| 摘要 |
PURPOSE:To protect an inverter circuit and induction motor by a method wherein an excess and underrate of a slip frequency are detected to cause the inverter circuit to be opened, in controlling speeds of the induction motor by a variable voltage- variable frequency inverter. CONSTITUTION:The variable voltage-variable frequency inverter (VVVFSIV) 5 effects speed control of the induction motor (IM)6, and a constant slip frequency and constant current controls of IM6 are performed by a tacho-generator 7, operational amplifier 8, CT11 and the like. If there appears an abnormal change in the slip frequency, an adder 32 detects the difference between an output fR of the tacho- generator and an inverter frequency output fINV of a control circuit 10 and by comparing the output DELTAf with an excess pattern fP1 and underrate pattern fP2 by means of comparators 24, 26, a line breaker 2 is turned off to permit VVVFSIV5 to be released when the slip frequency becomes excessive or underrate. |
