Electricity: motive power systems – Induction motor systems – Power-factor control
Patent
1986-05-30
1987-11-03
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Power-factor control
318812, H02P 540
Patent
active
047045701
ABSTRACT:
A motor drive circuit controlling the period of each cycle of line voltage which is supplied through an electronic switch to a motor winding. The phase difference between the current through and the voltage across the winding is measured and compared to a reference. The duration of the period of a cycle when the switch is closed and supplies power to the motor winding is varied in relation to the phase comparison so as to maintain an optimal phase angle or power factor for the motor. To eliminate misfiring of the switches in a single phase unit, an a.c. coupled power supply is used to power the control circuits and a varistor is located across the line. Also, fuses are used to protect the circuitry. In a three phase circuit, resistive dividers in current and voltage sensing circuits are matched within 1% of each other to provide proper triggering of the switches of each phase with respect to each other.
REFERENCES:
patent: 4333046 (1982-06-01), Lee
patent: 4388578 (1983-06-01), Green et al.
patent: 4426609 (1984-01-01), Nagy et al.
patent: 4459529 (1984-07-01), Johnson
patent: 4469998 (1984-09-01), Nola
Marshall Space Flight Center, "Fast-Response Power Saver for Induction Motors," NASA Tech Briefs, Spring 1979, pp. 10-11.
Nola, F. J., "Circuit Saves Power in AC Induction Motors", EON 9-5-79. p. 185.
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