Autophasing - ABB ACSM1 Firmware Manual

Autophasing

Autophasing is an automatic measurement routine to determine the angular position
of the magnetic flux of a permanent magnet synchronous motor or the magnetic axis
of a synchronous reluctance motor. The motor control requires the absolute position
of the rotor flux to control the motor torque accurately.
Sensors like absolute encoders and resolvers indicate the rotor position at all times
after the offset between the zero angle of rotor and that of the sensor has been
established. On the other hand, a standard pulse encoder determines the rotor
position when it rotates but the initial position is not known. However, a pulse
encoder can be used as an absolute encoder if it is equipped with Hall sensors,
albeit with coarse initial position accuracy. The Hall sensors generate so-called
commutation pulses that change their state six times during one revolution, so it is
only known within which 60° sector of a complete revolution the initial position is.
Rotor
The autophasing routine is performed with permanent magnet synchronous motors
in the following cases:
1. One-time measurement of the rotor and encoder position difference when an
absolute encoder, a resolver, or an encoder with commutation signals is used
2. At every power-up when an incremental encoder is used
3. With the open-loop motor control, repetitive measurement of the rotor position at
every start.
In the open-loop mode, the zero angle of the rotor is determined before the start. In
the closed loop mode, the actual angle of the rotor is determined with autophasing
when the sensor indicates the zero angle. The offset of the angle must be
determined because the actual zero angles of the sensor and the rotor do no usually
match. The autophasing mode determines how this operation is done both in the
open loop and closed loop modes.
Note: In the open loop mode, the motor always turns when it is started as the shaft is
turned towards the remanence flux.
A rotor position offset used in motor control can also be given by the user. See
parameter 97.20 POS OFFSET
N
S
USER.
Absolute encoder/resolver
Drive control and features
39