TMS320F28069M: Encoder delay

Robin Maubert

Hi TI team,

We are using an encoder to provide an accurate angle in motor control (PMSM). Encoder (MA732) has a little delay compared to the sensorless usual mode, which leads to a loss in terms of efficiency and control accuracy, but we do not have an idea of this delay. Is there any way to work on it or to improve ? Is this normal ?

Thanks for the help

over 7 years ago

0 Subrahmanya over 7 years ago

TI__Mastermind 24095 points

Hi,

I was trying to have a quick look at the MA732 spec. Are you are using MA732 with QEP or SPI interface?
Is the delay originating from the encoder itself or latency in CPU reading the results?

0 Robin Maubert over 7 years ago in reply to Subrahmanya

Intellectual 845 points

Hi!

With qep interface, using the embedded qep module. Sensor is set with a short filtering window.

The angle delay is just an idea about the efficiency loss but maybe not the right way.

Thanks

0 Subrahmanya over 7 years ago in reply to Robin Maubert

TI__Mastermind 24095 points

Hi,

From the MCU standpoint - the delay from receiving the QEP input to position count change would be minimal few system clock cycles.
I do not think that is the problem in your case.

Regarding filter, are you using the MCU gpio filters on QEP inputs?

0 Robin Maubert over 7 years ago in reply to Subrahmanya

Intellectual 845 points

I don't think so, I just set the gpio as inputs, do. I have to set anything else or chech something else?

I am using the same control as for sensorless mode, just the bandwidth is different (30rad/s with sensor, 40rad/s in sensorless)

0 Subrahmanya over 7 years ago in reply to Robin Maubert

TI__Mastermind 24095 points

Hi,

Ok. There isn't any other component in the MCU that could add to delay in the path of angle computation.

0 Robin Maubert over 7 years ago in reply to Subrahmanya

Intellectual 845 points

No I don't think so. Can we have the Yanming Luo thoughts?

0 Yanming Luo over 7 years ago in reply to Robin Maubert

TI__Guru** 117260 points

Just have several questions about this topic.

Is the delay a fixed degree which is not related to the running speed? Or is a fixed time? Did you do zero offset calibration of the encoder by forcing alignment before startup the motor every time? Is the calculation function of encoder running in ISR?

0 Robin Maubert over 7 years ago in reply to Yanming Luo

Intellectual 845 points

It is fixed time concerning the filtering.

Yes I do the zero calibration and the encoder computation is running in isr as showed in lab12.

Thanks for the help

0 Subrahmanya over 7 years ago in reply to Robin Maubert

TI__Mastermind 24095 points

Hi, I presume your issue is resolved now. If you need any further inputs please update here or you can post a new thread.

0 Robin Maubert over 7 years ago in reply to Subrahmanya

Intellectual 845 points

Nope... Waiting for Yanming answer :)

0 Subrahmanya over 7 years ago in reply to Robin Maubert

TI__Mastermind 24095 points

Thanks Robin - i'll update the status with Yanming and we'll respond back to you.

0 Yanming Luo over 7 years ago in reply to Subrahmanya

TI__Guru** 117260 points

Hi Robin,

You have to add a delay compensation function and do the real-time correction according to the motor speed and the data from the encoder if you have to add a filter on the encoder to eliminate the signal noise. You might collect the compensation data by comparing the angle from the encoder to the FAST estimator or other encoders with a precise feedback angle.

0 Robin Maubert over 7 years ago in reply to Yanming Luo

Intellectual 845 points

OK fine

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TMS320F28069M: Encoder delay