*3.2. Blocking Inductor*

Figure 6 shows the peak current in the inverter and rectifier stages depending on the blocking inductor. Regardless of the value of the two DCCB inductors, the impedance of the transmission line increases as the value of the blocking inductor increases. Therefore, the amount of current flow in the inverter stage is reduced. The graph does not clearly show the effect of the inductor when the blocking inductor is less than 10−<sup>4</sup> H. However, when it exceeds 10−<sup>3</sup> H, the peak current is greatly improved. When the value of the blocking inductor exceeds 10−<sup>3</sup> H, the peak current in the inverter stage decreases rapidly.

**Figure 6.** Graph of the peak current in the inverter and rectifier stages depending on the blocking inductor.

The peak current in the rectifier stage decreases significantly after passing the bifurcation point. This bifurcation point occurs at 4 mH (4 × 10−<sup>3</sup> H) when the sum of current limiting reactor values is 0.2 mH (2 × 10−<sup>4</sup> H), and at 2 mH (2 × 10−<sup>3</sup> H) when the sum of current limiting reactor values is 2 mH (2 × 10−<sup>3</sup> H). This kind of bifurcation point occurs when the value of the blocking inductor is greater than the value of current limiting reactors and the sum of the inductors of the main current branch exceeds 3 mH (3 × 10−<sup>3</sup> H). Increasing the value of the blocking inductor and exceeding the aforementioned bifurcation point can rapidly reduce the peak current in the rectifier stage.

However, since the blocking inductor is located in the transmission line, if an excessively large value is used, the time from initial transmission to steady-state may be extended. Therefore, the optimized value of the blocking inductors must cross the bifurcation point to rapidly reduce the peak current in the rectifier stage so as not to be excessive.
