CCS/LAUNCHXL-F28069M: Lab4a: torque control dependent on speed

sstefano78

Tool/software: Code Composer Studio

Hello,

I am using the LAUNCHXL-F28069M with the BOOSTXL-DRV8305 to run a BLDC motor.

I have specified all the parameters. All working well but I've got a strange problem.

I was wondering if there is a way to maintain torque when motor slows down.

I found this 3D about same problem/question, but I don't understand the solution. I'm in the same situation.

https://e2e.ti.com/support/microcontrollers/c2000/f/171/t/561747

Regards,

over 6 years ago

0 sstefano78 over 6 years ago

Intellectual 365 points

P.S.: The problem appear at low speed, not ZERO or near ZERO speed. I set Iq_RefA at 2Amps and the motor goes to max speed absorbing no load current (ok) but when I try to brake it, the current increase to 2Amps (ok) and then, when motor start to slows down also Amps goes down (not ok for me!). I want to maintain setpoint "Amps" at speed over stalling condition.

0 Yanming Luo over 6 years ago in reply to sstefano78

TI__Guru** 117220 points

What low speed do you mean? The torque current is difficult to be held if there is no right rotor feedback position, the feedback torque current is not correct since the rotor angle is not right. You may try to use sensored-FOC if you want to get a good low-speed performance.

0 sstefano78 over 6 years ago in reply to Yanming Luo

Intellectual 365 points

Hi,

The BLDC is used in a range of 400-3600rpm (3600rpm -> no load speed).

The problem already starts at speed < 700 rpm (~20% no load speed).

Best regards,

0 Yanming Luo over 6 years ago in reply to sstefano78

TI__Guru** 117220 points

You should add a proper load to keep the motor running with a speed, not brake it by hand. Or you may try speed closed loop control, but limit the torque output for speed controller as you want.

0 sstefano78 over 6 years ago in reply to Yanming Luo

Intellectual 365 points

I tried closed loop speed controller and it work well at low speed. Now I need to dynamically limit the max current absorbed by motor. How can I limit inner loop Iqref "on the fly"?

Best regards,

0 Yanming Luo over 6 years ago in reply to sstefano78

TI__Guru** 117220 points

Go to CTRL_runOnLine_User() in ctrl.h, find the codes as below, change the outMax and outMin to the IqRef value as you want.

_iq refValue = TRAJ_getIntValue(obj->trajHandle_spd);
_iq fbackValue = EST_getFm_pu(obj->estHandle);
_iq outMax = TRAJ_getIntValue(obj->trajHandle_spdMax);
_iq outMin = -outMax;

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CCS/LAUNCHXL-F28069M: Lab4a: torque control dependent on speed