Figure 6.2:Flowchart of the proposed algorithm for the rearrangement of row position of anm×nPV array.
6.2.2 PRM-FEC configuration of an array
The prime objective of the PRM-FEC configuration is to distribute shadows over the array under PSC by arranging the row position of anm×narray using the digits 1 tomfollowed by the algorithm, as shown in Figure 6.2. The proposed algorithm is designed form= odd and even for the arrangement of row position of anm×nPV array. In order to obtain the unique solution, the repetition of the digits in a particular row as well as a particular column (cln) of a PV array is avoided.
6.2 Different configuration of solar PV array
Let us consider
A(i, j)=
11 12 .. 1n 21 22 .. 2n
.. .. .. ..
.. .. .. ..
m1 .. .. mn
(6.2)
ism×nPV array in the TCT configuration wherem×nnumber of PV modules are placed. Without changing the cln position, the row position of an array is rearranged to get the PRM-FEC configura- tion. So
A(i,)=
1 1 .. 1
2 2 .. 2
.. .. .. ..
.. .. .. ..
m m.. .. m
(6.3)
The rearrangement of the PV modules in an array under PSC depends on the row length of an array, such asmis odd or even number. Form = odd number, the PRM-FEC configuration of a PV array is achieved by using the following steps:
1. If m is an odd number, the positions of the PV modules in j=2 are arranged by adding k with the row position for j=1 as follows:
A(i,2)=
k+1 2 k+2 2
..
..
k+m 2
(6.4)
where k =⌊m/2⌋.
If k+i (i=1,2, ...,m)>m, k+i will be replaced by k+i-m.
2. The positions of the PV modules in j=3 will be obtained by adding k with the row position of TH-1895_11610232
an array for j=2.
3. Similarly, the row positions of an array for j=3, 4, ... ,n are obtained.
Table 6.1: Arrangement of the PRM-FEC configuration of a 7×5 array
Cln 1 Cln 2 Cln 3 Cln 4 Cln 5
(Cln 1+ 3) (Cln 2+ 3) (Cln 3+ 3) (Cln 4+ 3)
1 4 7 10-7=3 6
2 5 8-7=1 4 7
3 6 9-7=2 5 8-7=1
4 7 10-7=3 6 9-7=2
5 8−7=1 4 7 10-7=3
6 9−7=2 5 8-7=1 4
7 10−7=3 6 9-7=2 5
For m = even number, the PRM-FEC configuration of a PV array is obtained by using the follow- ing steps:
1. The positions of the modules in an array for j = 2 are obtained in the similar way, as explained in step 1 for m = odd number.
2. The positions of the modules in an array for j = 3 are obtained by adding k-1 with modified row position for j =2 to avoid the repetition of the modules position with j=1.
3. For obtaining the next cln of an array, step 2 will be continued until there is no repetition of the module position with the earlier modified cln. If there is a repetition, then repeat the procedure of step 1 to obtain the module position in the next cln and so on.
In the present analysis, a TCT configuration of a 7×5 array, as shown in Figure 6.1(a), is consid- ered. The PRM-FEC configuration of an array, as shown in Figure 6.1(b), is obtained from the TCT configuration by arranging the digits 1-7 in the row position by using aforementioned algorithm, as explained in Table 6.1. In the PRM-FEC configuration, keeping the cln position fix, the modules of the same row in the TCT configuration are shifted to a different row position. Hence, the effect of
6.2 Different configuration of solar PV array
shadows in the same row is reduced and the row current is enhanced. Therefore, the power generated by a PV array is enhanced under the PSC.
5 10 15 20 25 30 35
500 1000 1500 2000 2500 3000
Number of shaded modules
Power (W)
TCT PRM−FEC
Figure 6.3:Power-number of shaded modules in row-wise curve for a 7×5 PV array.
To study the effect of PRM-FEC on the power generation of the array with respect to the TCT configuration, the modules of the array, as shown in Figure 6.1(a) and (b), are shaded one by one in the row sequence followed by 75, 74,..., 12, 11 and 55, 24,..., 42, 11 in the TCT and the PRM-FEC configuration respectively. Assuming that the unshaded and shaded modules receive solar irradiation of 1000 and 300 W/m2, respectively. The datasheet values of the 85 W modules used for the PV array are as follows: Isc = 5.17 A,Voc = 21.90 V,Imp = 4.84 A, Vmp = 17.9 V and Ns = 36.
Figure 6.3 shows the power verses number of shaded modules of a 7×5 PV array. It is observed that there is an improvement in the output power in the PRM-FEC with respect to the TCT configuration in each shading condition during the modules are shaded in the aforementioned row sequence.
The output power of a PV array increases under PSC by using different configurations, such as EAR, Futoshiki, and the PRM-FEC. But, the real-time implementation of Futoshiki configuration of a 7×5 PV array is not applicable. The implementation of EAR technique and PRM-FEC configuration of a 7×5 PV array is applicable, but EAR technique requires lots of switches and sensors for altering the electrical connection of the modules in accordance with PSC. However, the PRM-FEC configu- ration does not require lots of sensors, and switches due to the electrical connection of the modules remains fixed. The rearrangement of PV modules in the TCT configuration of an array is performed once at the time of installation for the real-time implementation of the PRM-FEC configuration, and TH-1895_11610232
this configuration is useful for any types of PSC.
To illustrate PRM-FEC method, a 35 ×200 large PV array of 1.75 MW and 1050 V, which can be integrated with the microgrid, is designed by assembling 200 numbers of 8.75 kW, 210 V, 7×5 small array arranged using the proposed method. Therefore, this large PV array is appeared as a 5 × 40 array, as shown in Figure 6.4. At the time of installation, the modules of all small arrays are rearranged using the proposed method so that when partial shading occurs on a 35× 200 large array, the shade is dispersed in a 7×5 small arrays, which make sure the improvement in the power generation. Hence, the PRM-FEC method can be used for the power improvement of a large array under PSC.
Figure 6.4: A 1.75 MW, 1050 V, 35×200 large PV array assembled by a 8.75 kW, 210 V, 7×5 small array arranged by the proposed method.