Method for operating asynchronous motors and corresponding device

A method for finding triggering times of two- or three-phase power controllers for operating asynchronous motors, the three-phase power controllers being connected to a three-phase network without connecting the start points of the stator winding of the asynchronous motor and the feeding network and comprising at least two pairs of antiparallel-connected thyristors, which are triggered at previously determinable times, having the following method steps:

• firstly, for the pairs of antiparallel thyristors, potential triggering pulses are defined which lie at a specific triggering angle (φ) before the respective zero crossing of the mains voltage,
• furthermore, a sinusoidal fundamental wave is defined at a frequency which corresponds to the desired rotational speed of the motor and whose frequency is lower than that of the mains voltage,
• then, two further, phase-shifted fundamental waves are defined at the same frequency, in each case being phase-shifted in relation to the first fundamental wave,
• for each phase, the previously marked potential triggering times which would cause a current of opposite polarity to that of the respectively associated fundamental wave are rejected,
• of the remaining potential triggering times, those times are selected for triggering each phase at which there is likewise a triggering time in one of the two other phases,
• the triggering times determined in this way are used as actual triggering times for the thyristors of the three-phase power controllers.