| 摘要 |
PURPOSE:To obtain a suitable torque even in a low frequency range and to further prevent a motor from overheating at the time of no load by setting the power factor angle of a load amount to be as a reference in response to the output frequency of an inverter. CONSTITUTION:A delay power factor detector 7 detects a delay power factor angle by using the detecting timing of the zero point of an output current, and a predetermined electric angle of the output voltage of an inverter 4. A discriminator 13 compares the power factor angle of a reference load amount set corresponding to the output frequency of the inverter with the detected delay power factor angle, and discriminates the amplitude of the load amount of a motor. In a V/F controller 5, the ratio of the output voltage corresponding to the output frequency of the inverter 4 is set to be increased or decreased on the basis of the discriminated result of the discriminator 13 responsive to the amplitude of the load amount. Thus, a decrease in the torque in a low frequency range is eliminated, and an induction motor can be operated at a suitable power factor. |
