| 摘要 |
PROBLEM TO BE SOLVED: To remove a trouble in a common-mode voltage caused by a step- shaped change by a method wherein a voltage whose magnitude is identical to that of the common-mode voltage generated in the switching operation of a semiconductor element at a power converter and whose polarity is opposite is superposed on the output of the power converter so as to offset the common- mode voltage. SOLUTION: Whenever an inverter 4 is switched, the output zero-phase voltage, i.e., the common-mode voltage, of the inverter 4 is changed stepwise. Thereby, a common-mode current i(t) flows to a grounding conductor through the stray capacitance between the winding of a motor 6 and a frame. At this time, the common-mode voltage of the inverter 4 is detected by a star-connected capacitor 8, a voltage whose magnitude is identical to that of the common-mode voltage and whose direction is opposite is output to a common-mode transformer 11 which is connected in series, and the common-mode voltage can be offset completely. As a result, the common-mode current i(t) does not flow. Thereby, the common-mode voltage and the common-mode current are removed. |
