| 摘要 |
PURPOSE:To reduce the capacity of a smoothing capacitor in a filter circuit by a method wherein a phase difference is selected between frequency signals supplied to inverters in response to a selection of carrier frequencies for pulse width modulation. CONSTITUTION:The system is constituted of pulse width modulation inverters 4A and 4B receiving power from a common filter circuit 3, induction motors 5A- 5H controlled by the respective inverters 4A and 4B, voltage control means 11A and 11B for controlling the inverter output voltages, and a frequency control means 9 for controlling inverter operating frequencies in response to revolving speeds. A phase shift circuit 28 is added to said system which provides a phase shift to frequency signals being fed to each inverter from frequency control means 11A and 11B, while said circuit 28 switches over the magnitude of the phase difference in accordance with the carrier frequency switching over of the pulse width modulation. The system being thus constructed, the ripple frequency in the output current from the filter circuit 3 is larger, realizing a smoothing capacitor 7 effectively functioning with a reduced capacity in the filter circuit 3. |
