| 摘要 |
PURPOSE:To secure required driving force as well as to keep off generation of heat in a motor by selecting an output voltage in an inverter output circuit automatically according to a load change at times of speed-up and rated speed. CONSTITUTION:Since an output current of an inverter output circuit 3 being fed to an a.c. motor 4 is large enough at time of speed-up, a current value being detected by a current detector 6 is larger than a reference value out of a reference circuit 8 whereby in this inverter output circuit 3, frequency and voltage both go up in accordance with control over an output voltage/ frequency control circuit 5. When a rotational speed is reached to the vicinity of rated speed, load of the a.c. motor 4 is decreased, and when the detected current value becomes smaller than the reference value, a comparator 7 outputs an output voltage signal to the output voltage/frequency control circuit 5, selecting an output voltage in the inverter output circuit 3 to the lower value. In addition, when a load change has been done at the rated speed during operation, the comparator 7 turns an output voltage selector signal to ON or OFF according to a fact that the detected current is less than the reference or more than it, thereby selecting the output voltage of the inverter output circuit 3. |
