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PWM dc motor speed control

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Medtronic

Medtronic

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Hi
Dear all my friends
I have a 12 dc motor ... i made a pwm controller to control the speed .... it function with no problem but at low speed the torque is very low ...
how can i control the speed with a constant or good torque

thanks very much

Medtronic
 

Drive the motor with chopper driver method.. that means constant current driving method..

Or try do with increasing the motor voltage.. .
 

low torque in low speed is inevitable for dc motors , if need constant torque need to use gear system with high side speed controlling.
 

low torque in low speed is inevitable for dc motors
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Why, particularly?

Unfortunately none of the links or suggested methods is capable of achieving a fairly constant speed over load variations, although this is basically a simple task.

For perfect speed regulation, you'll use a tacho generator or incremental ecncoder. But a load compensation that can be achieved without specific hardware features will be sufficient for many applications. It's based on the fact that load dependant speed drop will be mainly caused by the motor series resistance. Increasing the speed regulator output voltage proportional to motor current will create a negative resistance that compensates the speed drop. The compensation factor has to be adjusted to the specific motor.
 

Hi
FvM, input voltage, Current have little tolerance over torque for DC motors . you can't change much to get same torque in any speed. yes, if you use kind of tacho gen or encoder you can make close loop controller and watch the load(constant torque )and Keep the speed, but this can do only for certain range, isn't it ?
 

input voltage, Current have little tolerance over torque for DC motors . you can't change much to get same torque in any speed.
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Means exactly what?

Torque is roughly proportional to motor current. There's no principle reason why you shouldn't achieve the rated current and torque at lower speed, except for the problem that it's more difficult to keep a specific relative speed error.
 

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