Using a servomotor (synchronous with permanent magnet) to generate a constant torque

[sydro]

Hello,
I have a synchronous motor with permanent magnet. I want to use it as a "controlled brake", therefor it only have to generate a variable constant torque without fixing a speed.

I tryed to connect it with a resistance load through a 3 phase rectifier and then i modulate the resistance, but it only make a torque when it's short-circuited.
How can I do?

 

[mikekilroy]

buy a servo drive that can operate in current or torque mode. there are zillions out there.

 

[Skogsgurra]

Your approach seems OK. But you have to consider the available voltage across the speed range you want to run. And also make sure that your resistor can "absorb" the corresponding current and power at lowest and highest speed.

It should work well also when not shorted. If the resistor isn't way too high valued.

It isn't as simple as buying one of the zillion servo drives. A PM motor usually needs an encoder or some other means of position/speed feed-back. There are encoderless servos, but not cheap and possibly not suitable for your motor.

What data do you have? For motor and resistor. What speed range are you going to run? And what torque range?

Gunnar Englund

http://www.gke.org

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