2. INTRODUCTION
AC(~) DC(--)
Diode rectifiers are uncontrolled rectifiers
The level of DC output voltage can not be
controlled.
e.g. single phase half wave and full wave
rectifiers.
4. CONTROLLED RECTIFIER
Rectifier designed with SCR’s are
controlled rectifier.
AC is converted into regulated DC.
The phase relationship between i/p
voltage & o/p current can be controlled.
Level of the voltage can be regulated by
varying firing angle α.
9. Contd….
Thyristor turns ON at ωt= α & voltage
appears across Load & current starts
building up.
Inductor does not changes current
instantaneously, so load current does not
become zero at ωt = π.
10. Average value of output voltage
ttdvv iav sin2
2
1
)cos(cos
2
,
i
av
v
vonsolving
13. Operation
In the positive half cycle T1 and T2 are
forward biased.
In the negative half T3 and T4 are forward
biased.
T1 and T2 continue to conduct till T3 and
T4 are triggered.
14. Contd….
T1T2 α to π + α
T3T4 π + α to 2π + α
α to π Vo +ve
α to π Io +ve
π to π + α Vo -ve
π to π + α Io +ve
α to π L stores the energy.
π to π + α L releases the energy.
15. AVERAGE VALUE OF
OUTPUT VOLTAGE
ttdvV mav
sin
1
cos
2 m
av
v
V
onsolving
Thus, Vav is +ve from o ˂α ˂ π/2
Vav is –ve from π/2 ˂ α ˂ π
Vo
Io
-Vo
20. Contd….
The effect of inductance can not be
ignored in practical thyristor
converters.
The current commutation takes a finite
commutation interval u as in fig (d)