Method for controlling the starting of an AC induction motor utilizing close loop alpha control

摘要

A method is provided for controlling a three-phase, AC induction motor (12), each phase of the AC induction motor (12) is connected to an AC input source (18) by a thyristor switch (22a-22c) and a bypass contactor (24a-24c) connected in parallel in order to provide voltage and current to the AC induction motor (12). The method includes the steps of sequentially firing pairs of thyristor switches (22a-22c) at a predetermined initial alpha firing angle. A new alpha firing angle is calculated which is dependent upon the initial alpha firing angle. Thereafter, pairs of thyristor switches (22a-22c) are fired a the new alpha firing angle. The new alpha firing angle is provided as the initial alpha firing angle and a new alpha firing angle is calculated. The process is repeated until the AC induction motor (12) reaches its full operating speed.