*4.2. CC-CV Control Strategy*

*D* is gradually increased starting from the *Dtest* value, after the no-load condition test is passed. Thus, *V<sup>F</sup>* also increases. In each step, it is checked whether the forward current exceeds the allowable upper limit. The increase in *D* continues until *V<sup>F</sup>* = *VF*\_*set*. Thus, *VF*\_*set* = 60 V value to be applied for charging in constant current mode is reached. This part is shown as Section-II in the control algorithm.

When *V<sup>F</sup>* = *VF*\_*set*, and *I<sup>F</sup>* has not reached *IF*\_*sense* yet, the equivalent impedance value of the battery is quite low and charging has started in CC mode. The nature of SS topology tends to keep the secondary side current constant. The secondary side output voltage increases with the increase in state of charge (SOC). At this moment, if it is on the primary side, *I<sup>F</sup>* will increase. The charging process continues in CC mode until the *I<sup>F</sup>* = *IF*\_*sense*<sup>1</sup> condition is met. When *I<sup>F</sup>* = *IF*\_*sense*1, the charging process has reached the stage of switching to CV mode in CC mode. This part of the control strategy is shown in Figure 5 as Section-III.

In the CV mode of the charging process, the equivalent resistance of the battery bank tends to rise rapidly. The limit current value must be reduced to the second peak current level (*IF*\_*sense*2) so that *I<sup>F</sup>* current does not quickly reach the maximum value. As the charging process continues, *I<sup>F</sup>* tends to increase. After this point, *V<sup>F</sup>* is reduced to prevent the increase in *IF*. For this, *D* is gradually reduced. At each step, it is checked whether *I<sup>F</sup>* reaches the second peak current value. This loop continues until *V<sup>F</sup>* = *VF*\_*set* (Section-IV). If this condition is met, the battery is now full and the charging process is completed.
