Method for starting and stopping an asynchronous motor

A method for starting and stopping an asynchronous motor by a soft starter comprising thyristors connected in antiparallel in switchable phases, the method comprising the following steps:

• ascertaining all firing opportunities available for the thyristors of the soft starter at a calculation time in the future;
• forecasting, for all the firing opportunities thus ascertained, an electrical and/or mechanical motor behavior corresponding to the firing opportunities;
• deciding, based on the motor behavior thus forecast, whether and which firing opportunity is to be chosen;
• if a decision has been made to take a specific firing opportunity, generating one or more firing signals for one or more thyristors as a result of which anticipated motor behavior is established;
• repeatedly ascertaining a present rotor angle, a present rotor speed, a present grid phase angle, and present stator phase currents;
• using the present rotor angle, the present rotor speed, the present grid phase angle, and the present stator phase currents to anticipate a torque response for a torque acting on a rotor for first firing opportunities, in which a firing of thyristors turns on two phases, and for a second firing opportunity, in which firing of thyristors turns on three phases;
• and
• using the torque responses thus anticipated to decide whether each thyristor is fired.