| 摘要 |
PURPOSE:To inhibit voltage fluctuation at a neutral point without detecting voltage at the neutral-point terminal of a three-level inverter by equalizing the neutral-point voltage output time of each phase within a minute sampling time only by selecting and changing over on-off modes. CONSTITUTION:The voltage command values of each phase are input to a maximum-minimum command computing element 21 at every sampling time and the computing element 21 outputs the maximum value Xmax and the minimum value Xmin of the voltage command values, an adder 22 arithmetically operates-E-Vmin=G1 (where E represents DC power-supply voltage/2), and adders 23, 24, 25 arithmetically operate the voltage command values of each phase. An adder 30 arithmetically operates E-Vmax=G2, and adders 31, 32, 33 arithmetically operate the voltage command values of each phase. A triangular wave carrier 29 outputs carrier signals changing from-E to E and from E to-E, and comparators 26, 27, 28 and comparators 34, 35, 36 output the switching commands of each phase. The switching elements of each phase are controlled on the basis of these switching commands. |
