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.