| 摘要 |
PURPOSE:To suppress the influence of the error of the polarity of the rectangular wave signal of a compensation signal by a method wherein the rectangular wave signal to which a dither is applied is added to an AC voltage instruction as a compensation voltage to eliminate a distortion voltage. CONSTITUTION:An AC voltage generator 6 outputs AC voltage instructions VU, VV and VW in accordance with a voltage instruction V and a frequency instruction (f). On the other hand, currents of respective phases are detected by a current detector 3 and respective phase current signals IU, IV and IW are outputted. Comparators 10, 14 and 18 detect the polarities of the respective currents in accordance with the current signals IU, IV and IW. The current signals IU, IV and IW are supplied to oscillators 13, 17 and 21 through absolute value circuits 12, 16 and 20. The oscillators 13, 17 and 21 output high frequency rectangular wave signals of '+ or -1' when the current signals are not higher than a certain value and output high frequency rectangular signals of '1' when the current signals are higher than the certain value. Multipliers 11, 15 and 19 multiply the outputs of the comparators 10, 14 and 18 with the outputs of the oscillators 13, 17 and 21 to output compensation voltages. The compensation voltages are added to the outputs VU, VV and VW of the AC voltage generator 6 by adders 7, 8 and 9 and the resultant voltages are supplied to a PWM circuit. |
