| 摘要 |
PURPOSE:To prevent the occurrence of a stall during the operation of an inverter by setting the lower limit of an output frequency when reducing the output frequency of the inverter. CONSTITUTION:When a current feedback signal Irb is smaller than a stall level, an output frequency f0 is converted to an output frequency f1 by means of a frequency calculating circuit 10. When the current feedback signal Irb is larger than the stall level, the output of a comparator 12 is multiplied by a gain coefficient by means of a multiplier 11 and the obtained value is subtracted from the frequency command f0 as a means for preventing a stall. Therefore, the output frequency f1 of the frequency calculating circuit 10 will go on dropping until the anti-stall operation is cancelled. When the output frequency f1 will go down across the lower limit, an 'a' contact 8 is turned off and a 'b' contact is turned off by a comparator 7 and the output frequency f1 is clamped at the lower limit. By this method, such troubles can be prevented that depending on loads, motor current is not reduced even when a frequency is reduced or a motor is kept stopping when a main body of an inverter device has a trouble. |
