Submission by SRISHTI MITTAL 101805029 3EIC2
Experiment 1 : Single Phase AC to DC Power Converter (Fully Controlled).
Objective: To verify experimentally the operation of single phase full Converter
Apparatus: : (1) Converter Trainer kit (2) Load Resistance (3) C.R.O.
(4) Single phase Variac (5) Isolation Transformer
Theory/Working:
Here there are 4 thyristors used in the circuit. So it is called fully controlled converter.In half
controlled converter , there 2 diodes and 2 thyristors used.DC voltage(input to motor and it
is output after converting AC->DC) is used to control speed of motor(DC). To control DC input
voltage, we have to control AC input voltage or we can directly control DC output BY use of
thyristors.
In positive half cycle , thyristor 1 and 4 will work and in negative half cycle thyristor 2 and 3
will be on.So In both cases the voltage across load will be positive as current is moving in same
direction from +ve to -ve.Current will be unidirectional. It is the reason why 1st and 4th
quadrant operation will work here.The SCR will not turn ON if anode to cathode voltage is
+ve.It will turn ON if gate current is applied.
Gate current we can give at a firing angle from 0 to 180 degree.So duration of the on period
of thyristor can be controlled.To increase the output voltage , firing angle should be less. As
ON period is more . So speed will be more at lesser firing angle.
To measure firing angle - 1 division value is 18 degree.so according with 2 divisions the firing
angle wil be 72 degree.
T1,T4 will conduct from alpha to (pi+alpha). Only for 180 degree.After that T2 and T3 will
conduct from pi+alpha. During the time period [0 to alpha] and [pi to pi+alpha] the thyristor
is forward biased but not in conductive state.
So output voltage during that time period will be 0 and current will be linearly decreasing.It
is important that the thyristors completely turn off before turning on the next thyristor,
