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15 | Hadaeghi & Abdollahi

R  =   F$%      (11)                                                   kW.
      ?'&() F&
                                                                       B. Case II (Network Reconfiguration Using TLBO-BA
   Where fBH is the fitness value of the black hole and fi is the      Algorithm)
fitness value of the star i.
                                                                          According to Table I, it can be seen that after network
   6) In this paper, the criterion of maximum number of                reconfiguration, the opened switches are 37, 32, 14, 9 and 7 and
iterations is considered as the criterion of stopping.                 the active power losses reduced from 202.6 kW to 124.8 kW
                                                                       (38.4% reduction) which indicates the effective and useful role
C. Hybrid TLBO-BH Algorithm                                            of reconfiguration. The convergence curve of the hybrid TLBO-
                                                                       BH algorithm for this case can be seen in “Fig. 2”. It can be seen
   In this paper, the two mentioned algorithms are used in two         that the hybrid TLBO-BH algorithm converges to the optimal
separate steps to find the appropriate answer. Since the BH            global solution after 10 iterations. “Fig. 3” shows the results of
algorithm is more accurate than the TLBO algorithm and the             applying the proposed method in this case on network voltage
TLBO algorithm is faster than the BH algorithm, the search             profile. As shown in “Fig. 3”, the network voltage profile has
space is first reduced using the TLBO and then the BH algorithm        significantly improved after reconfiguration. For instance, in bus
is used to obtain a more accurate answer. In fact, first the TLBO      18, the voltage was 0.913 P.U. before the reconfiguration, while
algorithm is executed and completed, then the answers obtained         after reconfiguration it reaches 0.947 P.U. That is nearly 3.7%
by the TLBO algorithm are used as the inputs of the BH                 increase in bus voltage 18.
algorithm.
                                                                       C. Case III (Optimal DG Placement and Sizing Using hybrid
   The implementation process of TLBO algorithm is as                  TLBO-BA Algorithm)
follows:
                                                                          In this case, optimal placement and sizing of DG is
   First, the input data (e.g., load data, line data, DGs data, etc.)  determined using hybrid TLBO-BA algorithm. It can be seen
is imported. Then the initial population is generated. In the next     from the simulation that bus No. 6 is the optimal location for DG
step, based on the network configuration, power flow is                placement and its optimal capacity is 2575 kW. According to
performed and the corresponding objective function is                  Table I, after optimal DG placement and sizing, the opened
calculated. The population is then updated and again based on          switches are 11, 14, 17, 33 and 37 and the active power losses
the network configuration, power flow is carried out and the           reduced from 202.6 kW to 103.97 kW. The convergence curve
corresponding objective function is evaluated. In this step, if the    of the TLBO-BH algorithm and voltage profile for case III can
convergence criterion is satisfied, the configuration with the         be seen in “Fig. 4” and “Fig.5” respectively. According to “Fig.
minimum objective function is selected as the final solution,          4”, after 8 iterations, the hybrid TLBO-BH algorithm finds the
otherwise the population is updated and the process continues          best global solution. Comparing the results obtained in “Fig. 5”,
until the convergence criterion is met.                                it is clear that the system voltage profile in the presence of DG
                                                                       has been effectively improved.
                  IV. SIMULATION AND RESULTS
                                                                       D. Case IV (Network Reconfiguration and DG Placement and
   To illustrate the performance of the proposed method, it is         Sizing Using hybrid TLBO-BA Algorithm)
tested on a standard 33-bus radial distribution system according
to “Fig. 1”. The data of this 33-bus network is available in              In case IV, network reconfiguration and optimal DG
reference [19]. This network has a nominal voltage of 12.66 kV         placement and sizing are considered simultaneously. According
and the active and reactive loads installed in this network is         to Table I, in this case the opened switches are 9, 14, 16, 25 and
equal to 3715 kW and 2300 kVar, respectively. The total active         32 and the active power losses reduced to 79.67 kW which
power loss is equal to 202.6 kW. The system has 37 branches, 32        shows a 61% decrease compared to the first case. In this case,
sectionalizing switches and 5 tie switches. The switches 37, 36,       the bus No. 29 is the optimal location for DG placement and its
35, 34 and are open before the reconfiguration of the system.          optimal capacity is 1925 kW.

   In this paper numerical results are calculated in four different       Figure 6 shows the convergence curve of the hybrid TLBO-
cases. The first case is related to normal network conditions, the     BH algorithm for case IV. It can be seen that the hybrid TLBO-
second case is when network reconfiguration is applied                 BH algorithm converges to the optimal global solution after 11
separately, in the third case, DG placement and sizing is              iterations. The result of applying the proposed method in this
considered separately, and in the fourth case, DG placement and        case on network voltage profile is shown in “Fig. 7”. According
sizing and network reconfiguration are considered                      to “Fig. 7”, significant improvement of the network voltage
simultaneously.                                                        profile is clearly visible after network reconfiguration and DG
                                                                       placement simultaneously. For instance, the voltage of bus 18
A. Case I (Normal Network Conditions)                                  reaches from 0.913 P.U. to 0.967 P.U., which means an increase
                                                                       of nearly 5.91% in bus 18 voltage.
   Table I, shows the results of applying the proposed method
in all cases. As mentioned before, in the first case, network
reconfiguration and DG placement are not considered. In this
case, the network is in the normal condition and the switches 37,
36, 35, 34 and 33 are open. The network loss in this case is 202.6
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