Elevator control apparatus

Abstract From the Canadian patent

A bridge circuit including a couple of thyristors and a two diodes is connected between a three-phase AC power supply and a three-phase induction motor for driving an elevator car. The bridge circuit is adapted to make up a controlled rectifier circuit or an inverse-parallel connection circuit of thyristors, as the case may be by, switching a plurality of contactors. At the time of starting and accelerating the elevator car the bridge, circuit is changed to constitute an inverse-parallel connection circuit of thyristors to which a signal for a sufficiently high speed command is applied. This speed command is applied to a phase shifter, which fires the thyristors in inverse-parallel …