Three=phase AC motor speed control - uses variable frequency DC=AC converter and voltage control

摘要

The system is used for regulating the speed of a three-phase asynchonrous motor (1). The motor is connected to an intermediate circuit, and control at high speed is performed by varying the frequency of AC fed to the motor. The system is used for driving a lift or a hoist,control at low speeds is by varying the voltage. The current for the motor is supplied by a DC/AC converter (2) with external control. There is a firing pulse generator (6) connected to a switching circuit (7). The external control signal is fed to a comparator (10) connected to the switching circuit via amplifiers, (8,9) a frequency converter (12) and a computing network (13).