Speed deviation of sensorless vector control

Does anyone has an idea in what range the speed of a sensorless vector control driven motor will deviate from the real measured speed?

Most manuals list the specifications. I have seen values like 0.1% or 0.2% of base motor speed, sometimes accompanied by +/- a specific number of RPM. Read carefully, since the deviation percentage may not be linear throughout the full speed range.

OkiePC said:

Most manuals list the specifications. I have seen values like 0.1% or 0.2% of base motor speed, sometimes accompanied by +/- a specific number of RPM. Read carefully, since the deviation percentage may not be linear throughout the full speed range.

Click to expand...

And...

Not all "Sensorless Vector Control" drives are created equal. I recently came across one that claimed to be SVC, but had no option to input motor electrical data other than FLA and number of poles, yet also had no option for "Autotune" to set up the necessary motor model in the mP for use in an SVC algorithm. Bottom line, this can only mean that SVC cability was a lie from an engineering perspective, but since SVC is not really anything more than a marketing term officially, people can say what they want and get away with it. in that one, the clue was that the stated speed regulation was 1-2%, which is no better than what scalar control offers.

So caveat emptor; let the buyer beware.

And RTFM...

jraef said:

And...

Not all "Sensorless Vector Control" drives are created equal. I recently came across one that claimed to be SVC, but had no option to input motor electrical data other than FLA and number of poles, yet also had no option for "Autotune" to set up the necessary motor model in the mP for use in an SVC algorithm. Bottom line, this can only mean that SVC cability was a lie from an engineering perspective, but since SVC is not really anything more than a marketing term officially, people can say what they want and get away with it. in that one, the clue was that the stated speed regulation was 1-2%, which is no better than what scalar control offers.

So caveat emptor; let the buyer beware.

And RTFM...

Click to expand...

Agreed. I was actually told by an American drive manufacturer that "the SVC doesn't really work very good in this model drive".

The motor is often overlooked as a key component of speed regulation even in sensorless vector drives. The best possible speed regulation is a function of the motor full load slip and the processor's ability to manage it under varying load conditions.

In view of that, I usual say that an open loop drive can compensate for about half of the motor slip at best, a commodity-level sensorless vector system can compensate for up to 3/4 of motor slip, and the very best sensorless vector systems out there, Mitsubishi and ABB DTC, can compensate for all but 1/10th of motor slip.

So, choosing a motor with a nameplate speed of 1740 and another with a nameplate speed of 1770 is a 2/1 difference in speed regulation under any VFD control technology.
Today there are motors out there as tight as 1787rpm. That's only 13rpm slip or better than 1% speed regulation before any VFD is added.