Information Technology Reference
In-Depth Information
Source Current
(
i
s
)
Load Current
(
i
L
)
R-L
Load
R
S
, L
S
3-Phase
AC Supply
Non-linear load
R
F
,L
F
Filter Current
(
i
F
)
C
dc
Shunt APF
Gate Pulses
V
dc
i
s
Control Circuit
V
dc,ref
Fig. 1 Single line diagram of shunt active power
filter
The change in error (ce) at any sampling instant
'
k
'
can be calculated as:
ce
ð
k
Þ
¼
e
ð
k
Þ
e
ð
k
1
Þ
ð
1
Þ
1)th sampling
instants, respectively. The output of controller is the incremental change in peak
value of reference source current (
In Eq. (
1
), e(k) and e(k
1) are error values at kth and (k
−
−
I
max
) is added
with the peak value of current at previous sampling instant to obtain the peak
reference source current (I
max
), as given in (
2
).
δ
I
max
). This incremental change (
δ
I
max
ð
k
Þ
¼
d
I
max
ð
k
Þþ
I
max
ð
k
1
Þ
ð
2
Þ
In voltage control loop, the peak value of reference currents is estimated by
regulating the dc-link capacitor voltage. The actual capacitor voltage is compared
with a set reference value, and error signal is then processed in a FLC, to estimate
the peak value of reference source current (I
max
).
In current control loop, the peak value of the current (I
max
) so obtained, is
multiplied by the unit sinusoidal vectors, in phase with the respective source
voltages, to obtain the instantaneous reference compensating currents. Using
indirect current control technique, these estimated reference currents (i
sa
;
i
sb
;
i
sc
)
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