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PID constant in Lab10a

Junji Takiguchi
Prodigy 250 points

Good day.

I would like to know how to fix PID constant in Lab10awiyh DRV8312-69M-KIT.

By automatic calculation by INSTA Spin, PID velocity constant (Kp) is 14.1

But by this setting, motor rotation is unstable in high speed.

(About 50000rpm)

So I had to reduce this value from 14.1 to about 1.1. Then it rotates smoothly.

On the other hands, I had to increase current (Kp) from 0.26 to 0.5.

In both cases, Ki is not effective.

User’s Guide mentioned to current control loop parameters.

But I could not find an explanation for speed loop parameters.

How can I find best value of PID?

And if possible, please give me a logical explanation for it.

 

Regards.

  • 0
    TI__Guru** 119680 points

    Junji Takiguchi said:

    By automatic calculation by INSTA Spin, PID velocity constant (Kp) is 14.1

    But by this setting, motor rotation is unstable in high speed.

    InstaSPIN-FOC does NOT automatically calculate any sort of tuning for velocity.  We set some initial values for the velocity PI controller based entirely on the USER_MAX_CURRENT value you are using.  We know nothing about the friction or inertia of the system at this point....

    Also, a PI velocity controller often needs the gains "staged", meaning there are different gains for different operating points.

    Junji Takiguchi said:
    On the other hands, I had to increase current (Kp) from 0.26 to 0.5.

    This should not be necessary. The current control tuning that we use - when used in conjunction with the labs that use the angle compensation algorithm - really should not need any sort of additional tuning. You are free to change this of course if you do some testing, but we really don't find it necessary to change the tuning of the current controllers.

    There are some general guidelines for tuning the speed controller that are discussed in the lab guide, the QSG, the LaunchPad video series (manual tuning at 0 speed) etc.  Or, use InstaSPIN-MOTION which really makes velocity and/or position control tuning extremely simple.