Browse Prior Art Database

Method of Starting and Running a Single Phase Induction Motor

IP.com Disclosure Number: IPCOM000052638D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Fenton, BP: AUTHOR [+2]

Abstract

A sine-wave drive to the run winding of a single-phase induction motor is generated by using an oscillator output to address a read-only memory (ROM) in which a sine-wave profile is stored. Mains AC is applied to a start winding of the motor, and the oscillator is synchronized with the mains in a phase-locked loop. By preloading the ROM addressing circuit a predetermined phase shift with respect to the mains can be achieved so that a rotating magnetic field is created to start the motor.

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Method of Starting and Running a Single Phase Induction Motor

A sine-wave drive to the run winding of a single-phase induction motor is generated by using an oscillator output to address a read-only memory (ROM) in which a sine-wave profile is stored. Mains AC is applied to a start winding of the motor, and the oscillator is synchronized with the mains in a phase-locked loop. By preloading the ROM addressing circuit a predetermined phase shift with respect to the mains can be achieved so that a rotating magnetic field is created to start the motor.

The drawing shows the run winding drive but not the single phase motor itself or the application of mains AC to the start winding. To start a single-phase motor a rotating magnetic field must be temporarily created in the motor. Such a field is produced if there is a phase shift between the alternating voltage applied to the run winding and that applied to the start winding. With a common supply, this case has conventionally been achieved by means of a phase-shifting capacitor. However, in some circumstances, it is desirable to run the motor at a frequency above that of the mains, requiring an electronically generated drive voltage. The system shown combines electronically generated run drive voltages with mains- assisted start in an ingenious manner.

The run drive voltage is produced by means of a voltage-controlled oscillator (VCO) 10 whose output is divided by a factor n in counter 11. The output of the counter is used to address a read-only memory 12, loaded with a sinusoidal profile in digital form. As counter 11 cycles, the ROM 12 produces a digital output which is converted to an analog sinusoid by digital-to-analog converter 13. After filtering in filter 14, the resulting waveform is applied to drive the motor run winding.

When the motor is starting, the VCO 10 is phase locked to a mains derived reference by phase comparator 15 and feedback through filter 16, The VCO output and mains input are switched to comparator 15 by switches 17 and 18. During the start phase the VCO fine control line is unclamped, but its coarse control is clamped to a voltage V(START). The clamping takes place in response to application of a RAMP DOWN signal to a current source 19 which forward biases diode D2.

To achieve the desired phase shift, the divide-by-n counter 11 is preloaded from register 20 with the digital equ...