Elevator – industrial lift truck – or stationary lift for vehicle – Having specific load support drive-means or its control – Includes control for power source of drive-means
Patent
1993-03-04
1995-10-24
Wong, Peter S.
Elevator, industrial lift truck, or stationary lift for vehicle
Having specific load support drive-means or its control
Includes control for power source of drive-means
318434, 318802, 363 69, 363 70, 363 65, B66B 128, H02M 708
Patent
active
054602440
ABSTRACT:
The present invention provides an elevator speed control system in one mode, including: a plurality of converters connected in parallel for converting an AC voltage to a DC voltage by means of controllable devices; a capacitor for smoothing output voltages of the plural converters; a plurality of inverters connected in parallel which convert the voltages smoothed by means of the capacitors to an AC voltage whose magnitude and frequency are controllable, and which further supply the resulting AC voltage to a hoisting induction motor; current detectors for detecting the currents in each phase of the plural converters and inverters; a control means which calculates the sum of the resulting currents of the plural converters and inverters and which further controls the output voltages of plural converters and inverters so that the resulting sum is minimized.
In another mode of the present invention, there is provided a control means which calculates the difference in phase between output voltages of the plural converters and inverters, and which stops the plural converters or inverters if the calculated phase difference exceeds a predetermined value.
In the above configurations, the reduction in output is effectively avoided by suppressing the circulating current flowing through the parallel-connected converters or inverters.
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Mitsubishi Denki & Kabushiki Kaisha
Nappi Robert
Wong Peter S.
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