knjiga solarna energija dobra

880 POWER CONDITIONING FOR PHOTOVOLTAIC POWER SYSTEMS
U
[V/cell]
2.5
2.4
2.3
2.2
2.1
I
[A]
20
15
10
5
0
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00
t
[h]
Figure 19.13
T-CHEQ
Voltages and currents of 16 series-connected cells during charging with an activated
Figure 19.14 Experimental set-up with a 342-V/200-Ah sealed lead acid battery with eight cascaded
T-CHEQs
charging current of 16 A and an end-of-charge voltage of 2.35 V/cell. The upper curves
in Figure 19.13 show the 16 individual cell voltages and the lower curves show the
corresponding cell currents. The cells with a lower capacity are the first to be fully
charged – their voltage increases above the average voltage. As a result, the T-CHEQ
draws some of the charging current from these cells and directs it to the cells with a
lower state of charge. After 9 h, some cells are effectively charged only with 5 to 10 A,
whereas the charging current for others is around 20 A. At the end of the charging
phase, the T-CHEQ achieves a convergence of all the cell voltages and all the cells are
fully charged.
Investigations of a 342-V/200-Ah sealed lead acid battery (VRLA, Gel-type) with
eight cascaded T-CHEQs (Figure 19.14) show that such high system voltages can be
operated without any difficulties. This type of battery is very sensitive to overcharging
due to its demobilised electrolyte.