3.4.1. Switching Element Verification

Figure 8 shows the peak current in the inverter and rectifier stages when different cases. In case 1, all elements are in normal conditions in the DCCB. In case 2, the left and right parallel diodes are removed. In case 3, the reverse charging process, which is one of the use of the left and right bypass diodes, proceeds the same as in case 1, except that residual current flows in the DCCB after the main switch breaks. Case 4 assumes that both the left and right thyristors are both turned on and the LC resonant current is emitted without specifying the direction.

In case 2, the load on the parallel diodes disappears. Therefore, the influence of the residual current increases in the rectifier stage. In the DCCB in this paper, the peak current in the rectifier stage can be reduced by about 28% using parallel diodes. This can significantly reduce the adverse effects on the elements of the rectifier stage. There doesn't seem to be a significant difference in the result value for case 3 compared to case 1, but there is a problem with energy dissipation. This is described in Section 3.4.2. By using of the bypass diode, the residual energy caused by the LC resonant current can be efficiently dissipated. In case 4, the direction of the LC resonant current cannot be specified, since both thyristors are turned on. Therefore, part of the LC resonant current affects the inverter stage and creates a high load on the transmission line. In this paper, specifying the emission direction of the LC resonant current in the DCCB can reduce peak current in the inverter stage by about 17%. This reduction in current significantly reduces the load on the transmission line, mainly in the inverter stage.

**Figure 8.** Peak current in the inverter and rectifier stage when different cases; Case 1: All elements are operating under normal conditions; Case 2: Under normal conditions, the parallel diodes are removed; Case 3: Under normal condition, the bypass diode is changed to a thyristor, the mechanical switch is turned off, the changed thyristor is also turned off (The reverse charging process works the same.); Case 4: Under normal conditions, resonant current is emitted without specifying the direction of the thyristor (both the left and right thyristors are turned on).
