| 摘要 |
PURPOSE:To improve characteristics at a time when an induction motor is operated at low speed by adding a correction-voltage signal propertional to active currents to a voltage-command signal when output frequency from an inverter extends over a predetermined value or less. CONSTITUTION:Currents flowing through an induction motor 7 are detected by a current transformer 6, and an active-current section is arithmetically operated in an active-current arithmetic circuit 21. A correction-voltage generating circuit 22 outputs a correction-voltage signal Vc proportional to active currents. Consequently, when the value of a frequency-command signal (f) outputted from a speed regulator 12 reaches a prescribed value or less, a low-frequency detecting relay 23 is released, and a contact 23A for the relay 23 is closed. Accordingly, a voltage-command signal inputted to a pulse-width modulation circuit 14 takes a value acquired by adding the correction-voltage signal Vc to Vf outputted from a function generator 13, and the shortage of excitation is prevented when the induction motor 7 is operated at low speed. |
