Control system for polyphase induction machines

Abstract

A system for controlling the start-up sequence of an electric motor includes a contactor relay for supplying polyphase operating voltage to the motor. A plurality of output circuits are respectively coupled between the motor and the relay contacts. Each output circuit is responsive to an output control signal applied to an input thereof for applying the operating voltage to the motor. An acceleration ramp generator is responsive to a motor control circuit which energizes the relay for providing a first signal which gradually rises upon the initial activation thereof. A phase control ramp generator is responsive to the application of the polyphase operating voltage to provide a second signal which decreases from a given level upon the initial application of the operating voltage. A plurality of comparators are provided each comparator having first and second inputs respectively coupled to receive each phase control ramp generator signal and the acceleration ramp generator signal. Each comparator includes an output which provides a respective one of the output control signals when the level of the phase control ramp generator signal falls below the level of the acceleration ramp generator signal.