34 Program features AutophasingAutophasing is an automatic measurement routine to determine the angular positionof the magnetic flux of a permanent magnet synchronous motor or the magnetic axisof a synchronous reluctance motor. The motor control requires the absolute positionof the rotor flux in order to control motor torque accurately.Sensors like absolute encoders and resolvers indicate the rotor position at all timesafter the offset between the zero angle of rotor and that of the sensor has beenestablished. On the other hand, a standard pulse encoder determines the rotorposition when it rotates but the initial position is not known. However, a pulse encodercan be used as an absolute encoder if it is equipped with Hall sensors, albeit withcoarse initial position accuracy. The Hall sensors generate so-called commutationpulses that change their state six times during one revolution, so it is only knownwithin which 60° sector of a complete revolution the initial position is.The autophasing routine is performed with permanent magnet synchronous motorsand synchronous reluctance motors in the following cases:1. One-time measurement of the rotor and encoder position difference when anabsolute encoder, a resolver, or an encoder with commutation signals is used2. At every power-up when an incremental encoder is used3. With open-loop motor control, repetitive measurement of the rotor position atevery start.Several autophasing modes are available (see parameter 21.13 Autophasing mode).The turning mode is recommended especially with case 1 as it is the most robust andaccurate 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-loopcontrol), the shaft is turned only in one direction and the angle is smaller.Absolute encoder/resolverRotorNS
