| 摘要 |
PURPOSE:To make it possible to perform highly accurate automatic offset adjustment by opening and closing a subtractor, which subtracts the output of a V-phase ampilfier from the outputs of U-phase and W-phase amplifiers, and the output of the V-phase with the computaion-completed signal of the average value. CONSTITUTION:A voltage-type self-excited inverter 19 is driven by six PWM signals from an inverted signal device 18. The deviated amounts of duties of the PWM signals in U, V and W phases by 50% are measured with a duty counters 30. The outputs are filtered through low-pass filters 31 and amplified with U-phase and W-phase small-gain amplifiers 32. The results are subtracted from U-phase and W-phase current command values in a subtractor 27. When the duties in U-and W-phases become the gain switching levels, a switch 35 is switched, and fine adjustment is performed. The duties are adjusted to 50%, an average-value-computation request signal 34 is outputted. An average value computer 41 computes the average value of the duties in V-phase once so as to obtain the total sum of the duty deviations. A computation completion signal 40 of the average value is outputted, and a switch 46 is closed. As a result, highly accurate adjustment can be performed. |
