摘要 |
PURPOSE:To enable use of a small-capacity thyristor converter having components of low voltage/current rating by alternating a light-load variable- speed operation by the thyristor converter through an intermediate terminal and a rated-speed operation by a direct connection with AC main power through the main terminal of a stator winding. CONSTITUTION:A low-voltage variable-frequency operation is performed by applying an input voltage lower than the rated voltage of a winding through a thyristor converter 3. The input voltage may be applied between the neutral point of the stator winding of a synchronous motor 6 and an intermediate terminal obtained by wiring the winding at an intermittent pole connection. As a result, the required withstand voltage of the converter 3 is lower than the rated voltage, and the required current capacity is reduced in accordance with a load. Thus, as long as the output of the synchronous motor 6 at the time of variable speed operation meets the requirement of the load in a speed range up to the rated speed of the synchronous motor 6 corresponding to the frequency of an AC main power source, the required capacity of the thyristor converter 3 and the voltage/current rating of the thyristors of the converter 3 can be reduced. |