ISSN: 2776-0979, Volume 4, Issue 4, April., 2023
115
The active and reactive power losses between buses
i
and
i+1
can
be expressed as
follows:
2
2
( , 1)
, 1
2
|
|
i
i
loss i i
i i
i
P
jQ
P
R
V
+
+
+
=
(4)
2
2
( , 1)
, 1
2
|
|
i
i
loss i i
i i
i
P
jQ
Q
X
V
+
+
+
=
(5)
The main objective function is the minimizing total active power losses that can be
given as follows:
(
)
obj
loss
F
minimize P
=
(6)
where,
loss
P
is the total power loss.
The above objective function is subjected to some constraints such as DG size, bus
voltage, and branch current.
2.1
Equality constraints
The generated power must be equal to the demand loads and power losses as [10]:
1
1
1
( )
( )
( )
DG
N
L
N
swing
DG
Lineloss
d
i
i
k
P
P
i
P
i
P k
=
=
=
+
=
+
(7)
1
1
1
( )
( )
( )
DG
N
L
N
swing
DG
Lineloss
d
i
i
k
Q
Q
i
Q
i
Q k
=
=
=
+
=
+
(8)
where,
swing
P
and
swing
Q
are the active and reactive powers of swing bus,
DG
N
is the number
of DGs, and
L
is the number of transmission lines.
2.2
Inequality constraints
•
Voltage limitation
The bus voltages must be within the minimum voltage value (
min
V
) and the maximum
voltage value (
max
V
)
min
max
|
|
i
V
V
V
(9)
•
The limits of power generated from DG
The DG’s
installation capacity in the network is limited. Therefore, it must not exceed
the power provided by the substation [11] to prevent reverse power flow.
1
1
1
3
( )
*
( )
( )
4
DG
N
L
N
DG
Lineloss
i
i
k
P
i
P
i
Pd k
=
=
=
+
(10)
1
1
1
3
( )
*
( )
( )
4
DG
N
L
N
DG
Lineloss
i
i
k
Q
i
Q
i
Qd k
=
=
=
+
(11)
min
max
( )
DG
DG
DG
P
P
i
P
(12)
min
max
( )
DG
DG
DG
Q
Q
i
Q
(13)
ISSN: 2776-0979, Volume 4, Issue 4, April., 2023
116
where,
max
DG
P
and
min
DG
P
are the maximum and minimum active powers generated by DG
unit,
max
DG
Q
and
min
DG
Q
are the maximum and minimum reactive outputs of DG unit.
•
Transmission line current limitation
The maximum
transmission line current
must meet the following constants [12].
max,
k
k
I
I
(14)
where I
max
is the maximum allowed current through the branch
k
.
2.3
Loss
sensitivity index
The appropriate buses for the integrating of the DGs are definite by using the LSI. The
LSI widely used to solve DG sizing and locating problems in RDN [13-14].
LSI can be expressed as:
After determined the PLS index for all buses organized in descending order. The order
determines the priority of buses for DG installing. The calculated PLS index values are
illustrated in Fig. 2.
Fig. 2. The calculated LSI values.
2.4
Whale optimization algorithm
Mirjalili developed the WOA approach in 2016 [12] as a novel nature-inspired
heuristic technique to solve problems related to
engineering and different
mathematical optimization issues. The common behaviors of humpback whales are
the basis of the WOA. This optimization technique is inspired by the bubble net
hunting approach of humpback whales as they follow
a circular shaped route for
hunting small fish near the surface. This feeding process is a distinctive behavior of
humpback whales, making this optimization unique among other nature-inspired
optimization methods. To design the mathematical model of the WOA, three steps are
involved in the bubble-net hunting process[13-14].
2
2
*
(
)
loss
m
lm
m
m
P
Q
R
Q
V
=
ISSN: 2776-0979, Volume 4, Issue 4, April., 2023
117
3.
Numerical results and discussion
To show the effectiveness of the proposed approach applied to IEEE 33-bus RDS. This
RDS with real and reactive power is 3715 kW and 2300 kVAr, respectively. The base
power loss of this system is 210.98 kW and the lower bus voltage is 0.9038 p.u. Other
information can be found in [15].
The system power loss is decreased to 111.027 kW, 87.166 kW, and 72.79 kW by
integrating one, two, and three PV units, and power loss is decreased to 67.83 kW,
28.63 kW, and 11.74
kW by integrating one, two, and three WT units in RDS,
respectively.
Integration of one, two, and three PV units improves the minimum
voltage to 0.9424 pu, 0.9685 pu, and 0.96868 pu, and integration of one, two, and
three WT units improves the minimum voltage to 0.95835pu, 0.98025 pu, and
0.99212 pu, respectively as shown in Fig.4.
From these figure, it is clear that the
voltage profile of each bus has been significantly improved relative to the base case by
optimally determining the sizes and locations of the DG units by using the proposed
approach. Besides, the proposed approach obtains the minimum power loss compared
to other techniques as shown in Table.1[16].
Fig. 4. Impact of two DG units on the voltage profile.
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