
Here,
δ
is the phase difference between the supply (voltage) and the terminal (current). When
δ
is small,
Z o I 2 cos
P
EI
θ,
Z o I 2 sin
Q
EI
δ
θ.
Hence, roughly,
P
E and Q
δ
for any type of impedance Z o θ
. This is quite different from the case with a voltage source,
where these relationships change with the type of the impedance. The conventional droop
control strategy should then take the form
E
E i =
n i P i ,
(21.4)
ω i = ω
m i Q i .
(21.5)
This strategy is sketched in Figure 21.3. It is different from any of the droop control strategies
when the power is delivered to a voltage source discussed in Chapter 19. Note that, in order to
make sure that the P
loop are of a negative feedback, respectively,
so that the droop controller is able to regulate the frequency and the voltage, the signs before
n i P i and m i Q i are all negative, which makes them droop terms. The main advantage of this
E loop and the Q
ω
E i
ω
i
E *
*
ω
E
=
E
*
n
P
i
i
i
ω
=
ω
*
m
Q
i
i
i
Capacitive
Inductive
0
0
P i *
P i
Q i *
Q i
Figure 21.3
Droop control for inverters maintaining a constant output current (for any type of
impedances)
 
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