A Novel Three-Phase Oscillator for the Speed Control of Ac Motors

The oscillator described provides a three-phase, variable-frequency output of reversible phase sequence. The output frequency can be continuously varied from 0 to 60 Hz, and the range may be easily increased to any desired value. The device has been used as a reference source in a cycloconverter scheme for the speed control of a 30-hp squirrel-cage induction motor. The oscillator can be directly used to control the speed of small ac motors. It can also be used in conjunction with cycloconverters or inverters to control the speed of large ac motors.