Electricity: motive power systems – Induction motor systems – Power-factor control
Patent
1979-12-05
1981-06-02
Rubinson, Gene Z.
Electricity: motive power systems
Induction motor systems
Power-factor control
318798, 318812, H02P 540
Patent
active
042713862
ABSTRACT:
A phase-triggered, gate-controlled AC semiconductor switch, in series with an induction motor and its AC supply, optimizes power flow to the motor under changing mechanical load conditions by varying the amount of supply voltage applied to the motor over each half-cycle of the AC supply. The triggering point of the switch relative to the preceding zero crossing point of the supply voltage, that is, the switch firing angle or delay angle, is varied as a function of mechanical loading on the motor by means of a load current-induced feedback voltage augmenting to a varying degree the charging rate of a capacitor which triggers the semiconductor switch into conduction. Under increasing mechanical load conditions, the feedback voltage increases in proportion to the increasing load current, the increasing feedback voltage accelerating the charging rate of the capacitor to trigger the switch into conduction at a reduced firing angle, wherein power flow to the motor is increased. Conversely, under decreasing mechanical load conditions, the feedback voltage decreases in proportion to the decreasing load current, the decreasing feedback voltage decelerating the charge rate of the capacitor to trigger the switch into conduction at an increased firing angle, wherein losses caused by reactive current in the less-than-fully-loaded induction motor are reduced with a resultant optimization of power factor.
REFERENCES:
patent: 3441823 (1969-04-01), Schlabach
patent: 3443188 (1969-05-01), Mortimer
patent: 4052648 (1977-10-01), Nola
patent: 4176307 (1979-11-01), Parker
patent: 4190793 (1980-02-01), Parker et al.
Rubinson Gene Z.
The Scott & Fetzer Company
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