
20-6 Power Electronics and Motor Drives
bidirectional (Figure 20.4b and c). e ringing load is excited by a variable (Figure 20.4a) that is constant
in the interval α ≤ ω
s
t ≤ π − α and short-circuited in the interval π + α ≤ ω
s
t < 2π − α, where ω
s
is the
switching angular frequency. e circuit is interrupted during the rest of the period. e interrup-
tion interval shrinks to zero when ω
s
≥ ω
d
. e input variable is square-wave and quasi-square-wave in
Figure 20.4b and c, respectively. e RMS value of the fundamental component is
X X
irms p
=
2π
αcos
(20.14)
e output variable changes in proportion to the input. Varying angle α provides another