Electricity: motive power systems – Induction motor systems – Power-factor control
Patent
1980-03-21
1983-06-07
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Power-factor control
318798, 318809, H02P 540
Patent
active
043873294
ABSTRACT:
A three-phase power factor control system for an AC induction motor (10) monitors the power factor of a first-phase motor winding and produces a rectangular-wave pulse power-factor signal (f) which is used to directly control the duration of "on" time of each cycle of input power to the first-phase winding and to indirectly control the "on" time of each cycle of input power to second- and third-phase windings. To provide a signal for controlling the power to second- and third-phase windings the power-factor pulse signal is synchronized with a square-wave oscillator (30) whose frequency is three times that the power-factor pulse signal. Each second and third positive pulse (38 and 40) of the square-wave oscillator (30) is used to control the "on" time of each cycle of input power to the second- and third-phase windings.
A current sampler (72) for monitoring current flowing through the first-phase winding samples voltage across a triac and thereby avoids unduly loading the first-phase winding with a resistor as was done in the prior art. The current sampler (72) is coupled to following circuits through an optical isolator (74) for producing pulses corresponding to current phase.
REFERENCES:
patent: 3387196 (1968-06-01), Graham et al.
patent: 3441823 (1969-04-01), Schlabach
patent: 3506899 (1970-04-01), Graham
patent: 3529224 (1970-09-01), Bedford
patent: 4052648 (1977-10-01), Nola
patent: 4052651 (1977-10-01), Kamaike
patent: 4260948 (1981-04-01), Okado
patent: 4266177 (1981-05-01), Nola
Kenly et al, "Trial Speed Control of Three Phase Induction Motor With Phase-Locked Loop Regulation", IEEE Transactions on Industry Applications, Vol. 1A-12, No. 5, pp. 492-498, Sep.-Oct. 1976.
"Improved Power Factor Controller", Marshal Space Flight Center, Alabama, NASA Tech. Briefs, Summer 1980.
Electronic Assemblers Company
Rubinson G. Z.
Smith Jr. David
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