JPH05336788

PURPOSE:To enable automatic setting of an acceleration rate without depending on a human system, by setting the acceleration rate automatically so as to give a certain slip to an output frequency of a VVVF inverter and the number of revolutions of a hysteresis motor, when a hunting component is detected. CONSTITUTION:When hunting is detected by a hunting component detecting circuit 8, the number fHM of revolutions of a hysteresis motor 6 is read through a transformer 7. In the case when the relation of fINV-fHMf is established, on the other hand the acceleration rate is changed from f2/min. to [(f1+f2)/2]/min. by an acceleration rate automatic setting circuit 10. In the case of fINV-fHM=0, besides, the acceleration rate is changed further by the acceleration rate automatic setting circuit 10 and the VVVF inverter 1 is operated. According to this constitution, optimum setting of acceleration of the VVVF inverter is enabled.