| 摘要 |
PURPOSE:To make it possible to detect phase difference through an inexpensive method when an induction motor is controlled to suppress rotational fluctuation under low speed rotation. CONSTITUTION:A shunt resistor 11 is provided in the main switching element of an inverter 1A, e.g. the DC link arm of a transistor T2, in order to detect effective value of current. A load torque estimator 102 estimates load torque of an induction motor 2 by monitoring increase/decrease of link current when the output voltage of inverter is increased or decreased by a predetermined amount based on the detected current value. Furthermore, a phase angle converter 101 determines the power factor (phase difference) from the load torque thus realizing control for suppressing rotational fluctuation of motor. |
