Situation: We’re controlling a servo motor with a P66 for velocity control.

Servo motor is a 8LSA55.EA030D000-3, P66 is 4kW.

P66 configuration has been done for synchronous motor and tuning is on as well.

However, we encounter vibrations from the motor when operating the below the rated rpm (between 500 & 2000 rpm mainly). Currently no load is connected.

Has anyone else encountered such behavior? Are there more things we need to take into account? Thank you in advance!

Hi Jan,

Do you know the values RSA, LFA, IDA, and TRA that were measured by the tuning and the motor nameplate? Some things I would add are:

Make sure the tuning is done in a cold motor state

The nominal speed and pole pairs give the drive a nominal frequency of 200Hz.

Pole pairs * RPM / 60 = Frequency

4 * 3000 / 60 = 200 Hz motor nominal frequency.

If this is correct, let’s double check the rest of the name plate and the tuning parameters.

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@eric.oldfield, thanks for your return.

We executed homing on 2 motors of the same reference with the following results:

When we run on 3000 rpm (no vibration issues) we see the 200 Hz on the P66 screen.

Hi Jan,

Can we try to match as best as possible the tuning parameters from the data sheet? Specifically,

RSAS: 1.127 ohms from datasheet

For LDS and LQS, the square root of the sum of the squares should equal 12.5

Your autotuned values result in a magnitude of 9.24 and 9.17 respectively, so perhaps we could normalize your values to the correct magnitude.

For PHS, you have 80.6, but from the datasheet it’s 98.44

We always recommend using explicit values rather than autotuned ones when available, and in my experience I’ve seen it improve behavior. I would reserve relying on autotune parameters for 3rd part motors where this information is not supplied/not available/the manufacturer doesn’t know. In those cases you can use the autotuning as a starting point and adjust the parameters manually (guess & check) to improve the behavior.

Eric, thanks for the tip.

How should we normalize the value for Lqs & Lds?

Can we work with f.e. a fixed ratio Lds/Lqs in order to solve for both?

Hi Jan,

To normalize a vector to a magnitude of 12.5 (Using your 1st one as an example):

Current magnitude: 9.24

Desired magnitude: 12.5

Multiplying the inductance vector components by (12.5/9.24) gives

LDS = 5.65(12.5/9.24) = 7.64

LQS = 7.31(12.5/9.24) = 9.89

and we can see that sqrt(7.64^2 + 9.89^2) = 12.497, or about 12.5

Hi Eric

Using the new parameters strongly reduced the vibrations. We have some small vibrations left in a certain speed range but nothing problematic at the moment for the customer.

If you would have other ways to improve, don’t hestitate to add them here but for now I’ll check your response as solution.

Thanks a lot for your input!

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