| 摘要 |
A first half-bridge inverter is powered from an unfiltered full-wave-rectified ordinary 60 Hz electric utility power line voltage. This first inverter provides at a first inverter output, across which is series-connected a first tuned L-C circuit, a first squarewave voltage of fundamental frequency between about 30 and 33 kHz; which first squarewave voltage is magnitude-modulated at 120 Hz. The first tuned L-C circuit, which is series-resonant at about 30 kHz, is parallel-loaded by a full-wave high-frequency rectifier whose DC output is applied to substantially constant-magnitude DC voltage existing across a pair of energy-storing capacitors. At a constant 30 kHz inverter frequency, the waveshape of the current drawn from the power line is substantially that of a squarewave in phase with the power line voltage, thereby giving rise to a power factor of about 90%. However, by frequency-modulating the first inverter at 120 Hz, the waveshape of the line current is made to be substantially that of a sinewave in phase with the power line voltage, thereby giving rise to a power factor close to 100% and a total harmonic distortion of negligible magnitude. A second half-bridge inverter is powered from the substantially constant-magnitude DC voltage and provides at a second inverter output, across which is series-connected a second tuned L-C circuit, a second squarewave voltage of fundamental frequency between about 30 and 33 kHz. The second tuned L-C circuit, which is series-resonant at about 30 kHz, is parallel-loaded by three series-connected fluorescent lamps. The magnitude of the current supplied to these three lamps is adjustable be adjusting the frequency of the second inverter between about 30 and 33 kHz.
|
