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Motionless start-up method description [II]
Author: AM Reference Number: AA-00471 Views: 5206 Created: 20-01-2015 16:09 Last Updated: 18-10-2019 10:52 |
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The motionless start procedure is basically an algorithm that
needs to be tuned to be convergent. It has to converge on the
electrical angle on which the motor is positioned at the moment
of the motionless start procedure execution.
In order to do this, a PI controller is used and is fed an
electrical angle reference and then, by reading the motor
position (and knowing the no. of pole pairs and encoder lines) it
will try to control the motor to move on that position.
The motionless start consists of the following:
- the motor is energized and a current is applied to it (the
current value and current ramp are user defined test parameters)
- the initial angle for this current is set to zero, which means
that the motor will start to align itself with the electrical
angle zero. Assuming the current imposed to the motor is big
enough to move the motor, then we can have 2 situations: the
motor is moving or the motor is not moving.
Assuming the motor is not moving, this might mean 2 things
(again, assuming the rest is ok) - either it already is aligned on the
electrical angle zero (and therefore it actually doesn't need to
move anymore) or it is trying to push against a mechanical limit.
Since we can't differentiate between these 2 cases, a new
angle reference is applied: +90 degrees.
Now again we can have the 2 situations: moving or not moving.
Assuming it is still not moving, then this only means that the
motor was already on the mechanical limit, and the new
electrical angle command is still pushing it against the
limit. In this case, a third angle reference command will be applied: -90
degrees.
This time, for sure the motor will move.
- when movement is detected (it doesn't matter if it moves in the first try, second or third attempt - it's only important that it
moves), the electrical angle PI controller is active and is already trying to make the motor get
back to its starting position (electrical angle).
For example, let's assume the motor is at 37 degrees angle and is
commanded to move to 0 degrees. It will start moving toward
0 degrees and in the same time a displacement will be seen on the
encoder (APOS will start to change - increase or decrease). The
electrical angle PI controller will try to move the motor back
to its starting position (which is 37 degrees) by adjusting the
electrical angle command: if a positive motor displacement is
noticed, then the new electrical angle command will try to
generate a negative displacement command and based on the Kp and
Ki it will converge sooner or later (with oscillations or not)
on the starting position that is 37 degrees. Actually it doesn't
have to converge EXACTLY on that position - an error of several electrical degrees is accepted.
This way, the initial position of the motor (37 degree) which
is unknown to the drive, is determined with a precision of several degrees.
To validate the current level needed and the Kp and Ki of
the motionless start electrical angle PI controller, the Motionless Start Test from EasyMotion Studio needs to be used.
This test is doing a slightly different thing - it is actually
trying to align the motor to a known electrical angle
(-90degrees +/- the initial motor position - the initial motor
position is determined with a standard pole lock procedure). The test is considered successful when the detected electrical angle is within 10 degrees to the known starting electrical angle. In case the motionless tuning test included in EasyMotion Studio is not enough to get valid/reliable results, for the motionless start mode parameters, they can be obtained manually. The attached document present step by step how to do the manual tuning of the motionless start-up procedure.
Attachments
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P100.034 Manual setting of the motionless start mode v181019-1.pdf |
1.1 Mb |
Download File |
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