ABB ACS880 Firmware Manual page 103

is only known within which 60° sector of a complete revolution the initial position
is.
Many encoders give a zero pulse (also called Z-pulse) once during each rotation.
The position of the zero pulse is fixed. If this position is known with respect to
zero position used by motor control, the rotor position at the instant of the zero
pulse is also known.
Using the zero pulse improves the robustness of the rotor position measurement.
The rotor position must be determined during starting because the initial value
given by the encoder is zero. The autophasing routine determines the position,
but there is a risk of some position error. If the zero pulse position is known in
advance, the position found by autophasing can be corrected as soon as the zero
pulse is detected for the first time after starting.
Rotor
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 signals 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.
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Program features 103
Absolute encoder/resolver