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MCF8316A: Question about speed and current gains

Felipe Campelo
Prodigy 10 points
Part Number: MCF8316A

Tool/software:

I'm not sure about the unit for the speed reference. Is it percentage (0 ~ 100) or in Hz (0 ~ MAX_SPEED).

I ask this because I calculated the speed KP using the unit A/Hz. I'm not sure whether this is the value I should input into the SPD_LOOP_KP register or if I need to normalize it based on MAX_SPEED.

And what about the current gains? Is the unit V/A?

Regarding the KI gains (speed and current), I modeled them as continuous gains (A/(Hz·s) for speed KI). Since this is a discrete control loop, do I need to scale this gain by the control loop frequency, or should I use the continuous gain value directly?

  • 0
    TI__Expert 6011 points

    Hi Felipe,

    Thanks for reaching out, could you briefly explain how you derived the Kp and Ki values? Just to understand if you are doing the same things as in the MCF

    Regards,
    Sachin S

  • 0 in reply to Sachin S
    Prodigy 10 points

    Hi Sachin,

    Unfortunately I don't have that information. My colleague calculated those gains and gave them to me to configure the driver.

    He just said that in the control block diagram, the speed input of the speed control is in Hertz, the output (input for current control) is in Amps and the output of current control is in Volts.

  • 0 in reply to Felipe Campelo
    TI__Expert 6011 points

    Understood, 

    You are right in assuming this, but the Kp and Ki within the device are calculated differently. We would be releasing an application note in the next month regarding this. 

    Felipe Campelo said:
    He just said that in the control block diagram, the speed input of the speed control is in Hertz, the output (input for current control) is in Amps and the output of current control is in Volts.

    Regards,

    Sachin S