Environmental Engineering Reference
In-Depth Information
2. phase-controlled rectifier with inductive energy storage and capacitor
On the d.c. side of the rectifier an inductor is the storage element. Under phase-
control the rectifier consumes a reactive load which is adjustable, and amounts to-
gether with the set-value capacitor to a resultant reactive power as under a1 (a2).
3. self-controlled inverter with capacitive energy storage
An active front-end inverter with an inductor on the a.c. side and a capacitive
storage device on the d.c. side is capable of supplying and absorbing reactive
power (a3).
Figure 3.10b illustrates in principle characteristic admittances over reactive power
in a four-quadrant graph. Note that admittances are defined as follows:
Y
=
1
Z
1
;
Y
L
=
;
Y
C
=
j
ω
1
C
(3.16)
j
ω
1
L
In the figure inductive admittance values are positive, the capacitive ones
negative.
3.2.4 Self-Excited Operation
While in grid operation the reactive power required for magnetizing the machine is
supplied by the utility, different source must be available for island operation.
The classical option is to use capacitors connected to the machine terminals
which allow self-excitation. When driven and running on no-load, the machine is
acting as an inductance drawing lagging current while the capacitive load supplies
a leading current:
U
1
ω
1
L
1
;
|
I
10
|
=
|
I
c
|
=
U
1
·
ω
1
C
(3.17)
Self-excitation of the machine is possible due to its non-linear magnetization
characteristic. This is illustrated by Fig. 3.11 in normalized representation. At rated
Search WWH ::
Custom Search