Environmental Engineering Reference
In-Depth Information
V
DC
-
+
u
f
i
o
i
v
o
L
CB
u
IGBT
H-bridge
PWM
C
AC bus
(a) Used for physical implementation
V
DC
-
+
u
f
i
v
o
L
CB
u
IGBT
bridge
PWM
C
AC bus
(b) Used for controller design
Figure 7.1
Single-phase inverter
which gives
v
o
=
v
r
−
Z
o
(
s
)
·
i
with
Z
o
(
s
)
=
sL
.
That is, the output impedance
Z
o
(
s
) is inductive. Inverters with inductive output impedance
are called L-inverters.
7.2 Inverters with Resistive Output Impedances (R-inverters)
7.2.1 Controller Design
The inductor current
i
can be measured to construct a proportional controller
K
i
,asshown
in Figure 7.2, so that the output impedance of the inverter is forced to be resistive and that it
dominates the impedance between the inverter and the AC bus. This is also widely referred
to as a virtual resistor (Dahono 2003, 2004; Dahono
et al.
2001; Li 2009) to dampen the
resonance of the LC filter.
The following two equations hold for the closed-loop system consisting of Figure 7.1(b)
and Figure 7.2:
u
=
v
r
−
K
i
i
,
u
f
=
sLi
+
v
o
.
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