Protection circuit and method for variable speed drives utilizin

Details Protection circuit and method for variable speed drives utilizin Protection circuit and method for variable speed drives utilizin

1992-01-31

1993-06-15

Beha, Jr., William H.

Electric power conversion systems

Current conversion

Including an a.c.-d.c.-a.c. converter

361111, 363 54, H02H 7127, H02M 7162

Patent

active

052204944

ABSTRACT:
A method and circuit for detecting rapid increase in line voltages applied to variable speed drives utilizing a phase controlled converter. A three phase alternating current line voltage is applied to a full wave bridge rectifier to generate a direct current signal. A buffer amplifier having a high input impedance is coupled to the output of the rectifier and a diode is utilized to ensure that only positive voltage transients are detected. Positive voltage transients output through the buffer amplifier rapidly charge a capacitor through the low output impedance of the buffer amplifier and that charge is permitted to bleed off slowly through an associated resistor. The rate of change of the capacitor charge level is compared to a preset voltage level and increases beyond that preset level are utilized to trigger an inhibit signal which momentarily resets the delay angle of the switching devices within the phase controlled converter. In this manner, a rapid increase in the average slope of the input line voltage, whether or not preceded by a decrease, may be detected and removed from the input of a variable speed drive.

REFERENCES:
patent: 4589050 (1986-05-01), Cutler et al.
patent: 4815052 (1989-03-01), Walker
patent: 4843533 (1989-06-01), Roof et al.
patent: 5038244 (1991-08-01), Tuusa

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