LAUNCHXL-F280049C: Speed Measurement Range

Are you saying the max allowable commanded speed set by USER_MOTOR_FREQ_MAX_HZ also sets the max measureable speed for the control loops?

I need to make sure I'm using this parameter properly and I want to know how to  scale the DAC output for motorVars.speed_krpm. How can I scale the DAC output in volts to obtain speed in krpm if I don't know the max measureable speed (ie 3.3V out on the DAC = ??? krpm if I set the USER_MOTOR_FREQ_MAX_Hz to 100Hz)? 

And if I have a desired application speed range of +/- 1500rpm for a 4 pole motor do I set USER_MOTOR_FREQ_MAX_HZ to 100Hz? Or should I pick something 1.2-1.3x higher (120Hz - 130Hz) to allow some margin as is suggested in the user guide for parameter USER_IQ_FULL_SCALE_FREQ_Hz (this parameter does not appear in any version of TI code I have seen)

You've answered part of my question by saying the maximum output of the DAC will be scaled to USER_MOTOR_FREQ_MAX_Hz. But this means I will be unable to observe any overshoot in the speed response because that overshoot will be higher than the maximum allowable voltage on the DAC if I command a step change to the max speed. Does that mean I'm setting this value incorrectly?

I am currently using the parameter, USER_MOTOR_FREQ_MAX_Hz, to control the maximum allowed speed command to the motor. An example would be helpful because this parameter is not defined in the user guide but it shows up in the code. When you say this shout be set based on my motor, are you referring to a certain datasheet parameter?

That explains the DAC portion, but according to the InstaSPIN Projects and Labs User’s Guide, the variable USER_MOTOR_FREQ_MAX_Hz is used in the gain equations on p. 76 and p. 77.

USER_MOTOR_FREQ_MAX_Hz shows up in the code but is not described in the InstaSPIN User Guide, SPRUHJ1H. Instead there is a parameter with a similar name, USER_IQ_MOTOR_FREQ_MAX_Hz that is not present in the code. On p. 205 of SPRUHJ1H it suggests USER_IQ_MOTOR_FREQ_MAX_Hz should be set larger than the maximum speed expected for the motor. Then on p. 223 it says adding 20-30% headroom is recommended for this parameter. 

I know these aren't the same two parameters, but this is why I’m asking about how the control loops measure the speed when it’s above USER_MOTOR_FREQ_MAX_Hz.

Do I need to set USER_MOTOR_FREQ_MAX_Hz 20-30% above my desired operating speed. And if I change this value will it change the calculated gains in the control loops. And does this parameter affect anything else?

There is still something that doesn't make sense. USER_MOTOR_FREQ_MAX_Hz goes into these four functions in the example lab code.

TRAJ_setMinValue(trajHandle_spd, -USER_MOTOR_FREQ_MAX_HZ);
TRAJ_setMaxValue(trajHandle_spd, USER_MOTOR_FREQ_MAX_HZ);

float32_t speed_min_Hz = -USER_MOTOR_FREQ_MAX_HZ;
float32_t speed_max_Hz = USER_MOTOR_FREQ_MAX_HZ;

For our application, the max speed for the application and the motor max speed are essentially the same thing. We do expect to have some overshoot when performing a step change to max speed but not much, less than 5% is expected. 

I would like to use USER_MOTOR_FREQ_MAX_HZ to limit the speed command and at the same time allow for a certain amount of overshoot in the control loops. I believe this is what the user guide is suggesting by recommending the 20-30% margin. The problem is, there is only one parameter that seems to simultaneously affect the speed command limit and the 'measured' limit for the control loops.

For example, if I want to limit the commanded speed to +/-200 Hz and the motor speed could overshoot to +/-210Hz worst case during acceleration to a max commanded speed of 200Hz. How should I set the parameters above to limit the commanded speed to +/-200Hz and at the same time allow for a 5% max overshoot?

If I set USER_MOTOR_FREQ_MAX_HZ to 20-30% higher than 200Hz as you suggested, this will not limit the speed command to 200Hz.

If I set USER_MOTOR_FREQ_MAX_HZ to 200Hz, this will limit the speed but I have not allowed for any overshoot as you suggested.