Hello,
I wish to design a full wave controlled rectifier to control a 1HP 180V 5.5A separately excited DC motor.I have studied the circuit from theory and its schematic.My problem is that I am not able to understand whether to choose IGBT or SCR..Also, how should i calculate the rating of the power devices?


Pls help.

 

IGBT usually means you will need a DC power supply, for an SCR bridge, you just need two diode rectifiers and two SCR's connected across the 240vac supply.
The devices will need to supply current at least up to the peak torque (current) of the motor.
The voltage will be the PIV for the bridge will be 2x 240 and the IGBT's will be whatever the DC supply V is plus a margin.
IGBT or Power FET's offer smoother and quieter control than supply phase angle control.
The field can be supplied with a small bridge and capacitor at the required fixed field voltage.
Max.

 

Thanks Max I can now decide the ratings of the power devices. I still have a doubt. Can we replace SCRs with IGBTs in the full bridge converter topology? and why are IGBTs preferred in DC chopper circuits?

 

IGBTs are used for DC since they can be turned off by their control voltage. An SCR won't turn off until their anode-cathode current drops to near zero, thus they are typically used with AC circuits where the current goes to zero twice each cycle.

Substituting IGBTs for SCRs requires a different control signal since an SCR can be turned on with a pulse but an IGBT requires a steady control voltage to stay on, as any transistor does.

 

IR on the subject of IGBT's over Mosfet's.
Max.