| 摘要 |
PROBLEM TO BE SOLVED: To prevent the capacity of a power converter from being increased by connecting the output of one power converter with the primary winding of a transformer, the output of the other power converter with one end of the secondary winding, and AC motor with its other end, respectively. SOLUTION: A three-phase transformer 13 whose transforming ratio is m (0<m<k) has a Y-Y connection, and the secondary winding is separated. A power converter 11 is connected with one end of the secondary winding of the transformer 13, and AC motor 1 is connected with the other end. The output of a power converter 12 is also connected with the primary winding. When an AC voltage vector V1 is outputted by the power converter 11 and an AC voltage vector V2 is outputted by the power converter 12, the currents of the power converter 11 and the power converter 12 become 1 and m×1, and their apparent powers become V×1 and m<2> ×V2 ×1, however, in case of the cut-off frequency of the transformer 13 or lower, the output of the power converter 12 is not transformed to the secondary side of the transformer 13. As a result, variable speed control frequency for the AC motor can be extended to DC, therefore, it is possible to prevent the power of the power converter from being increased. |
