Bldc motor torque control

[bldcmotorcontro]

Hi,

With referance to the document available  (AN2892   3-Phase BLDC Motor with Hall Sensors and Speed Closed Loop, Driven by eTPU on MCF523x) we control the speed of BLDC motor. Here the input is actual speed and the intended speed.

If I want to control the toque of Bldc motor then can I provide the PID controller the feedback (the replica of current flowing through the motor which is propotional to torque) ie the actual torque and the intended torque (command )and drive the PWMs accordingly. The HALL  inputs will only help on deciding the commutation sequence. Can I also use the hall sensor

output to detect motor jam.

Regards

Arya

[rocco]

Hi Arya,

If your intention is to close a current-loop with the eTPU, then whether you can successfully accomplish that depends on a number of factors.

The first thing to consider is the bandwidth. The motor/driver combination will have a fixed electrical time-constant. If the motor inductance is high enough, that time-constant will be slow enough for the eTPU to keep-up. If the motor inductance is low, the eTPU may not be able to regulate the current adequately.

After that, you need to consider dynamic-range. If you don't have enough resolution in your current-loop, then you may have too much current-ripple, and that could cause mechanical vibration and noise. Motor inertia can mitigate that, but load inertia can exacerbate it if the coupling is not stiff enough.

So it depends on your application.

Both bandwidth and resolution can be made very high in an analog design, which is why, even today, most current loops are analog-driven PWM.