Electric motor speed control - is adapted for polyphase async. motor with continuously falling torque-speed characteristic and produces specified speed-dependent voltage

摘要

The speed control is for a polyphase asynchronous motor whose controllable phases are independent of one another. The motor has a torque-speed characteristic which drops continuously. It is connected to an a.c. supply through controlled semiconductor switches. A speed measuring device produces a voltage containing 10-30% harmonics w.r.t. its d.c. voltage's effective value. The frequency of this voltage is greater than 3 times the mains frequency when the motor is running at max. speed.