| 摘要 |
PURPOSE:To make a stable speed control possible by equipping a speed- switching means for switching a rotational speed to a speed estimated by a speed estimation means when the rotational speed detected by a speed detection means exceeds a speed fluctuation range calculated by a speed fluctuation range-calculating means. CONSTITUTION:The output of a power supply 1 is smoothed by a converter 2 and inputted to an inverter 3 so that an induction motor 4 is operated at a variable speed, while a speed detector 5 is connected with the induction motor 4 so that a speed signal 6 indicating a rotational speed is obtained. On the other hand, a torque current participating in output torque and excitation current participating in excitation are detected by a current detector 7 from three-phase power outputted from the inverter 3. Then, when the rotational speed detected by the speed detector 5 exceeds a speed variation range calculated by a speed fluctuation range calculator 11, the rotational speed of the induction motor 4 is switched to a speed estimated by a torque current signal 8 from the current detector 7. As a result, the stable speed control of the motor 4 is made possible. |
