Standard programposi features 73
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 for accurate control of motor torque.
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 are 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 commutation pulses that change their
state six times during one revolution. It is only known within which 60° sector of a
complete revolution the initial position is.
The autophasing routine is performed with permanent magnet synchronous motors
and synchronous reluctance 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 signal is used
2. At every power-up when an incremental encoder is used
3. With open-loop motor control, repetitive measurement of the rotor position at
every start
4. When the position of the zero pulse must be measured before the first start after
power-up.
Note: In closed-loop control, autophasing is performed automatically after the motor
identification run (ID run). Autophasing is also performed automatically before starting
when necessary.
Absolute encoder/resolver
Rotor
N
S
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