Civil Engineering Reference
In-Depth Information
FIGURE 11-3
Three-phase full bridge AC to DC silicon-controlled rectifier circuit.
11.2
AC to DC Rectifier
The circuit diagram of the full-bridge, three-phase, AC to DC rectifier is
shown
Figure 11-3
.
The power switch generally used in the rectifier is the
silicon-controlled rectifier. The average DC output voltage in this circuit is
given by the following:
32
V
=
V
cos
α
(11-1)
dc
L
π
where V
= line-to-line voltage on three-phase AC side of the rectifier
L
α
= angle of firing delay in the switching.
The delay angle is measured from the zero crossing in the positive half of
the AC voltage wave. Equation 11-1 shows that the output DC voltage is
controllable by varying the delay angle
α
, which in turn controls the con-
duction (on-time) of the switch.
The load determines the DC side current:
D
C
load power
V
DC
I
=
DC
In the steady state operation, the balance of power must be maintained
on both AC and DC sides. That is, the power on the AC side must be equal
to the sum of the DC load power and the losses in the rectifier circuit. The
AC side power is therefore:
