In open-loop control, the zero angle of the rotor is determined before starting. In
closed-loop control, the actual angle of the rotor is determined with autophasing
when the sensor indicates zero angle. The offset of the angle must be determined
because the actual zero angles of the sensor and the rotor do not usually match.
The autophasing mode determines how this operation is done both in open-loop
and closed-loop control.
The rotor position offset used in motor control can also be given by the user – see
parameter 98.15. Note that the autophasing routine also writes its result into this
parameter. The results are updated even if user settings are not enabled by 98.1.
Note: In open-loop control, the motor always turns when it is started as the shaft
is turned towards the remanence flux.
Bit 4 of 6.21 indicates if the rotor position has already been determined
Autophasing modes
Several autophasing modes are available (see parameter 21.13).
The turning mode (Turning) is recommended especially with case 1 (see the list
above) as it is the most robust and accurate method. In turning mode, the motor
shaft is turned back and forward (±360/polepairs)° in order to determine the rotor
position. In case 3 (open-loop control), the shaft is turned only in one direction
and the angle is smaller.
Another turning mode, Turning with Z-pulse, can be used if there is difficulty using
the normal turning mode, for example, because of significant friction. With this
mode, the rotor is turned slowly until a zero pulse is detected from the encoder.
When the zero pulse is detected for the first time, its position is stored into
parameter 98.15, which can be edited for fine-tuning. Note that it is not mandatory
to use this mode with a zero pulse encoder. In open-loop control, the two turning
modes are identical.
The standstill modes (Standstill 1, Standstill 2) can be used if the motor cannot be
turned (for example, when the load is connected). As the characteristics of motors
and loads differ, testing must be done to find out the most suitable standstill
mode.
The drive is capable of determining the rotor position when started into a running
motor in open-loop or closed-loop control. In this situation, the setting of 21.13
has no effect.
The autophasing routine can fail and therefore it is recommended to perform the
routine several times and check the value of parameter 98.15.
An autophasing fault (3385) can occur with a running motor if the estimated angle
of the motor differs too much from the measured angle. This could be caused by,
for example, the following:
• The encoder is slipping on the motor shaft
104 Program features
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