Breaking from one speed to another

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Breaking from one speed to another

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juanmas
Contributor I

Hi! i'm using KMS and I want to break a motor from one speed to another. Actually I break from 30000rpm to 3000rpm in 400ms. How can i do to break more fast? I modify acceleration limit and Jerk limit but i can't break more fastly.

Thanks!

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philip_drake
NXP Employee
NXP Employee

Moving between speeds can be modeled with the Motor Manager, under the Motion Sequences Tab.

Go to Trajectory Testing and input initial speed, final speed, Curve Type as well as Acc and Jerk Limit.  Se the Generate curve to Yes and Run Test Trajectory.

TrajTest.png

the result is a plot of the

You would increase the acceleration and Jerk until the test responds in the time needed. 

Key things to consider in a mechanical system is the amount of torque needed to drive the electronics to change quickly. 

I put in your speed profile and generated the curves until the resulting .4 seconds was reached. You are changing 27,000 RPM in .4 seconds which translates to Acc 75,000 RPM/S and Jerk 70,000 RPM/sec2. This amount of change may be unattainabe within your torque budget. It may break something trying to do this.  If your inertia is large than the torque needs go up.  The 5 A, 24V power supply and FRDM-MC-LVPMSM Evaluation hardware are underpowered and will not achive this rate of change.

TrajTest_2.png

TrajTest_plot.png

I hope this helps.

Philip

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juanmas
Contributor I

Hi! thanks for your help.

Im using the Tower circuit to disipate and I active that when DCBus is 25V. Im using 10A 24V.

is this time limitation a caracteristic from my motor or the KMS have an extra acceleration and jerk limitation that we can't modify?

I have the same issue when I accelerate.

SpeedFeedback-2017-06-13T15-09-02.png

Thanks!

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philip_drake
NXP Employee
NXP Employee

It's not a limitation set somewhere in KMS.  By the way I'm using the latest version of KMS 1.1.0. 

Did you try to use the Trajectory Test Tool?

You have to realize that this is basically a large change in speed that is limited by the physics of the motor and driver capabilities, including the inertial load, the available current, voltage, and the control loop timing.   

If you have not modified the TWR-LV3PH, than it's good to 8 Amps of phase current and 36 V. Asking for more than that is problematic.   When I have pushed my power drivers too far I usually end up with sparks and smoke.

TWR-lv3phspecs.png

I'm not sure how to calculate what you would need to achive the speed rate of change you are requesting. 

Philip

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juanmas
Contributor I

Hi Philip,

Yes, I used  Trajectory Test Tool but I had the same result.

Is very strange that the slope of desaceleration is lineal. Are you sure that the KMS library NOT limit the acceleration speed? For example: if I configure a desaceleration of 100.000, the library limit that to 80.000.

Thanks a lot.

Juan Pablo

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