Electronics Interview Question:

Is it possible to build an AC or DC variable-speed generator with a variable field current, controlled by a signal from a torque sensor connected to the shaft of the generator (i.e., net torque = 0)?

Submitted by: Administrator

You can control the field with anything, but why would you do it with torque? Why do you say net torque=0? What is the significance of variable speed?

I am trying to think of why you would do this. If the torque were low, you could increase the field to generate more energy, which would make the torque go up. That is positive feedback, but maybe it is constant power into a resistive load (voltage would go up). If you did negative feedback, that would mean the field would reduce as the torque went up, reducing the torque, so you would have a torque regulator. This would probably be good for a wind generator, as you want to control the torque to match the wind speed to get maximum energy out, but this would also vary the output of the generator a lot. Maybe if you were heating water this would work.
Submitted by: Administrator