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filter, phase angle lag of fundamental wave is approximately 40
◦
,thencancal-
culate
θ
1
=40
◦
. The transfer function
R
1
(
z
) of fundamental resonant controller
in the Z-domain is:
R
1
(
z
)=
0
.
0238
z
−
0
.
0244
1
314.1593
1
.
9990
z
+1
·
(16)
z
2
−
In accordance with the principle of priority to the stability, taking
K
p
1
=1
.
4,
then transfer function
PR
1
(
z
) of fundamental PR controller in the Z-domain is:
PR
1
(
z
)=
K
p
1
+
R
1
(
z
)=1
.
4+
0
.
0238
z
−
0
.
0244
1
314.1593
1
.
9990
z
+1
·
(17)
z
2
−
If taking load current
i
o
as one kind of disturbance of the current inner loop,
the transfer function of compensation voltage
u
o
is:
PR
1
(
z
)
G
h
(
z
)
1+
PR
1
(
z
)
G
h
(
z
)
·u
i
+
C
(
z
)
1+
PR
1
(
z
)
G
h
(
z
)
·i
o
u
o
=
(18)
Where: the second is the effect of interference value
i
o
in current inner loop on the
compensation voltage
u
o
,
C
(
z
) is the transfer function of capacitance integral
link in Z-domain. Because the gains of fundamental PR controller t
PR
1
(
z
)
end to infinity in fundamental frequency, the second item in (18) tends to zero.
Simultaneously, the first item in (18) basically equals to the given compensation
voltage. Therefore, the fundamental PR controller can not only achieve zero
steady-state errors, also inhibit the influence of load current on output.
5 Experimental Result
In addition to compensating voltage drops, DVR-prototype still can compen-
sate voltage harmonics of system. One single experiment only with compensat-
ing harmonics and another comprehensive experiment with contemporaneously
compensating voltage sags and harmonics are respectively studied on DVR-
prototype.
Therefore, DVR prototype mainly aimed at the 3rd, 5th and 7th harmonic
voltage higher in load voltage to be compensated. The non linear load was added
into system when the work voltage is normal, its compensation effect on harmonic
voltage is shown as Fig.2. After DVR-prototype compensation, 3rd harmonic
distortion rate reduced to 0.58% from 13.25%, 5th harmonic distortion rate
reduced to 0.46% from 11.37%, and 7th harmonic distortion rate reduced to
0.75% from 7.82%. Three, five and seven times harmonic content are all qualified
in scope, meanwhile THD also drops from 36.28% to 4.69%.
The non-linear load also was added into system, but when the voltage sags
occur, the compensation effect on harmonic voltage shown as Fig.3. At this
point, the system output voltage is stabilized at 220
0.7 V, the steady-state
precision is 0.32%. Additionally, 3rd times harmonic distortion rate reduced
to 0.93% from 13.25%, 5th harmonic distortion rate reduced to 0.57% from
±
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