How is torque controlled in Field-Oriented Control ?

[cadena]

Hi everyone,

I am trying to control the torque in an FOC algorithm but I don't know how to. I have seen FOC block diagrams (see attached picture) and I am trying to simulate this in MATLAB but I still don't get how to control torque in my SIMULINK model (see attached picture). Also I don't want a speed loop since I only want to control Torque. Please any help would be greatly appreciated.

[cadena]

Note: I am even measuring my motor speed and I get 0 which makes no sense.

[Wolfram]

Torque comes from the part of the stator current that is in quadrature with the rotor field. As far as I understand, you should be able to control torque by feeding your desired torque value into the Iq error amplifier (the signal labelled Vq_ref in your diagram).

[max_torque]

Looking at that model,you can't control "Torque" because the model doesn't include a suitable motor model that characterises the torque per amp of the motor.

If you just want to simply add that, then just use a fixed constant (ignore saturation etc) and assume that the motor makes 100% of that torque constant when the current is 100% in the q axis, and makes 0 % when the current is in the d axis. 


ie, assume for your virtual eMachine a value of say 1Nm per Amp in the q axis.  If you have 10 amps, all in the q axis, then assume 10Nm, if you have 10 amps total, 5 in q, 5 in d, then the assumed torque is 5Nm etc etc

For a real eMachine, the relationship between current and torque is complex, and control inverters are calibrated on test rigs to determine that characteristic and to map that into the inverter, allowing the end user to demand Torque rather than axis current.  That mapping is of course intrinsically bi-directional, so is also used as feedforward to the  FoC controller.

[max_torque]

Just looked closer, there is a what i assume to be a load torque being fed into the motor model, so in THAT block there probably is some of the torque estimator stuff?