Controlling speed of DC motor by controlling current into it?

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treez

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Please can you confirm that one controls the speed of a DC motor by controlling the voltage supplied to it, and not the current supplied to it?
 

Its working principle is flow of charge (essentially current) in a magnetic field thereby generating motion. In the heart of it , it is the current that needs to be modified.
However, in working to control a DC motor we apply varying voltage(controlled by us) which in turn changes the current and so the speed of the motor.
 
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A DC motor draws a high current when its is not turning which happens when it starts and when it is overloaded. The current increases as it is loaded.
If you simply reduce the voltage to it then it will probably not start running and it will slow down or stop when loaded.

Pulse-Width-Modulation (PWM) is used to feed full-voltage pulses to control the speed without the problems above.
 
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The question isn't particularly clear. I presume, you are talking about PMDC or separately excited DC machines.

Generally speaking, it's a matter of the controller topology. Motor current is equivalent to torque and motor voltage to speed. So at first sight, you'll set the motor voltage for a specific speed, or you'll even compensate the rotor resistance by a respective negative resistance.

If the controller uses speed feedback from an external sensor, you may be talking about an underlying (inner loop) controller, which can be possibly a current controller.
 
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the thing is, I cant find anywhere an article which shows a dc brushed motor being driven by a current output regulated smps....and I cannot understand this...all dc brushed motors that I read about are controlled by bridge inverters.....has anybody seen eg a current output regulated smps feeding a dc motor?
 

Are you talking about a speed controller with inner current control loop (manipulated value of the speed controller becomes the setpoint of the current controller) or a pure current control, e.g. for a constant torque application like a reel drive.
 
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The motor speed is sensed and put into an error amplifier...if we are below required speed (8000rpm), then the current is increased until we get to 8000rpm.
Its only a pump.
 

O.K. inner current control loop. That's not unusual in motor control, I think. In case of a buck-boost converter, there must be an additional limit governor to keep the output voltage within safe limits.
 

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