Power electronics digital notes b. Tech III year

3-phase half wave converter
is 
f
s
, where 
f
s
is the input supply frequency. 
3 
The 
3-phase half wave converter
is not normally used in practical converter systems because of 
the disadvantage that the supply current waveforms contain dc components (i.e., the supply 
current waveforms have an average or dc value). 
 
To derive an expression for the average output voltage of a 3-phase half wave converter for 
continuous load current 
The reference phase voltage is 
v
RN
=v
an
=V
m
sinωt
. The trigger angle is measured from the cross 
over points of the 3-phase supply voltage waveforms. When the phase supply voltage
V
an
begins 
its positive half cycle at ω
t
=0 , the first cross over point appears at ω
t
=(∏/6)
radians
30°. 
The trigger angle α for the thyristor
T
1
is measured from the cross over point at . The 
thyristor 
T
1
is forward biased during the period ω
t
=30° to 150° , when the phase supply 
voltage 
v
an
has higher amplitude than the other phase supply voltages. Hence 
T
1
can be triggered 
between 30° to 150°. When the thyristor 
T
1
is triggered at a trigger angle α, the average or dc 
output voltage for continuous load current is calculated using the equation
V
avg
=
π
π
α
π
α
= 
= 
=
Operation of three phase half controlled rectifier with R and RL loads
Figure: 2.18 circuit diagram three phase half controlled rectifier