| 摘要 |
PURPOSE:To improve an operation efficiency in controlling the multistage speed by a method wherein voltage in respective phase of an AC source which the three phases are converted to the six phases are periodically changed over at specified timing to be applied to the three-phase induction motor through a two-way control rectifier. CONSTITUTION:The 3-phase AC source 1 is converted to the 6-phase AC source by means of a transformer 2, and the respective phase thereof are connected to the 3- phase induction motor 4 through the 2-way control rectifier. For example, a 2- way control rectifying circuit 3 is controlled by a frequency setter 6 and a gate control circuit 5, and the individual phase outputs of the three phases and the individual phase oututs of the opposite phases are alternately changed over at the maximum point of the phase voltage in frequencies of n-times (n represents an integer of more than 3) a source period. Further, change-over control phase rotations of the respective rectifiers THU-THW1 in this case are made opposite to the phase rotation of the power source 1 to enable the frequencies of (1-1/n) times the source frequency to be obtained in steps. Thereby, the operation efficiency can be improved by suppressing the components of control frequencies and frequencies twice the former to appear in the inputs of the motor 4. |
