Why the negative voltage is not possible in semiconverter?

In a semiconverter, which typically consists of a combination of diodes and thyristors, the output voltage cannot be negative because the diodes only conduct in one direction, allowing current to flow only during the positive half-cycle of the AC input. When the thyristors are triggered, they also only allow current to flow in the forward direction. As a result, the output voltage remains positive or zero, but cannot achieve negative values, limiting the operational range of the semiconverter.