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MCT8316A: How to tune a speed loop?

Kenji
Intellectual 530 points
Part Number: MCT8316A

Hi Team

I want to know how to tune the speed loop.

First I have few questions about GUI tool.

Q1. When KP is changed with KI=0, there is no speed change even if the speed command value is changed. 
    When changing KI with KP=0, speed changes depending on the speed command value. And also overshoot can be confirmed.

   I think that the parameter setting is reversed from the phenomenon.


Q2. CL_ACC and CA_DEC is valid when use speed loop as CLOSE_LOOP_MODE?
       In my environment, it seems only valid when select "disable" as CLOSED_LOOP_MODE.



I use this version.

  • 0
    TI__Genius 9010 points

    Hi Kenji-san,

    The Kp and Ki tuning must be done experimentally through trial and error when Speed Loop is enabled. A simple way is to monitor the FG output and plot its frequency with respect to time to visualize the response after changing speed command. 

    I've double checked the GUI and verified that the Kp Ki widgets are mapped to the correct Kp and Ki registers in the device. Please allow me some time to check with our algorithm development team to clarify what the expected behavior of changing either Kp or Ki while keeping the other 0 should be.

    Regards,
    Eric C. 

  • +1 in reply to Eric Chen
    TI__Genius 9010 points

    Hi Kenji-san,

    To follow-up on your questions, I checked with our algorithm team:

    1. This seems to be expected behavior. Regarding Kp, since output is Kp*error depending on the Kp value, which is typically small, the output impact will be minimal and thus the speed change would be minimal. Perhaps increasing Kp to the maximum can result with some change in speed output, but it also depends on the current speed and targeted speed.
      But with Kp=0, Ki will keep on adding the error value to the output and output keeps on changing till the error is zero.
    2. CL_ACC and CL_DEC are only applicable when (CLOSED_LOOP_MODE = Disabled, otherwise known as voltage control mode), hence they are defined as V/s. They control how quickly the voltage reference is changed during acceleration/deceleration (perhaps it's a bit confusing to call this mode "Disabled" and can probably be called Voltage control mode). With Speed Loop or Power Loop control modes, Kp and Ki decide the transient dynamics instead.

    Regards,
    Eric C.