An Elevator Speed-Control System Using Squirrel-Cage Induction Motors

An electronic control system with speed feedback to achieve excellent riding comfort and accurate floor-levelling in medium-speed elevators driven by squirrel-cage induction motors is described. Stepless control of both acceleration and deceleration of the elevator car is obtained, employing only two thyristors and two diodes in the power control circuit. Accurate floor levelling and smooth deceleration are achieved using a novel digital speed-reference circuit which uses programmable memory to generate the speed pattern directly as a function of the position of the elevator car. The system described is simpler, lower in cost, and easier to maintain compared to dc motor-driven elevators of the same performance for car speeds up to 2 m/s.