96 Program features
Settings
• Parameters 19.20 Scalar control reference unit (page 233), 97.12 IR comp step-
up frequency (page 491), 97.13 IR compensation (page 492) and 99.04 Motor
control mode (page 495)
• Parameter group 28 Frequency reference chain (page 285).
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 in order to control 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. 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.
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.
To Next Page
Loading...
