Now consider the hard-switched direct AC/AC converter.
Based on the current direction shown in Figure 1. and
assuming the voltage to be positive (0 < ωt < π), diodes D1
and D4 are always forward biased. In this condition, the
switching losses are experienced by only one switch. In this
case, switch S2. As this is not an obvious observation, a
sample conceptual plot depicts this case in Figure 2. For
other conditions, when V and I are arbitrarily positive or
negative, a similar argument holds and switching loss is still
witnessed by only one device. As for the conduction loss, at
any instant of time one switch and one diode conducts.