3.1.3.5 Commutation Offset Detection
3.1.3.5.1 Overview
Controlling a motor with Field Oriented Control requires precise measurement of the motor’s electrical angle.
With phase order and commutation angle offset detection (hereinafter referred to as “Offset Detection”), the
relationship between the motor electrical angle and the motor mechanical angle (position sensor feedback)
is identified, afterwards the motor position sensor feedback is used to determine the motor’s electrical angle
for motion control.
Note
This feature is needed for every motor control setup. The application will not work properly before the
Offset Detection routine is successfully executed.
If an incremental encoder without index is used for commutation, the offset detection has to be done
on every power on. Otherwise, the routine only needs to be done once during the first commissioning
and after mechanical changes of the motor or of the commutation encoder.
3.1.3.5.2 Basic Principles
The Offset Detection routines identify two parameters for the relationship between the motor electrical
angle (rotor magnetic field angle) and the motor position sensor feedback:
1. The motor phase configuration (NORMAL or INVERTED) (0x2003:5)
Normally, both rotor angle and sensor angle should increase/decrease at the same time. This situation is
called “NORMAL motor phase configuration” and is shown in Fig. 1.
However, sometimes the angle of position sensor is not increasing in the same direction of rotor angle. This
can happen if the position sensor is mechanically flipped, or if two of the stator phases are flipped. Figure 2
shows such a situation where the rotor angle and the position angle are not increasing/decreasing in the
same direction. This situation is called Inverted motor phase configuration.
2. The commutation angle offset (0x2001:1)
In most cases, the provided sensor angle contains a shift respect rotor angle. Figure 3 shows such a case
where the provided sensor angle has an offset respect rotor angle:
Offset Detection is carried out in
Note
When quick stop is commanded during Offset detection, the procedure is aborted and the drive is
disabled.
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