hi, i'm a final yr student doing thesis now on dc motor drive... i was assigned to design a thyristor (SCR) converter for a 24vdc motor... i've done the schematics of controlled rectifier and the firing circuit for SCR, which i used UJT relaxation oscillator to trigger...

now my problems are:
1. my design is basically a open loop design, i do not how redesign it into closed loop, so that i'd maintain the speed...

2. i also do not how to modify my circuit so that the motor can be operated in 4 quadrants (bi-directional)... is it i must use a dual conveter method??

would appreciate ur help in this... thank you.

 

1. How you switch off at SCR for DC circuit?
2. You need bridge circuit for bi-directional operation.

 

> 1. How you switch off at SCR for DC circuit? <

Use AC for the input.

> 2. You need bridge circuit for bi-directional operation. <

You can use a reversing relay but that's crude. I would indeed use a bridge.

Regards

cww

 

what do you mean by brige circuit? is it H-bridge circuit? i've no idea on building this circuit. i'm using center-tapped, controlled rectifier (using) so, how 2 build the H-bridge? plz advise... thanks.

 

Using a center tapped controlled rectifier, consider what would result if you used another pair of SCRs, reversed from the first pair. Now by controlling which pair you trigger, you can deliver either polarity to the load. A bridge works somewhat differently, the best way to describe it non schematically is that it works like a reversing relay. None of this should be at all hard to find. I am curious why you are contemplating power control if you have no idea about classic methods. But, I'll try to help. Watch your di/dt, both for commutation and to
prevent demagnetizing your motor.

Regards

cww