| 摘要 |
PROBLEM TO BE SOLVED: To prevent insufficient torque at low speeds in proximity to zero speed due to errors in estimated speed by, controlling the output current of the power converter to a value higher than a no-load current value in normal operation regardless of output torque when the output frequency command value of a power converter is equal to or less than a specified value. SOLUTION: In ranges other than zero speed, an output frequency command value ω1*, equivalent to 'speed command value ωr* + slip frequency calculation value ωs*' is outputted and a reference value Id* is outputted from a d-axis current commander 11. At this time, the entire operation is that of a speed sensorless vector control system. That is, the output frequency of the converter is controlled substantially according to the speed command value ωr* and further a required motor voltage is calculated at a voltage calculator 13 based on the reference value Id*, a current command value Iq, and the output frequency command value ω1*. As a result, the output voltage of the converter is controlled. Since internal voltage drop in the motor is compensated by means of the voltage calculator 13 to exercise control so that induced electromotive force takes a specified value, sufficient torque is obtained even at low speeds. |
